# Bearcat vs Corsair



## Salim (May 14, 2006)

Greetings all.

I was doing some independant research on naval aircraft of world war 2 (and those that COULD have taken part, but didn't get the chance) and I thought that the F8F bearcat was a spectacular aircraft, but some nagging feeling told me that the corsair (and I'm talking the later models of F4U-4 and -5 variants) were better. So here I ask, which one do you folks think is the better airplane over all?

Also, since I'm asking here, can I have your feedback regarding another aircraft that could have been in world war 2 but didn't (due to the atom bombings of Hiroshima and Nagasaki) is the F7F tigercat, a twin engined aircraft that, at the time of development, couldn't operate off the decks of current carriers (but could off the decks of Midway class carriers that were completed after the conclusion of the war). I really have a facination with these 'what if' aircraft.

I patiently await your answers.


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## plan_D (May 14, 2006)

The F4U-4 overall would be superior to the F8F because it had more versatility in it's roles. The Bearcat had the dogfighting capability, but that was about it. The Corsair was still very fast, and was no slouch in a fight. But it could also fly further than the Bearcat, and carry much more equipment and ordnance.


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## Jank (May 14, 2006)

In the air to air role, the Bearcat is the superior performer.

An armament of four .50's though is pretty marginal though.


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## Bullockracing (May 14, 2006)

World War II ended without the Bearcat having seen operational service. The navy reduced its contracts to 770 aircraft but added an order for 126 F8F-lB Bearcats, with four 20-mm (0.79-in) cannon. Of the original order, 15 aircraft were revised as night fighters, with the designation F8F2N, with APS-6 radar. Navy squadrons continued to re-equip with the Bearcat and by 1948, the type was in service with 24 units.

Another version, the F8F-2, appeared in 1948 armed with 20-mm (0.79-mm) cannon. There were 293 of these built, as well as 12 night fighters, designated F8F-2N. Other changes included a taller fin and rudder, and the engine cowling was revised. Grumman also produced 60 F8F-2P photographic aircraft.

Four 20s will turn most any dogfighter into swiss cheese...


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## helmitsmit (May 14, 2006)

Tough call as the F4U also had cannon later on.


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## syscom3 (May 14, 2006)

I'd say the F4U was the better of the two. The only thing the F8F was good for was dogfighting. Plus the F4U had the superior range.

The F7F was marginal. If it couldnt operate off of the Essex class carriers, which comprised basically the whole Carrier fleet, then why bother with it.


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## Bullockracing (May 14, 2006)

I personally love the F7F, what a beautiful plane. Not in the same class as the F8F or the F4U, but gorgeous anyway.


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## Gnomey (May 14, 2006)

Yeah it is, agreed about it not being in the same class as the F4U and F8F (but then it is twin while the others are single engined....)

Of these two I would pick the F4U, in a dogfight the F8F may have the advantage but the F4U is able to hang around longer and do more roles (meaning one aircraft instead of multiple aircraft).


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## Salim (May 14, 2006)

Hmm, some good stuff here, but after doing a little more thinking, I think that the F8F might actually have a bigger advantage in some way.

You guys say that the F4U has more range, but the sources I checked out gave the internal fuel supply of an F4U is enough for 1,005 miles (1,617 km) and 1,560 miles (2511 km) with drop tanks. The F8F had a range of 1,105 miles with internal fuel. It could also carry two 150 gallon droptanks and I'm fairly certain this gave it substantially more range.

Anyway, in regards to more versatility, I have to say that the F4U really is the winner in this regard since it had a bigger capacity for carrying bombs (it could pack 4,000 lbs of bomb. A load which NO single engine fighter could do at that time) and more rockets. But I still believe that the F8F is still adequate for the ground attack role. Not as much as the F4U, but still good.

Anyhow, I got another question to ask. Since the F8F was powered by the Pratt Whitney R-2800-34W double wasp engine, and the final engine of the 'wasp' series was the R-4360 Major wasp engine, do you people think that the F8F could have been able to fit that engine? If it could, then I believe that it would give it substantially more performance than the F4U!


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## chris mcmillin (May 15, 2006)

The current holder of the 3KM World Speed Record for piston powered propeller driven airplanes is 528 mph held by the F8F, though highly modified with a Wright R-3350. The Pratt&Whitney R-4360 was considered for this racer but was thought too long, heavy and complex for the task of 4000hp. In racing practice the Wright R-3350 makes 4000 plus hp and the P&W R-4360 makes about 4500hp for 5 minutes, then fails.

The practical advantage would be to power the Bearcat with the R-2800, and at WEP it can out do a Corsair, or any other fighter, in a fight. 

With the small size and short moments of the Bearcat, carrying a lot of ordinance is not as comfortable as the Corsair. I never saw a Bearcat carry drops on the wings except in racing. Does anyone have photos of a Navy ship with wing pylon drops? They have a centerline drop like the Tigercat and Hellcat.

The Bearcat was not as well suited as a fighter bomber, but the French used them for quite sometime in Viet Nam with some success. 

I didn't know that the Essex class carriers weren't able to handle the F7F. Funny, they were able to handle the 14,000 pound and up Panther and Banshee jets. I have a feeling if it were necessary the F7F would have flown off of whatever carrier was available. All it takes is a little testing and the need. I don't think it was an issue after the bomb. Look at the Corsair and all of the attitude change about it on the boat.

Chris...


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## Soundbreaker Welch? (May 15, 2006)

The only thing the F8F was good for was dogfighting




Which is what made the Spitfire great, remember. If a fighter is excellent when fighting other enemy fighters, then it's doing what fighters do best.


But bombing is a good asset. Since the Corsair was better at lifting weight then it wins in this area.


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## R Leonard (May 15, 2006)

Not so much a matter of Essex class carriers not being able to handle the F7F, more a matter of the F7F being less than optimal for carrier operations. 

Of course it could be done, first time in November 1944 aboard Shangri La (the same day they tested the PBJ and the P-51), but it was IIRC considered too stressing on the airframe. I'd have to dig out the info from the files, but I believe that there were problems with the tailhook assembly that raised some eyebrows.

Also some F8F discussion at

http://www.ww2aircraft.net/forum/polls/bearcat-good-late-war-japanese-fighters-3960.html

Rich


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## R Leonard (May 15, 2006)

And here's Charlie Lane’s F7F (BuNo 80291) aboard USS Shangri-La, 15 Nov 44.

Rich


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## lesofprimus (May 15, 2006)

Nice info RL...


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## helmitsmit (May 15, 2006)

Salim said:


> Anyhow, I got another question to ask. Since the F8F was powered by the Pratt Whitney R-2800-34W double wasp engine, and the final engine of the 'wasp' series was the R-4360 Major wasp engine, do you people think that the F8F could have been able to fit that engine? If it could, then I believe that it would give it substantially more performance than the F4U!


Didn't the later Corsairs get an engine change? the F2G?


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## Salim (May 15, 2006)

Yes, the F2G did get the Major Wasp engine. I was just wondering if it was possible to fit that particular engine into the F8F bearcat frame and make it operational for combat.



> The current holder of the 3KM World Speed Record for piston powered propeller driven airplanes is 528 mph held by the F8F, though highly modified with a Wright R-3350. The Pratt&Whitney R-4360 was considered for this racer but was thought too long, heavy and complex for the task of 4000hp. In racing practice the Wright R-3350 makes 4000 plus hp and the P&W R-4360 makes about 4500hp for 5 minutes, then fails.



Thanks for the info there. Actually 4000 hp is still tons of power and I would dare say that had this been available to the Allies early in World War 2 it would have made a huge difference to the air war (which would have made a huge difference to the war in general).

Edit: I just looked something up on the bearcat. It held the world record for fastest climb rate (10,000 feet in 91 seconds) for 30 years before it was broken by the F-16 falcon! Now that's a major plus as a dogfighter.

But I guess you guys are right about the Corsair being a more versatile aircraft over all. The only thing that the Corsair couldn't do is carry torpedoes... or could it...


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## Jank (May 15, 2006)

Salim said, "I would dare say that had this been available to the Allies early in World War 2 it would have made a huge difference to the air war"

Early in the war, yes. The thing that made a huge difference in the air war later on was the ability to put up 10, 20 and even 30 fighters for each axis fighter in the sky. With lopsided numbers like that, the extra performance of such engines wouldn't have conferred much of an advantage.


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## Salim (May 15, 2006)

Don't forget that the Allies (except the Russians) not only had superior numbers, but had better quality pilots to boot. Yes I know that there were still many German aces who flew the ME-262 jet fighter and the T-152, but a few good men really can't turn the outcome of a doomed war anyway. Most of the German and Japanese pilots were mostly hastily trained young men who could barely fly the plane they were in, let alone fight, and had practically no combat experiance to boot.


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## red admiral (May 15, 2006)

> Don't forget that the Allies (except the Russians) not only had superior numbers, but had better quality pilots to boot.



That would be because the better axis pilots had already been shot down by far superior numbers of Allied aircraft.


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## plan_D (May 15, 2006)

The Bearcat could easily be beat to 10,000 feet by the English Electric Lightning. Because the said plane could easily beat a F-16 to the same altitude. 

The German pilots were not hastily trained. They were remarkable pilots with far and above average skill in a lot of circumstances. But this did not make them invincible, and a lot of the greats were being shot down in 1943. So, come the major offensive in 1944-1945 the German greats were either on the Eastern front or had been blasted out of the air a year before. The victory was a simple matter of economy, the Allies could produce more planes and throw more pilots into the air than Germany.


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## helmitsmit (May 16, 2006)

good point


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## R Leonard (May 16, 2006)

> The Bearcat could easily be beat to 10,000 feet by the English Electric Lightning. Because the said plane could easily beat a F-16 to the same altitude.



Well, geez, a 2000 hp R2800 radial versus two 13,200-pound thrust RA34R/310 turbojets. I never would have guessed. Kind of apples and oranges, n'est ce pas?

Rich


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## lesofprimus (May 16, 2006)

> The victory was a simple matter of economy, the Allies could produce more planes and throw more pilots into the air than Germany.


And that my friends, sums up the Luftwaffes downfall in a nut shell....


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## Twitch (May 16, 2006)

That sums up everyone's downfall in a nutshell. If it wasn't for America's production capacity GB and even Russia to some extent would have been S.O.L.


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## maxs75 (May 18, 2006)

plan_D said:


> The Bearcat could easily be beat to 10,000 feet by the English Electric Lightning. Because the said plane could easily beat a F-16 to the same altitude.



From the j-aircrafts forum:


> (an off topic comparison I love is a "video taped" encounter between 2 F-16's after a single engine Cessna(sp?) which was drug running. After numerous passes on the drug runner to shoot it down the F16s simply had to give up as the slow plane would simply out maneuver them each pass, it even noted if he had been an armed plane would have been able to shoot them down them being so slow trying to match him the Jets were floundering and vulnerable..........Yet which would any of us say is superior in combat?).



Max


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## plan_D (May 18, 2006)

Does anyone else want to bring back the argument I had against Lunatic aboug the EE Lightning vs. F8F Bearcat ? 

As R.L pointed out, you can't even compare the two planes. You're stating, and the source is stating, that a piston-engined plane with a climb rate of , what ? 4000 + FPM ... against a plane with an initial climb rate of 50,000 FPM ... come on, use some sense. 

The Lightning does not need to warm up, so don't bring that out. The Lightning has a famous story around it ... a pilot took off and went "ballistic" (vertical) ... the air traffic asked him to contact them when he reached 10,000 feet ... he replied "Sorry, I cannot. I have passed that mark and have just passed 18,000 feet." 

If anyone wants, just find me the arguments where I had to rant about the EE Lightning ... or I'll just punish EVERYONE with them again.


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## helmitsmit (May 19, 2006)

plan_D said:


> Does anyone else want to bring back the argument I had against Lunatic aboug the EE Lightning vs. F8F Bearcat ?
> 
> As R.L pointed out, you can't even compare the two planes. You're stating, and the source is stating, that a piston-engined plane with a climb rate of , what ? 4000 + FPM ... against a plane with an initial climb rate of 50,000 FPM ... come on, use some sense.
> 
> ...




Didn't the R.A.F do mock combats between the Spitfire Mk XIX and a Lightning in the 60s? Is there any reports on that?


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## plan_D (May 19, 2006)

I've heard of that, but I don't have any solid evidence to back it up.


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## helmitsmit (May 24, 2006)

me neither I found it in a book.


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## chris mcmillin (May 25, 2006)

The Time to Climb record for the piston engined weight class of the Bearcat is held by the same F8F, N777L that holds the 3KM record. It is 91 seconds from a standing start to 3000 meters. The pilot was Lyle Shelton set at Thermal, California in 1972.

It was pretty neat to watch, the airplane was tied to a large cast concrete sewer fixture that was covered in asphalt and concrete scrap. The Bearcat's prop blast blew all of the dirt away and pulled the fixture up to the edge of the runway where it stopped on the ledge. The chains were connected to an electric switch attached to a bridle connecting the tailhook mount. When the pilot was ready with full race power and water injection on, he flashed a thumbs up and the crew chief would signal the release by a drop of his hand. The airplane was oriented on the very left side of the runway, pointed at a 45 degree angle to the right. On release the airplane bolted forward and left, accelerating in about 200 feet to 100 knots and airborne, aerodynamic controls effective and the gear coming up. The airplane accelerated down the runway to 165 knots and then the nose was raised to maintain that speed. It was like watching a car going down the freeway straight up. 

This was and is a privately owned airplane and paid for by workers wages. There were no English Electric Lightnings there that day, or in my then 11 year old mind. Lightnings were Lockheed's, and there were several on my mind that day up in Santa Barbara for sale, if only the old man had had MY vision!

Chris...

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## davparlr (May 25, 2006)

Salim said:


> Edit: I just looked something up on the bearcat. It held the world record for fastest climb rate (10,000 feet in 91 seconds) for 30 years before it was broken by the F-16 falcon! Now that's a major plus as a dogfighter.
> 
> This is incorrect. The F8F (Rarebear) record was set for "piston powered" aircraft in 1972. The T-38 set a time to climb record of 95.74 seconds to 12,000 meters (39,372 ft.) in 1962. The F4H (phantom) set a time to climb record of 34.52 seconds to 3000 meters (9843 ft.) in 34.52 seconds, also in 1962.


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## R Leonard (May 25, 2006)

First F8F record, climb to time, to 10000 feet was set on 22 November 1946, at 100 seconds. The next record was set the same day, again in an F8F, at 97.8 seconds.
So, if “Rarebear” beat that in 1972, and I don’t doubt your statement to that effect, then that would be 26 years.

Of course, Rarebear was not a standard USN version. Both the F8Fs in 1946 were standard -1 models, armed, with no ammo though; equipped with the standard armor and self-sealing tanks and carrying 50% fuel. Both F8Fs were assigned to TacTest.

R


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## davparlr (May 25, 2006)

R Leonard said:


> First F8F record, climb to time, to 10000 feet was set on 22 November 1946, at 100 seconds. The next record was set the same day, again in an F8F, at 97.8 seconds.
> So, if “Rarebear” beat that in 1972, and I don’t doubt your statement to that effect, then that would be 26 years.
> 
> Of course, Rarebear was not a standard USN version. Both the F8Fs in 1946 were standard -1 models, armed, with no ammo though; equipped with the standard armor and self-sealing tanks and carrying 50% fuel. Both F8Fs were assigned to TacTest.
> ...


I couldn't confirm your numbers but I have no reason to doubt them. However, the statement that it wasn't beaten until the F-16 is not right. In fact, while previously mentioned T-38 and F4H numbers are official, many earlier aircraft easily passed the F8F time to climb although most were unofficial. The earliest was probably the F-86D in 1950, whose initial rate of climb was 12000 ft/min. Others were the F4D with a time of 2 minutes to 40000 ft. in 1955, and the F-104 who, in 1958, went past 10000 ft in about 41 seconds on a record setting attempt at a much higher altitude. You can throw in others I did not look up, F-100, F8U, F101, et.al. 

Still an impressive number for the F8F. The F8F is a beautiful plane. I saw one fly at an airshow in Pensacola in about 1958. It was led by a P-51 who had to abort because of overheating. The weather was hot. Then, after much bragging by the Navy announcer about the superority of the air cooled Navy engines, the F8F took off an flew. But only for a few minutes, as it had to land because of overheating! Like I said, it was hot that day.


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## R Leonard (May 25, 2006)

Yes, but comparison of pistons vs jets is apples and oranges.


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## syscom3 (May 25, 2006)

R Leonard said:


> Yes, but comparison of pistons vs jets is apples and oranges.



Well said.


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## davparlr (May 25, 2006)

syscom3 said:


> Well said.


The statement was made that the F8F time to climb to 10000 was not beaten until the F-16 implying that it could best all the aircraft till then. That is incorrect. Apples and oranges comments still does not make that statement any more correct!


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## pbfoot (May 25, 2006)

davparlr said:


> The statement was made that the F8F time to climb to 10000 was not beaten until the F-16 implying that it could best all the aircraft till then. That is incorrect. Apples and oranges comments still does not make that statement any more correct!


 i even think 10000 in a 104 in 41 secs is slow did he even light the burners I personally can't count the number of times I've seen ac go verticle to fl350 in under a minute it was almost a ritual on the excercises I partook in for the last guy back for the night to do that the thought was is if I'm awake everybody will be


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## davparlr (May 25, 2006)

pbfoot said:


> i even think 10000 in a 104 in 41 secs is slow did he even light the burners I personally can't count the number of times I've seen ac go verticle to fl350 in under a minute it was almost a ritual on the excercises I partook in for the last guy back for the night to do that the thought was is if I'm awake everybody will be



That number was a eyeball interpretation of a time verses altitude chart for a successful attempt at a time to climb record to a much higher altitude. There is a large probablity of error, error would probably be in the direction you suggested.


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## chris mcmillin (May 26, 2006)

davparlr said:


> Salim said:
> 
> 
> > Edit: I just looked something up on the bearcat. It held the world record for fastest climb rate (10,000 feet in 91 seconds) for 30 years before it was broken by the F-16 falcon! Now that's a major plus as a dogfighter.
> ...


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## R Leonard (May 26, 2006)

> The statement was made that the F8F time to climb to 10000 was not beaten until the F-16 implying that it could best all the aircraft till then. That is incorrect. Apples and oranges comments still does not make that statement any more correct!



Well, since you seem to want to be pedantic, “Rarebear,” as pointed out, was not so named until long after the 1972 event. I’d also point out that this aircraft was NOT a true F8F having been modified in both airframe and engine. Further, eyeballing performance charts does not count when you’re talking about setting records. Flights for record require continuous monitoring and recording of the event, so any guestimate one might make from a chart is strictly a WAG. 

So, you can contest to your heart’s content whether the record breaker was an F-16 or an F8U or any other aircraft (and, frankly, jets versus pistons, who really gives a crap), but if the aircraft in question was not actually making a flight for record, then it doesn’t count. And since every plane you seem to want to drag out is a jet powered fighter, exactly what are you trying to prove . . . that there was an airplane in competition for the record prior to the F-16 cited in the post? Okay, I’ll buy that as long as the aircraft was actually in competition and you aren’t just picking a point on a climb chart. I am sure that the jet aircraft you named could probably have beat a climb to time record set by a R2800 powered F8F in 1946, but to my knowledge none did actually so compete, i.e., making a monitored and recorded attempt to supplant the existing record.

It is still apples and oranges to compare jet fighter performance, even for record, to piston fighter performance, just as it is also apples and oranges to compare a military equipped F8F performance to some bastardized civilian hybrid.

And as for my numbers on the 1946 record . . . it helps when I have the pilots log book for one of the actual pilots.


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## davparlr (May 27, 2006)

R Leonard said:


> Well, since you seem to want to be pedantic, “Rarebear,” as pointed out, was not so named until long after the 1972 event. I’d also point out that this aircraft was NOT a true F8F having been modified in both airframe and engine. Further, eyeballing performance charts does not count when you’re talking about setting records. Flights for record require continuous monitoring and recording of the event, so any guestimate one might make from a chart is strictly a WAG.
> 
> So, you can contest to your heart’s content whether the record breaker was an F-16 or an F8U or any other aircraft (and, frankly, jets versus pistons, who really gives a crap), but if the aircraft in question was not actually making a flight for record, then it doesn’t count. And since every plane you seem to want to drag out is a jet powered fighter, exactly what are you trying to prove . . . that there was an airplane in competition for the record prior to the F-16 cited in the post? Okay, I’ll buy that as long as the aircraft was actually in competition and you aren’t just picking a point on a climb chart. I am sure that the jet aircraft you named could probably have beat a climb to time record set by a R2800 powered F8F in 1946, but to my knowledge none did actually so compete, i.e., making a monitored and recorded attempt to supplant the existing record.
> 
> ...





Salim said:


> Edit: I just looked something up on the bearcat. It held the world record for fastest climb rate (10,000 feet in 91 seconds) for 30 years before it was broken by the F-16 falcon! Now that's a major plus as a dogfighter.



I wasn't the one who started the comparisons between props and jets. All I said was that this statement is incorrect as noted below.

"21 February The F4H-l Phantom II established new world records for climb to 3,000 and 6,000 meters withtimes of 34.52 and 48.78 seconds. LieutenantCommander John W. Young and Commander DavidM. Longton piloted the plane on its respective recordflights at NAS Brunswick, Maine". 1962.


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## Twitch (May 30, 2006)

The Bearcat was being used for climb demonstrations for a very long time. At the 1951 National Air Races in Detroit an F8F allegedly beat a F2H-1 Banshee to 10,000 from a standing start in less than a minute. I dunno?!?!

Kinert, Reed
Racing Planes Air Races Vol. 2
Aero Publishers, Fallbrook, CA 1969


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## syscom3 (May 30, 2006)

Thats quite possible. The early jets were not known as fast accelerators in those days.


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## davparlr (May 30, 2006)

syscom3 said:


> Thats quite possible. The early jets were not known as fast accelerators in those days.



They were real dogs. Most jets of this era were woefully underpowered. Also, props generate power at standstill, jets build as airspeed increases.


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## the lancaster kicks ass (May 31, 2006)

Douglas Bader once commented that when sitting in the meteor putting the throttle forward with the brakes on he expected to accelerate like a rocket, upon releasing the brakes he went to comment it was more like a lorry, until you actually got into the air where she picked up serious speed..........

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## evangilder (May 31, 2006)

The spool up time on the early jets was really slow. Watch a group of L-29s take off after watching an F-18 take off and you will see a huge difference. But we are also talking about a huge difference in engines.

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## Ericson (Jan 6, 2015)

My dad flew all three birds (*F8F*, *F4U*, and *F7F*) as well as the *F6F*, *F4F*, and *FM2* (the latter in combat.) In a number of discussions with him about their characteristics, it was clear that the *F8F* was his favorite because of its responsiveness. In a pure dogfight, I think it would have proven to be the best of the WW2 designs. However, the *F4U*, as mentioned previously, could do so many things well - in the early days in Korea it was the clear choice for a carrier fighter. My dad's younger brother commanded a squadron of Corsairs at that time and I know he thought highly of the plane's capabilities. Later he flew *F9F*s and *F3H*s, but he still regarded the Corsair as an outstanding performer. It was able to absorb punishment and return its pilot to the ship on many occasions, a not inconsequential quality. An interesting observation my dad once shared was that the *F4U* manufactured by Goodyear had the exhaust routed down and around the fuselage so that it exited underneath, and that was much easier on the pilot's hearing and made the plane more pleasant to fly, especially on long jaunts (he once flew a Corsair from Virginia to California in a day.) I did not know he had flown the Tigercat until relatively recently when I asked him, and he replied that they were nice planes but could not compete with the single-engined Grummans. On the subject of pilot training, keep in mind that the U.S. had so many young men in the pipeline during the war that they sometimes "washed out" guys for bogus medical problems because they had too many. Gas and ammo was also almost unlimited, so that many Ensigns and JGs had relatively many training hours when their squadrons reported to the fleets, unlike the fresh German and Japanese pilots later in the war who had comparitively little training.

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## drgondog (Jan 7, 2015)

As a Dogfighter the F8F was arguably the best of the US fighters with reservation in comparing to P-51H which makes the discussion not so cut and dried. Having said that, The Spitfire and the last Yak and La series of fighters were also exceptionally agile.

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## grampi (Jan 7, 2015)

drgondog said:


> As a Dogfighter the F8F was arguably the best of the US fighters with reservation in comparing to P-51H which makes the discussion not so cut and dried. Having said that, The Spitfire and the last Yak and La series of fighters were also exceptionally agile.



The Cat was probably better, or least equal to the P-51H and late model Spits at lower altitudes, but at higher altitudes it would be at a disadvantage...


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## l'Omnivore Sobriquet (Jan 7, 2015)

Bearcat versus Corsair, ah, what a show.

I'm glad those things existed.

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## BiffF15 (Jan 7, 2015)

evangilder said:


> The spool up time on the early jets was really slow. Watch a group of L-29s take off after watching an F-18 take off and you will see a huge difference. But we are also talking about a huge difference in engines.



That's funny, I always thought the Hornet was slow to spool up!


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## Ericson (Jan 14, 2015)

Some years ago I read an account of the only Bearcat vs Mustang encounter known to me. Shortly after hostilities ceased on VJ day, a carrier with a squadron of F8Fs was in the Gulf of Mexico and called on the port of New Orleans as a PR exercise. Nearby, on shore, was based a squadron of P51s. The guy relating the story was one of the Bearcat pilots. He said that several times both units would go up and "happen to" meet for simulated dogfights. He pointed out that no F8F was ever bested in these encounters. Who can say what the relative quality of the pilots was, flight time, etc., but it is the only example of such an encounter I'm aware of. Another account by a pilot who flew both planes said the 'Cat was clearly the stronger performer - that its throttle response was instantly felt seat-of-the-pants, while the Mustang first made more noise, then began to accelerate. The Bearcat would have been an excellent anti-kamikaze device, though that was not its initial designed purpose. The Mustang proved superb as a long range bomber escort and many B-17 aircrew survived the war because the P51 could go all the way there and back on the long missions. Hats off to William Overstreet, who passed in 2014. He flew 100 P51 missions, survived being shot down 3 times, flew a FW190 back to England for one of his escapes, and chased a 109 under the Eiffel Tower, shooting it down over Paris. Many eyewitnesses corroborated this event.

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## GregP (Jan 14, 2015)

Of the pilots I know who fly both, all seem to prefer the Bearcat for outright performance at VFR altitudes, but all also love the P-51, particularly if they are paying for the fuel. You can fly a P-51 at 1 U.S. gallon a minute or very slightly less. You can't do that in a Bearcat, but the Bearcat will definitely thrill you with the available power.

One thing a P-51 will do that you can NEVER do in a Bearcat is to still be flying 6+ hours from when you start the engine without the benefit of refueling.


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## tomo pauk (Jan 14, 2015)

A thing might also be that there is no privately own P-51H fighters around, but mostly the -D?


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## GregP (Jan 14, 2015)

The P-51H was lighter than the P-51C/D by a bit, but not enough to make it into something the C/D units weren't. It was faster by about 10% climbed a bit better but not enough to climb with a Bearcat. It could roll about the same as a P-51C/D and the Bearcat was better at that, too. I very strongly doubt it could accelerate with a Bearcat, but it very certainly COULD fly higher and go farther.


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## spicmart (Jan 14, 2015)

drgondog said:


> As a Dogfighter the F8F was arguably the best of the US fighters with reservation in comparing to P-51H which makes the discussion not so cut and dried. Having said that, The Spitfire and the last Yak and La series of fighters were also exceptionally agile.



Can one include the late war Doras as well? Or maybe even the late war 109s as classical dogfights occur at speeds where the 109 were the most agile. I guess..


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## GregP (Jan 14, 2015)

The only people who wanted to dogfight at the best speed of a Bf 109 were Bf 109 pilots. Everyone else wanted to be faster. You can say the same for the Mitsubishi A6M Zero ... NOBODY would fight it while going slow by 1943. By then, EVEY pilot in the ETO knew what speed NOT to use to dogfight a Bf 109.


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## tomo pauk (Jan 15, 2015)

GregP said:


> The P-51H was lighter than the P-51C/D by a bit, but not enough to make it into something the C/D units weren't. It was faster by about 10% climbed a bit better but not enough to climb with a Bearcat. It could roll about the same as a P-51C/D and the Bearcat was better at that, too. I very strongly doubt it could accelerate with a Bearcat, but it very certainly COULD fly higher and go farther.



I'd venture to guess that the P-51H would out-accelerate the F8F-1 from 400-420 mph on without trouble. As far as the RoC, I don't believe that F8F-1 was able to out-climb the P-51H above 20000 ft, let alone if the fuselage tank of the P-51H was without fuel.


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## grampi (Jan 15, 2015)

Ericson said:


> Some years ago I read an account of the only Bearcat vs Mustang encounter known to me. Shortly after hostilities ceased on VJ day, a carrier with a squadron of F8Fs was in the Gulf of Mexico and called on the port of New Orleans as a PR exercise. Nearby, on shore, was based a squadron of P51s. The guy relating the story was one of the Bearcat pilots. He said that several times both units would go up and "happen to" meet for simulated dogfights. He pointed out that no F8F was ever bested in these encounters. Who can say what the relative quality of the pilots was, flight time, etc., but it is the only example of such an encounter I'm aware of. Another account by a pilot who flew both planes said the 'Cat was clearly the stronger performer - that its throttle response was instantly felt seat-of-the-pants, while the Mustang first made more noise, then began to accelerate. The Bearcat would have been an excellent anti-kamikaze device, though that was not its initial designed purpose. The Mustang proved superb as a long range bomber escort and many B-17 aircrew survived the war because the P51 could go all the way there and back on the long missions. Hats off to William Overstreet, who passed in 2014. He flew 100 P51 missions, survived being shot down 3 times, flew a FW190 back to England for one of his escapes, and chased a 109 under the Eiffel Tower, shooting it down over Paris. Many eyewitnesses corroborated this event.



I'd be willing to bet the P-51s in these scenarios were "D" models, which were not on par with the Bearcats performance wise...if these scenarios would've taken place between the Cats and the "H" model, the outcomes would've been different...


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## grampi (Jan 15, 2015)

tomo pauk said:


> I'd venture to guess that the P-51H would out-accelerate the F8F-1 from 400-420 mph on without trouble. As far as the RoC, I don't believe that F8F-1 was able to out-climb the P-51H above 20000 ft, let alone if the fuselage tank of the P-51H was without fuel.



Based on the climb charts I've seen, the F8F wasn't able to outclimb the P-51H at ANY altitude...


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## GregP (Jan 15, 2015)

We'll have to disagree on the acceleration, Tomo, and I believe it has been clearly established that the F8F was a great fighter up to about 20,000 feet, so any meaningful comparions would have to come where you would FIND an F8F flying about, and that is not much above 20,000 feet in any case.

It COULD have been made into a high altitude fighter with a 2-stage supercharger or a turbocharger, but that Navy didn't need that capability and never developed it. I see a lot of things attributed in here to the P-51H that, in my own experience, weren't necessarily that way. We have several pilots at the museum who flew P-51H models and they have never expressed any great preference for it over a D. I get the feeling that it COULD be faster and but they really didn't spend much time doing it. It would be nice to see a dedicated thread on the benefits of the H from people who FLEW them, not from paper specifications.

Of interest to me would be the real-world performance and the real-world reliability. It also might be of interest to know the earliest time at which the H COULD have been fielded had it been deemed very important to do so. We KNOW it got to the war late, but COULD it habe gotten there a lot sooner?

That's the part of what-ifs I don't like. Anything is possible to the person suggesting it, but if the premise were have been done in real life, what would have been affected that could produce a negative that would outweigh any potential positive gains?


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## grampi (Jan 15, 2015)

GregP said:


> We'll have to disagree on the acceleration, Tomo, and I believe it has been clearly established that the F8F was a great fighter up to about 20,000 feet, so any meaningful comparions would have to come where you would FIND an F8F flying about, and that is not much above 20,000 feet in any case.
> 
> It COULD have been made into a high altitude fighter with a 2-stage supercharger or a turbocharger, but that Navy didn't need that capability and never developed it. I see a lot of things attributed in here to the P-51H that, in my own experience, weren't necessarily that way. We have several pilots at the museum who flew P-51H models and they have never expressed any great preference for it over a D. I get the feeling that it COULD be faster and but they really didn't spend much time doing it. It would be nice to see a dedicated thread on the benefits of the H from people who FLEW them, not from paper specifications.
> 
> ...



Considering the "H" model had 600 more HP, and 600 pounds less weight than the "D" model, I don't see how it's performance wouldn't have been much better than that of the "D" model...

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## GregP (Jan 15, 2015)

Let’s put this P-51H myth to bed once and for all.

The V-1650-9 that powered the P-51H (and a few V-1650-11s, too) was rated at 1380 HP at full military power at sea level and about 1380 at 19500 feet while the P-51D’s V-1650-7 was rated at 1490 HP at full military power at 19400 feet. Both of these ratings were at about 67 inches of Mercury or close to +16 psi boost. So the P-51H didn’t make more HP more than the V-1650-7 engine up to full throttle at normal boost pressures at 19400 feet or so. The 2200 HP WEP that the V-1650-9 and -11s were capable of was at 81 inches of mercury or about +25 psi boost, WITH water-methanol ADI injection. The ADI usually lasted about 4.5 – 5.0 minutes and then the Merlin had to be throttled back to 67 inches of Mercury, where it basically equal to the -1, -3, and -7 engines of the D models. The WEP setting for the P-51D didn’t use water-methanol injection and was available for 15 minutes or however long the pilot wanted to gamble his engine.

The P-51D was 7125 pounds empty and 10,100 pounds normal weight. The P-51H was 6585 empty and 9500 pounds normal weight. That means both are full internal fuel and armament, but clean. Let’s say the weight for comparison purposes is the empty weight plus 65% of the difference between empty and normal weights to allow for takeoff, climb, and cruise to some arbitray point.

That puts the P-515D at 9059 pounds and the P-51H at 8480 pounds. At 19500 feet the P-51D had 1490 HP available and the P-51H had about 1350 HP available at that same height using normal manifold pressures. If the P-51H went to 81 inches, then he had the 2200 HP and was a VERY sprightly performer for about 4.5 – 5.0 minutes, after which he was back to normal manifold pressure and normal rates of climb.

For the record, USAAC Report #TSCEP5E-1898 lists the rate of climb for the P-51H at 3395 feet per minute at 67” of Mercury at low blower critical altitude and 2640 feet per minute at high blower critical altitude. In that particular test, the P-51H ran fine but would not go into WEP as the engine started running rough when they tried, so they used mil power where it ran just fine. I have seen at least two other reports saying the same thing, though obviously many P-51Hs were capable of WEP.

That means the P-51D had a weight to power ratio of 6.08 pounds per HP while the P-51H had a ratio of 6.14 pounds per HP at the same manifold pressure. Pretty damned equal if you ask me, and I know you didn't. The P-51D could get to 1700 HP WER without ADI and sustain that for three times or more longer than the finicky P-51H could.

At WEP the P-51D had a weight to power ratio of 5.33 pounds per HP while the P-51H could get as low as 3.85 pounds per HP for a very short time IF WEP was available and was then back to 6.14 pounds per HP and normal manifold pressures.

So, YES, the P-51H could get some sparkling numbers, but not for very long. When it was out of ADI the two planes were VERY equal with the P-51D still having a non-ADI WEP available.

Bottom line is YES, the P-51H could put up sparking numbers for a very short time. After that time it wasn’t any better than the P-51D and the P-51D could still go to WEP and out-perform the P-51H once the P-51H's ADI was gone.

The Bearcat's empty weight (F8F-1) was 7070 pounds and 9600 loaded. If we use the same 65% of the difference, the test weight is 8714 pounds with 2300 HP on tap. The comparative weight to power ratio is 3.79 pounds per HP and the Bearcat is still climbing at 3060 feet per minute at 20000 feet even though it isn't a "high altitude" fighter.

You can favor the P-51H all day; I'll stick with the Bearcat, especially since it's great big HP advantage was NOT using ADI and was avilable as long as you had fuel. Admittedly, that wouldn't be for too long relative to the P-51H, but it also wasn't restricted to only a few minutes of high power.

Please don't take this wrong. I love the P-51, all models including the P-51H. But the P-51H wasn't the all-conquering hero that it is usually made out to be except for 4.5 - 5.0 minutes IF the ADI works, and then it is hell on wings for a short time after which it back to P-51D type numbers VERY rapidly.

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## wuzak (Jan 16, 2015)

Given that the V-1650-9 was basically the same as the Merlin 130/131 in the Hornet, I can't see how your numbers add up.

The 130/131 was rated at >2000hp without ADI.

The RM.17SM was rated at 2,200hp @ 2,000ft MS gear and 2,100hp @15,000ft FS gear without ADI (pased type test but didn't go into production). 

Wiki lists the Packard Merlin performances as:


V-1650-1: 1,390 hp (1,040 kW); Based on Merlin 28, used in P-40 Kittyhawk and Curtiss XP-60 fighters
V-1650-3: 1,280 hp (950 kW); Based on Merlin 63.
V-1650-5: 1,400 hp (1,000 kW); Experimental.
*V-1650-7: 1,315 hp (981 kW)*; Similar to Merlin 66, primary powerplant of the P-51D Mustang.
*V-1650-9: 1,380 hp (1,030 kW)*; 2,218 hp WEP with Water methanol injection.
V-1650-9A: 1,380 hp (1,030 kW);
V-1650-11: 1,380 hp (1,030 kW); Modified fuel system.
V-1650-21: 1,380 hp (1,030 kW); Opposite rotation for P-82 Twin Mustang

I wouldn't mind seeing a graph of power vs altitude for the F8F-1 and the P-51H. Both at WEP or normal power, so we can see what the power difference really is.


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## GregP (Jan 16, 2015)

Hi Wuzak,

They don't have to add up. They are from "Allied Aircraft Piston Engines of WWII" by Graham White. I extracted the HP from two data points that were about the same height lower and higher than the V-1650-7 engine. It is very close and any difference would be small.

The -9 was 1380 HP at sea level, 1500 HP at 13750 feet and 1210 HP at 25800 feet. I extrapolated the HP at about 19400 feet so they would be at the same altitude. Both are at about 67 inches of MAP. The 2200 was at 81 inches with ADI and was not allowed to go to WEP without ADI or the engine would fail almost immediately. When they do that at Reno these days, they fail almost immediately, too. That is WITH hot rod parts, not stock Merlin rods that self destruct at just about 2400 - 2800 HP or so. That's why Voodoo and Strega are both running Allison G-series rods ... so they DON'T self destruct, even at 4000 HP.

The -7 was rated at 1700 HP WEP at 6400 feet and 1490 at 19400 feet without ADI.

Both from multiple sources.

I don't condsider Wiki a source. It may be something to quote as a start to a discussion, but I wouldn't trust Wiki for a recipe for a muffin. Graham White I trust one hell of a lot more ...

Of course, you are free to disagree as you have, but I'm not very far off the mark if at all. Too many people who flew them say the same thing. I REALLY trust the guys who flew them. They loved the 5 minutes of ADI and after thaht it was a stock P-51D or close to it with a bit more speed .... maybe 450 mph versus 435 - 437 at best P-51D altitude. That isn't enough extra for ME to build it at all, and certainly not enough to warrant a wartime production interruption.

As I've said on numerous occasions, top seeds are for test pilots. The only time service pilots see top speed is ina dive or in a deliberate training exercise to reach top speed. Other than that they rarely ever get above takeoff and climb power except in combat. If I was 500 miles from home over Berlin, I would NEVER use WEP. If I had to goose it a bit I would, but getting home would, for me, preclude long stints at WEP that ultimately destroys a Merlin. The only question is when.

They'll criuse and run at Mil power for a LONG time, but WEP is very hard on them.If you broke the throttle wire to go into WEP, it was a sign for your crew chief to change engines ... assuming he liked you.

You may well disagree and have wanted it in serial production at the earliest possible date. I'd understand while being a dissenter. For the 5 minutes of ADI, I might agree. After that, it was nothing but a production interruption that was not acceptable to the actual wartime people in charge until very late war ... or it would have entered service sooner.

It didn't.

ALL the Merlins that made 2000+ HP did so at elevated boost and sometimes elevated rpm. They'll tolerate the rpm and the boost to a point and then give up.

The engines in Streaga and Voodoo cannot go 8 laps (64 miles) at full race power. They CAN go 8 laps at reduced power, and have been optimized for that by very judicious use of stronger rods, custom parts, custom pistons, frequent main bearing replacement, and modern ignition and mixture control. You might recall that the world record 1930s Merlin predecessor engines from Rolls Royce were expected to run at full power for all of 15 minutes, after which all bets were off.

Wartime Merlins used essentially the same parts and weren't far from the Buzzard and R internally. Better, yes, incrementally. Wildly different? No.


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## cimmex (Jan 16, 2015)

Thank you Greg for this informative post 63. Very credible!


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## GregP (Jan 16, 2015)

Hi Cimmex,

Thanks!

The P-51H is held up as a high standard and it COULD do very well if the ADI was still there and working. After that is was a bit better than the P-51D, but not a lot. To be so it needed the extra power that ADI and the boost increment afforded.

The Ta 152 could ALSO do VERY well if everything was perfect. I have a hard time believing that it was perfect most of the time as very few ever flew in combat and it USUALLY takes some time to work out the kinks in a new plane whether it is British, U.S., Japanese, or German ... or anyone else's for that matter. Maybe the Ta 152 was the exception and everything was perfect right off the drawing board, I can't say. But after the ADI ran out, the Ta 152 was back to P-51D type speeds and climb rates (426 - 435 mph or so and 3200 - 3400 feet per minute climb rates or so). So it was NOT a bad plane by any stretch of the imagination. 

The Fw 190D / Ta 152 series and the late war P-51s were quite equal after the nitrous and water methanol ran out. The thing working against the D models was sheer volume of Allied fighters in the air compared with the number of Fw 190Ds in the same airspace. While the boost was there, either the P-51H or the Ta 152 was necessarily slightly better depending on altitude and starting position, but the two never fought so we can't say which was superior under full boost ... it is a true "what if." The Fw 190 and Ta 152C were better at rolling than ANY Allied planes, but that is not decisive in itself since they also had a vicious stall and could not turn with some Allied fighters near the stall/cornering limit, especially at low altitude since if it DOES stall, it would usually invert and spin into the ground ... not a good outcome for the Focke Wulf driver. The P-51D did that, too, but gave the pilot a very good stall buffet warning before it happened. I've ridden in a P-51D when the owner was practicing for a flight review. He didn't stall it but DID fly stall approaches, and it does shake enough to warn you unless you are on drugs or are just not paying attention.

Not too sure about the LONG wing Ta 152H's roll rate, but it HAD to slow down from the dazzling radial Fw 190 and Ta 152C roll rates due to span if nothing else. I belive the Ta 152 had more engine boost time than the P-51H did ... about 15 minutes as I recall, maybe incorrectly.

My biggest "observation" about the Ta 152 C or H is the low number fielded, which made them ineffective against 1000+ plane bomber and fighter streams. They would run out of ammunition after several attacks if nothing else, but they WOULD have attracted a lot of Allied attention after a firing pass and there were a LOT of P-51s around to answer the challenge.

One on one they are as good as the best we had, maybe slightly better (assuming equal pilots), especially in armament and when the boost is available. Not all the Germans were Erich Hartmann and not all the U.S. pilots were Richard Bong, either.

Wish we had a real Ta 152 / Fw 190D to fly at our museum! That would be marvelous! We HAVE a replica Fw 190F and it is very cool to see it fly! (flies behind a Pratt Whitney R-2800)

Would be better if we could install a real BMW 801 radial ... WITH the automatic mixture and rpm controls, that is.

You don't happen to HAVE one, do you?


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## cimmex (Jan 16, 2015)

it was not my intention to start a Ta152/ P-51H contest but BTW have you heard about that: “mail from Tehachapi - Mike Nixon / Vintage V12´s is restoring one of the rarest german engines, the powerful Jumo 213 - again Mike is doing a fantastic job ! Thanks to Mike Nixon for sharing this restoration with us”.
https://www.facebook.com/pages/MeierMotors-GmbH/196699400376090


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## tomo pauk (Jan 16, 2015)

As Shortround6 says - dont know where to start from 



GregP said:


> Let’s put this P-51H myth to bed once and for all.
> 
> The V-1650-9 that powered the P-51H (and a few V-1650-11s, too) was rated at 1380 HP at full military power at sea level and about 1380 at 19500 feet while the P-51D’s V-1650-7 was rated at 1490 HP at full military power at 19400 feet. Both of these ratings were at about 67 inches of Mercury or close to +16 psi boost. So the P-51H didn’t make more HP more than the V-1650-7 engine up to full throttle at normal boost pressures at 19400 feet or so. The 2200 HP WEP that the V-1650-9 and -11s were capable of was at 81 inches of mercury or about +25 psi boost, WITH water-methanol ADI injection. The ADI usually lasted about 4.5 – 5.0 minutes and then the Merlin had to be throttled back to 67 inches of Mercury, where it basically equal to the -1, -3, and -7 engines of the D models. The WEP setting for the P-51D didn’t use water-methanol injection and was available for 15 minutes or however long the pilot wanted to gamble his engine.



Either it is not a myth, or it refuses to go to the bed (just like my older daughter).
When V-1650-9 was using WI, almost 2300 HP was available on 90 in Hg, and ~2150 on 80 in Hg, that is for 1st gear (under 10000 ft). In 2nd gear, it was 1750-1800 HP, depending whether 80 or 90 in Hg was used. Altitude about 20000 ft; the P-51D on 67 in has some 1500 HP at that altitude.
WEP setting (67 in Hg on 130 grade fuel) for the P-51D was available for 5 minutes, not 15 minutes. Military power was using 61 in Hg. 
Once the water is gone, the V-1650-9 still has an option to use the 'dry WER' rating, 3000 rpm and 70 in Hg.



> The P-51D was 7125 pounds empty and 10,100 pounds normal weight. The P-51H was 6585 empty and 9500 pounds normal weight. That means both are full internal fuel and armament, but clean. Let’s say the weight for comparison purposes is the empty weight plus 65% of the difference between empty and normal weights to allow for takeoff, climb, and cruise to some arbitray point.



If I may suggest:
Let's not fill fuselage tank, that would shave 300 lbs from the P-51H, ie. take off weight of is now 9300 lbs, with 210 gals and full ammo load. For the P-51D, it is 85 gals = 510 lbs, for take off weight of 9600 lbs (184 US gals aboard; full ammo)



> That puts the P-515D at 9059 pounds and the P-51H at 8480 pounds. At 19500 feet the P-51D had 1490 HP available and the P-51H had about 1350 HP available at that same height using normal manifold pressures. If the P-51H went to 81 inches, then he had the 2200 HP and was a VERY sprightly performer for about 4.5 – 5.0 minutes, after which he was back to normal manifold pressure and normal rates of climb.



Covered above - once the water is out, there is still 'dry WER' available, along with military power for the P-51H.



> That means the P-51D had a weight to power ratio of 6.08 pounds per HP while the P-51H had a ratio of 6.14 pounds per HP at the same manifold pressure. Pretty damned equal if you ask me, and I know you didn't. The P-51D could get to 1700 HP WER without ADI and sustain that for three times or more longer than the finicky P-51H could.



Quirk is that P-51H does not need to be run on same manifold pressure as the P-51D. Only 5 min for the WER of the P-51D.


> So, YES, the P-51H could get some sparkling numbers, but not for very long. When it was out of ADI the two planes were VERY equal with the P-51D still having a non-ADI WEP available.



Other people, that really flew fighter aircraft, might confirm that 5 minutes is like ages once in air combat? Most engines of the ww2 have had the 'emergency rating' that spanned between 3-5 minutes, nobody complained.



> The Bearcat's empty weight (F8F-1) was 7070 pounds and 9600 loaded. If we use the same 65% of the difference, the test weight is 8714 pounds with 2300 HP on tap. The comparative weight to power ratio is 3.79 pounds per HP and the Bearcat is still climbing at 3060 feet per minute at 20000 feet even though it isn't a "high altitude" fighter.



Let's not use the 65% rule of the thumb. The Bearcat already has only 185 US gals aboard, ie. less than P-51H with only wing tanks full. Meaning the take off weight of 9670 lbs, per SAC table. 370 lbs greater than the P-51H, or thereabout with P-51D. At 20000 ft, the P-51H climbs at 3600+ fpm, or more than 20% better than the F8F-1.
At 30000 ft, it is ~1250 fpm (F8F-1) vs. 1900 fpm (P-51H). At 10000 ft, it is 4200 vs. 4250 fpm, minimal advantage for the P-51H. All values for the P-51H are with fuselage tank empty (ie. for total of 210 gals).



> You can favor the P-51H all day; I'll stick with the Bearcat, especially since it's great big HP advantage was NOT using ADI and was avilable as long as you had fuel. Admittedly, that wouldn't be for too long relative to the P-51H, but it also wasn't restricted to only a few minutes of high power.



2300 HP was used for take off. Without ADI, F8F-1 drivers have 2100 HP on disposal at 3000 ft, and 1700 HP at 16000 ft. Surely beating the V-1650-9 wihout ADI. However, at 20000 ft, there is only 1500 HP available, vs. 1400 for the -9; not enough to overcome the disadvantage in weight and drag vs. the P-51H. 
At 30000 ft, it is 1000 HP vs. 1200 for the V-1650-9. In case both F8F-1 and the P-51H are using ADI, the P-51H has more power in 10-20 kft belt.
The F8F-1 could not use max power ratings for 'as long as you have the fuel' neither. Max continuous is not equal to military power.

Quite a bit of data about the F8F-1 and P-51H are available on the Williams' site and here (F-51H, per post-was nomenclature)

edit: the RoC figures I've posted are from SAC sheets, and actually are for 260 gal fuel (ie. all 3 internal tanks full), not just for 210 gals as stated above


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## Bad-Karma (Jan 16, 2015)

Seems to me its a classic example of Interceptor vs Escort. F8f dominating down low with the P51H being dominant up high.


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## GregP (Jan 16, 2015)

Hi Cimmex!

Do you happen to know what the Jumo 213 is going into? Maybe a Focke-Wulf? I'd really lover to hear it run. Always liked the numbers for the Jumo 213. I'll bet Steve Hinton knows. If I manage to find out, I'll post it. Mike is also overhauling a DB 601 that came out of a Bf 109E that was found at the bottom of a Russian lake. We have the airframe at the musuem and it belongs to a private party. The engine was in good shape except for the nosecase which, being Magnesium, was gone. The owner had a new one made from Aluminum. The owner is unsure whether to restore this one or to use it as a template to build another one from scratch.


Hi Tomo,

we'll have to disagree, but that's OK. I got my weight numbers from multiple sources, including Boeing (who bought and owns what used to be North American Aviation some time back).

Tell you what, do a comparion atfer the P-51D and P-51H have both been airborne and in cruise for 3 - 4 hours or so and see what you come up with. The HP numbers for the V-1650-9 come from Graham WHite's excellent book. The source you use won't matter, it'll be close even if slightly different. The -7 and -11 were not cleared for elevated WEP MAP without ADI. Without the ADI they were to be run at 65 - 67 inches of MAP ... close to +16 psi of boost. At that level of boost they were VERY equal to the V-1650-1, 3, 7 engines.

Whether or not the R-2800 required ADI was largely dependent on the myriad dash number. I have the R-2800 book and will gladly look up the HP for any dash number if anyone is interested. Some WEP powers were wet (ADI) and and some were dry (no ADI). Several had two WEP number for both wet and dry.

The 3000 feet per minute climb at 20000 feet for the F8F-1 came from a flight report and I doubt if very many Bearcats ever got that high except as an exercise. The flight report was for a clean airplane with pilot, fuel, and ammunition and no drop tanks or external ordnance. The Bearcat could get that way by taking off with drop tanks, using them and dropping them. I was trying to do some figuring under similar conditions ... full internal load, clean airplane, and fuel about 1/2 to 3/4 full at some point in the flight. What I didn't do was to figure it by fuel flow. Instead I chose to take empty weight and use 65% of the normal loaded weight number. The F8F didn't get into combat for the U.S.A. in the WWII era and several years afterwards, but did for the French in Indochina. When the French fought with them, they were always down low, even performing ground attack. Had they been using P-51Hs, the same would have been true so any comparisons would have been at low altitude anyway.


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## cimmex (Jan 16, 2015)

hi Greg
Well, I found this in a German aviation forum. Most members speculate that the engine is for a Flugwerk D-9 replica. AFAIK two of them are around and at least one is owned by Jerry Yagen


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## cimmex (Jan 16, 2015)

double post


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## GregP (Jan 16, 2015)

Hi Cimmex,

That makes perfect sense, and is about what I figured. There is almost no point in overhauling a Jumo 213 unless you intend to actually run it. After an overhaul, if an aviation engine of large displacement sits around for as litle as 5 years, it needs another overhaul before you try to run it. That being said, overhauling a Jumo 213 almost has to mean it is going into an aircraft.

I heard the Fw 190D-13 that Doug Champlin run once. They didn't have the high-speed unit for throttle control, so it only ran at idle power, but it DID run and sounds different from the usual Allison and Merlin V-12s we hear most of the time. That aircaft is now in Paul Allen's collection in Seattle, Washington.

We DO get to hear the Argus inverted V-12 that is in our Pilatus P-2 every once in awhile and it has a unique sound to it, too. If anyone is interested, I can get pics tomorrow as Saturday is my volunteer day at the museum. In fact, if you like I can get pics of ALL the German items there and post tomorrow or Sunday.

The Pilatus has a couple of interesting features. It is Swiss, of course, and they are frugal if nothing else. They had a group of Bf 109s due to retire when they decided to make a trainer, and they took the landing gear and instrument panels from the Bf 109s and used them directly on the P-2s. The left main gear is the Bf 109s right main ghear and vice versa, and it folds inward! Pics on the way ...


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## tomo pauk (Jan 16, 2015)

GregP said:


> Hi Tomo,
> we'll have to disagree, but that's OK. I got my weight numbers from multiple sources, including Boeing (who bought and owns what used to be North American Aviation some time back).



I have no problems with your weight numbers for the weights, they are as good as it gets.



> Tell you what, do a comparion atfer the P-51D and P-51H have both been airborne and in cruise for 3 - 4 hours or so and see what you come up with. The HP numbers for the V-1650-9 come from Graham WHite's excellent book. The source you use won't matter, it'll be close even if slightly different. The -7 and -11 were not cleared for elevated WEP MAP without ADI. Without the ADI they were to be run at 65 - 67 inches of MAP ... close to +16 psi of boost. At that level of boost they were VERY equal to the V-1650-1, 3, 7 engines.



On 130 grade fuel, the max manifold pressure, without ADI, was 67 in Hg for the V-1650-9. 
70 in Hg should be on 145 to 150 grade fuel, at least that is my understanding. Same for the 90 in Hg - uses ADI and 145 to 150 grade fuel. A chart with different engine power settings resulting powers: pic. On 67 in Hg, the power was about the same as what V-1650-3 offered - no wonder, since the supercharger size and gearing were pretty much the same, and the engine RPM was same. 



> Whether or not the R-2800 required ADI was largely dependent on the myriad dash number. I have the R-2800 book and will gladly look up the HP for any dash number if anyone is interested. Some WEP powers were wet (ADI) and and some were dry (no ADI). Several had two WEP number for both wet and dry.



About the R-2800-34W: it did have ADI, useful up to about 15000 ft. No ADI - no WER here. Was also true for the other R-2800s, at least war-time examples, I'll bow to superior data, however.
The ADI for the V-1650-9 was useful up to ~25000 ft, so was for the R-2800-18W (late war version, 2-stage S/C, used on the F4U-4).


> The 3000 feet per minute climb at 20000 feet for the F8F-1 came from a flight report and I doubt if very many Bearcats ever got that high except as an exercise. The flight report was for a clean airplane with pilot, fuel, and ammunition and no drop tanks or external ordnance.



The SAC (link) for the F8F-1 also shows 3000 fpm at 20000 ft. Achieved with fully combat-capable aircraft, so full ammo internal fuel. 


> The Bearcat could get that way by taking off with drop tanks, using them and dropping them. I was trying to do some figuring under similar conditions ... full internal load, clean airplane, and fuel about 1/2 to 3/4 full at some point in the flight. What I didn't do was to figure it by fuel flow. Instead I chose to take empty weight and use 65% of the normal loaded weight number.



This is why I didn't followed you on the 65% thumb rule - I've simply listed the related performance figures for it, for the 'combat weight'. They are very good, and will put any Merlinized P-51 in troubles under 10000 ft, but not above 15-20 kft.


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## wuzak (Jan 16, 2015)

Lumsden Data on V-1650-7 and V-1650-9 on 100/130 grade fuel:

V-1650-7
Takeoff: 1,315hp, 3,000rpm, +12psi
WEP MS: 1,705hp, 3,000rpm, +18psi, 5,750ft
WEP FS: 1,580hp, 3,000rpm, +18psi, 13,500ft

V-1650-9
Takeoff: 1,380hp, 3,000rpm, +14psi
WEP MS: 1,920hp, 3,000rpm, +20psi, 9,500ft
WEP FS: 1,620hp, 3,000rpm, +20psi, 21,750ft

Lumsden doesn't have Normal power for the Packard Merlins, but we can use values for the similar Rolls Royce models:

Merlin 66 (V-1650-7)
Normal MS: 1,415hp, 2,850rpm, +12psi, 8,500ft
Normal FS: 1,310hp, 2,850rpm, +12psi, 18,000ft

Merlin 110-114 (~V-1650-9)
Normal MS: 1,380hp, 2,850rpm, +12psi, 15,500ft
Normal FS: 1,200hp, 2,850rpm, +12psi, 30,000ft

The Merlin 130/131 
Normal MS: 1,430hp, 2,850rpm, +12psi, 11,000ft
Normal FS: 1,280hp, 2,850rpm, +12psi, 14,000ft

The V-1650-7 is listed as weighing 1,645lb (746kg) and the V-1650-9 1,690lb (767kg).

The V-1650-7 was a 60-series Merlin, basically similar to the Merlin 66.

The V-1650-9 was a 100 series Merlin with end to end lubrication, overhung first stage supercharger impeller and single point fuel injection (into eye of supercharger impeller). I assume the overhung first impeller reduced losses due to the intake (big improvements in performance were found when the intale to the supercharger was improved by Hooker).

The supercharger impellers were 12.0"first stage and 10.1"second stage for both -7 and -9. The supercharger gear ratios were MS 5.8:1 and FS 7.34:1 for the -7, MS 6.39:1 and FS 8.095:1 for the -9.

So the -9 was a higher altitude rated engine.

Greg mentions the V-1650-1, -3, -7 and -9. The -1 was a 20-series Merlin with single stage two speed supercharger. The -3 was an early 60-series engine, equivalent to the Merlin 63. It lacked the strengthening that the later engines received, and so did not have the capability of higher pressures.

A note about ADI and Merlins: None of the Rolls-Royce Merlins used ADI during the war. The stronger engines (eg Merlin 66) were good for +25psi boost on 100/150 grade fuel without ADI.

According to White, _R-2800 Pratt Whitney's Dependable Masterpiece_ the R-2800-34 had the following performance with 100/130 grade fuel:

Takeoff: 2,100hp @ 2,800rpm
Military LO: 2,100hp @ 2,800rpm, 3,000ft
Military HI: 1,700hp @ 2,800rpm, 16,000ft
Normal LO: 1,700hp @ 2,600rpm, Sea Level
Normal LO: 1,700hp @ 2,600rpm, 8,500ft
Normal HI: 1,500hp @ 2,600rpm, 18,500ft

Unfortunately boost/MAP is not shown.

Boost Pressure/MAP Equivalents:
+12psi = 54.4inHg MAP
+14psi = 58.4inHg MAP
+16psi = 62.5inHg MAP
+18psi = 66.6inHG MAP
+20psi = 70.6inHG MAP
+25psi = 80.8inHg MAP
+30psi = 91.0inHg MAP


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## GregP (Jan 16, 2015)

The Bearcat mostly used the -22W and -34W, not the -34. The F8F-2 used the straight -30.

The -22W and -34W used water injection, not water-methanol, and the -30 made 2250 HP without water.

I wouldn't think you'd want to spend non-combat time climbing at WEP or you won't have any ADI left for combat. That being said, the P-51H climbed almoist exactly like a P-51D unless it was at WEP, which was my point to start with. If you are betting your life on WEP, you'd best be really careful about under what circumstances you use it. So there would be virtually ZERO non-combat use of WEP requiring ADI ... unless it was a peacetime joyride.

Now we all know that these engines (both Allied and Axis) could be run at slightly higher rpm and MAP than the manufacturers recommended as maximum, but these numbers are not published ANYWHERE. They are in the minds of the former crew chiefs and pilots. As it happens I know some of the settings they used for the -7 and -9 Merlins, and they were VERY comparable until the ADI went in and the manifoild pressure went up to 81 inches or so. That's when the -9 and -11 could really shine, but you better be careful how long you make use of it or the crew chief will be changing it before the next flight.

I've heard it said that the -7 could ALSO be flogged at 81 inches and make very comparable power, but it was HIGHL:Y frowned upon by the crew chiefs and squadron commanders because of the engine wear ... and they could tell by looking at the color of the spark plus and exhaust manifolds near the cylinder ports, sort of like on a Harley Davidson motorcycle today. A lean run is VERY apparent on the pipes, and even auto-rich wasn't rich enough for 81" unless the engine was a -9 or -11.

As for the radials, the 2100 HP was max at 2800 - 2850 rpm with water. Later R-2800s that went into the Bearecat could make a few hundred more. The -30 could make 2250 HP dry. They even made one fan-cooled R-2800 that could produce 2800 HP and another variant that made 3400 HP, but they ran on a test stands (dynamometers) and never flew. Most Bearcats were 2100 or 2250 HP untis, some of the late ones were 2400 HP. I've seen at least three Bearcats personally that the owners said had the 2400 HP unit in them. That was the power level late in the war, and many survivors have been fitted with them. I suppose it you are building one today from parts, you might as well get the best engine.

That doesn't change the fact that I read a flight test report that said a clean Bearcat could still climb at 3000 feet per minute at 20000 feet. Hardly any real Bearcats DID since they would mostly be climbing at reduced cruise-climb power unless they were in combat where all the stops are pulled. The same can be said for ALL the piston fighters.

The numbers we throw around in here are possible but not very likely ..., unless in combat.


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## pbehn (Jan 16, 2015)

Can you compare a merlin in line water cooled v engine with a P&W air cooled engine? The Merlin with a meredith effect radiator had a small frontal area and little cooling drag. The P&W 2800 had massive max horsepower and torque but the frontal area eats horsepower. Horses for courses.


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## tomo pauk (Jan 16, 2015)

The -22W was used only in prototype (maybe). Think we can forgive Wuzak for not typing the 'W' behind '34' 



> The F8F-2 used the straight -30.



Actually, it was -30*W*; SAC.

Re. a fan cooled R-2800: it flew, propelling the XP-47J to around 500 mph. Granted, turbo helped to get to that speed. 2800 HP was available (without fan here) for bread'n'butter P-47Ds, with ADI and on 150 grade in the same time. Plus for the P-47M and -N.
Unfortunately, fan cooled R-2800s were not used on the Beacrcat.



> The -22W and -34W used water injection, not water-methanol, and the -30 made 2250 HP without water.



Care to back up that it was only water, not water-methanol? What was used as anti-freeze, with alcohol absent?



> That doesn't change the fact that I read a flight test report that said a clean Bearcat could still climb at 3000 feet per minute at 20000 feet.



That values is stated in the SAC, no worries.


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## GregP (Jan 16, 2015)

Yah, I can forgive Wuzak for almost anything. 

About backing up thw water only, that's what I heard from an old crew chief, and he said they weren't worried about freezing until they had to. That was in the Pacific at 15,000 feet and under while flying around carrier task groups. I suppose you WOULD have to add some antifreeze in the ETO since there IS a winter there as opposed to the South Pacific winter.

We could comare the radial against the liquid-cooled engines, but you'd have to have the drag numbers to do much with it. I believe Drgondog has done some of these comparisons in here in the past, but I can't recall the post title. You can do a seach for it. The words will include cd0 or CDO or zero lift drag coefficient.

I don't want to do it for a general answer because then someone asks somethign specific and you have to ignore it or do it all over again. However, the puiblished top speeds for the fighters, and remember these are at best altitude only, can give you a good feel for the differences. Most radial planes were a bit bigger than most inline planes, with the Bearcat as a notable exception. 

The Bf 109 was the classic smallest airframe which could be wrapped around a big engine. 

The P-47 was the other end of the spectrum, with the Brits joking that they could take evasive action by jumping around inside the fuselage if attacked. But it was the best or one of the front-running top high altitude fighters of the war. Being big and heavy, it was no slouch at diving away or diving toward anything. The trick was to stay in the middle of the air and avoid the ground.

The fastest aircraft of WWII included the Dornier Do 335 Pfiel, the P-51H at WEP, the Ta 152H at WEP, the Republic XP-72 (a prototype) and the XP-47J. After the war the Commonwealth CAC-15 was also right there at just over 500 mph.

Then we fixated on jets and abandoned big piston engine development work about 1946 or so. The big pistons were hard to work on, expensive to maintain, and ate fuel like crazy, and the civilian market potential was limited at best. So it all made sense economically anyway. I believe the last big piston fighters made included the Douglas Skyraider, Sea Fury, the Hispano Ha.1109, 1110, and 1112 and a few prototypes, of which my personal favorite is the FMA I.Ae.30 Namcu of 1950. 

It looks like nothing so much as an all-metal Mosquito / Hornet combination. It was fast at 460 mph and had SIX 20mm cannons! Unfortunately the total population is one prototype. Bet that puppy could lay down some supressing fire!


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## wuzak (Jan 16, 2015)

GregP said:


> The Bearcat mostly used the -22W and -34W, not the -34. The F8F-2 used the straight -30.



Greg, the -34 was the same as the -34W, only without ADI. The figures White has for the -34/-34W are without ADI and are the same for both versions.

The F8F-2 was a couple of years later (1947) and not really contemporary with the P-51H.




GregP said:


> The -22W and -34W used water injection, not water-methanol, and the -30 made 2250 HP without water.



Autorised ADi mixtures for the R-2800 (from White):

Methyl Alcohol 50%/Water 50%
Methyl Alcohol 60%/Water 40%
Methyl Alcohol 25%/Ethyl Alcohol 25%/Water 40%
Methyl Alcohol 60 parts/Water 40 parts/Anti-Corrosion Oil 1 part

So straight water was not authorised for the R-2800.




GregP said:


> I wouldn't think you'd want to spend non-combat time climbing at WEP or you won't have any ADI left for combat. That being said, the P-51H climbed almoist exactly like a P-51D unless it was at WEP, which was my point to start with. If you are betting your life on WEP, you'd best be really careful about under what circumstances you use it. So there would be virtually ZERO non-combat use of WEP requiring ADI ... unless it was a peacetime joyride.



The V-1650-9 had 215hp more at WEP in MS gear to an altitude 3,750ft higher. And 40hp more at WEP in FS gear at an altitude 8,250ft higher. Basically it had more power more of the time.

The 66 (~V-1650-7) seems to have more power for normal climb than the Merlin 110-114 (~V-1650-9). It is 35hp in MS gear, but 7,000ft lower. The advantage in hp is greater in FS gear at 110hp, but so is the altitude difference at 11,000ft. The two engines are rated for different heights, but I suspect that the -7 has the advantage in normal power mainly in MS gear - in FS gear its peak is only a few thousand feet above the -9s MS peak, so possibly the two would be about equal at that point. Basically the -9 has the advantage for most of the altitude range.

Add that to the weight advantage and it isn't hard to see that the H woudl climb better than the D.




GregP said:


> Now we all know that these engines (both Allied and Axis) could be run at slightly higher rpm and MAP than the manufacturers recommended as maximum, but these numbers are not published ANYWHERE. They are in the minds of the former crew chiefs and pilots. As it happens I know some of the settings they used for the -7 and -9 Merlins, and they were VERY comparable until the ADI went in and the manifoild pressure went up to 81 inches or so. That's when the -9 and -11 could really shine, but you better be careful how long you make use of it or the crew chief will be changing it before the next flight.



I have shown that the -9 has a significantly higher FTH in both MS and FS gears. There were a number of mechanical improvements in the -9 over the -7 which helped increase the FTH, increase the hp and allow for more boost.

The -9 should handle 81inHg (+25psi) without ADI (since Rolls-Royce Merlins could) - 100/150 fuel required, of course. ADI allowed the -9 to use 91inHg
(+30psi) for even more power.

It is my understanding that WEP was limited to 5 minutes mainly because of oil and coolant temperatures, the cooling circuits not designed for such high powers (if they were they would be very large and draggy).

The pilot could use WEP multiple times - but would have to let the system cool before using it again.




GregP said:


> As for the radials, the 2100 HP was max at 2800 - 2850 rpm with water. With ADI that went up, and later R-2800s that went into the Bearecat could make a few hundred more.



Well since there weren't later military Merlins, particularly not the Packards, later R-2800s are irrelevent to the discussion.




GregP said:


> The -30 could make 2250 HP dry.



In 1947. White gives the maximum power as 2,300hp @ 2,800rpm for the -30W, but doesn't say at which height. It is shown as 1,600hp @ 22,000ft, or very similar to the V-1650-9 dry (1,620hp @ 21,750ft).

The RM.17SM could make 2,200hp @ 2,000ft and 2,100hp @ 15,000ft dry (type tested rated power) - in 1944/45.




GregP said:


> They even made one fan-cooled R-2800 that could produce 2800 HP and another variant that made 3400 HP, but they ran on a test stands (dynamometers) and never flew.



The R-2800 with 2,800hp flew with the P-47M and N.

As for test bench engines, what of it? The RM17SM ran 2620hp on the test bench (3,150rpm, +36psi/103inHg, ADI).




GregP said:


> Most Bearcats were 2100 or 2250 HP untis, some of the late ones were 2400 HP. I've seen at least three Bearcats personally that the owners said had the 2400 HP unit in them. That was the power level late in the war, and many survivors have been fitted with them. I suppose it you are building one today from parts, you might as well get the best engine.



Late in the war with ADI.




GregP said:


> That doesn't change the fact that I read a flight test report that said a clean Bearcat could still climb at 3000 feet per minute at 20000 feet.



And the P-51H can climb at nearly 4,000fpm at that altitude.

http://www.wwiiaircraftperformance.org/mustang/p-51h-booklet-pg15.jpg

Left hand chart is for 81inHg (+25psi) boost and should be without ADI.




GregP said:


> Hardly any real Bearcats DID since they would mostly be climbing at reduced cruise-climb power unless they were in combat where all the stops are pulled. The same can be said for ALL the piston fighters.



It depends in what situation.

As the Bearcat was designed as an interceptor its primary goal was to get to altitude quickly. You won't be languishing around using the lower 30 minute climb rating when you have but a few minutes to get to the required altitude.

If, on the other hand, you were setting off for a long escort mission there is no need to flog the engine during the climb. There isn't quite the urgency.


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## wuzak (Jan 16, 2015)

GregP said:


> The fastest aircraft of WWII included the Dornier Do 335 Pfiel, the P-51H at WEP, the Ta 152H at WEP, the Republic XP-72 (a prototype) and the XP-47J. After the war the Commonwealth CAC-15 was also right there at just over 500 mph.



The CA-15 recorded 500mph after a shallow dive. The top level speed was 460mph. About the same as a Spitfire 24, Martin-Baker MB5 and Hawker Sea Fury.


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## GregP (Jan 16, 2015)

Is there a good book on the CAC-15?

I have only seen what I have seen on it, and it isn't really very much.

As for that giant reply above, I'll have to read it later. Have some things to do just now.


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## GregP (Jan 16, 2015)

Hi Wuzak,

The P-51 was introduced to active service in 1942 and was retired from active service by 1951, with some air National Guard units retaining them later than that. P-51H: The first USAAF flights were from 4-14 Apr 1945 and 222 had been delivered by 30 Jul 1945. The last P-51H rolled out of the plant in Nov 1945.

The F8F Bearcat was introduced to active service in 1945 and was retired in 1961 from the VNAF. The first operational squadron was active on 21 May 1945 and it was out of active US Navy service by early 1950. The F8F-2 had the R-2800-30W that could make 2250 HP. F8F-2 Bearcat: Active service in 1948 and retired from active service by the end of 1950. 

Neither was combat during the war and both were out of active service within about a year of one another. With no war going on the pace of development was glacial and they were contemporary to all purposes. In fact, ALL of the post-WWII big piston fighters were very firmly rooted in WWII development ... there being almost no development at all after WWII. The F8F-2 was a "fixed" F8F-1, nothing more. They added the -30W engine because it was available ... it was not developed for the Bearcat, it was near the end of the line in fact.


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## GregP (Jan 16, 2015)

About the big reply, we have to disagree. No surprise there, is there?

I can't find any F8F delivered with a -30 or -34 engine, all were of the W variety. Don't really care what was authorized, such as water methanol, they probably used whatever they wanted. Liquid was needed and methanol was antifreeze. If you needed it, then the methanol was vital. If it worked OK without it, you can bet it happened.

Later R-2800's are not irrelevant to the discussion unless you don't want to talk. After the war, the useful life of big pistons was about 5 - 8 years before being sold for scrap, all of it until the Korean war was non-combat. Anything out there during the time they operated is relevant, especially since neither one patipated in WWII combat. Our ONLY comparion is post-war and I choose to make a comparion.


Wayne, I don't care at all what the full throttle height is. The HP ratings at altitude are known and recorded. I have them as well as you do. If you are NOT at those reported altitudes, you interpolate. You can bet none of the "best" ratings are left out of the specs, but if a plane makes 1500 HP at 15000 feet and 1200 HP at 28000 feet, we can all get pretty close at 19000 feet without having a test report in front of us. I can and I know you can. I bet a;most all the frequent responders in here can, too.

The -9 was not allowed to run at 81 inches without ADI. Whatever it should do had nothign whatsoever to do with Rolls Ropyce or the RAF. It was in US service, not British service. I was not talking about RM.17M engines, I was talking about the P-51H. It ran a V-1650-9 and -11 only. No other engines were delivered with the planes or flown in active service.

What do you mean' what of the test engines?" Go read what I wrote. I said the test engines never flew and that's as far as it went. I made no other claims. But I can extrapolate. AN engine taht can make 3400 HP in later lodels can usually make more than rated power and more rpm if called upon in an emergency. That is, all of them probably can except for the Briston Centaurus. It can make more power, but cannot tolerate more rpm without failure. Exceed max rpm by as little as 75 and it will grenade. I know too many people who have done just that! And in privcate hands, too. All of them still flying the Centarurs do NOT exceed rpm limits ... EVER. The Queen's Battle oif Britian Memorial Flight doesn't, either ... EVER. Joe did the cylinders for them recently and spoke with the operations office.

The P-51H cannot climb at 4000 feet per minute at 2000 feet, even at 90 inches. At 67 inches it went from 3370 feet per minute at 13400 feet down to 2400 feet per minute at 23100 feet. At 80 inches it went from 4590 feet per minute at 8300 feet down to 2150 feet per minute at 21500 feet. It could get close to 4000 at 90 inches (but not there) but after initial tests, it was not allowed 90 inches in servcice to the best of my knowledge. The max allowable was 81 inches ... with ADI. All the above numbers were at critical altitude from actual flight test reports. It got worse everyhere else, but that doesn't make for good reading in a sales pitch, does it?

Your chart is a sales pitch for the P-51H and is obviously of modern origin. No original USAAF or USAF chart looks like that. Modern charts created for the internet are not exactly the most reliable charts for historic data.

And the 471 mph was at 90 inches which, again, was cut to 81 inches in service, where the max speed was less.

As for the last paragraph, what are you thinking? In peactime climbing at reduced rates is normal and is done all the time. If you need to push the climb rate, it is for an operational reason related to unknown incoming traffic, and that is no longer peacetime, it is intercept time to address a potential threat to the Naval task force or to the base in question. All bets are off until peaceful intent is established. Otherwise, conserve the equipment and the expendable fuel, and woe be unto you if you drop a drop tank in peacetime without a declared emergency, much less blown an engine and lose the aircraft you signed for due to stupidity.


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## wuzak (Jan 16, 2015)

The F8F-1 was contemporary with ethe P-51H. Having similar devlopment periods and introduction to service.

The Merlin devlopment in the US was pretty much stopped at the end of WW2. In the UK military developments were stopped too - the RM.17SM didn't go into production, even though it was type tested.

Development continued for the R-2800 post war, however, for both civilian and military purposes. The -30W was a result of that continuing development.

Regarding teh P-51D vs P-51H, the latter was ~1,000lbs lighter empty than the former. Given the same fuel and ammo, the P-51H will still be 1,000lbs lighter. At AUW the difference is around 10% - that's a big chunk of weight.

I have shown that power is better in the -9 for WEP (dry) than the -7, and that climb power is better over most altitudes. 

So with less weight, more power and some improvement to aerodynamic details the H must climb and accelerate better than the D.


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## GregP (Jan 16, 2015)

Hi Wuzak,

The P-51 was introduced to active service in 1942 and was retired from active service by 1951, with some air National Guard units retaining them later than that. P-51H: The first USAAF flights were from 4-14 Apr 1945 and 222 had been delivered by 30 Jul 1945. The last P-51H rolled out of the plant in Nov 1945.

The F8F Bearcat was introduced to active service in 1945 and was retired in 1961 from the VNAF. The first operational squadron was active on 21 May 1945 and it was out of active US Navy service by early 1950. The F8F-2 had the R-2800-30W that could make 2250 HP. F8F-2 Bearcat: Active service in 1948 and retired from active service by the end of 1950. 

Neither was combat during the war and both were out of active service within about a year of one another. With no war going on the pace of development was glacial and they were contemporary to all purposes. In fact, ALL of the post-WWII big piston fighters were very firmly rooted in WWII development ... there being almost no development at all after WWII. The F8F-2 was a "fixed" F8F-1, nothing more. They added the -30W engine because it was available ... it was not developed for the Bearcat, it was near the end of the line in fact.


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## wuzak (Jan 17, 2015)

GregP said:


> I can't find any F8F delivered with a -30 or -34 nengine, all were of the W variety.



The -30W is a -30 engine, just with ADi added.
The -34W is a -34 engine, just with ADI added.

The ratings for the -30W and -30 are identical when ADI is not in use.
The ratings for the -34W and -30 are identical when ADI is not is use.

The ratings I posted earlier are for the -34 _*and*_ -34W, and are not with ADI.




GregP said:


> Don't really care what was authorized, such as water methanol, they probably used whatever they wanted. Liquid was needed and methanol was antifreeze. If you needed it, then the methanol was vital. If it worked OK without it, you can bet it happened.



So they used whatever the hell they liked? So much for testing and tuning at the factory.




GregP said:


> Later R-2800's are not irrelevant to the discussion unless you don't want to talk. After the war, the useful life of big psitons was about 5 - 8 years before being sold for scrap, all of it until the Korean war was non-combat.



Of course later R-2800s are irrelevent. It's like comparing a Spitfire Mk IX with a later version of the Merlin with the Spitfire Mk II and Bf 109E.

Things are improved and tweaked over time. 2 years extra development would have been handy for the V-1650 in the P-51H.




GregP said:


> Wayne, I donlt care at all what the full throttle height is. The HP ratings at altitude are known. If you are NOT at those altitudes, you interpolate. You can bet none of the "best" ratings are left out of the specs, but if a plane makes 1500 HP at 15000 feet and 1200 HP at 28000 feet, we can all get pretty close at 19000 feet without having a test run in front of us. I can and I know you can. Don't go there.



You can interpolate between two points in the same supercharger gear. You cannot interpolate between the power in MS gear and the power in FS gear. There is a drop off in power after FTH (point of max power in that gear) until a gear change, where the power rises again until the next FTH is reached.







You also cannot interpolate power from a point below FTH to a point above FTH.




GregP said:


> The -*9 was not allowed to run at 81 inches without ADI. Whatever it should do had nothign whatsoever to dop with Rolls Ropyce or the RAF. It was in US service, not British service.








This supports your view that 80inHg was only to be used with ADI. Which is strange, since the -7 was rated for +25psi boost _dry_.

Now the V-1650-7 was rated RM.10SM. The -9 was rated RM.16SM.

The R = Rolls-Royce, M = Merlin, S = fully supercharged, M = medium suprcharged.

The -7 and -9 were not developed in isolation from Rolls-Royce. They were developed in consultation with them, as can be seen by them having the Rolls-Royce development rating.




GregP said:


> I was not talking about RM.17M engines, I was talking about the P-51H. It ran a C-1650-9 and -11 only. No other engines were delivered with the planes.



You were talking of bench and development engines. Of which teh RM,17Sm is one.




GregP said:


> What do you mean' whay of the test engines?" Go read what I wrote. I said the test engines never flew. That's as far as it went. I made no other claims.



So why put it in?




GregP said:


> The P-51H cannot climb at 4000 feet per minute at 2000 feet. At 67 inches it went from 3370 feet per minute at 13400 feet down to 2400 feet per minute at 23100 feet. At 80 inches it went from 4590 feet per minute at 8300 feet down to 2150 feet per minute at 21500 feet. It could get close to 4000 at 90 inches but, after initial tests, was not allowed 90 inches in servcice. The max allowable was 81 inches ... with ADI. All the above numbers were at critical altitude from flight test reports. It got worse everyhere else, but that doesn't make for good reading in a sales pitch, does it?



Here is some data for the P-51D and P-51H climb rates at 67.0inHg:


Alt (ft)P-51D MAPP-51D ROCP-51H MAPP-51H ROC06736006732004800673600500066.535756732851000056.32925673350138006733951500047.2227516000673200190006732002000065.230506730602500055.52375672750267006726403000046.4170059.422753500037.7100049.415104000029.832540.64404160027.5100

P 51D Performance Test
P-51H Performance Test

Note that the FTH (critical altitude) for the -7 in D is 4,800ft in MS and 19,000ft in FS gear. Gear change is at ~15,000ft.
The FTH for the -9 was 13,800ft in MS and 26,700ft in MS gear. Not sure when teh gear change was, as the data shows the manifold pressure maintained up to FTH in FS gear.

The -7 is shown to be a lower altitude engine, hence the better RoC down low. But its advantage is short lived.

The P-51D climbs to 20,000ft in 6.6 minutes, the P-51H in 6.1 minutes. The D gets to 30,000ft in 10.9 minutes, the H in 9.85. The D is faster to 10,000ft, 2.9 minutes vs 3.0.

Both had wing racks but no external load. The take-off weight for the D was 9,760lbs, including 21USG of oil, 185USG fuel and full ammo.
The takeoff weight of the H was 9,484lb with "full fuel" and ballast for full ammo load. Given the empty weight difference, teh H was relatively more heavily loaded for these tests.

This shows the hp of the engines and highlights the different characteristics of the -7 and -9.


Alt (ft)V-1650-7 MAPV-1650-7 hpV-1650-9 MAPV-1650-9 hp06717806715034800671730500066.517206715481000056.31470671590138006716221500047.2123216000671580190006715002000065.214556713202500055.51225671340267006713473000046.4102559.412093500037.785549.410124000029.870040.6830




GregP said:


> Your chart is a sales pitch for the P-51H.



Maybe so, but WEP is used for teh F*F's excellent climb rate too. No doubt including ADI.




GregP said:


> And the 471 mph was at 90 inches which, again, was cut to 81 inches in service, where the max speed was 467 mph or so.



I'm sure that the MAP was cut during service because the war was over. The RAF did the same - no point flogging the engines any more than they have to.




GregP said:


> As for the last paragraph, what are you thinking? In peactime climbing at reduced rates is normal and is done all the time. If you need to push the climb rate, it is for an operational reason related to unuknown incoming aircraft, and that is no longer peacetime, it is intercept time to address a potential threat to the task force. All bets are off until peaceful intent is established. Otherwise, conserve the equipment and the expendable fuel, and woe be unto you if you drop a drop tank in peacetime without a declared emergency.



Peace time climb rates don't reflect the aircraft's capability. That said, it is entirely in keeping with what I said in my last paragraph - it depends on the situation.

As these were warplanes, what they do in peace time is of little interest. What they are capable of in combat conditions is. You can bet your bottom dollar that if the US was still at war with Japan into 1946 that the P-51H would climb gently when going off on B-29 escort missions. If, however, they were set up to intercept high altitude fast moving raiders they would use a combat climb, and use teh ADI to get up there PDQ.


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## wuzak (Jan 17, 2015)

Just to show you I can interpolate, I have filled out the missing values for the jp table.


Alt (ft)V-1650-7 MAPV-1650-7 hpV-1650-9 MAPV-1650-9 hp067178067150348006717301546500066.517206715481000056.314706745901380012896716221500047.2123215641600067158015151900067150013692000065.214556713202500055.512256713402670011576713473000046.4102559.412093500037.785549.410124000029.870040.6830


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## GregP (Jan 17, 2015)

I'm surprised you argee with what I said, and I'm assuming you meant P-51, not P-61. If we're talking about the Black Widow, all before is for naught and isn't even on topic. Personally, I've never made a typo! That's my joke for the post.

About the graphs of HP versus height, they don't advertise the bad points, they always spec at the best points. Nobody gives you the lower HP numbers ... they always give the best, meaining the top of all the lines, just before they decrease. But you know that.

I mentioned the test stand engines because I wanted to. I think like me, not like you, and reserve the right to do that just like you do. But you know that.

Later R-2800's are not irrelevant since they served alongside the P-51H's concurrently until both were gone. Concurrent service MAKES them relevant. Neither of these birds fought in WWII, so a WWII timeframe is uttrerly irrelevant by definition ... they weren't there and didn't fight in that war. What IS relevant is the fact they were in service at the same time in peacetime. Being peacetime, neither got much development that ever made it to the service squadrons. They basically served as delivered until retired and sold as surplus or overhauled and sold to other nations.

I am talking about US airplanes using US-built Merlins, not anything Rolls-Royce ever made. We didn't use RR engines ... we used Packard Merlins. The limitations of their operation were different due to having different national air arms dictating the limits, and the parts are mostly NOT interchangeable between British and US Merlins. Some are, not all. We blew up our fair share of Merlins, as did the British. Mostly not since the Merlin is a great engine if ever there was one and was quite reliable if treated well, but they DID fail, and they failed catastrophically mostly at WER power or working up to it. Hence the desire to save the engine by all crew chiefs and pilots who were away from a friendly airfield or countryside.

The point I was trying to make about cruise climb is thaht nobody much climbed at WER unles they were in combat. They would climb at reduced power or, at most, normal power. Not mil power or WEP/WER. But you know that and are protesting just to protest. We aren't all that far apart and you know that, too. 

You just like to disagree somewhat like I do at times, too. I have no doubt the P-51H COULD climb very well if pushed hard. The data prove that. My point was that the Bearcat could be pushed hard, too. When it is, the P-51H doesn't get away except very slightly in top speed. In acceleration, climb, roll, and turn, the P-51H is no better than the F8F ... -1 OR -2, and is really not as good in many areas. A bit speedier, but only at the risk of blowing the engine, which nobody would do unless combat dictated it.

But you know that, too.

Cheers!


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## wuzak (Jan 17, 2015)

GregP said:


> About the graphs of HP versus height, they don't advertise the bad points, they always spec at the best points. Nobody gives you the lower HP numbers ... they always give the best, meaining the top of all the lines, just before they decrease. But you know that.



I don't know what you mean.

The numbers I posted are for WEP (dry), with maximum boost of +18psi. It shows when the power is lower as well as higher. Not sure what you mean by "bad points".




GregP said:


> I am talking about US airplanes using US-built Merlins, not anything Rolls-Royce ever made. We didn't use RR engines ... we used
> Packard Merlins. The limitations of their operation were different due to having different national air arms dictating the limits, and the parts are mostly NOT interchangeable between British and US Merlins. Some are, not all. We blew up our fair share of Merlins, as did the British. Mostly not since the Merlin is a great engine if ever there was one and was quite reliable if treated well, but they DID fail, and they failed catastrophically mostly at WER power or working up to it. Hence the desire to save the engine by all crew chiefs and pilots who were away from a friendly airfield or countryside.



The parts were mostly interchangeable between Rolls-Royce and Packard Merlins. Packard for US service used SAE spline prop shafts wheras RAF bound engines used the SBAC spline shaft. The supercharger gearbox was different (Farman on RR built aircraft and epicycic on Packards) and the carby was different.

Rolls-Royce drove the development of the Merlin, and Packard mostly followed. 




GregP said:


> I have no doubt the P-51H COULD climb very well if pushed hard. The data prove that. My point was that the Bearcat could be pushed hard, too. When it is, the P-51H doesn't get away except very slightly in top speed. In acceleration, climb, roll, and turn, the P-51H is no better than the F8F ... -1 OR -2, and is really not as good in many areas. A bit speedier, but only at the risk of blowing the engine, which nobody would do unless combat dictated it.



You said several posts ago that the P-51H wasn't that big an improvement over the P-51D, especially in climb rate. I'm quite sure I proved that wrong.

As for the F8F-1, all its performance figures that are trumpeted are when being pushed with ADI and WEP, including its climb rate. So if the F8F's performance figures used are with maximum power (max MAP and ADI) then why shouldn't the P-51H's.

One thing to note is that the F8F had a low altitude engine, whereas the P-51H had a high altitude engine.


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## drgondog (Jan 17, 2015)

The P-51H airframe was superior to the P-51D/B airframe - period.

The 1650-9 engine was the 1650-3 with heavier construction to be able to withstand higher boost pressures plus water injection plus Simmonds Boost Control unit for better management of boost pressures set by the pilot - at all altitudes. The engine had a speed density injection type carburetor.

The 1650-9A was simply the same engine with WI removed.

The P-51H was a superior airframe which resulted in a.) less weight, b.) lower weight for full combat load, c.) lower drag wing, d.) more directional stability at both take off and all flight regimes, e.)no aft cg issues due to extending the fuselage ~ 13" and reducing the fuselage tank from 85 gallons to 50 and increasing the wing tanks from 180 to 205. The P-51H had better visibility over the nose for deflection shooting as well as taxi, take off and landing. The P-51H was slightly more economical in cruise speeds than the P-51B with the 1650-3 and superior to the 1650-7 when comparing P-51B/D with full combat load to P-51H full combat load. The throttle and RPM settings were slightly different from each other at different altitudes, depending on engine differences in comparisons.

the P-51H out climbed the P-51B and P-51D at same power settings and far exceeded both in service ceiling at normal power and comparable internal load. The placard for the -9 at 80" was 7 minutes and this stress was common without engine changes, particularly while testing the P-51H climb to 25,000 feet (=6.7min @ max power from SL) as an interceptor. 

The wing area of the P-51H was 236 sq ft compared to the B/D of 233 so one can expect that turn performance is also slightly better based on lower wing loading due to a.) Gross Weight and b.) greater wing area.

The post war saw removal of the WI capability as the P-51H was retired from interceptor role and steered toward Fighter Bomber tasking as they moved into National Guard and Reserve units. The engines were then the -9A. The P-51D's also used -9A from time to time as they do today.

The F8F is the only conventional fighter built in US that is comparable/slightly better/slightly worse than the P-51H



The P-51H was superior structurally as it was designed for actual target Gross Weight in combat operations, whereas the P-51B/D had both grown significantly over the original XP-51 design loads and stress allowances.

There is a big difference in trying to do comparisons based on Warbird operations versus combat ops -with respect to fuel and use of WEP. It is disingenuous to make comparisons between different warbirds or even racers as both of those categories are out of the envelopes flown by combat pilots -simply because nobody wants to risk blowing up an engine or failing the bird structurally.

As usual I have a different experience anecdotally from Greg in that I never talked to an Air Force pilot that flew both that liked the P-51B/D over the H.

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## Shortround6 (Jan 17, 2015)

Something to remember about today's war birds (and perhaps even more true with warbirds in the 60s/70s) is that they often flew with the wrong engines. How many flew with the correct self sealing fuel tanks (30-70 year old rubber?) armor and weapons load (how many carry ballast if the guns are dummies? 

Many a F4U or P-47 _used_ to fly with ex commercial airline R-2800 "C" series engines (DC-6, Convair 340/440) as they were cheap and easy to find vs the "correct" B series engines. I have no Idea what the engine situation was in F8F-1s but the F8F-2s used a special "C" series engine ONLY used in the F8F-2. 

I don't know if some of the warbirds flying now have gone back to more "historical" engines but if they have it is even more reason not flog the engines to no good purpose. The "C" series engines having much better cooling, strong parts and in the later engines even different length connecting rods.


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## wuzak (Jan 17, 2015)

Shortround6 said:


> I have no Idea what the engine situation was in F8F-1s but the F8F-2s used a special "C" series engine ONLY used in the F8F-2.



The F8F-2's R-2800-30W was an E-series engine according to White.


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## Shortround6 (Jan 17, 2015)

You are correct. I was in a hurry 

The only other "E" series engine was the one used in the F4U-5 and it used a totally different supercharger.

The "C" series engine used in the F8F-1 was also used in a number of other military aircraft and while it may be close to a certain model commercial engine I don't know which one it would be.


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## GregP (Jan 18, 2015)

We'll have to disagree on the superior airframe part. But that's OK. I still like them all. At similar boost the D and H perform similarly. If you add a 2200 HP V-1650-11 at 81 inches to a P-51D, I bet you get great performance, too.

Before you trash me too badly for that statement, you might recall the two fastest P-51s in the entire history of the planet are both P-51Ds. That would be Voodoo and Strega in no particular order. They aren't exactly "stock," but neither are they P-51Hs either. 

There are numerous small aerodynamic changes to be sure, but the biggie is a 3850 HP Dwight Thorne-inspired hybrid engine that has a Merlin engine case and cranksahft, but not much Merlin anything else. The rods are Allison G-series, the pistons are custom, and the valves are very likely custom, too. The mags have been replaced and the generator is new along with numerous other small bits.

It says "Rolls Royce" on the T-shirt and valve covers, but it just ins't the case in reality.

As for rate of climb, you might recall that a stock grumman F8F-1 Bearcat seta record in 1946 by climbing from a standstill on the runway to 10,000 feet in 94 seconds. That is in military condition, with armament and no modifications. The current rate of climb record is held by Rare Bear, set in 1972, and is standstill to 3000 meters in 91.6 seconds. Mustangs, including the P-51H aren't in the record book for rate of climb, but it is littered with Bearcats.

The current world seppd records is held by a Rare Bear at 528.33 mph. Several planes today, including the Bear, can break that record. The reason it hasn't been broken to date is the cost of doing so. There is no other reason for not besting that record. Rare Bear, Strega, and Voodoo can all hit 540 mph straight and level on the course. It is a question of whether or not they DO so while staying together for a backup run in the other direction.


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## drgondog (Jan 18, 2015)

GregP said:


> We'll have to disagree on the superior airframe part. But that's OK. I still like them all. At similar boost the D and H perform similarly. If you add a 2200 HP V-1650-11 at 81 inches to a P-51D, I bet you get great performance, too.
> 
> *No question - but recall that the handling characteristics of the B/D increasingly degraded with increased HP (ditto the 109 and 190 - hence one of the reasons for the plug in the 190D. The increased fuselage length of the H solved not only the aft cg problem but also high speed yaw issues that led to all the mods to the B/D such as reverse rudder boost, etc. It also made take off more benign with respect to rudder feed.
> 
> ...



And your point is?


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## GregP (Jan 18, 2015)

The current records are held by Bearcats. You are probably right about the Few P-51H models out there, but Steven Hinton Jr. Says Strrega and Voodoo fly just fine with 3850 HP. Naturally they are flying at full down elevator trim at 500 mph, but the H-model would, too.

I can't say what the racers' Cdo is because I don't know, but whatever it is ... it would be hard to best even with an H-model aitrframe. Heck, A modified P-51H might BE faster, but we may never know.

All I can say right now is the Bearcat is definitely on top of the record book, with modified P-51D moels sitting right there, ready to challenge if the money magically appears. In an all-out speed record attempt, I lean toward the Strega-Voodoo side, but we all KNOW the Bear can hit 540 mph in a straight line, too. It wouldn't be an easy victory for any of the three planes.

Regardless of the above, if you are out of ADI, the P-51H performs just about like a P-51D, albeit a bit faster in top speed. Add in the V-1650-11 and the same would be true in climb rate, too, for the P-51D. And the P-51H didn't have much ADI to play with, so it was mostly right in the same perfromance arens as the P-51D.

That was and is my point. The biggest difference between them, performance wise anyway, was the engine and the extra 14 pounds of boost, not the aerodynamics.


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## wuzak (Jan 18, 2015)

GregP said:


> That was and is my point. The biggest difference between them, performance wise anyway, was the engine and the extra 14 pounds of boost, not the aerodynamics.



I thought the biggest difference between them was the 1,000lb difference in empty weight?


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## GregP (Jan 18, 2015)

Not at all. The engine makes the difference.

Go to Reno once and ask EVERY unlimited pilot out there and they'll ALL tell you it's the engine. Sure, the rest helps, but only very slightly. A good fillet might add 1 -2 mph, but 400 more HP will blow that out of the water by a LONG way.

The WWII Merlins were making maybe 1,400 HP or more at 5,000 feet. The front running racers are making more than 3,000 more HP at 500 feet and there is NO aeroduynamic modification that comes even close to that. Go look at the speeds in 1964 where almost every racer out there was stock, and then go look at the speeds in 2014 in the Unlimited Gold class, where no single racer is stock. The biggest difference, by a very long mile, is horsepower. 

In fact, the ONE Unlimited racer that shows this ina very BIG way is called Miss America. The airframe is largely but not entirely stock, but the plane has had progressively more HP in its various developments. Each and every increase in HP results in a faster plane. All the rest of the mods were quite minor by comparison.

Weight has almost nothing to do with it once the power surplus is enough, despite any protestations to the contrary. Once the power surplus is enough, weight is almost meaningless up to the point where it starts impacting the power surplus significantly. Of course, I'm talking reasonable weights, and am not thinking of a 16,000 pound P-51. If you have one of those, don't try to fly it. Rent it out as ballast or put it in a park for the kids to play on.


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## wuzak (Jan 18, 2015)

You are talking Reno racers again, which bears little, or not at all, on the relative performance of the P-51D and P-51H.

The H weighed 1,000lbs less empty. Add the same fuel and ammo, pilot etc, it will still weigh 1,000lb less.

The figures I posted above show that the D did indeed out-climb the H in some bands when using the same boost (ie +18psi). Mainly at the lower altitudes, where the V-1650-7 had more power than the V-1650-9.

But given the same engines the extra 1,000lbs of weight will have an effect on climb. It will also have an effect on acceleration. And, no doubt, manoeuvrability.


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## GregP (Jan 18, 2015)

Wayne, Reno has a HUGE relationship with WWII fighters.

They started flying stock WWII fighters and found out what makes them go faster.

P-51H at 500 feet flying at 1400 HP may or may not be faster than a P-51D at the same altitude and HP, probably slightly faster. But give the P-51D a shot of HP and it rockets ahead, extra weight and all.

It is EXACTCLY what I'm talking about. At equivalent power levels they, the P-51D and H, are just not very far apart. And .. if the -9 and -11 engines were avilable for the P-51H, then they were ALSO available for the P-51Ds at the same time. They might not have been installed, but they were there, ready, and avilable.

If they HAD been installed, the results would be equally spectacular.

To me, we didn't need the H at all. Just improve the D a bit and help the engine. You have the same thing for a LOT less money.


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## wuzak (Jan 18, 2015)

GregP said:


> Wayne, Reno has a HUGE relationship with WWII fighters.
> 
> They started flying stock WWII fighters and found out what makes them go faster.



But that doesn't mean anything for the P-51H vs P-51D comparison.




GregP said:


> P-51H at 500 feet flying at 1400 HP may or may not be faster than a P-51D at the same altitude and HP, probably slightly faster. But give the P-51D a shot of HP and it rockets ahead, extra weight and all.



I'm sure it would have been faster, with slightly improved aerodynamics.

But straight level speed is only one part of the equation. 

The H climbed better over most altitudes, and would have done so over all altitudes if equipped with the same engine. Remember that the B/D went from the V-1650-3 (Merlin 63) to V-1650-7 (Merlin 66) to help with its climb rate.

Bill told you it was more stable, listing reasons why, That must make it a better gun platform?

The lower weight will do a little for speed, but 10% less weight (in the same loading configuration) should do a lot for acceleration and manoeuvrability, as well as climb. 




GregP said:


> It is EXACTLY what I'm talking about. At equivalent power levels they, the P-51D and H, are just not very far apart. And .. if the -9 and -11 engines were avilable for the P-51H, then they were ALSO available for the P-51Ds at the same time. They might not have been installed, but they were there, ready, and avilable.
> 
> If they HAD been installed, the results would be equally spectacular.



It may have been nearly as fast in a straight line, but I doubt the D would have climbed, accelerated or turned as good as the H.


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## GregP (Jan 18, 2015)

Yes it DOES definitely mean something for the P-51H versus D comparison. It means the P-51H is a spetacular performer for a few minutes while the ADI is flowing, after which it was more or less equivalent to a P-51D.

And that's my whole point. I can allow you 5 minutes of really supoerior performance but after that, the fight's on, and the P-51H is NOT a favorite or an underdog ... it's down to the pilots. That is just about the definition of equal ... after the ADI is gone, that is.

I'd about have time to drink a Gatoraid and the P-51H would be out of ADI and VERY equal to a P-51D.


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## tomo pauk (Jan 19, 2015)

Let's not forget that main job of the P-51H was to be an escort fighter, with as good performance as possible. Both P-51D and -H have about same quantity of fuel aboard, but the -H have had less in fuselage tank - 50 vs. 85 gals. It also had revised fuselage and tail. The -H was 1st to use wing tanks and drop tanks until all 4 are empty, and then switch to fuselage tanks. Unlike the P-51D, that got to burn a half of it's fuselage tank fuel in order to get the CoG in manageable limits, prior switching to drop tanks. Not long after the fuselage tank was introduced, the practice was to fill only 65 gal in the 85 gal fuselage tank, per CoG reasons.
Net result: in practice, the P-51H have had longer radius than the P-51D.


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## GregP (Jan 19, 2015)

I agree, Tomo. But they'd have gotten just about the same from putting the -9 / -11 into the P-51D airframe. When it could already get from London to Berlin and back I'm not too sure it needed more range. By that time the pilots were ready to bail out just to get out of the thing.


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## drgondog (Jan 19, 2015)

GregP said:


> Wayne, Reno has a HUGE relationship with WWII fighters.
> 
> They started flying stock WWII fighters and found out what makes them go faster.
> 
> ...



The H was an improvement over the D.. and there was no place to go further with the D to solve the aft cg issues or high speed yaw issues. When the contract was awarded, the P-51B had only been fighting for five months and the first P-51D was headed to ETO after AAF acceptance testing. The battle over Germany was beginning to peak, and the US was facing a very long war in both Europe and Pacific and CBI.

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## pbehn (Jan 19, 2015)

I thought the P51 H was an improvement over the B/C/D models. It had an uprated engine, why not when it is available, the LW were improving theirs. It had cleaned up dynamics, why not it increases range and speed? The biggest change was to the weight and location of internal fuel to greatly improve the utility of the plane. A P51D loaded with maximum internal and external tanks was on the borderline of being able to fly, little more than gently climb and cruise to RV point, no one would race it at 500ft in an oval. Despite big, draggy external tanks it had to burn off internal fuel first to bring the CoG issue under control. The longer fuselage and larger wing tanks meant the P51H had much greater ability throughout a mission. The US may have agreed to load up its escorts with fuel until they were borderline on safety because they had no choice at the time but I suppose they have some responsibility to correct the situation. The P51B/C/D with maximum fuel must be one of the few planes with a minimum combat radius as well as a maximum. Reno air races mean little in this, the planes and engines bear little similarity to the original.


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## tomo pauk (Jan 19, 2015)

GregP said:


> I agree, Tomo. But they'd have gotten just about the same from putting the -9 / -11 into the P-51D airframe. When it could already get from London to Berlin and back I'm not too sure it needed more range. By that time the pilots were ready to bail out just to get out of the thing.



USAF was not looking it the same way you do. They were eager to have the P-47N, that have had 1000+ miles combat radius when 'measured' by high fast cruise that was used there We can recall that USA Allies were also fighting a war in Asia/Pacific, where there was no such thing as too much radius.
When fueled-up for the mission beyond Berlin, like escort to the Leuna fuel facilities, P-51H was a far better fighter than the P-51B to -K. 
The pilot that baled out above occupied Europe or above Pacific (due to having no fuel?) will not be there to fight another day and further, so I'd discount that as a serious proposal.

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## Shortround6 (Jan 19, 2015)

Long range escort missions were _one_ of the reasons for the P-82 twin Mustangs. The two pilots could 'relieve' each other at times so one pilot didn't have to fly *all* of the hours a long range mission took. 
Imagine an 8-10 hour car trip with NO stops in a more confined space/lumpier seat than even most small cars, a worse heat/ventilation system, a relief tube or jar for bodily functions and rather limited snacks/liquid refreshment and no music. Now make several such trips per week  

Bailing out _might_ look better than hours 9 and 10.

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## GregP (Jan 19, 2015)

Hi Bill,

Let's say we disagree on the improvement part, except for the engine. The racing P-51D's flying today are far and away faster than the H ever was (mostly due to engines) and, as I said earlier, I don't think more range was needed in the first place. The war was winding down and we had airfields closer to Germany, so LESS range was needed if anything, making the D model easily far ranging enough for the tasks left to it.

I can appreciate the 5-minute improvement with ADI, if it was needed. Where I mostly go the other way is I don't think the P-51Hs were neeeded at all. I like the H model and am not trying to run it down at all. Just don't think it was ever needed, The relatively low production numbers and short service life (front-line service, that is) seem to validate that view for me. 

We could very easily have done without the P-51H as well as some other late piston developments. After the war, the pistons stayed around for awhile and then were replaced with jets, never to reappear except in guise of the truly great Douglas Shyraider. Love that plane! Wish it was still around in numbers. If ever there was a great attack plane for limited wars and wars where local air superiority is assured, the Skyraider is it.


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## Milosh (Jan 19, 2015)

The war in the East was still going on Greg and would have gone on longer if not for the Bomb.

How many bombs can those racing P-51s carry?

How many guns are fitted to those P-51s?

How far can those P-51s fly?

Those racing P-51s remind me of a certain Messerschmidt > Me209.


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## GregP (Jan 19, 2015)

The P-51Ds of the time carried six 50-cal MG, as you well know Milosh. They weren't bombers, as I assume you also well know, though they COULD be employed as fightter-bombers; they were escort fighters. Using thema s fighter-bombers was not very wise. You can look up the bomb load as easily as I can. Since the P-51Ds of WWII actually DID escort duty in the PTO over Japan, they actually COULD do escort duty in the PTO over Japan. So, where was the critical need for the P-51H? I can't see it.

Racing P-51s of today are not relevant to WWII. My entire point was that the speed was THERE in the P-51D airframe if they used the engine from the P-51H in a P-51D airframe, and you are no doubt aware of THAT, too, since I stated it pretty clearly along the way. We did NOT need more range and you're just stirring the pot.

If the racing P-51s remind you the Me 209, well and good. They don't remind me of it at all and don't have tricycle gear. They remind me of P-51Ds, but looks are in the eye of the beholder. My favorites are mostly radial-powered but, again, that is is just personal and is not a statement about the looks of any particular configuration. I actually like all the WWI fighters and they all have their strong points and weak points.


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## wuzak (Jan 19, 2015)

Greg, Reno racers are extensively modified - it's not just the engine, but also the airframe and aerodynamics.

The fact is that a P-51H similarly modified would be faster. Though being cleaner to start with, there are fewer possible modifications to improve aero, so they would get closer.

But in standard military trim the H is significantly lighter, more stable and slightly less draggy. Give the same engines they will be faster and they will climb better.


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## GregP (Jan 20, 2015)

The aerodynamics are a drop in the bucket when compared with horespower. That's the story from the crews and pilots of the winners of more than 15 Reno Unlimited Championship races. You can believe whatever you want. I'll take the word of guys like Pete Law, Steven Hinton Jr., John Penney, Dave Cornell, Daryl Greenameyer, and Tiger Destefani ... particularly Pete Law and Dave Cornell. These guys did the calculations that resultd in the boil-off systems, engine mixtures, spray bars, ADI systems, and wing profiling, gap sealing, seam sealing, etc. ... and they KNOW where the speed comes from.

And they aren't giving away any secrets when they say the wing was "profiled" because none of them will tell you what profile (NACA or other airfoil) they are using. Most of the teams, however, DID the profiling and then flew the beast to see the gains ... and then put in the extra horsepower and flew it again. They'll tell you it is power, but won't tell you how to GET the power or what fuel formula, rpm, or MAP they are using.

If there's anybody in the real world who knows where most of the speed comes from, it's these people and they, one and all, say the engine is by FAR the biggest contributor. The aerodynamics DO help of course, but incrementally when compared with horsepower injections. These guys PROVE it every year at Reno, they don;t just talk about it.

Want to seriously argue, go get a P-51H and beat them. Until then, the winners are correct in my book. They are well more than 100 mph faster than a stock P-51D ... and it is very much by horsepower.

Take standard formulas. If a P-51D that can make 1680 HP at 5,000 feet goes 370 mph at Reno, how fast will it be, assuming no change in drag, if he makes 3850 HP? The aswer is 488 mph. Considering that Voodoo and Strega both have lapped at 510 mph or so, the aerodynamics gained them a whopping 22 mph compared with 118 mph gained through horsepower. 

I volunteer at the museum that has owned the Reno Unlimited Gold Championship for the last 6 straight years and is the current reining national champion. I think they KNOW a thing or two about speed and where it comes from, wouldn't you say? Hhhhmmmmm ... I'd say, give me a hot engine and we'll look at the aerdynamics when we have the chance! Where the heck IS that spray bar, anyway?

With a Cdo of 0.0176 or so, the P-51D was just fine as a figher in WWII and is STILL one of the fastest piston planes in the world, admittedly in somehwat modified form ... though the Bearcat will have to rank as fastest until someone comes up with the money to unseat it with an actual record attempt.


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## wuzak (Jan 20, 2015)

Of course power is easier to improve greatly than aerodynamics.

A 10% improvement in drag should get a 10% improvement in speed. 
A 10% improvement in power will not get you a 10% improvement in speed.

The figures you quote are for power improvement of >200%, but the speed improvement is only around 30%.

Back to the P-51D vs P-51H.

The H has improved aerodynamics and lower weight. Less weight means lower drag configuration during level flight (less lift required). So the H should go faster on the same installed power.

But the big improvement in the H was climb and manoeuvrability, thanks to that weight loss.


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## GregP (Jan 20, 2015)

I'll have to say that I already allowed the H was very slightly faster, on the same power, as the P-51D was. The rest of it I dispute. Will it be more maneuverable by a small bit? Sure. Enough to make a diffference? I don't think so, and the H didn't even make WWII as a combat plane, neither did the Bearcat and Tigercat, though they were really very close to being there until the war ended what might be called somewhat prematurely due to the the Atomic bomb. Any end to a war is a good thing as far as I'm concerned, as long as it ends.

To me, the "improvement" the P-51H represented is not and never was worth the development costs. To a P-51 lover like Bill, it probably WAS worth the cost. In the end, they DID develop it but made only a few that didn't last very long in post-war first-line service. I suppose had the war continued, we'd have some combat statistics to discuss. But it didn't and we don't. So I'll say it was a very modest improvement and allow that anyone else in the world may differ in opinion. If that's what you think, then by all means think it in good health and be happy.

You won't convince me the P-51H was worth the effort and cost simply because it was never USED in combat by our armed forces in the war for which it was conceived and produced. Add to that it was among the last developed piston fighters that flew from the production line straight and true into obsolescence as jets developed, and I call the P-51H more or less irrelevant to WWII. Not because I wouldn't love to own and fly one ... I would. But it is like the Ta 152 for Germany ... it did little to nothing to help the war effort and wasted enormous resources. Since we won the war, the P-51H never had to face the fate the Ta 152 did, and that was to be among the best ever developed, but having almost no impact on the war effort to show for all the inherent greatness of the design. In the case of the P-51H, it soldiered on for a short in both active and reserve service, but had the war gone the other way, it would have been summarily scrapped and forgotten like the Ta 152 was. The P-51B/D would NEVER be forgotten due their sterling war records, but the P-51H never GOT a war record to make it notable in any way, other than as a great little ship to flit about in on weekends for the post-war reserve pilots.

It would have been really interesting to have had a flyoff between the Ta 152 C or H against the P-51H in the 1946 timeframe just to be able to see the results today, with pilots and crews familiar with both so the test would have been fair. I'd have to pick the Ta 152H at high altitudes as a dogfighter, due to the high-aspect ratio wing that favors high altitudes. Both were almost identically fast with the P-51H having a very decided edge in climbing ability while the ADI was flowing, but then becomming much more equal when the ADI ran out. I am not sure if the Ta 152's climb data was on wet or dry power but, if memory serves, the best climb rate was in the 3,500 feet per minute range give or take a bit, which is very close to where the P-51H was without ADI and down at 67 inches of MAP instead of 81 inches of MAP. The Ta 152 would easily win in armament category. Had it been developed into a reliable fighter, I'm sure it would have been near the top of the class.

The only reason I have consistently had little to say about the Ta 152 over the years has NOTHING to do with it's performance and potential, which were pretty darned good. It has almost entirely to do with its performance in combat. I can say the same for the P-51H. It is quite interesting and I like the plane, but it did nothing whatsoever for the war effort. It was a situation not at all the fault of the quality and potential of P-51H or its designers ... the war simply ended before the potential could be demonstrated, making it something of a WWII non-participant that was a waste of effort in the end. 

Of course, hindsight DOES have 20-20 vision, doesn't it? It was quite possibly not so clear when the P-51H was conceived and proceeded with.


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## Milosh (Jan 20, 2015)

Greg, the Me209 was a tail dragger. It was especially built to set the world speed record, and did.

Messerschmitt Me 209 - Wikipedia, the free encyclopedia

P-51Hs were being prepared to be sent to the Pacific when WW2 ended and would have replaced the P-51D/Ks.


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## GregP (Jan 20, 2015)

My mistake, Milosh ... I was thinking oif the Me 309, not the very fast Me 209. Duuuuhhhhh ....

I knew they were slated to go into combat service, but never made it due to the end of hostilities. The last genertrion of piston fighters was pretty impressive all around, performance-wise, for pistons. It was just historical luck-of-the-draw that they competed against the early jets. Had the early jets not been there, I'm sure the last-gen pistons would have given us something to write about.


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## eagledad (Jan 20, 2015)

Gentlemen,

In regards to the P-51D vs P-51H, the following is taken from Mustang A Documentary History by Jeffery Ethell

“The only way to obtain increased strength or any substantial amount of increased stability is to start from scratch and design a new airplane. This has been done in the P-51H. Actually, the model designation of this airplane is some what confusing because the airplane structurally is no longer a P-51 – it is a brand new airplane. The airplane is designed to devevlop over 11g ultimate pullout factor at a designed gross combat weight of 9600 pounds. Further, the arrangement of the airplane has been changed slightly so that it is always stable, regardless of the disposal of fuel or armament load... The P51H [is] a truly worthy successor to all previous P-51 Series airplanes.” 1/

So from the above IMHO it sounds like the 51H would be a better airframe to modify for Reno than the D. Perhaps it is a relative lack of H airframes compared to D’s that prevents this? Anyway, it sounds like North American listened to the pilots’ concerns with the early Merlin powered Mustangs and addressed them in the H.

Further in Ethell’s book is a report from Eglin AFB dated 10/1946. It was a comparison between a D-25 and a H-1. The P-51D used 67” of manifold pressure, the P-51H ran 80” and water. The tests were done twice, so each pilot got a turn flying each airplane The testing attitudes were 10,000 and 25,000 feet. I will present parts below:
*Turning Circle:* At both altitudes there was no real difference in minimum turning radius. Using maneuver flaps on the P-51H-1 yielded no advantage.
*Rate of Roll:* At both altitudes up to about 400 mph indicated the 2 aircraft were rated equal. Above 400 mph, the advantage went to the D, although it was noted that the H did not have the modified ailerons of the latter versions.
Level and Dive acceleration fromnever cruising power: As expected, the H pulled away from the D in both level and dive situations at both altitudes. Accelerating from cruise speed at both tested altitudes saw the H gain about 400 yards after 3 minutes at full power.
*Zoom from full power level and from full power dive:* The P-51 H gained an advantage of about 500 feet when the indicated airspeed declined to 130 mph. It was noted that the H was extremely sensitive to ram-effect on power, manifold pressures decreasing materially in a turn or zoom from full power in level flight. 
Range: The P-51D has a slightly longer radius of action than the P-51H due primarily to the larger internal fuel supply(269 gallons for the P-51D as compared to 255 gallons for the P-51H); but this advantage was considerably reduced by the fact that the P-51D is not sufficiently stable with full fuselage tank to permit violent manurvering.
*Stability:* No stick-force reversal was reported during high acceleration turns with a full fuselage tank on the P-51H. The H was more stable than the D under full external loaded conditions. It also had better stall, landing and taxing characteristics than the P-51D. The P-51H was also considered a better gunnery platform than the P-51D.

Conclusions:

“The P-51H type airplane, without the use of water is operationally suitable, but does not have sufficient advantage over the P-51D type airplane to warrant standardization.
The P-51H type airplane released for power greater than 67” HG manifold pressure is a desirable replacement for the P-51D airplane” /2

So, IMO it appears that performance-wise, the H is a superior aircraft if the AAF was willing to run the engines at high manifold pressures which would be OK during wartime, but perhaps expensive from a maintenance point of view during peacetime. With the end of the war, only marginal performance advantages over the D at 67” manifold pressure, and the advent of jet fighters, the H really didn’t have a place in the Air Force’s inventory.

Eagledad

1/ Mustang, Ethell, page 67.
2/ Mustang, Ethell, page 133

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## GregP (Jan 20, 2015)

Great post Eagledad, and it says it all. If the power were the same in both planes there was little to choose between them. If they fitted the -9 / -11 engines of the H to the D, they again would have been very much the same plane, albeit with the H being a bit more stable with full fuel. I have no worries there because there was almost nobody stupid enough to try to attack a 1000-plane raid while it was forming up near home base. That would be virtual suicide.

The fact that the war ended made the P-51H unneeded. Had the war continued, I'm sure it would have been a good mount , at least while the ADI was flowing. After that, it was basically a D ... not at all a bad thing to emulate.

All in all a good plane that was unneeded and had a very short poast-war service life in front-line service.


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## drgondog (Jan 20, 2015)

GregP said:


> I'll have to say that I already allowed the H was very slightly faster, on the same power, as the P-51D was. The rest of it I dispute. Will it be more maneuverable by a small bit? Sure. Enough to make a diffference? I don't think so, and the H didn't even make WWII as a combat plane, neither did the Bearcat and Tigercat, though they were really very close to being there until the war ended what might be called somewhat prematurely due to the the Atomic bomb. Any end to a war is a good thing as far as I'm concerned, as long as it ends.
> 
> *Ah, Greg, generous in your praise always. Pick up your slide rule. Harken back to the good old days when you were modeling P-51B canopies as an undergrad and pick up a slide rule. Assume the CDo of both the P-51D and P-51H is the same. Stick a 1650-3 or 7 in both airframes. Look up the charts on HP vs boost vs altitude. Take the P-51D at empty and the P-51H at empty for case A. Take both and load to full combat load of internal fuel plus ammo plus oil, pilot as case B.
> 
> ...



Now prove it Greg. You have the weights, the physical data and can take the P-51H 80 and 90" Boost out of the equation.

Calculate W/L and then explain your thesis regarding why the higher W/L (the P-51B/D) translate to better climbing and turning performance that the lower W/L P-51H

Calculate SL velocity for the two and explain why the heavier one with the same horsepower and higher W/L and higher induced drag seems slower.

Calculate ROC and explain why the heavier one seems to climb slower at all altitudes with same HP, same prop, same thrust, same activity factors as the lighter one.

Calculate Acceleration and explain why the heaver one seems more sluggish with same HP, thrust, same prop, same activity factors than the lighter one.

If you want to explore the CDo of the P-51H do some reverse engineering on the NAA calcs of November 1945. Then re-plug the drag with slightly better CDo, better CL, lower CL^^2 and thus lower induced drag and figure out why the P-51H had a higher calculated range on internal fuel than the P-51H (slight - but it had 14 gallons less fuel).

In other words - lay out some facts and present them. It would help if you could define "Very Slightly", "Slightly" and "darned good, by gum" to help frame your reported calcs


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## davparlr (Jan 20, 2015)

Well, I haven't commented much on this subject but I'll pontificate some. First, the F4U-4 and the F4U-5 were both noticeably faster than the contemporary F8F-1 and F8F-2 (the F4U-5 was some 20 mph faster than the F8F-2). Climb rate was an F8F forte however the F8F-2 was only slightly better than the F4U-5. I am sure maneuverability was also a strength of the lighter F8F, however both of these aircraft would be of diddly squat use in Post 1945 air-to-air combat with Me 262s (and possibly other advanced German jets) and Mig 17s, so maneuverability is somewhat negated. F4U ruggedness and air-to-ground capability was well known but the F8F performance in air-to-ground combat was unknown. F4U had a small advantage in range. Lots of F4U logistics capability existed. So, I think the Navy decision was correct.


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## GregP (Jan 20, 2015)

As always Bill, you discuss by attacking, putting people down, and trying very hard to be superior and condescending. Unfortunately it comes across in a way I'd best not describe in here as it would be against forum policy.

You're doing a good job of it, so hark back and do it yourself. I already know the P-51D and H fly just about the same at the same power levels ... I don't need a slide rule for that as I also know people who have flown both. And I already mentioned that had the war dragged on, the P-51H would have had its chance to garner a combat record worth discussion. I already stated that the main reason it was a useless exercise was the end of the war coupled with the dawn of jet age ... not any specific shortcoming of the P-51H ... it was just a development that was at the wrong time and turned out not to be needed.

My slide rule collection works just fine but I use Microsoft Excel these days and have since the day after it was a product. You should try it. That way, at least you might find something you like other than the P-51 and yourself. And I did, in fact, put some numbers out for speed and climb. Must not have been looking for it, huh?

Almost everyone else in here is civil. You should try it on a regular basis. If you want to talk with me, please be civil. It makes things a lot easier.

Last, When I called you a P-51 lover, it was not in any way an intended insult. I like 'em myself and thought you would be pleased to see it, given your history with the P-51. Just goes to show you that perception is not always reality. OK, if it makes you feel better, perhaps you are NOT a P-51 lover ... I don't know anymore and it is not on my list of things to investigate.


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## drgondog (Jan 20, 2015)

GregP said:


> As always Bill, you discuss by attacking, putting people down, and trying very hard to be superior and condescending. Unfortunately it comes across in a way I'd best not describe in here as it would be against forum policy.
> 
> *I guess if you listen very hard you will hear the strains of violin music as I struggle to comprehend your insults. Wuzak, Tomo and I raised specific points to your assertions of equivalence between the D and the F which seemed to elude your attention - but each deserved a thoughtful reply other than your normal vapid platitudes. *
> 
> ...



So, Excel person - what did you use for your HP vs altitude plots for 61" and 67" of HG, for which engines, which prop efficiency, which CDo, which Thrust delta and why - if you used a different engine between the comparisons? Do you have a V-1650-9 Power Spec which is different from a V-1650-3 and if so, where do you source it? What is your CDo for the P-51H and how did you derive it? What is your source for the CL vs Alpha and CL vs CD plots for the NACA/NAA 45-100 and the NACA 65-(1.8) 15.5?

Or is it back to your usual flailing about how I treat you like a stepchild?


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## pbehn (Jan 20, 2015)

Discussion about whether the P51H was needed or necessary depended on the A Bombs working, the Russians halting when the Germans surrender and solutions to jet engine reliability and thirst. The bombs did, the Russians didn't and jets were sorted, hind sight is very clear. A lack of war record doesn't detract from an aircrafts abilities, many great planes were not used because the situation changed, others time in the sun came too late, it doesn't detract from the AC. If the Germans had swept across Belgium and France then started attacking England in 1939 the Hurricane not the Spitfire would be England's saviour (if it won).


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## GregP (Jan 20, 2015)

Typical Bill. Almost anyone in here can look up a Merlin in any of the dash numbers and find specs. I did and I bet YOU can, too. I have faith in you there.

I didn't mention a lot of aerodynamics, not that they are all that difficult. I DID mention that at eqivalent power levels the P-51H could hit about 450 mph at the same altitude where the P-51D, using the same power, can hit it's best speed, which is typically quoted as 437 mph. That's about 2.97% faster on the same power. Doesn't seem like much math is needed here to me. I'm sure you know the best height as well as I do.

From the difference in speed, you can find the difference in drag. Go do it ... or don't, I don't care ... I already KNOW the speed difference, and that's all I need to know to realize it isn't a major change in aerodynamics at least as far as drag goes.

My entire contenion was not an aerodynamics course, which is NOT the purpose of this forum or the thread or what the thread has morphed into, it was a simple observation that at similar power settings they perform quite similarly. If I can find that out, you probably can, too. Eagledad left you a link if nothing else comes to mind.

So as I said above, hark back and go to it all you like. I'm VERY comfortable with my observations since they are shared by pilots who flew and continue to fly them. Your opinion seems to differ. OK, it differs. By now that is apparent to anyone who gets this far in the thread. 

I do not appear to ge the one flailing about here. You do.

I like the P-51H and have so stated, It just wasn't a factor in WWII combat and if you contend differently, then we must be reading different accounts. There is nothing whatsoever wrong with the P-51H ... it just wasn't needed at all ... but that's just my opinion.

Go bury your head in aeroidynamics if you seriously need to, but don't go asking me to do so. I will when I want to, and that's usually when some undeveloped version is comtemplated by me ... not by you. When a real live plane that has performance numbers is available I don't need an aerodynamic estimate, I have real-world numbers. Aerodynamics is all about predicting the performance. You don't need it at all when you HAVE the performance.

Take away the 81" and ADI of the -9/-11 engine, which could have been installed in the P-51D had anyone desired to do so, and how much beter is the P-51H? I know the answer and so do you. The fact that someone doesn't agree with you seems to rankle your intellectual sense of pride for some reason, but it has nothing to do with you personally or aerodynamics at all. The real numbers of these 2 planes at equivalent power levels are what matter, and I've already said what I need to say.

So how important was it to go 450 mph instead of 437 mph at full throttle sometime about May - Aug 1945 over Japan? On my reality scale, it rates a zero. Maybe I'm missing something here as none of the Japanese oppostion was that fast except the very few jets that flew,and they didn't attack anything. After the war, the P-51D would have served just as well as the P-51H ... and it DID. It also served in Korea, not because the P-51H was too vlauable a resource as you suggest, but because there were more of them around with more spare parts scattered over our bases in the vicinity.

Settle down, Bill, before you have a heart attack, this isn't personal and won't be. And it certainly isn't worth an aerodynamics argument in a non-aerodynamics forum as the performance numbers are already known, so we don't need to make aerodynamic predictions. If you think the P-51H was a wonder plane, by all means erect a monument to it. I simply don't agree.

Big surprise there, huh?

Here's a link to a test when the high boost didn't work. How much difference IS there between a D and an H at equal horsepower? Huh? OK, make your case, as you asked ME to do. This report, where the boost wasn't available, say otherwise. If the same power was available in the D, it would be VERY close ... because it IS.

file:///E:/pdf/P-51H%20Performance%20Test.html


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## pbehn (Jan 20, 2015)

eagledad said:


> Range: The P-51D has a slightly longer radius of action than the P-51H due primarily to the larger internal fuel supply(269 gallons for the P-51D as compared to 255 gallons for the P-51H); but this advantage was considerably reduced by the fact that the P-51D is not sufficiently stable with full fuselage tank to permit violent manurvering.



Excellent post eagledad. Just one question. The D version had an 85 gallon rear tank but had to burn off approximately 60 gallons before switching to external tanks I believe. Therefore any P51H forced to drop its tanks would probably have more internal fuel than a D in the same situation. The D would be burning internal fuel while having maximum weight and drag so the H probably had approximately the same range or possibly more than the D. Or do I read it wrong?


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## eagledad (Jan 20, 2015)

Pbehn,

I am out of my league here trying to answer your question, as I am not a pilot, but will give it a try. My understanding is that both aircraft would take off using internal fuel, I believe that was SOP for safety reasons (Drgondog, feel free to chime in on this). So neither aircraft would have full internal fuel when drop tanks are released. I went to my copies of the P-51 H and P-51 D flight manuals and found that if both aircraft are clean (wing racks only), and are carrying the same amount of internal fuel, (in this case 240 gallons), the manual claims that at the best crusing speed, the P-51H has a range of 1270 miles, the P-51D has a range of 1330 miles. The P-51D with 220 gallons would have a range of 1220 miles, and with 200 gallons a range of 1110 miles. So (pilots correct me if I am wrong, ) a P-51D with 210 gallons (269-60, about 210) would have a range of 1165, (half the value of 220 and 200) about 105 miles less than the P-51H.
So according to the flight manuals I have, the D has a slightly longer range carrying the same amount of fuel as the H has, but would have a shorter range if the 60 gallons of internal fuel was burned from the fuselage tank before switching to drop tanks. If you re-read my first post, the evaluators stated that even though the P-51D had a greater combat radius than the P-51H, the CG problems encountered with fuel in the D’s fuselage tank offset that advantage. It appears it would be unusual for the P-51D and P-51H to enter combat with the same amount of internal fuel. (the P-51H should have more as most P-51D pilots would use the 60 gallons of internal fuel mentioned) 

Eagledad


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## grampi (Jan 21, 2015)

Greg P...where did you get the top speed of 450 for the P-51H? It's top speed is generally listed as 487 MPH...


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## Milosh (Jan 21, 2015)

grampi said:


> Greg P...where did you get the top speed of 450 for the P-51H? It's top speed is generally listed as 487 MPH...



That is with 67" of boost most likely.

P-51 Mustang Performance


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## GregP (Jan 21, 2015)

I was looking at the performance at 67" as Milosh says. I was putting out an estimate of the top speed of the P-51H at 67" at anywhere from 17,500 feet to 21,500 feet ... which is close to where the P-51D achieved it's top speed. The entire discussion above is centered around the fact that while the P-51H DOES have great performance at 81" and using ADI, there isn't very much ADI in the plane and the sparkling performance is only for about 5 minutes or so. After that, the engine performs much like the engine in the P-51D and puts out just about the same HP, albeit at slightly different critical altitudes.

Hence my assertion that the P-51H wasn't a big step over the P-51D, it was an incremental improvement at best, and not much at that unless the power was screwed in hard. Had they simply put the -9 or -11 engine in the D, they'd have had almost the same thing without the very slight incremental improvement to the stability with full fuel and external load. I don't think it was all that unstable anyway since many thousands of P-51D pilots flew them many thousands of miles over Europe escorting B-17s and B-24s.

As it turns out, when the war in Europe was over, they got transferred to the PTO where the enemy planes were somewhat slower than the German planes, so they didn't need the extra 5 minutes of speed as they were already faster than the opposition and so could dictate combat or not as they chose anyway.

It was not and IS not that the P-51H wasn't a good plane, it was, but the war was essentially over and the next generation was going to be a jet generation. So the P-51H, which otherwise would have been a very good step, turned out to be the last gasp of the piston fighters that basically came into service just when the wer ended. It's production was cut short due to the elimination of the wartime need for it and, through no fault of the designers or the people who acquired it, it just wan't really needed at all.

It was probably a good thing they pursued it at the time, though, since the war was still on, and hindsight does have pretty good vision. When I say the plane was a waste of effort, it is nothing against the aircraft at all. It just means the war was won by the existing planes already in the field and the expense of the P-51H didn't play a part in the victory, that's all. After the war it didn't stay active for long and was sent almost immediately to the reserves and the guard. I call that reserve service, not first-line active service.

So the "useless" part was relative to WWII, not the quality of the aircraft. This is a WWII forum and I try (maybe don't always succeed) to stick with WWII in general while I'm in here. There is a "Modern" forum where post war is discussed.

And this is just my opinion. Bill's opinion is no less valid or valuable. Perhaps North American learned something that helped the F-86 from the P-51H effort, I don't know. If so, maybe it was a good thing after all. Whatever the case, it's worth maybe a discussion but not an acrid argument. I hope that isn't a vapid plattitude ...


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## snowmobileman (Jan 21, 2015)

I just had a quick look at the posted link...some of that P-51H altitude performance looks a little suspicious to me! Really, almost 5000 fpm climb at 20K feet, with a 47,000' ceiling? This beats the XP-51G by a large margin!


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## tomo pauk (Jan 21, 2015)

The top speed figure of 487 mph might come from factory estimates, eg. the chart in the Williams' site, dated as of 1944 (here). One of the charts is with just 105 gals of fuel and 4 HMGs (here). 
There is a test, on 90 in Hg, where the top speed is just 451 mph (here). Contrary to that, the SAC for the F-51H (redesignated post-war P-51H) show max of 412 kts, or 474 mph (here, browse a bit until F-51H docs). The colored speed charts at the Williams' site show 480+ mph, without racks and on 90 in Hg (here) and 480 mph with racks (here). In the ballpark with factory estimates.


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## GregP (Jan 21, 2015)

Looks that way to me, too. But I wasn't there and don't know for sure.

When the engine was at full rattle, the P-51H appears to have been a great ride, doesn't it? But a mission can last 6 - 7 hours and that great performance is available for about 5 minutes at best, which is why I was trying to look at the performance after the ADI was gone in the first place.

You could, of course, say the same for all the planes that had a wet max power system. Some of the Focke Wulf Fw 190 series had good performance wet and then were back to regular performance the rest of the time, too, just as we were. It would be useful to look at performance at rated power dry since that is what was encountered MOST of the time.

I doubt any pilot would automatically go to wet power for combat since it might be gone when he really needed it to save his own life later if he got jumped. Maybe rookies would. I doubt veterans would.


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## tomo pauk (Jan 21, 2015)

Even if the mission is 6-7 hours long, that does not mean that LR fighter will routinely spend like 30 min or more in combat during a mission. The USAF rule of the thumb was 5 min on WER (whether dry or wet) and 15 min on military power, even for LR work.
Five minutes, multiplied with so much LR aircraft = so many combats can be decided in the favor of the LR fighters if more engine power is needed.


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## cimmex (Jan 21, 2015)

Wasn’t the emergency power actuator lead sealed? I read somewhere that the pilot had to write a detailed report if the seal is broken.
cimmex


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## bobbysocks (Jan 21, 2015)

iirc my father said there was a wire that acted as a stop. going to the wire was full throttle and to get WEP you pushed and broke through the wire. and i dont recall him saying anything about having to write a report if he used it. he probably told his crew chief if he used it alot so that they could pull spark plugs and check them for leading.

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## grampi (Jan 21, 2015)

GregP said:


> Hence my assertion that the P-51H wasn't a big step over the P-51D, it was an incremental improvement at best, and not much at that unless the power was screwed in hard. Had they simply put the -9 or -11 engine in the D, they'd have had almost the same thing without the very slight incremental improvement to the stability with full fuel and external load. I don't think it was all that unstable anyway since many thousands of P-51D pilots flew them many thousands of miles over Europe escorting B-17s and B-24s.
> 
> QUOTE]
> 
> Even if the power being used is equal to that of the "D" model, the "H" model's 600 lb weight difference alone is enough to make a considerable difference in performance...600 lbs less weight is nothing to shake a stick at!


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## GregP (Jan 21, 2015)

It doesn't make a considerable difference.

If you fight them at the same power level, there is nothing to choose between them.

And I'm not saying the 5 minutes WEP was never used or was a bad thing or was useless at all. The point is the main difference between them, at full performance, was the extra 14 inches of boost available in the -9 and -11 engines over the -7 engines in the D models. The -9 / -11 would have fit into the D models, too. Had they done thath, the performance increase would have been very close to the same, at LEASST in speed, and climb would not be far behind, either. 500 pounds to a 9500 pound airplane doesn't make a huge difference. Some, yes ... not much.

You know, I've said it too many times already so this is it.

Nothing above knocks the H as a bad airplane. The war was won without it, making it unnecessary, and my main point is stated above, that the main diffrence in performance was power avilable. If there is ANYONE out there who thinks otherwise, you are welcome to do so in peace and harmony. 

It won't change the fact that at the same power level, the performance was just about the same between the D and H model P-51s, which goes a LONG way to proving my point ... Add the extra power to the D and they STILL won't be that far apart. 

Heck, go to Reno and watch it happen in person ... if these guys thought an H model was faster in any meaningful sense, they'd have raced it a LONG time ago. It's not like they weren't available when the planes were surplussed.

And that's all for this thread. Cheers.


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## wuzak (Jan 21, 2015)

GregP said:


> It was probably a good thing they pursued it at the time, though, since the war was still on, and hindsight does have pretty good vision. When I say the plane was a waste of effort, it is nothing against the aircraft at all. It just means the war was won by the existing planes already in the field and the expense of the P-51H didn't play a part in the victory, that's all. After the war it didn't stay active for long and was sent almost immediately to the reserves and the guard. I call that reserve service, not first-line active service.



When the light weight Mustang developments began the war was far from over.

To not try and improve the breed would be unthinkable.


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## wuzak (Jan 21, 2015)

GregP said:


> When the engine was at full rattle, the P-51H appears to have been a great ride, doesn't it? But a mission can last 6 - 7 hours and that great performance is available for about 5 minutes at best, which is why I was trying to look at the performance after the ADI was gone in the first place.



67inHg MAP (+18psi boost) was WEP, a 5 minute limit.

61inHg MAP (+15psi boost) was Military Power, a 15 minute limit.

If WEP was required for a second or third time then, sure, ADI would be of no help.

I still can't fathom why the V-1650-7 (Merlin 66) was cleared for +28psi boost (87inHg MAP) dry, the 100-series Merlins were cleared for +25psi boost (81inHg MAP) dry, but the V-1650-9 (Merlin 100-series) was only cleared for +18psi boost (67inHg MAP) dry.


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## wuzak (Jan 21, 2015)

GregP said:


> It doesn't make a considerable difference.
> 
> If you fight them at the same power level, there is nothing to choose between them.
> 
> ...



The weight difference should make a noticeable difference in climb rates, at least. The problem in comparing climb rates between the D and H is that the D makes more power down low (at 67inHg MAP). But the H still beats the D to 20,000ft by a half minute using the 67inHg limit.

At 20,000ft the V-1650-9 is making 1,320hp, the V-1650-7 1,455hp, despite the V-1650-9 using 67inHg and the V-1650-7 65inHg. The climb rate for the D is 3,050ft/min at that altitude, the H is 3,060ft/min. Not much difference, but the D is using 10% more power.

Given the same engine I'm sure the climb rate difference would be larger.


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## BiffF15 (Jan 21, 2015)

I think 600 lbs in the climb or cruise would make a bit of an impact, it's when you start to turn that it would show. 600lbs at 1 gravity (g) is only 600lbs. However at 4 g's it would be 2400lbs (or is my thinking off here)...

The lessor weight in the turn means less airspeed bleed or altitude given up to hold / sustain speed.

Cheers,
Biff


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## grampi (Jan 22, 2015)

GregP said:


> It doesn't make a considerable difference.
> 
> If you fight them at the same power level, there is nothing to choose between them.
> 
> ...



The Reno thing is not a good example...those planes are so highly modified it doesn't really matter which version you start with...also, I'm sure the rarity of the H models would be a huge factor too...I heard there's only like 1 or 2 still in existence...


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## drgondog (Jan 22, 2015)

GregP said:


> Looks that way to me, too. But I wasn't there and don't know for sure.
> 
> When the engine was at full rattle, the P-51H appears to have been a great ride, doesn't it? But a mission can last 6 - 7 hours and that great performance is available for about 5 minutes at best, which is why I was trying to look at the performance after the ADI was gone in the first place.
> 
> ...



Greg - post the P-51D flight test you want to use, but make sure it has all the data for GW, load of fuel, ammo and ballast - as well as the HP 'from tables' that you want me to compare.

In the meanwhile - ponder this.

From the NAA Drag and Power Analysis Report:
The P-51H Zero lift Parasite Drag at 9x10^^6 R.N is .0151 vs .0160 for P-51D at R.N. of 9x10^^3
The P-51H Wing area is 235.73 vs 233.19 for the P-51D
The P-51H Empty Weight is 6586 pounds vs 7205 for the P-51D
The P-51H Combat Gross weight for 255 gallons of fuel plus water and 1820 rounds of ammo = 9544 pounds vs P-51D with 269 gallons, 1820 rounds, no water = 10,208 pounds

P-51H Limit Load = 7.5G at 9500 pounds----------> 7.46G at 9,544 pounds
P-51D Limit Load = 8.0G at 8000 pounds----------> 6.26G at 10,208 pounds

P-51H W/L at Combat GW = 9544/235.75 = 40.5
P-51D W/L at Combat GW = 10,208/233.19 = 43.7

P-51H CDo = .0153 at RN=9x10^^6
P-51D CDo = .0160 at RN=9x19^^6 Both Values at ~ 150mph at SL with zero correction for compressibility 

Corrections at .5M ~ 1.1, at .65M = 1.2

So, You decide on the "Best Airframe". The one with 95% of the Parasite Drag, 94% of the mass, 93% of the W/L, 86% of Induced Drag at all comparable speeds - or the "other one"? 

Given the SAME power at all altitudes the P-51H will outperform the P-51D 'significantly'

When I looked at the only chart with raw data plotted, namely the Rate of Climb vs Boost for the P-51H test in which the test report discussed issues with both the WI and carburetor, it was clear that there was significant spread of plotted values for both 61" and 67" Hg - look for yourself and decide whether you think the -9 engine was putting out HP to the Packard Standard Chart as plucked by the test pilots?


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## drgondog (Jan 22, 2015)

There is a Report out there which has the P-51H-5 using 90. 80, 67, 61 and 46" with 130/100 fuel which was basis of 1949 SAC report - which I am looking for as the -9 had less HP for most altitudes below 24,000 feet when compared to the 1650-7. 

I don't recall checking to see if the table pick ups from Packard were faithfully transcribed to the Flight test reports but I have found many errors in the flight test reports for the included HP in the data.


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## tomo pauk (Jan 22, 2015)

wuzak said:


> 67inHg MAP (+18psi boost) was WEP, a 5 minute limit.
> 
> 61inHg MAP (+15psi boost) was Military Power, a 15 minute limit.
> 
> ...



The 67 in Hg was the limit for 130 grade fuel, the colored power charts on the Williams' site do show 70 in Hg - that being for post-war 145 grade fuel? On 150 grade fuel, the earlier Merlins in Mustang being cleared for +25 psi in RAF use, albeit only (or 'only') 75 in Hg in USAF use? The +25 psi only for low gear?
The V-1650-9 have had a similar 'hi-alt' supercharger gearing as did the -3, unlike the -7 that was 'mid-alt' engine - will heat the charge less on same boost, so the -7 could use a bit more boost than the -3 and -9?
On ADI, it was 90 in Hg for the -9, though.

Plenty of question marks, I'd love to have more information on this


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## pbehn (Jan 22, 2015)

I cannot believe that a weight difference of 600 pounds is insignificant. It takes a lot of work to raise 600 pounds to 25,000ft and keep it there for 6 hours. An increase in weight may not have a great difference on top speed but must have a greater influence on climb, time to climb and consumption at altitude. Similarly having an extra 30 mph, if only for 5 minutes cannot be insignificant. In the BoB 30 mph extra would have the Spitfire completely outclassing the 109 and the Hurricane fighting on par. 30 mph extra for the 109 would have completely changed the BoB in the LW favour. Many, if not most combats last less than 5 minutes.


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## drgondog (Jan 22, 2015)

pbehn said:


> I cannot believe that a weight difference of 600 pounds is insignificant. It takes a lot of work to raise 600 pounds to 25,000ft and keep it there for 6 hours. An increase in weight may not have a great difference on top speed but must have a greater influence on climb, time to climb and consumption at altitude. Similarly having an extra 30 mph, if only for 5 minutes cannot be insignificant. In the BoB 30 mph extra would have the Spitfire completely outclassing the 109 and the Hurricane fighting on par. 30 mph extra for the 109 would have completely changed the BoB in the LW favour. Many, if not most combats last less than 5 minutes.



It makes a difference. Under same power output the P-51B outclimbs and out turns the P-51D for combat load GW and all comparable load outs. Having said that, for full combat load the P-51B has two less machine guns and 600 rounds less ammo... 

The P-51H on the other has the same combat capability with 600 pounds less weight - which is another reason that the 51H had the same reason with 14 gallons less fuel - and no cg problems for any loading


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## GregP (Jan 22, 2015)

I'll revisit this one more time just for completeness.

If you go to the WWII Aircraft Performance website you can find a calculated test for the P-51H. It is report NA-8284-A. There it lists the calculations for the P-51H airplane. It lists speed and rate of climb at two combat power ratings, 90” and 80” Hg. at 3000 rpm, War Emergency Rating of 67” at 3000 rpm, Military rating of 61” at 5000 rpm, and Normal rating of 46” at 2700 rpm.

If you go to the Mustang Performance website you can find two reports for the P-51D airplane. One is USAAF report 44-15342 with flight test data and the other is report NA-46-130 with calculated data from North American.

These are not MY calculations, these are official reports from North American and the USAAF.

Since my contention is that the P-51D and P-51H airplanes were very similar at similar power levels, I’ll use the WER rating of 67”, 3000 rpm, and blower in appropriate gear for the altitude, the Military rating of 61”, 3000 rpm, and the Normal rating of 46”, 2700 rpm. I ignored the 90” and 80” M. P. numbers because the P-51D can’t make those power settings and is thus not relevant to this post. Let’s see what the reports say.

Please note the critical altitudes change with manifold pressure, as expected.

P-51H at critical altitude:
WER, 29800 feet, 447 mph
WER, 17800 feet, 433 mph
WER, sea level, 360 mph
Military, 32000 feet, 441 mph
Military, 20400 feet, 431 mph
Military, sea level, 342 mph
Normal, 32000 feet, 407 mph
Normal, 21900 feet, 397 mph
Normal, 301 mph
Time to climb from sea level to 20000 feet at 67” M. P. and 3000 rpm is 6.37 minutes.

P-51D at critical altitude:
WER, 26000 feet, 442 mph
WER, 10000 feet. 417 mph
WER, sea level, 375 mph
Military, 28000 feet, 439 mph
Military, 13200 feet, 413 mph
Military, sea level, 364 mph
Normal, 29400 feet, 420 mph
Normal, 16200 feet, 387 mph
Normal, sea level, 323 mph
Time to climb from sea level to 20000 feet at 67” M. P. and 3000 rpm is 6.4 minutes.

So, overall we see that the P-51H at 67” M. P. and 3000 rpm climbs from sea level to 20000 feet 0.03 minutes faster than a P-51D at the same power setting. That’s a whole 1.8 seconds quicker, assuming the 6.4 minutes was really 6.40 minutes. It was quoted at 1 decimal place. Less than one half of one percent seems pretty similar to me. So the 500 or so pounds of weight savings in the P-51H bought you nearly nothing in climb, at least to 20000 feet.

The P-51H goes 447 mph at 29800 feet at WER while the P-51D goes 442 mph at 26000 feet at the same power setting. A whole 5 mph delta. So the P-51D is 1.1% slower at a slightly lower altitude where we would expect it to be slightly slower.

The P-51H goes 433 mph at 17800 at WER while the P-51D goes 417 mph at 10000 feet at the same power setting. Most of the 16 mph delta is due to the large difference in altitude between the aircraft due to engines developing their best power at different critical altitudes.

The P-51H goes 360 mph at sea level at WER while the P-51D goes 375 mph at sea level. The P-51D makes better power at sea level than the P-51H does. Again, almost entirely engine-related.

You can read the numbers above as easily as I can and they rather heavily support my contention that the P-51H and P-51D were VERY similar at similar power levels. Hence my claim that had they fitted the P-51D airframe with the same engine as the P-51H had, the P-51D would have performed VERY similarly to the P-51H.


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## FLYBOYJ (Jan 22, 2015)

As an observer on the sidelines, I'll throw this in here - I see speed and climb data, lots of it, where are we on wing loading, turn and roll performance and acceleration between the D H?

*EDIT - I think Bill was starting to go in that direction on the last page...


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## GregP (Jan 22, 2015)

I'd love to explore an answer to that Joe but, unfortunately, the fight test and calculated data don't enumerate turn rates. I think the P-51H is almost certainly a bit better than the P-51D, as I have said numerous times, but I don't believe the difference between the P-51D with a -9 / -11 engine and a P-51H with the same engine is enough to justify the development cost.

Apparently, Bill does.

Our disagreement is NOT about whether or not the P-51H was a good plane, it was. It is entirely about whether or not the difference with equal engines would be worth the cost.

In the relative scheme of things, it's a very minor disagreement after all and, in the end, they DID proceed with the development of the P-51H. It's really nothing to get excited about. We apparently have a different idea about whether or not they should have spent more money than was required in WWII for P-51 development that was never used in the war. 80 years after the fact, it makes no difference at all. I feel we could have gotten substantially the same aircraft with a simple engine change and he thinks the P-51H's new airframe was significantly better.

From the real-world data I can find, it wasn't quantitatively much better, top speed wise or climb-wise. He thinks otherwise.

That's nothing much to get upset about from my end, but I will respond to sarcasm and personal attacks, hopfully within the rules of the forum. I've been trying to stay focused on the point I was trying to make but, alas, am not very good at turning the other cheek, so to speak. Perhaps we just like to explore alternative "what ifs" differently. 

I'd be happy to discuss it ... without having it escalate into personal attacks just because we don't think alike.

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## drgondog (Jan 22, 2015)

FLYBOYJ said:


> As an observer on the sidelines, I'll throw this in here - I see speed and climb data, lots of it, where are we on wing loading, turn and roll performance and acceleration between the D H?
> 
> *EDIT - I think Bill was starting to go in that direction on the last page...



Joe - I went there early. What I didn't want to do is deal solely with the single flight test on Mike Williams' site that a.) clearly had engine issues with 80" and 90" boost, and b.) confusing HP values for -9 in the report for 61 an67". When I looked at those I noted quite a few 'pick and insert' errors from the V-1650 Power tables for B/C/D tests

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## pbehn (Jan 22, 2015)

drgondog said:


> It makes a difference. Under same power output the P-51B outclimbs and out turns the P-51D for combat load GW and all comparable load outs. Having said that, for full combat load the P-51B has two less machine guns and 600 rounds less ammo...
> 
> The P-51H on the other has the same combat capability with 600 pounds less weight - which is another reason that the 51H had the same reason with 14 gallons less fuel - and no cg problems for any loading



I was being polite, the bomb load carried by "strategic" bombers like the stirling and fortress were not in many cases strategic. A 4 engined bomber dropping 1.5 tons is light to medium bombing with little accuracy is no strategy at all. I know you cannot extrapolate directly from a single to a four engined aircraft but to say a S/E aircraft can carry 600 LBs to Berlin and back with no detriment is also to say all allied bombers could carry an extra ton (or tonne) of bombs with no ill effects, obvious nonsense.


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## eagledad (Jan 22, 2015)

Gentlemen:

The following information is found in Sport Aviation, September 1983 page 42 in an article written by John Reader NACA/NASA retired. The Article is titled “The Mustang Story”.





This chart is roughly comparable to figure 46 in NACA report 868, page 165.

Eagledad

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## GregP (Jan 22, 2015)

Good find, Eagledad.

Thanks.

I believe that Spitifre IX in the chart had to be a clipped wing version, not a full universal wing.

Also, I've read in at least 15 texts on the subject that there was no other WWII fighter that could out-roll an Fw 190, particularly the radial engined models. This is the first time I have seen anything that even suggests a Spitfire could out-roll one, even with a 50-lb stick force.

Let's remember, it came from Sport Aviation. Is there any otehr corroboration out there that anyone has seen? Not saying anything in particular except that it is contrary to what I've read for a lot of years.


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## tomo pauk (Jan 23, 2015)

The graph kindly posted by eagledad does not have the roll rate for the serial produced P-51. The roll capability of those was lower than the Fw 190A at 10000 ft until up to 350 mph indicated. Above that, the P-51 was better. Graph from NACA report no. 868: pic.

BTW, that might also explain why the later Fw 190D were to receive hydraulically operated ailerons, those help in achieving maximum aileron movement (where the pilot does not have enough strength for that), and hence roll rates at high speed,


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## FLYBOYJ (Jan 23, 2015)

Just a few more observations here...

As a pilot (and a sometimes wanna be fighter pilot), in a close in engagement I'd want a mount under me that 1) accelerated well, 2)good turning and roll rates, 3) good climb rate and lastly speed. It seems the P-51H might have brought those to the table with only a marginal "mark-up" in speed and climb, depending where you were on the flight envelope. (Biff, chime in and let me know if my priorities are in order)

As far as time and cost for a slight or marginal improvement (in some folks opinion) I think it would depend on how much commonality the P-51D had with the H, how much would it cost to convert tooling and manufacturing methods and lastly if the customer (Uncle Sam) was willing to fork out the expense of modifying the production line. IMO, if all these factors can easily be incorporated with no disruption of production, degradation or quality or excessive add-on costs, I see no reason why the P-51H should have been continued, especially with P-51D production lines still rolling.


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## drgondog (Jan 23, 2015)

Joe - I am going to break this out in two parts.

First - I will use the Relevant physical attributes stated by NAA for the P-51D and P-51H as the basis for Performance comparisons.

Then I will use the best case P-51D Flight Tests obtained by AAF in June 1945 for Dash speeds at specific altitudes with the V-1650-7 and the P-51H during the May 1945 Flight test with the V-1650-? and make some comments regarding the Test conditions of each airplane, but particularly the 1650 used in the P-51H test as reported.

Discussion 1
P-51H Limit Load = 7.5G at 9500 pounds----------> 7.46G at 9,544 pounds
P-51D Limit Load = 8.0G at 8000 pounds----------> 6.26G at 10,208 pounds

P-51H W/L at Combat GW = 9544/235.75 = 40.5
P-51D W/L at Combat GW = 10,208/233.19 = 43.7

P-51H CDo = .0153 at RN=9x10^^6
P-51D CDo = .0160 at RN=9x19^^6 Both Values at ~ 150mph at SL with zero correction for compressibility 

Corrections at .5M ~ 1.1, at .65M = 1.2

So, what does it mean that the P-51H has 95% of the Parasite Drag, 94% of the mass, 93% of the W/L, 86% of Induced Drag at all comparable speeds? 

FIRST - take the engine out of the equation - for two reasons. 
A.) any of the V-1650 engine/prop combinations could have been used including the -3, -7, -9 and -9A and "GregP" suggested using only the one P-51H Test Report of the -9 which a.) The Water Injection System and Simmons Manifold Pressure regulator system were malfunctioning, and b.) the delivered V-1650-9 had not been calibrated and c.) that HP data in the report had been pulled from the Engine Spec AC-10356 Dated November 1944.
B.) Assigning the SAME engine/prop system to both the P-51D-15NA and the P-51H-1NA eliminates debates about "plot vs spec sheet vs actual HP' for any altitude or any speed run so any equation below which depends on THRUST can assign the Same Thrust to each airframe and focus on the Physical attributes to derive Acceleration, Climb, Corner Speed(Maneuver Point on the V-n Diagram), Rate of Turn. 

Given the SAME power at all altitudes the P-51H will outperform the P-51D 'significantly'.

For example: Acceleration

For equal Power, equal prop efficiency The aircraft with less weight and Same drag will out accelerate the greater weight a/c. In the case of the P-51H is has both less Drag (=greater net Thrust) AND lower mass. Net THRUST = Thrust available - Thrust required. Acceleration is Thrust/Mass. Acceleration is inversely proportional to Mass for a given Thrust. The Mass of the P-51H at full combat load at 9544 is 92.7% of the P-51D at full combat load of 10,288 pounds.

*For same Power, same Thrust, starting at same velocity, with same engine and prop the Acceleration of the P51H is 1/.927 = 7.8% greater than the P-51D.* 

This is before taking into account the lower Drag of the P-51H. The Induced Drag of the P-51H and the Zero Lift Parasite Drag will individually and collectively be less than the P-51D at the same airspeed for same combat load out. At top speed of the P-51D and the same speed for the P-51H. the Induced drag for the P-51D will be slightly greater than the P-51H, but for the sake of clarity, assume both are = zero. For that assumption, the Drag comparisons are:

Drag of P-51H = 96% of the P-51D (.0153/.016 at RN=9.6x 10^^6. The Drag of both increased as the velocity increases but maintain their relationship for level flight)

Therefore the Net Thrust for the P51H = Thrust Available - .96 Drag of P-51D ----> driving incremental acceleration more positive for the P-51H over the P-51D.

The same logic and process follows for ROC. ROC = Excess Power/W where Excess Power = T*V-D*V
For the same Prop/engine system, and the same Trust developed at same Velocity, the P-51H once again has greater Power Available than the P-51D because the P-51H Drag = 'K'( 9544/10288)/(235.75/233.19) where K= 1(.5*Rho*V^^2) and same for both the P-51H and D.

*Therefore the P-51H Drag as a % of the P-51D = .927/1.011 = 91.7% of the P-51D Drag.

Extending that back to the ROC equation Excess Power for the P-51H compared to the P-51D;

V*(T-.917*D) for the P-51H and V*(T-D) for the P-51D, 

Now, the ROC of P-51H = V*(T-.917*D)/9544 while the ROC for the P-51D = V*(T-D)/10288 

As we don't know either Thrust or Drag as we have not specified at Velocity (or Power) we can get a rough understanding of the comparison by using P-51D Drag = 1/2 Thrust and 3/4 Thrust for illustration:
Case 1 D=1/2*T
P-51H ROC = V*(T-.917(.5*T)/9544 = V*T*(.542)/9488= V*T*(5.68x10^^-5)
P-51D ROC = V*(T-.5*T)/10288 = V*T*(4.86x10^^5) 
The ROC advantage for the P-51H in this case is 17%.
Case 2 D= 3/4T
P-51H = V*(T-.917(.75*T)/9544= V*T*(.312)/9544 = .0000327*V*T
P-51D = V*(T-.75*T)/10288 = V*T(.25)/10288 = .0000243*V*T.
The ROC advantage for the P-51H in Case 2 is 34%

Summary - For same Power at same altitude with the same engine, the aerodynamic superiority of the P-51H gives it a decided advantage in Acceleration and Climb - as well as Velocity but for this exercise the actual value for power is not introduced.*

I will lay out the May 1945 P-51D-15 vs P-51H-1 Flight Test Reports using Military Power in the next post.

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## FLYBOYJ (Jan 23, 2015)

Bill, great post! You make it easy for me to understand, whish you were my high school math teacher!!

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## drgondog (Jan 23, 2015)

Next - the Flight Test Report of June, 1945 does not represent a fully functioning V-1650-9 and because of the following comments contained in the report, raises questions regarding even the actual power produced by that specific engine. The comments included
"Water Injection System not working"
"Simmons Manifold Pressure Regulator not working"
"A Bendix Stromburg PD-18C-3a carburetor was installed to replace the speed density pump"
"At present time the V-1650-9 has not been calibrated and all power data are extracted from calculated power curves"
"all power figures based on Power curves from Spec. No. AC-10356 dated 29 November, 1944"

These remarks raise questions across the board for this 1650-9 engine with respect to how well it operated even with respect to 46 and 61" of boost. I suspect the fuel metering substitution of a Carb for the faulty Simmonds manifold pressure and speed density pump may have been flawed to metering a higher Rich mixture.

Next - The Flight Test Report dated 15 June, 1945 for the P-51D-15NA is tested at or around 9760 pounds at takeoff and speed/climb runs largely at 9660-9570 pounds. The fully loaded Combat Weight for P-51D is 10,288 for everything except external load out. So, all the resulting data points are for a GW=< 94%, where as the P-51H speed and climb runs were at 9450 to 9350 for a GW=> 98%. So, for every data point the P-51H is laboring under a 4-5% weight handicap when compared to the P-51D. 

I will extract the comparative 61" boost figures for comparison - both for level speed and climb.

For the ROC values I will put a suggested 'weight' factor to reflect how uploading the tested P-51D climb rate would be reduced when adding 500+ pounds of Fuselage Tank fuel to complete a Combat Load load out.

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## wuzak (Jan 23, 2015)

drgondog said:


> I will extract the comparative 61" boost figures for comparison - both for level speed and climb.



I did some figures of RoC at 67inHg several pages back.


Alt (ft)P-51D MAPP-51D ROCP-51H MAPP-51H ROC06736006732004800673600500066.535756732851000056.32925673350138006733951500047.2227516000673200190006732002000065.230506730602500055.52375672750267006726403000046.4170059.422753500037.7100049.415104000029.832540.64404160027.5100

P 51D Performance Test
P-51H Performance Test

This shows the hp of the engines and highlights the different characteristics of the -7 and -9.


Alt (ft)V-1650-7 MAPV-1650-7 hpV-1650-9 MAPV-1650-9 hp06717806715034800671730500066.517206715481000056.31470671590138006716221500047.2123216000671580190006715002000065.214556713202500055.51225671340267006713473000046.4102559.412093500037.785549.410124000029.870040.6830


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## wuzak (Jan 23, 2015)

Bill, do you know why the V-1650-9 wasn't cleared for +25psi boost (81inHg) dry, even though the equivalent Rolls-Royce engines were?


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## drgondog (Jan 23, 2015)

FLYBOYJ said:


> Bill, great post! You make it easy for me to understand, whish you were my high school math teacher!!



LOL. Joe a couple of points about 'real world' on the above formulas.

For actual ROC, you have to integrate over the climb trajectory to correctly differentiate the change in Thrust as a function of the changes in velocity, as well as the change in Drag for those comparable velocities as altitude increases and density decreases. The Parasite Drag also adds an Angle of Attack component to account for the increased Form Drag as well as the Propeller stream tube delta for the fuselage - which increases due to the new AoA.

But Point by Point in the trajectory the relationship to Drag and Weight I posed is correct and easier to understand (I think) the way I showed it.

The Corner Velocity Maneuver Point is higher for the P-51H, largely because the increased G limit and wing area offset the lower CLmax for the P51H. I used clean stall speed (difficult to nail precisely) for both the P-51H and P-51D, arriving at 1.65 and 1.77 respectively for data that I have found - but not quite sure of.

The W/L to Clmax ratio for the H is 22.9 and 24.7 implying that Rmin for the P-51H is slightly less ((~7%) for same power. Consequently the rate of turn is greater for the P-51H as well... by the ratio of the square roots of CLmax*N to W/S ratio. For this example the 51H has a turn RATE about 10% faster. This all depends on whether I picked the Clmax correctly.

So far - I haven't found one category in favor of the D, given equal power output. When comparing 1650-7 vs the -3 and the -9 and the -9A, as you know the -7 at 67" is the most powerful from SL to FTH in Low Blower and the 1650-3/-9/-9A were better above Low Blower FTH for the -7... so net, net the P-51D at SL at 67" than the P-51H at SL with a good -9 at SL.

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## GregP (Jan 23, 2015)

Since the time to climb from sea level to 20,000 feet for the P-51H in the flight test I was using and the P-51D I was using wwere withing about 2 seconds of one another, I'd say either your equation is missing something somewhere or we have an issue with the flight tests.

In the P-51H flight test I used, the P-51H was not having any trouble at 67 inches ... it was having trouble going to 81 inches with ADI, meaning it was having issue getting to the extra power that gives the P-51H it's performance jump over the D model. The engine was running fine at 67" per the report. As you know, the speeds and rate of climb to 20,000 feet were VERY cloe to one another, and that does not agree with your analysis above, Bill.

Can you think of an explanation other than the engine wasn't calibrated?

I might add that the P-51H flight test I used was from North American and the the P-51D flight test was from the USAAF, not from a private party analysis, and that is not knocking your calculations at all. All I'm saying is that real world flight testing didn't find that amount of differnece between them, on at least several occasions. I like calculations and calculating as well as the next enginer, but I throw them out when real data are avialable ... and in this case, they are, at equivalent power settings. 

That does NOT mean that 67" in the V-1650-9 pdocudes the same HP as 67" in the V-1650-7 at the same altitude ... it says they are both set to 67" and 3000 rpm, and that is why I was careful to say power settings, not power levels.

There is Eagledad's reference that says that at equal pwoer settings ( and that was a private flight review), there was little to choose between them, and there are the flight tests I used that say essentially the same thing.

So while I agree with your calculations in principle, they don't seem to track in real life. That is also from two current P-51 pilots who have flown the P-51A, B/C, D/K, H, and careful modifications of some D models. Today, in private hands, none of the P-51's are seeing 67 inches since we aren't flying with gasoline that will sustain it ... except at Reno where high quality aviation fuel is avilable. Today they take off at 45 - 55 inches, sometimes less, and throttle back. So today they are flying at very nearly equivalent power settings ... and don't see much of a difference.

What they really do when flying together is that the leader sets a power level and the other(s) form up in formation, and they talk back and forth on the radio to see who is flying at what power (rpm and MAP). When they do, there isn't much difference, but there is sometimes a small bit. Ed Maloney's P-51D (Spam Can) typically takes about 1 more inch of manifold pressure to keep up with Steve Hinton's P-51D (Wee Willy) at most VFR altitudes, or if did before it got polished and the tail was repaired. Now the pwoer levels required for formation are the same. When they actually fly with a P-51H (on rare occasions), they don't see much difference bewteen Steve's plane and the H while in formation. To me, as an engineer and an observer, that says very close to the same drag when they are running the same MAP and rpm while in formation. And it's mostly at about 235 knots since the speed limit below 10,000 feet is 250 knots, as Joe and Bill well know.

Hence, my post. And since they still fly that way, I'd sat some investigation is in order for anyone really interested. Not being a P-51 pilot nyself, I take our museum and my frinds word for it. The only time I ever flew a P-51D in formation with another P-51, it was another P-51D and I was in the back seat having fun, not playing fight engineer.

And, as I stated erlier, I throw out the calculations when real data are avilable. In this case, they are.


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## wuzak (Jan 23, 2015)

GregP said:


> Since the time to climb from sea level to 20,000 feet for the P-51H in the flight test I was using and the P-51D I was using wwere withing about 2 seconds of one another, I'd say either your equation is missing something somewhere or we have an issue with the flight tests.



These are the flight tests I was looking at:

P 51D Performance Test 
P-51H Performance Test

The D test was done in June 1945, the H test in May 1945. This may be the one to which Bill is referring, as it mentions problems with the ADI and pressure regulator.

The condition of the aircraft was similar for the climb tests - ie clean with wing racks in place. Weights were 9,760lb for the D and 9,484lb for the H at take-off for the tests. This suggests to me that the H was relatively more heavily loaded.

Time to climb to 20,000ft with 67inHg MAP was 6.6 minutes for the D and 6.1 minutes for the H. That's a difference of 30s. Or, to put it another way, it took 8% longer for the D to climb to 20,000ft than the H. This is despite the hp advantage the D had at lower altitudes.

The reports don't have climb dat afor the D at 61inHg, but the H climbed to 20,000ft in 6.75s, or 9s longer than the D took at 67inHg.

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## wuzak (Jan 23, 2015)

Greg, since you have repeatedly stated your opinion that the P-51H was not required during WW2 because it never went into combat and therefore was a waste of money, would you say the same of the Bearcat since it never went into combat and was not required to defeat the Japanese?


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## eagledad (Jan 23, 2015)

Wuzaak,

Just a quick point on the P-51D test... it says that the fuel load was only 209 gallons, the fuselage tank behind the pilot only had 25 gallons, so the D and the H were relatively close in weight. (9760 for the D vs 9484 for the H)

Eagledad


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## GregP (Jan 23, 2015)

http://www.wwiiaircraftperformance.org/mustang/Comparative_Fighter_Performance.jpg

Just for info, above is a link to a comparative test of three WWII fighters, including a P-51H. If you look at the chart, the power setting used for the P-51H was 3000 rpm and 70 inches. It's not 67 inches like a P-51D would be using, but it is reasonably close. 

Take a good look at the numbers. Speed and climb are right where I said they would be. The speed at 20,000 feet is just under 450 mph and the climb rate at that altitude is close to 2600 feet per minute, right where you'd expect to find a P-51D. 

So here is another flight test of the P-51H, near P-51D power levels that shows the P-51H right where the P-51D is expected to be. It is dated 12/18/44 and the report appears to be Y-122981. However, I bet M. Williams can tell us for sure if anyone is intetested in asking.


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## GregP (Jan 23, 2015)

You're starting to sound downright unfriendly for a friend, Wayne. 

The Bearcat obviously wasn't required for WWII since it got there but didn't manage to get into combat. It DID get into combat post WWII for France, Thailand, and South Viet Nam.

Virtually every fighter that flew from late 1944 onwarrd didn't make WWII combat and was therefore technically not needed for WWII. That doesn't mean and I never said they are or were bad aircraft ... I said they were not needed for WWII and therefore were a waste of money ... relative to WWII. This IS a WWII forum, after all.

The P-51H served well in the reserve and guard, post war. The P-80 also didn't get into combat, but survived for nearly 50 years in the form of the T-33. It wan't needed for WWII either, but paved the way for future jets. The only thing that saved these planes instead of having them go the way of the Focke Wulf Ta 152 is the fact that we won the war and left these planes in service, albeit in lower numbers than a wartime footing would otherwise dictate. 

Had Germny won the war, my bet is the Ta 152 and Me 262 would have equipped not a few squadrons of planes for some years. too, much like the P-51H and P-80, which would have been nearly-forgotten footnotes in history.

Sometimes the future hinges on relatively unimportant-at-the-time events, such as having the USA move toward entering WWI by having the Lusitania, a non-US-flagged ship, sunk without warning.

I'd say that Hitler's decision to invade the USSR was the turning point of WWII. If he hadn't done that one thing, he might have carried the day anyway, even with all the other mistakes the Nazis made. Thank heaven he wanted something in the USSR!


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## wuzak (Jan 23, 2015)

eagledad said:


> Wuzaak,
> 
> Just a quick point on the P-51D test... it says that the fuel load was only 209 gallons, the fuselage tank behind the pilot only had 25 gallons, so the D and the H were relatively close in weight. (9760 for the D vs 9484 for the H)
> 
> Eagledad



In other words, teh P-51D was more lightly loaded relative to the P-51H. Had they had equal fuel and ammo loads the advantage in climb of the H would have been more pronounced.


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## wuzak (Jan 23, 2015)

GregP said:


> http://www.wwiiaircraftperformance.org/mustang/Comparative_Fighter_Performance.jpg
> 
> Just for info, above is a link to a comparative test of three WWII fighters, including a P-51H. If you look at the chart, the power setting used for the P-51H was 3000 rpm and 70 inches. It's not 67 inches like a P-51D would be using, but it is reasonably close.
> 
> ...



And here is a speed graph of the D

http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_Level.jpg

This is at 67inHg. At 20,000ft the speed appears to be ~420mph (421mph in the table in the test).

I have previously stated the climb rates at 20,000ft for this particular D on that test. The H in the test I posted earlier is recorded as 431.7mph.


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## GregP (Jan 23, 2015)

Looks like we're all quoting different tests. Maybe a good procedure would be to take 5 tests for each one around the same time, throw out the high and low, and take the average of the remaining three.

After that, go back and recalculated if the P-51D had the V-1650-9 or -11 and see what the differences would be. Of course, that would HAVE to be with calculations since they didn't build one.

I for one think there wouldn't be enough difference to warrant the devlopment costs of the P-51H. There may be some justification, but I can't see it or agree with it. We all know it was built, so the decision was made already ... during the war, to do it. With hindsight, I'd change a lot of things, not just this one small decision.

Hindsight is like experience, you get it right AFTER you need it.


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## wuzak (Jan 23, 2015)

You can't see how 600-700lbs weight saving would be a good thing?


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## GregP (Jan 24, 2015)

Are you being obtuse on purpose, Wayne? Have you even read my replies? I was using actual data and actual calculations from the manufacturer and USAAF, not calculations based on numbers I mostly can't seem to find. I didn't make any claims the data didn't show.

I already said the H was a small bit better than the D, not very much ... at equal power. At full rattle it was significantly better.

If you won't believe real data, then you won't. It makes no difference this long after the war anyway. I won't try to confuse you with manufcturer's and USAAF data anymore if your mind is made up.


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## RayB (Jan 24, 2015)

Confusion about V1650-9 power settings

The data indicates that the V1650-9 produced 2200+ hp with 90” Hg using water injection and about 1600 hp with 67” Hg dry using 130 octane fuel. Something is missing here: what is the power output using 145 octane fuel without water injection? Wouldn’t it be about 2000 hp? And shouldn’t the comparison being made be between the P-51D using 145 octane fuel (widely available since mid-1944) at 75 Hg and the P51H using 145 octane fuel at 80 Hg, and also using water at 90Hg?

When water ran out for the P-51H, it would still be able to produce power at 80 Hg, somewhat better than the P-51D at 75 Hg.

From other sources, the max speed of the P-51D using 75 Hg was about 450MPH. The P-51H (not a P-51 at all but a complete redesign based on the P-51) at the same power setting was about 10MPH faster than the P-51D. We can now answer the central question: what part of the improved performance of the P-51H was due to improved aerodynamics and what part was due to using water injection. The P-51H gained about 10MPH from better aerodynamics and 10+MPH from using water injection. Was the overall improvement, 20+MPH, worthwhile? Greg says no. But what if the war in Europe had continued and the allies has had to face numbers of 335’s and 152’s. The extra speed would have been useful and the higher rate of climb even more so. Wouldn’t have helped against the 262 though.

What about the future? The Hawker P1030 and the Supekrmarine 391 both had projected speeds of about 510MPH using the 3500 hp RR Eagle engine. That seems to represent the absolute limit for a combat aircraft that the combination of reciprocal engine and propellor was capable of, at least using a WWII wing.


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## drgondog (Jan 24, 2015)

Wayne - I think I see where he is missing the obvious. Greg seems to be equating Manifold Pressure setting results as 'equal power". If so, he is missing the very obvious data points of different HP for same boost between 1650-7 and -9 (and thus the -3 and -9A) leading to another conclusion that he forgot that T=D at top speeds for any given altitude and that Boost does Not equal HP, nor does HP = Thrust.

For the moment I suspended belief that the -9 Engine tested actually achieved the 'HP picks of the Flight Test, when they had to run with fuel metering carb instead of the Simmons manifold Pressure system with speed density pump.

Will run some numbers for the May flight test on the H with the 61" HP data. Do you suppose Greg realizes that the P-51D-15 was tested with an fuselage fuel tank was 400 pounds shy of full while the H ran full Combat load with 100% fuel and ammo load out?


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## wuzak (Jan 24, 2015)

drgondog said:


> Will run some numbers for the May flight test on the H with the 61" HP data. Do you suppose Greg realizes that the P-51D-15 was tested with an fuselage fuel tank was 400 pounds shy of full while the H ran full Combat load with 100% fuel and ammo load out?



I didn't mention fuel specifically, but I did mention that the D was, relatively speaking, more lightly loaded.

Eagledad pointes out the fuel load of the D earlier.

I noticed on tests of British aircraft that the figures were often corrrected to 95% of MTOW. Was there any standard like that in the USAAF?


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## drgondog (Jan 24, 2015)

GregP said:


> Are you being obtuse on purpose, Wayne? Have you even read my replies? I was using actual data and actual calculations from the manufacturer and USAAF, not calculations based on numbers I mostly can't seem to find. I didn't make any claims the data didn't show.
> 
> *Greg - Wayne has forgotten more about Physics than you know, and easily understands the applications ON HIS OWN. If something doesn't smell right, he questions it. The May, 1945 Flight Test results didn't quite 'smell right' so your repeated 'replies' using actual calculations and contractor data didn't make any sense to him or me. So when NAA issues a revised Report which downgrades ALL of the 1650-9/Simmons data to 1650-9 Fuel Metering Carb data - You missed it even though it was explained in detail in all 97 pages of the NA-8284-A report you threw at him and me.
> 
> ...


*

Greg - If you won't read what Ed Horkey signed off on, on all 97 pages, then you are simply lazy and ill-informed on this subject. You should start these discussions with the following disclaimer.

"I Have a 1st Amendment Right to express an opinion independent of a.) the facts available, or b) my ability to comprehend them" - because both of these conditions seemingly apply.

What you should Really do is apologise to Wayne.*


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## drgondog (Jan 24, 2015)

RayB said:


> Confusion about V1650-9 power settings
> 
> The data indicates that the V1650-9 produced 2200+ hp with 90” Hg using water injection and about 1600 hp with 67” Hg dry using 130 octane fuel. Something is missing here: what is the power output using 145 octane fuel without water injection? Wouldn’t it be about 2000 hp? And shouldn’t the comparison being made be between the P-51D using 145 octane fuel (widely available since mid-1944) at 75 Hg and the P51H using 145 octane fuel at 80 Hg, and also using water at 90Hg?
> 
> ...



Thin line between advanced development tested with combat loads and an operation aircraft purchased and placed into service.

The XP-51G was clocked 1t 498MPH with 2000 HP Rolls Engine. If production ready the 14 S.M. would have been used instead of the 1659-9.


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## RayB (Jan 24, 2015)

Drgondog - The point you're making seems decisive. At the same power setting, the P-51H was about 20MPH faster than the P-51D. Why then did the P-51H in SAC service have a max speed of only about 470MPH when using water? I believe I've read that the P-51D had a max speed of about 450MPH when using 75" Hg. Seems like the P-51H in SAC sevice should have had a max speed closer to 490 than 470.


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## wuzak (Jan 24, 2015)

RayB said:


> Drgondog - The point you're making seems decisive. At the same power setting, the P-51H was about 20MPH faster than the P-51D. Why then did the P-51H in SAC service have a max speed of only about 470MPH when using water? I believe I've read that the P-51D had a max speed of about 450MPH when using 75" Hg. Seems like the P-51H in SAC sevice should have had a max speed closer to 490 than 470.



You have to look at the altitudes as well as teh top speed.

For instance, the top speed of the H at 90inHg was 471mph @ 22,700ft, at 80in Hg was 466mph @ 25,700ft and at 67inHg was 447mph @ 29,800ft.

P-51H Performance

For the V-1650-7 in the D the maximum speed at 67inHg was at a lower altitude - [email protected] 25,000ft.

This is because the different altitude ratings of the engine (different gear ratios in the supercharger drive).

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## drgondog (Jan 25, 2015)

RayB said:


> Drgondog - The point you're making seems decisive. At the same power setting, the P-51H was about 20MPH faster than the P-51D. Why then did the P-51H in SAC service have a max speed of only about 470MPH when using water?
> 
> *The top speed with 90" for full combat load out of all ammo and fuel but with external racks attached at 22.7K is 410kts/472mph and 406kts/467mph at 25K. The Light version at 8283 pounds GW at take off is 412/474 and 408/470 respectively for those altitudes. It is in the 'Light" config that ROC is 5850 fpm at SL*
> 
> I believe I've read that the P-51D had a max speed of about 450MPH when using 75" Hg. Seems like the P-51H in SAC sevice should have had a max speed closer to 490 than 470.



The top Calculated speed from NAA was 487mph at 90"/3000RPM without bomb/fuel tank or rocket racks, and based on the Performance spec for the -9 engine dated September, 1944. The data for sea level for the engine and all subsequent altitudes was adjust by combination of calibration, more flight tests and is published in the November 1946 report I referred to above, and is attached to the NAA Report following the May, 1945 Flight Test report on Mike Williams' site. It was lower than expected. AFAIK the use of ADI was never fully sorted out and the when the Simmons 
speed density boost pump was sorted out, it remained and that version became known as the V-1650-9A.

I suspect, but do not know, that the 1949 and 1950 Tables were derived from the use of the 9A

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## GregP (Jan 29, 2015)

Hi,

I decided to visit this thread one more time and throw in some aerodynamics for those who like it.

My premise was that if they took the P-51D and installed the V-1650-9 engine in it instead of the V-1650-7, they would have had substantially the same aircraft instead of the total redesign that the P-51H incorporated. To that end, I have calculated the top speed at altitude had the V-1650-9 been installed in the P-51D. It assumes no increase in drag, which is reasonable since the engines are the exact same size when you put them side by side. We HAVE at the Planes of Fame.

I took the power versus altitude for the V-1650-9 from: http://www.wwiiaircraftperformance.org/mustang/p-51h-powercurve.jpg

I took the power versus altitude for the V-1650-7 from: http://www.wwiiaircraftperformance.org/mustang/V-1650-3_7_power_curve.jpg 

I got the speed versus altitude from the same sources in different tables. The speed versus altitude comes from: http://www.wwiiaircraftperformance.org/mustang/na-46-130-chart.jpg for the P-51D and the speed versus altitude for the P-51H comes from the link just above the power table for the H.

Almost everyone in here knows the speed gain with horsepower increase comes from the old speed times the (new power divided by the old power) raised to the 1/3 power. Everyone who knows aerodynamics knows it at any rate. Physics rules the world in real life.

The data looks like this: 







My calculations. The second chart is speed versus altitude for the D and H and the third is speed versus altitude for the D, H, and new model. Speed is mph, altitude is feet, HP is HP. Simple.

So, the New P-51D with the -9 engine gets you 60 to 80% of the performance gain of the P-51H from sea level to 18,000 feet or so and again from 24,000 feet up to 32,000 feet or so. Between those altitudes it gets from 20 to 50% of the performance gain … *just like I said it did*. 

And it does this IMMEDIATELY for almost no cost since the -9 engine fits the same engine mounts and avoids the entire cost of the P-51H’s new airframe development. It ain’t exactly a P-51H but it gets into combat with substantially better performance before the war ends and costs almost nothing to accomplish except installing a new Merlin variant. I've worked on changing Merlin variants, and it isn't a big deal if it fits.

And it DOES fit.

What it doesn't get you is a static change in C.G. I could live with that, even if I was flying it. Almost everone else did ... but, to be fair, not all.

The point is and was not to say the P-51H was a bad plane, it wasn't and I never said it was. I said it was useless to WWII since it didn't get into combat.

The intent was to get a better-performing P-51 into the war before it ended. Changing the engine DOES, without doubt, at least in my mind. If I were running the war, and I wasn't, I'd rather have had a P-51D with a -9 engine before the war ended in combat than a P-51H that flew around at 250 mph impressing someone's girlfriend and doing airshows after the war was over.


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## FLYBOYJ (Jan 29, 2015)

Greg, good information, but again we're looking at straight up linear speed and altitudes. Acceleration and maneuverability needed to be factored in as well and there were other refinements to the P-51H that "would have" more than justified it's production had the war continued.

_"Almost all the parts from the D line were not usable in the P-51H. This was the first production P-51 with a complete overhaul. The wing did not have that famous leading edge kink in it. The landing gear was visibly smaller. The profile shows new lines with a taller tail (later versions). The fuselage was a bit more slender and the length was increased to 33.33 feet. The wingspan stayed the same. The belly scoop inlet profile was not angled any longer but was now square again like the first P-51s. The chin scoop for the engine was decreased in size. 

The wheels now had disk brakes. The oil cooler was moved from inside the belly scoop to in front of the oil tank ahead of the firewall. This eliminated the oil lines that ran from the engine to the old location in the scoop. The oil was now cooled by a heat exhanger mounted next to the engine intercooler. 

The engine mounts were incorporated into the structural engine cradle, thus saving weight. The engine would not be the newer RS.14.SM Merlin as in some of the lightweight prototypes. The Rolls Royce Merlin V-1650-9 was chosen. Take-off horsepower was actually down from the -7 series to 1,380. But, the new -9 Merlin used water/alcohol injection and was able to up the war emergency power to 2,200 at 10,200 feet. This was the fastest production P-51 clocking 487 mph at 25,000 feet. 

The propeller of the P-51H was the Aeroproducts 11'1" 4-blade Unimatic otherwise know as the "H prop". This prop is even lighter than the K model Aeroproducts but it looks much different. The blades are wider and keep approx. the same width almost the whole blade. The tips are rounded. 

Armament was the same as in the P-51D. Removable ammo boxes and a redesign of the ammo doors were added. This saved time reloading and must have eased up on the laminar flow killing scratches and scuffs on the wings. The earlier models had to be loaded by hand out of portable ammo boxes. The top surfaces of the wings were taking a huge beating and disrupting the true laminar flow of the wing surface. I honestly doubt the crews in the field either knew or cared much about that. 

Fuel in the fuselage tank was decreased to 55 gallons max. The fuselage skins were lighter and thinner, made from a new alloy. The cockpit panel was improved and simplified. The canopy was redesigned and the "hump" moved further forward. The pilot sat higher for a better angle using the gunsight." _

P-51 Mustang Variants - P-51H - MustangsMustangs.com

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## GregP (Jan 29, 2015)

I believe the H was a good decision had the war continued, and don't believe I ever said otherwise. What I said was it didn't make it into combat in the war.

The "new" D model I suggested would have been a stop-gap unit, improving the breed until the H got into the war, which it never did, but at least the new D would have made the war.

It's all in whether or not the end of the war was predictable. It really wasn't because even the nuclear scientists weren't really sure if the bomb was going to work when it was dropped for real. If it hadn't worked, the war would have drug on for another 8 months to a year or more and the H would have been in the fray. Had that happened you would have seen hordes of the US Navy version of the V-1, the JB-2 Loon, raining down on Japan. As it is, they (and WE) got away with many fewer casulaties the way the war really ended than would have otherwise been possible.


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## pbehn (Jan 29, 2015)

FLYBOYJ said:


> P-51 Mustang Variants - P-51H - MustangsMustangs.com



Flyboy from your quoted article it says this, which surprised me (apart from the spelling of "Brittish")
quote
Brittish fighters were lighter than U.S. fighters. Schmued ask for detailed weight statements from Supermarine on the Spitfire. Schmued wanted to know why the Spitfires were so much lighter than the P-51. Supermairne did not have such data on the Spitfire, so they started weighing all the parts they could get a hold of and made a report for Schmued. The Brittish had design standards that were not at strict in some areas of design as the U.S. Landing gear, angle of attack and side engine design loads were higher in the U.S. 
unquote

I am no expert but I cannot believe that it took until the design of the "H" to notice that British fighters were lighter, the P51 was always heavier than a Spitfire with the same engine. I think the above quote was really the US going to a lower design standard that had worked in practice to allow a weight reduction not allowed under USA design regs. I personally find the statement "all the parts they could get hold of" amusing, since the US operated Spitfires and the lease lend agreement meant sharing all British technology there is no part of a Spitfire that wasnt available to any US scientist/engineer who the US wanted to have it, I think the weighing and evaluating of components was to see just how much (or little) they could get away with. This is a soft ball soft Flyboy, upon your reply depends the status of the P51H, did North American really have to weigh parts of a Spitfire to get the design right? I think they did an engineering/design revue to see where weight could safely be saved using other almost comparable designs as a precedent/base for study.


edit...from the original post I cannot really tell who did the weighing, Supermarine or US engineers working for Schmeud?


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## GregP (Jan 29, 2015)

The US standards are and were not lower or higher than British standards. They worked to different set of requirements. The Spitfire was many things, but one of them was fragile. So was and is the Hurricane, as fabric-covered planes must necessarily be. It also makes them very repairable in the case of minor damage that has a lot a fabric tears. US fighters are not and were not fragile.

Doesn't mean one way or the other is wrong, it just means we spcified different things be strressed to different design criteria. The British specs worked for the ETO and resulted in a great aircraft. We got the same in other aircraft on our own. Together they carried the airwar in the ETO.

US aircraft ALWAYS have a detailed weight breakdown and I'm sure the North American guys were quite surprised that British didn't have one done for the Spitfire already. If you donlt HAVE one, how do you know where to start looking for weight savings? It's a case of different thinking, not superior or inferior design.


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## wuzak (Jan 29, 2015)

The Spitfire was fragile?


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## GregP (Jan 29, 2015)

Quite fragile relative to a US fighter. You might expect that given how much lighter it is. If you didn't expect that mauybe you didn't think about it in terms of more weight means more metal.

I say that having had one for more than 6 years at the museum. The difference in care that must be taken during servicing it versus a P-51 is an eye opener. Land a Spitfire on a carrier a few times and it starts coming apart if you aren't careful at touchdown. It jsut wasn't designed for hard landings. British squadron commanders were famous for requiring their pilots to 3-point the Spitfire, even after battle. It may technically be the correct way to do it but it almost always results in a touchdown at the lowest possible airspeed, too. Best way to get a soft landing.

There's nothing wrong with it being a bit fragile, but you DO have to think about it if you are used to servicing a P-40 or P-51 and find yourself servicing a Spitfire. Mind you it's unkilely since US planes don't have Whitworth fasteners and you'd need a new set of tools ... but it is noticeable.


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## tomo pauk (Jan 29, 2015)

R. W. Gruenhagen states on the pg. 117, about E. Shmued's visit to the UK in 1943:
_After visiting the Spitfire construction plants, it was obvious to Schmued that an airframe weight reduction was necessary in the Mustang. A staff was assembled to assist him in acquiring data on the construction of the Spitfire. The British system of engineering did not provide the answers needed by Schmued and the team had to weight and measure the airframe components to satisfy their needs. This was a tedious task but the information was finally assembled for transfer to the Inglewood._

However, same author says that already by Jan 2nd 1943 NAA planed to construct two experimental light weight fighters using British load factors as a guide to construction. After Schmued's visit to the UK and consolidation of the data, the number was increased to 5 aircraft.
NAA techicians also examined Bf 109, per same author. 

Hopefully an owner of the book 'Mustang designer' could provide additional info, especiailly since Gruenhagen's book, for all it's qualities, is woefully short of footnotes and sourcing.


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## rochie (Jan 30, 2015)

Jeez Greg where do you get this crap from, never heard a Spitfire or Hurricane described as fragile before ?

Hurricanes were fabric covered because they were progression of Hawker's earlier designs but we're turned into carrier aircraft and fired off CAM ships with rockets.
Spitfires were comparable with the best prop driven fighters from its birth to its retirement which was a lot longer than most.
And all the time it was hardly recorded they were any weaker or more fragile than anything else around !


Beginning in late 1943, high-speed diving trials were undertaken at Farnborough to investigate the handling characteristics of aircraft travelling at speeds near the sound barrier (i.e., the onset of compressibility effects). Because it had the highest limiting Mach number of any aircraft at that time, a Spitfire XI was chosen to take part in these trials. Due to the high altitudes necessary for these dives, a fully feathering Rotol propeller was fitted to prevent overspeeding. It was during these trials that EN409, flown by Squadron Leader J. R. Tobin, reached 606 mph (975 km/h, Mach 0.891) in a 45° dive. In April 1944, the same aircraft suffered engine failure in another dive while being flown by Squadron Leader Anthony F. Martindale, RAFVR, when the propeller and reduction gear broke off. The dive put the aircraft to Mach 0.92, the fastest ever recorded in a piston-engined aircraft, but when the propeller came off the Spitfire, now tail-heavy, zoom-climbed back to altitude. Martindale blacked out under the 11g loading, but when he resumed consciousness he found the aircraft at about 40,000 feet with its (originally straight) wings now slightly swept back.[113] Martindale successfully glided the Spitfire 20 mi (32 km) back to the airfield and landed safely.[114] Martindale was awarded the Air Force Cross for his exploits.

Not bad for a fragile one trick pony !

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## GregP (Jan 30, 2015)

I don't get this crap from anywhere, I observe it. Go do the same and come back. A Spitfire in a hangar is not going to appear fragile. But go maintain it for awhile and the difference is quite clear.

If you don't know, don't call crap on it, guy, 12 thousand posts or not.

Maybe ask Joe? He might know, being in the industry. 

And fragile doesn't mean it can't be repaired or isn't serviceable at all, it means it's easy to damage and doesn't tolerate rough handling. It didn't and doesn't.


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## pbehn (Jan 30, 2015)

GregP said:


> The US standards are and were not lower or higher than British standards. They worked to different set of requirements. The Spitfire was many things, but one of them was fragile. So was and is the Hurricane, as fabric-covered planes must necessarily be. It also makes them very repairable in the case of minor damage that has a lot a fabric tears. US fighters are not and were not fragile.
> 
> Doesn't mean one way or the other is wrong, it just means we spcified different things be strressed to different design criteria. The British specs worked for the ETO and resulted in a great aircraft. We got the same in other aircraft on our own. Together they carried the airwar in the ETO.
> 
> US aircraft ALWAYS have a detailed weight breakdown and I'm sure the North American guys were quite surprised that British didn't have one done for the Spitfire already. If you donlt HAVE one, how do you know where to start looking for weight savings? It's a case of different thinking, not superior or inferior design.


From the same article
Quote
The Brittish had design standards that were not at strict in some areas of design as the U.S. Landing gear, angle of attack and side engine design loads were higher in the U.S. 
Unquote

The Hurricane and Spitfire started life designed around a 850HP engine a twin blade prop and carrying 4 x .303 mgs. During WWII the Spitfire approximately doubled its weight. Supermarine/Vickers must have known the weight of the aircraft and before any change must have considered the weight. In a detailed study you may weigh each nut, bolt and component or the weight of each assembly. If the British weighed each assembly then that data would not be of use to North American if they wanted to compare differences down to each nut and bolt.


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## rochie (Jan 30, 2015)

GregP said:


> I don't get this crap from anywhere, I observe it. Go do the same and come back. A Spitfire in a hangar is not going to appear fragile. But go maintain it for awhile and the difference is quite clear.
> 
> If you don't know, don't call crap on it, guy, 12 thousand posts or not.
> 
> ...



well that told me !

on the contrary i think spitfires look very fragile in a hanger.

i am glad we only used them on sunny days in august from long perfectly smooth concrete runways and didnt try to make a carrier fighter out of it or operate in the desert or rough european and paciific airfields, telling the pilots not to try and turn too fast in case the wings came off.

luckily we didnt try and re arm / re fuel in a hurry in case we scratched the paint as it seems that was all that was holding it together.

just as well we never actually fought in them as any thing more than a BB pellet would of had them falling from the sky in droves !

my point being i dont recall history labelling the Spitfire fragile, it might not have had the legendary toughness of a P-47 but hardly fragile either !

as i said before.

not bad for a fragile one trick pony !

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## drgondog (Jan 30, 2015)

GregP said:


> Hi,
> 
> I decided to visit this thread one more time and throw in some aerodynamics for those who like it.
> 
> ...



It did all that while the ETO battle was still being fought, Greg. Your hindsight is often 20/20 but even you have to feel a little silly pontificating on a decision You would have made in January/February 1944 when the NAA team was putting a wrap on discussions with the Brits and conceptualizing the H for presentations to AAF? Just a little bit?


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## drgondog (Jan 30, 2015)

GregP said:


> The US standards are and were not lower or higher than British standards. They worked to different set of requirements. The Spitfire was many things, but one of them was fragile. So was and is the Hurricane, as fabric-covered planes must necessarily be. It also makes them very repairable in the case of minor damage that has a lot a fabric tears. US fighters are not and were not fragile.
> 
> *Please do some research. The US Standard for Ultimate load was 12 for the symmetrical aero (read dive pull out) loading, the Brit standard was 11. The NAA team also designed for a lateral 2G load due to the engine. The XP-51F and subsequently the P-51H was designed to 11G ultimate/7.26G Limit. The P-51H was stressed for 11/7.26G at 9400 pounds GW. The XP-51 was designed for 12G/8G for 8000 pounds. By the time the B/D was in service at 9700 and 10,300 combat GW without external load, the rating was 6.59 and 6.21 Limit load respectively for those GW's. *
> 
> ...



Do you perhaps have any data comparing the robustness of the Mustang to the 'Fragility' of the Spitfire?


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## Balljoint (Jan 30, 2015)

Fragile is a tricky term, particularly with regard to Gs. A lightweight plane imposes lower forces on its structure at a given G loading. However, it may not do as well with someone walking on the wing or a stone strike. My opinion is that the Spit was plenty strong but perhaps not as robust as the P-51.


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## drgondog (Jan 30, 2015)

Balljoint said:


> Fragile is a tricky term, particularly with regard to Gs. A lightweight plane imposes lower forces on its structure at a given G loading. However, it may not do as well with someone walking on the wing or a stone strike. My opinion is that the Spit was plenty strong but perhaps not as robust as the P-51.



Balljoint - the way Limit Load analysis works for Aero loads (i.e - pulling out of a dive in which the lift load far exceeds W), for say N=8G and the airplanes is stressed for all areas pertinent to surviving the loads (.i.e the Spar and fuselage carry through structure first, then secondary items like the shear panels surrounding the spar which distribute the loads - or the engine mounts supporting the engine and beam the G load into the longerons) at the Design Gross Weight.

The P-51 started with a design Gross weight of 8000 pounds. The N=+8G says to the airframe stress engineer that the lift load to be absorbed is 8x8000 pounds distributed over the 'beam' (i.e Spar) with the distribution curve supplied by the Aerodynamics team.

When that airplane adds fuel, guns, more ammo it rarely goes back for re-design and re-engineering to accommodate the 'weight creep"- so that wing (in the case of XP-51-P51A/A-36 to P-51B to P-51D 'grew' in Gross Weight from 8,000 pounds to 10,300 pounds for the D for full fuel and ammo.

As a result, the aerodynamic loads at 8G translates to 82,400 pounds distributed along the span at the spar instead of the original design target of 64,000 pounds. If the D actually pulls 8G Now, then many stresses designed at Yield point move from the elastic range to the Plastic region and parts 'stretch' causing a dangerous movement toward failure of the subjected part of interest.

If the P-51D at 10,300 pounds GW it hits the design stress load of 64,000 pounds at 6.21G. (64000/10700), it hits the Limit Load. 50% more than that causes the structure to approach Ultimate where it normally 'Breaks'.

Back to the Spitfire. The original Mark I had a design Gross weight of about 5280 pounds. The Mark IX was about 6622 pounds. We do not know (at least I do not know whether any re-design and manufacture the wings and carry through structure to accommodate the increase in GW. If so then perhaps the Spit maintained the 11G ultimate Load limit for stress analysis as the weight increased from 5280 to 6622 pounds. If it remained unchanged then the original Ultimate load of N=11G translates to 58080 pounds of beam load on the wing but when it grew in weight, only 8.7G would load up the Mark IX wing to Ultimate failure range or about 5.8 Limit versus the P-51D Load of 6.21 for Limit G load.


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## drgondog (Jan 30, 2015)

So, Greg - illustrate your grasp of Physics and Aero (I presume you are one of the 'everyone who knows aero' per your comments above as well as physics) and start where you should start.

Two equations are necessary when iterating climb, acceleration and top level speed when the a.) Thrust HP is known, b.) the propeller efficiency is known for ALL Ranges of Thrust HP, c.) Drag (Base parasite plus parasite drag of miscellaneous items (including friction) plus increments of angle of attack parasite drag) multiplied by the CDm/CDp ratio related by increase in R.N. along the velocity plot, c.) Induced Drag

Force = Mass*Acceleration
Thrust = Drag

Why, you ask? 

Well the P-51H is about 8.5% cleaner in parasite drag and the W/L for level flight is 40.5 for Combat load versus 43 for the P-51D at 10,300 pounds (Report uses 9700 for W/L=41.6)) meaning the Induced Drag for the P-51H is also lower than the P-51D.What this should suggest to you is that the P-51H Performance Chart and Report from NAA has accounted for all the above and extrapolated the Performance envelope for the correct Gross Weight but the P-51D values must be re-calculated based on a lower Gross Weight from a true load out equality AND a different THP rating all along the profile.

You didn't do this.

You then pick a velocity slightly different and iterate based on T=D and F=Ma as you move from excess Thrust to insufficient thrust for the top speed calculations until T=D. 

It (The resulting top speed comparison with same engine and boost envelopes) is less of an effect on change to top velocity for the slightly different airframes as it is to acceleration and climb performance calc where the 6% in Gross Weight increase to move the P-51D from the NA 'model' state to an new analysis will yield significant advantage for the P-51H.


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## rochie (Jan 30, 2015)

i will add that if we are talking fragilility during servicing and turn around or maintenance then would i be correct in thinking a P-51's Laminar flow wing is more fragile than the conventional wing on a Spitfire ?


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## drgondog (Jan 30, 2015)

No, Rochie. The Mustang wing was very strong - so was the Spitfire wing.

I imagine that you are referring to the fact that the NACA/NAA 45-100 never truly achieved 'laminar flow' and that minor imperfections on the surface of the wing degraded some aerodynamic benefits.

Having said this the surface treatment at the NAA factory was to fill the flush rivet imperfections forward of the 30% chord line, prime, sand and paint to achieve a smoother surface than the Spit.


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## wuzak (Jan 30, 2015)

drgondog said:


> Having said this the surface treatment at the NAA factory was to fill the flush rivet imperfections forward of the 30% chord line, prime, sand and paint to achieve a smoother surface than the Spit.



I think this is the point that Rochie is making - that the filling and paint are relatively easily damaged and have more of an effect on performance for the Mustng thsn they do for the Spitfire.

The arrangements for reloading ammunition were changed on the H compared to the D.



FLYBOYJ said:


> Armament was the same as in the P-51D. Removable ammo boxes and a redesign of the ammo doors were added. This saved time reloading and must have eased up on the laminar flow killing scratches and scuffs on the wings. The earlier models had to be loaded by hand out of portable ammo boxes. The top surfaces of the wings were taking a huge beating and disrupting the true laminar flow of the wing surface. I honestly doubt the crews in the field either knew or cared much about that.



In that way, the H could be described as less fragile than the D.


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## rochie (Jan 30, 2015)

Thanks Bill, wuzak is right, it was laminar flow properties of the P-51's wing I was asking about, wondering if it was as difficult to maintain as is sometimes wrote about ?

Never doubted the physical strength of the actual wing structure


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## pbehn (Jan 30, 2015)

All prop planes are fragile, If you take a P51 at max speed and fly downwards the wings and prop fall off very quickly. The design of all these aircraft was a compromise, strength costs weight.

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## drgondog (Jan 31, 2015)

"To Be Laminar Flow or Not to Be Laminar flow". The NAA 45-100 never achieved hoped for results for "Laminar" flow to the max T/C point at ~ 38%, and shuffling about on the leading edge of the wing sure affected surface roughness, along with hail, operating on a dusty runway, etc.

Having said that, the wing still achieved a remarkable reduction in drag due to the shape and the benefits continued for delay of Mach wave formation as well continued performance of the wing in comparison with the classic types such as NACA 230xx with mac T/C of ~25%. 

Any scuffling aft of the spar - as in the ammo box section was in an area where the region was immersed in an adverse pressure gradient or large build up of the boundary layer. IWhile I agree most of Joe's points, I see the ammo storage and resupply and stiffer door to serve faster operational turnaround with portable ammo containers, than preserving any laminar flow illusions in that section of the wing. IIRC the wing aft of about 30-35% was not treated with putty, primer and paint - just primer and paint as it was immersed in a boundary layer stage that negated any 'laminar flow' attributes.

Another point - the theoretical transition point from Laminar fluid flow to Turbulent fluid flow, based on the Mean Aerodynamic Chord is in the R.N. range of ~ 500,000 which is barely moving. The R.N. range of 9x10^^6 is about 150 mph at SL densities.

Then to add to the point I was making above, the P-51H was significantly 'stronger' with respect to target G limits at Combat Gross weight simply because the airframe never grew any heavier due to modifications while both the Mustang and Spitfire grew significantly as new engine and extra fuel, etc was added. 

I don't know that Supermarine engineers did Not beef up any part of the Spit to conform to original Stress vs G load but I do know that NAA did Not alter any structure to accommodate the original 8 G target for limit load as the airframe continued to grow. The XP-51 wing through the P-51B was exactly the same and the very first opportunity to re-design the spar/root chord/carry through structure came with the D - but it is clear from the Pilot Handbook that 8000 pounds remained the GW standard for Mark I, P-51, P-51A, A-36, P-51B/C, P-51D/K - all designed at 8G Limit and 12G Ultimate for 8,000 pounds GW.


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## rochie (Jan 31, 2015)

thanks for the explanation Bill

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## pbehn (Jan 31, 2015)

drgondog said:


> Then to add to the point I was making above, the P-51H was significantly 'stronger' with respect to target G limits at Combat Gross weight simply because the airframe never grew any heavier due to modifications while both the Mustang and Spitfire grew significantly as new engine and extra fuel, etc was added.
> 
> I don't know that Supermarine engineers did Not beef up any part of the Spit to conform to original Stress vs G load but I do know that NAA did Not alter any structure to accommodate the original 8 G target for limit load as the airframe continued to grow. The XP-51 wing through the P-51B was exactly the same and the very first opportunity to re-design the spar/root chord/carry through structure came with the D - but it is clear from the Pilot Handbook that 8000 pounds remained the GW standard for Mark I, P-51, P-51A, A-36, P-51B/C, P-51D/K - all designed at 8G Limit and 12G Ultimate for 8,000 pounds GW.



From what I have just read on the net modifications to the Spitfire wing were more for torsional strength and performance in dives the later marques of the Spitfire and the Spiteful looking increasingly like a Mustang in the wing department. 

from wiki

Redesigned late wing[edit]
As the Spitfire gained more power and was able to fly at greater speeds the possibility was that pilots would encounter aileron reversal so the Supermarine design team set about redesigning the wings to counter this possibility. The original wing design had a theoretical aileron reversal speed of 580 mph (930 km/h),[8] which was somewhat lower than that of some contemporary fighters. The new wing of the Spitfire F Mk 21 and its successors was designed to help alleviate this problem; the wing's stiffness was increased by 47%, and a new design of aileron using piano hinges and geared trim tabs meant that the theoretical aileron reversal speed was increased to 825 mph (1,328 km/h).[8][9][10]


and for the Spiteful

Design and development[edit]
By 1942, Supermarine designers had realised that the aerodynamics of the Spitfire's wing at high Mach numbers might become a limiting factor in increasing the aircraft's high-speed performance. The main problem was the aeroelasticity of the Spitfire's wing; at high speeds the relatively light structure behind the strong leading edge torsion box would flex, changing the airflow and limiting the maximum safe diving speed to 480 mph (772 km/h) IAS[nb 1]. If the Spitfire were to be able to fly higher and faster, a radically new wing would be needed.[1]

Joseph Smith and the design team were aware of a paper on compressibility, published by A D Young of the R.A.E, in which he described a new type of wing section; the maximum thickness and camber would be much nearer to the mid-chord than conventional airfoils and the nose section of this airfoil would be close to an ellipse[nb 2]. In November 1942 Supermarine issued Specification No 470 which (in part) stated:

A new wing has been designed for the Spitfire with the following objects: 1) To raise as much as possible the critical speed at which drag increases, due to compressibility, become serious. 2) To obtain a rate of roll faster than any existing fighter. 3) To reduce wing profile drag and thereby improve performance.


The wing area has been reduced to 210 sq ft (20 m2) and a thickness chord ratio of 13% has been used over the inner wing where the equipment is stored. Outboard the wing tapers to 8% thickness/chord at the tip.[1]

Specification 470 described how the wing had been designed with a simple straight-tapered planform to simplify production and to achieve a smooth and accurate contour. The wing skins were to be relatively thick, aiding torsional rigidity which was needed for good aileron control at high speeds. Although the prototype was to have a dihedral of 3° it was intended that this would be increased in subsequent aircraft.[1] Another change, to improve the ground-handling, was replacing the Spitfire's narrow-track, outward-retracting undercarriage with a wider-track, inward-retracting system. (This eliminated a weakness in the original Spitfire design, giving the new plane similar, safer landing characteristics, comparable to the Hurricane, Typhoon, Tempest, Mustang, and Focke-Wulfe 190.) The Air Ministry were impressed by the proposal and, in February 1943, issued Specification F.1/43 for a single seat fighter with a laminar flow wing; there was also to be provision made for a wing folding scheme to meet possible Fleet Air Arm requirements. The new fighter was to use a fuselage based on a Spitfire VIII.[2]


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## drgondog (Jan 31, 2015)

That summary strongly suggests changes to the wing such as increased skin thickness to create stiffer torque box (which would also de facto increase beam cap thickness for the spars) resulted in raising the Spit back to a 7.2/11.0 Load capability at the 1942 GW.


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## rochie (Jan 31, 2015)

great bit of info pbehn, thanks


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## wuzak (Jan 31, 2015)

drgondog said:


> I don't know that Supermarine engineers did Not beef up any part of the Spit to conform to original Stress vs G load but I do know that NAA did Not alter any structure to accommodate the original 8 G target for limit load as the airframe continued to grow. The XP-51 wing through the P-51B was exactly the same and the very first opportunity to re-design the spar/root chord/carry through structure came with the D - but it is clear from the Pilot Handbook that 8000 pounds remained the GW standard for Mark I, P-51, P-51A, A-36, P-51B/C, P-51D/K - all designed at 8G Limit and 12G Ultimate for 8,000 pounds GW.



I'm not entirely certain, but I think the "universal wing", which was used on Mk V and subsequently the Mk IX, was strengthened from the wing that Mks I and II had. 

The VIII also got an upgraded wing, which had small leading edge tanks in board of the cannon bays. These wings were used on the XIV too.

Griffon variants were strengthened with new longerons, among other things, to take the higher loads from the heavier engine.


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## pbehn (Jan 31, 2015)

drgondog said:


> That summary strongly suggests changes to the wing such as increased skin thickness to create stiffer torque box (which would also de facto increase beam cap thickness for the spars) resulted in raising the Spit back to a 7.2/11.0 Load capability at the 1942 GW.


I see your "beam cap thickness" with cold working, and raise you with the "Bauschinger effect".

I know very little about aerodynamics above that of an interested layman. Once in Italy we had a problem with Yield, every high result was blamed on "cold working" every low result was blamed on the "Bauschinger effect", the true cause was the external water quench which wasnt admitted until it was replaced. Basically what I am saying is I haven't a clue what beam cap thickness is.

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## drgondog (Feb 1, 2015)

pbehn said:


> I see your "beam cap thickness" with cold working, and raise you with the "Bauschinger effect".
> 
> I know very little about aerodynamics above that of an interested layman. Once in Italy we had a problem with Yield, every high result was blamed on "cold working" every low result was blamed on the "Bauschinger effect", the true cause was the external water quench which wasnt admitted until it was replaced. Basically what I am saying is I haven't a clue what beam cap thickness is.



If we use an "I" Beam as the cross section of a spar the upper and lower flange are part of the individual 'caps' and the vertical web is the material that takes out the shear due to the bending loads placed on the spar when one cap absorbs compressive load and the other a tensile load.

When sheet metal is effectively 'affixed' to a spar as described above, a specified portion of the cross section can be considered as 'additive' to the cross sectional area of the original I beam caps... thus the Stress = P/A is reduced by the effective increase in Area. Having said this, the skin attached to the spar must also carry shear loads imposed by the bending and subsequent deformation of the spar at the cap, even as the web between the caps carries the shear between the compression and tensile portions of the cap.

During the analysis phase, the cap region must first be analyzed for compressive and tensile loads/divided by the area for allowable stress, the web must be analyzed for buckling while carrying the shear transfer, then the skin/rivet design must be analyzed to determine whether the stress is a.) too high on the rivet cross section within the skin, then b.) look for rivet hole deformation/failure due to the rivet/fastner and c.) look to the spar cap for the interaction of the rivet attaching skin to spar cap as above.

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## drgondog (Feb 1, 2015)

I hope that makes sense


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## swampyankee (Aug 15, 2017)

Jank said:


> In the air to air role, the Bearcat is the superior performer.
> 
> An armament of four .50's though is pretty marginal though.


Which is why they upgraded to 20 mm pretty quickly 

The Corsair was, however, a more versatile aircraft, probably the closest thing to a WW2-eral equivalent of the fighter/attack F-18.


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## swampyankee (Aug 15, 2017)

Salim said:


> Don't forget that the Allies (except the Russians) not only had superior numbers, but had better quality pilots to boot. Yes I know that there were still many German aces who flew the ME-262 jet fighter and the T-152, but a few good men really can't turn the outcome of a doomed war anyway. Most of the German and Japanese pilots were mostly hastily trained young men who could barely fly the plane they were in, let alone fight, and had practically no combat experiance to boot.



I think that by 1944, certainly 1945, the Soviet pilots were quite good, if for no other reason than the bad ones had all been shot down.

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## pbehn (Aug 15, 2017)

drgondog said:


> I hope that makes sense


It does Drgondog, I don't know how I missed it years ago, apologies.


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## drgondog (Aug 21, 2017)

Ericson said:


> Some years ago I read an account of the only Bearcat vs Mustang encounter known to me. Shortly after hostilities ceased on VJ day, a carrier with a squadron of F8Fs was in the Gulf of Mexico and called on the port of New Orleans as a PR exercise. Nearby, on shore, was based a squadron of P51s. The guy relating the story was one of the Bearcat pilots. He said that several times both units would go up and "happen to" meet for simulated dogfights. He pointed out that no F8F was ever bested in these encounters. Who can say what the relative quality of the pilots was, flight time, etc., but it is the only example of such an encounter I'm aware of. Another account by a pilot who flew both planes said the 'Cat was clearly the stronger performer - that its throttle response was instantly felt seat-of-the-pants, while the Mustang first made more noise, then began to accelerate. The Bearcat would have been an excellent anti-kamikaze device, though that was not its initial designed purpose. The Mustang proved superb as a long range bomber escort and many B-17 aircrew survived the war because the P51 could go all the way there and back on the long missions. Hats off to William Overstreet, who passed in 2014. He flew 100 P51 missions, survived being shot down 3 times, flew a FW190 back to England for one of his escapes, and chased a 109 under the Eiffel Tower, shooting it down over Paris. Many eyewitnesses corroborated this event.


The Bearcat in flight comparisons with a P-51D should always win at low to medium altitude. Different missions. The XP-51F/G and P-51H on the other hand, carrying as much fuel as the F-8F in every category except turn and maybe roll. The XP-51G with full internal combat load of 205 gallons had a 7500 fpm climb rate and 497mph dash speed at WEP at 22,000 feet. The XP-51F/G didn't go into production because without a fuselage tank, it didn't have the desired Combat radius of the P-51B/C - but it would have much better range, climb, dive, acceleration, ceiling, speed in all power settings - than the F-8F.


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## Peter Gunn (Aug 21, 2017)

Would the P-51G have been based on the razorback P-51B/C or would it have been the new bubble top model?

EDIT - Nevermind, sorry, a quick search on the intewebz answered that.


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## GregP (Aug 23, 2017)

Hi Bill,

Regarding post 201 above from about 2 years ago, it is difficult for me to believe that the V-1650-9 engine was materially larger or longer than a V-1650-7. Both were 2-stage Merlins. So, it should fit into a P-51D without major surgery. That is assumption #1.

I simply used a tried and true old formula and the new top speed for an aircraft with more power would be an easy estimate. I know that a P-51D has a top speed of 437 mph on 1490 HP at somewhere around 22,500 feet. Or close to that. For the purpose of illustration, assume it is correct.

I also know that k = P / V^3. Since we know P- and V, k = 1.785E-5. Actually, 1.78543E-5.

The new power is 2,200 HP. Leaving k as a constant, V becomes 486.5, assuming a 7% increase in frontal area due to a larger radiator (assumption #2 on my part). It is a good first-order estimation. It isn't a complete analysis, but I also didn't have complete data or the desire to go that deeply into a supposition, so a first-order approximation was OK with me. It will likely be off by a little, but the basic number should be pretty valid and should be at least close, according to several lectures and professors back in 1969 - 1970.

Nothing magic and not very thorough, either. But it gives me a place to start thinking about it. When I suggest an aircraft modification, I will likely never go to the effort to do an analysis just for alternate suggestions in a thread that wanders into what-if and, truth be know, I would have to dig up old college notes to DO the analysis, and probably would handle it wrong anyway just due to the fact that it has been since 1970 that I was in aero. That was the year I decided to leave aero and go into electrical engineering.

They had just finished the F-111 and General Dynamics (and almost everyone else, too) everyone laid off many, if not all, of their the aero engineers. That was widely reported, and was a watershed day for me at college. I SHOULD have chosen mechanical engineering, but went with electrical. It has been OK but, in hindsight, I probably should have either stayed in aero or gone mechanical engineering. Both were more along my lines of actual interest than electrical ever has been, though I have enjoyed coming up with several circuit inventions.


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## wuzak (Aug 23, 2017)

GregP said:


> Regarding post 201 above from about 2 years ago, it is difficult for me to believe that the V-1650-9 engine was materially larger or longer than a V-1650-7. Both were 2-stage Merlins. So, it should fit into a P-51D without major surgery. That is assumption #1.



Hi Greg,

The V-1650-9 should fit in the same place that a V-1650-7 or V-1650-3 could.



GregP said:


> I simply used a tried and true old formula and the new top speed for an aircraft with more power would be an easy estimate. I know that a P-51D has a top speed of 437 mph on 1490 HP at somewhere around 22,500 feet. Or close to that. For the purpose of illustration, assume it is correct.
> 
> I also know that k = P / V^3. Since we know P- and V, k = 1.785E-5. Actually, 1.78543E-5.
> 
> The new power is 2,200 HP. Leaving k as a constant, V becomes 486.5, assuming a 7% increase in frontal area due to a larger radiator (assumption #2 on my part). It is a good first-order estimation. It isn't a complete analysis, but I also didn't have complete data or the desire to go that deeply into a supposition, so a first-order approximation was OK with me. It will likely be off by a little, but the basic number should be pretty valid and should be at least close, according to several lectures and professors back in 1969 - 1970.



The -9 doesn't have 2200hp @ 22,500ft. Probably about 1800hp

http://www.wwiiaircraftperformance.org/mustang/p-51h-booklet-pg10.jpg


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## wuzak (Aug 23, 2017)

P 51D Performance Test

This has the D maximum speed of 442mph @ 26,000ft using 1410hp.

The -9 has ~ 1800hp at 26,000ft at WEP with ADI.

I get around 480mph.


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## Zipper730 (Aug 23, 2017)

FLYBOYJ said:


> _The engine mounts were incorporated into the structural engine cradle, thus saving weight. The engine would not be the newer RS.14.SM Merlin as in some of the lightweight prototypes. The Rolls Royce Merlin V-1650-9 was chosen._


What's the RS.14 SM Merlin?



pbehn said:


> The Brittish had design standards that were not at strict in some areas of design as the U.S. Landing gear, angle of attack and side engine design loads were higher in the U.S.


This might be a big question despite it's small size: What were the US landing-gear, angle of attack, and side-engine loads, and what were the British comparisons?



GregP said:


> I also know that k = P / V^3. Since we know P- and V, k = 1.785E-5. Actually, 1.78543E-5.


Questions

Does k = P/V^3 apply to true airspeed or indicated airspeed when calculating performance of aircraft at altitude?
1.78543E-5 = 1.78543 * 10^-5?
E = Exponent?


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## wuzak (Aug 23, 2017)

Zipper730 said:


> What's the RS.14 SM Merlin?



It's a family of 2 stage Merlin engines with medium and full supercharging.




Zipper730 said:


> This might be a big question despite it's small size: What were the US landing-gear, angle of attack, and side-engine loads, and what were the British comparisons?



42




Zipper730 said:


> Questions
> 
> Does k = P/V^3 apply to true airspeed or indicated airspeed when calculating performance of aircraft at altitude?
> 1.78543E-5 = 1.78543 * 10^-5?
> E = Exponent?



1. drgondog would answer this better, but I suspect it applies to both
2. yes
3. -5 is the exponent, 10 is the base. Don't think E has a name - it is just shorthand for calculators and computers.

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## Zipper730 (Aug 23, 2017)

wuzak said:


> It's a family of 2 stage Merlin engines with medium and full supercharging.


Three speeds (Low-speed, medium-speed, full-speed), two-speed.


> 42


That's the answer to the universe, but the question was never specified


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## wuzak (Aug 24, 2017)

Zipper730 said:


> Three speeds (Low-speed, medium-speed, full-speed), two-speed.



2 speeds - MS and FS gears (often denoted simply as S).

3 speeds would be SML.

The code does not identify the engine as a 2 stage or a single stage.




wuzak said:


> The development numbers signify the engine rating.
> 
> Rolls-Royce engine mark numbers can vary in details but still have the same rating. Things such as a different reduction ratio would mean a different mark number.
> 
> ...


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## wuzak (Aug 24, 2017)

Zipper730 said:


> That's the answer to the universe, but the question was never specified



I doubt there was a central standard for undercarriage for either the British or American aircraft designers.

Just looking at them you will see that the P-51 setup is quite different from the P-40's.


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## Zipper730 (Aug 24, 2017)

wuzak said:


> 2 speeds - MS and FS gears (often denoted simply as S).


Ok


> I doubt there was a central standard for undercarriage for either the British or American aircraft designers.
> 
> Just looking at them you will see that the P-51 setup is quite different from the P-40's.


OK


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## pbehn (Aug 24, 2017)

Zipper730 said:


> What's the RS.14 SM Merlin?
> 
> This might be a big question despite it's small size: What were the US landing-gear, angle of attack, and side-engine loads, and what were the British comparisons?
> 
> ...


Zipper, I have had enough of you lumping posts together for others to sort out into a sensible reply. Your "quote" of a post by me was not actually by me (as you know). It was itself a small part of a quoted text from an article linked by Flyboy *TWO AND A HALF YEARS AGO* . Do your own research, don't try tricking me into doing it for you. Here is my full post as a starter, note the "quote" and "unquote" statements

"Flyboy from your quoted article it says this, which surprised me (apart from the spelling of "Brittish")
*quote*
Brittish fighters were lighter than U.S. fighters. Schmued ask for detailed weight statements from Supermarine on the Spitfire. Schmued wanted to know why the Spitfires were so much lighter than the P-51. Supermairne did not have such data on the Spitfire, so they started weighing all the parts they could get a hold of and made a report for Schmued. The Brittish had design standards that were not at strict in some areas of design as the U.S. Landing gear, angle of attack and side engine design loads were higher in the U.S.
*unquote*

I am no expert but I cannot believe that it took until the design of the "H" to notice that British fighters were lighter, the P51 was always heavier than a Spitfire with the same engine. I think the above quote was really the US going to a lower design standard that had worked in practice to allow a weight reduction not allowed under USA design regs. I personally find the statement "all the parts they could get hold of" amusing, since the US operated Spitfires and the lease lend agreement meant sharing all British technology there is no part of a Spitfire that wasnt available to any US scientist/engineer who the US wanted to have it, I think the weighing and evaluating of components was to see just how much (or little) they could get away with. This is a soft ball soft Flyboy, upon your reply depends the status of the P51H, did North American really have to weigh parts of a Spitfire to get the design right? I think they did an engineering/design revue to see where weight could safely be saved using other almost comparable designs as a precedent/base for study.


edit...from the original post I cannot really tell who did the weighing, Supermarine or US engineers working for Schmeud? "


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## FLYBOYJ (Aug 24, 2017)

Zipper, we don't mind newbees asking questions, even us old farts are here to learn, but please stop with the long drawn out multi posts and asking multitude simplistic questions, it is getting tiring to read and its obvious you're pissing off some of the membership. Some advise....

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## GregP (Aug 24, 2017)

Hi Wuzak,

OK, I'll bite. So, you say the V-1650-9 had about 1,800 HP at about 22,500 feet. That's about 82% of the rated power. Let's say the V-1650, either a -3 or -7, is rated also at about 82% of rated power. That's 1,219 HP.

So, the P-51D goes 437 mph at 22,500 feet on 1,219 HP.

Enter the V-14650-9, with a WER rating of 2,200 HP, but 1,800 HP at 22,500 feet. Using the same formula, I still get 486 mph for the P-51D on 1,800 HP at 22,500 feet, when fitted with a -9 engine (still assumes a 7% increase in frontal area for cooling). In real life, it might be closer to 470 mph, but that's still a damned good P-51D airframe number. I am inclined to believe the P-51H was a great advance in the P-51 family, and only suggested the -9 engine for the P-51D airframe as an interim measure, until the P-51H airframe was available.

I am also not really up on when the engine dash numbers and airframes were available, but just thought that adding the big HP to the P-51D airframe has long been a factor at Reno every year. Why not in WWII?

Not suggesting the -9 version of the P-51D airframe replace the P-51H, I was just thinking in print, and wondering where the P-51D might go if fitted with a -9 engine. No other agenda here.


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## CORSNING (Aug 24, 2017)

Thank You Joe.

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## Shortround6 (Aug 24, 2017)

There was a V-1650-9A with external installation features the same as the V-1650-7 to suit installation in existing P-51D airframes.
How many were built I have no idea.


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## CORSNING (Aug 24, 2017)

I do not have all the documents that I would like to have on the
RR Merlin V-1650-9, but the USAAF Summery that I do have
from 1949 and 1950 give this engine the power ratings of
2,220 hp./3,000 rpm./9,000 ft.
1,790 hp./3,000 rpm./22,700 ft.

, Jeff

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## pbehn (Aug 24, 2017)

FLYBOYJ said:


> it is getting tiring to read and its obvious you're pissing off some of the membership.


I am completely exasperated more than pissed off. I have told Zipper to stop posting multiple questions, it means he saves his time but spends everyone elses trying to make a coherent reply. I have told him to stop quoting a single sentence out of a statement. It is literally taking things out of context, this means I (and others) must go back and rebuild the context. His question about a selected quote from a selected quote by myself from two and a half years ago took the biscuit. Having rooted through the previous posts and found where it was buried it is perfectly obvious to anyone I don't know what the answer is anyway. I find this increasingly impolite to the point of ignorance but more importantly I cannot see how Zipper or anyone else can learn from the discussion, I cannot even follow it at times, sliced, diced and cut to pieces with one word comments like "mmmmmph"

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## wuzak (Aug 24, 2017)

GregP said:


> OK, I'll bite. So, you say the V-1650-9 had about 1,800 HP at about 22,500 feet. That's about 82% of the rated power. Let's say the V-1650, either a -3 or -7, is rated also at about 82% of rated power. That's 1,219 HP.



No, I checked a flight test of a P-51D which had a maximum speed of 442mph @ 26,000ft using 1400hp.

At 26,000ft the V-1650-9 at WEP had aroun 1800hp.

Which I calculate would give the P-51D a speed of about 480mph at that altitude.

Jeff's numbers confirm the power of the -9.




GregP said:


> I am also not really up on when the engine dash numbers and airframes were available, but just thought that adding the big HP to the P-51D airframe has long been a factor at Reno every year. Why not in WWII?



I assume the -9 came along relatively late, otherwise it, or a similar engine, would have been put in the P-51D.




GregP said:


> I am inclined to believe the P-51H was a great advance in the P-51 family, and only suggested the -9 engine for the P-51D airframe as an interim measure, until the P-51H airframe was available.



The P-51H was lighter and had improved aerodynamics. If nothing else, the climb rates for the H should have been better with the same engine.




GregP said:


> Not suggesting the -9 version of the P-51D airframe replace the P-51H, I was just thinking in print, and wondering where the P-51D might go if fitted with a -9 engine. No other agenda here.



I think it is clear that a P-51D/V-1650-9 combination would go very well.


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## drgondog (Aug 25, 2017)

Hi Bill,

Regarding post 201 above from about 2 years ago, it is difficult for me to believe that the V-1650-9 engine was materially larger or longer than a V-1650-7. Both were 2-stage Merlins. So, it should fit into a P-51D without major surgery. That is assumption #1.

I simply used a tried and true old formula and the new top speed for an aircraft with more power would be an easy estimate. I know that a P-51D has a top speed of 437 mph on 1490 HP at somewhere around 22,500 feet. Or close to that. For the purpose of illustration, assume it is correct.

I also know that k = P / V^3. Since we know P- and V, k = 1.785E-5. Actually, 1.78543E-5.

*The equation is an excellent rule of thumb (at best), and only approximate for incompressible flow... it loses granularity as M ~ .5M. In that region the Parasite drag rise escalates non-linearly and significantly different between different aircraft as V ~ 0.6M and above. That is the first 'complication'. The second important contribution to total Drag in those regions, is Form Drag due to CL. More linear but also non-linear. The third issue is that Performance estimates may start with Thrust HPr = (W/375)*CD/CL)*V (where V=mph). It does Not start with T=D (in pounds-force). 

These calcs start with known altitude density ratio, know weight and desired velocity. Tables will be generated with each set of calculated data to recalculate as potential velocity desired reveals that more HP than the engine you use is capable of delivering

Sequentially CL is calculated, CD is derived by a.) deriving a CDp which includes the zero lift Low RN wind tunnel data at (RN1/RN2) to an empirical power, b.) calculating the CDm for compressibility (CDm=CDp/Sqrt(1-M^^2), c.) calculating the form drag as function of CL, d.) calculating CDi and e.) summing up for CDtotal. The process usually reveals that the velocity you desire is higher than the HP you have available and you drop the original V to a lower value and begin again until your V achievable approximates HP available.*

The new power is 2,200 HP. Leaving k as a constant, V becomes 486.5, assuming a 7% increase in frontal area due to a larger radiator (assumption #2 on my part). It is a good first-order estimation. It isn't a complete analysis, but I also didn't have complete data or the desire to go that deeply into a supposition, so a first-order approximation was OK with me. It will likely be off by a little, but the basic number should be pretty valid and should be at least close, according to several lectures and professors back in 1969 - 1970.

*The Hard part begins, because for a conventional prop system, the discussion launches into Power Available versus Power Required for each set of flight conditions (level, climb, high speed, climb speed) which require RN, pressure losses in the plenum, the carb intake, increased drag due to higher velocity over the airframe within the prop vortex..

Power Available includes prop thrust and exhaust thrust. Because drag due to momentum loss of the engine air and increased velocity within the area immersed by slipstream/vortex they are subtracted from the total thrust (prop/exhaust). Calculating Exhaust thrust without the tables requires a very strong Thermo background. It requires ability to accurately calculate Mass flow rates of exhaust gasses per cylinder, area of each stack, angle of inclination of exhaust stack from flight line, fuel to air ratio, mechanical efficiency, atmospheric properties, fuel combustion properties, and I forget the rest.*

*Curves and plots available to the aero include Ram as function of A/C Mach number, impeller mach number, adiabatic temp rise. Like the earlier V vs THPreqd, calculating Ram is also iterative.*

*Calculating slipstream velocities also depend on Prop Thrust and Freestream velocity.*

*Once the slipstream velocities are derived, you have to calculate what the incremental Power Required value has to be before arriving to point where you can close on the velocities attainable, in theory.*

Nothing magic and not very thorough, either. But it gives me a place to start thinking about it. When I suggest an aircraft modification, I will likely never go to the effort to do an analysis just for alternate suggestions in a thread that wanders into what-if and, truth be know, I would have to dig up old college notes to DO the analysis, and probably would handle it wrong anyway just due to the fact that it has been since 1970 that I was in aero. That was the year I decided to leave aero and go into electrical engineering."


Greg - I didn't post all this BS above to refute your assumptions and beginning point for thumbnail performance estimates. I was trying to point out that so much of what we learned in Aero 101 (and 201 and 301) started and ended with basic Cl, Cd and T=D. Professors like Hoerner smooth the way into doing basic Speed and Drag and Thrust equations which lead to the Power and Velocity relationships you posted to start this dialogue.

That said, you among a few of our community on this forum understand that "performance Calcs are complicated". I am eternally amused at guys like Soren, and even Ho Hun who was a level above Soren, were so glibly distributing bovine fecal matter when pontificating on turn and climb calculations. As I hope I showed, Total Drag for high angle of attack, airframes immersed in prop vortex, low speed (where Cooling drag soars and prop efficiencies wither) and asymmetric flight where stall conditions are very different from one wing to the next at the 'break points', and trim drag of ailerons and rudder become important - are 'kinda like rocket science'.

High speed level flight more straightforward if aware of all the major drag rise components and where they occur on the Mach meter - but still not calculable with high degree of confidence with simple, easy to understand equations.

To answer the fundamental question, the P-51H with and installed V-1650-3 or -7 would have out performed the B/D at same combat loading, same fuel, same MP, same RPM, same altitude, same airframe condition and stores. The only area I have reservations in is roll. The ailerons of the B/D were smaller but greater throw at max 15 degrees +/- compared to H with larger aileron area at +/- 10 degrees. Flight tests suggested parity in roll.

The V-1650-9 was the same as 1650-3 and -7. The improvements included a much better shaft/bearing lubrication for the -9 as well as carburation and WI to boost to 80" w/o WI and 90" w/WI. Net net, when the 9 finally got bugs worked out, the thrust HP was greater at WEP at all altitudes and the CDmin of the H was ~ 3% less at all altitudes. More thrust/less drag.

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## Zipper730 (Aug 25, 2017)

FLYBOYJ said:


> Zipper, we don't mind newbees asking questions, even us old farts are here to learn, but please stop with the long drawn out multi posts and asking multitude simplistic questions, it is getting tiring to read and its obvious you're pissing off some of the membership. Some advise....


I'll do a search if you'd like


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## GregP (Aug 25, 2017)

Nice reply, Bill.

My aero days are long ago, and I believe you entirely.

I still want a copy of your new Mustang book!


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## Peter Gunn (Aug 25, 2017)

^^^^ You ain't the only one!


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## CORSNING (Aug 25, 2017)

Damn Bill, will you hurry up and get the book written?


That's right, Jeff is waiting for his copy sir.


Uh, can I use some of the information over on warbirdsforum
in the AIRCRAFT PERFORMANCE section?.........Please?...
Pretty Please?

All my best man and God speed be with you.

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## BiffF15 (Aug 25, 2017)

Put me down for a copy as well! Autographed if that's an option.

Cheers,
Biff


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## drgondog (Aug 26, 2017)

Gentlemen - thank you. I will sign them. Corsning you may use what I posted.

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## Robert Porter (Aug 26, 2017)

Me too please! Would love a signed copy! Tell me where to ship Jan to as payment!


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## tomo pauk (Aug 26, 2017)

drgondog said:


> Gentlemen - thank you. I will sign them. Corsning you may use what I posted.



Bill - please post some details about the book.


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## CORSNING (Aug 26, 2017)

Thank you Bill. As always, you are the Man.


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## drgondog (Aug 27, 2017)

Jeff - a note about the Performance analysis approach above. It requires Wind Tunnel data to derive all the Parasite drag contributions of wing, empennage, cockpit enclosure, fuselage, carb intakes, etc. The Wind tunnel data is also required to plot Drag vs RN. and CD vs CL.


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## drgondog (Aug 27, 2017)

The new book will be "Long Range Escort - How the Bastard Stepchild Mustang saved the 8th AF" or words to that effect.

The core will be a development of the struggle from Casablanca agreed Combined Bomber Offensive, POINTBLANK objectives defined, and the narrative of 8th FC from May 1943 through May 1944 to contribute to neutralizing the LW ability to resist Overlord. Key to the narrative was the USAAF shock/dismay that the "bomber will achieve Strategic objectives" without effective escort fighters and the activities both in ETO, AAF HQ, Material Command and NAA/Republic/Lockheed design engineers to solve the problem of Range w/Performance.

I will carve out development milestones in the US, Service Command activities in the UK and MTO to apply various patches to the existing fighters in-theatre. These initiatives included the first conversion of Ferry tanks to combat tanks, RR/RAF drive to install the Merlin 61, NAA building the P51B, Lockheed trying to solve Intercooler/turbo issues and compressibility issues, and Republic trying to solve combat Range issues in the background - to fixing operational bugs experienced by P-47C and D, P-38G/H in mid 1943 through P-47D-11, P-38J-10 and Merlin P-51B introduction in late Fall 1943.

It is important IMO to set the table with Germany response to 8th/12th and 15th reaction to deep incursions - including Milch's ramp of day fighter production, gradual to steady shift of tactical fighter units from East and South to Germany, reorganization and tactics to concentrate more fighters on bombers, but still avoid attrition from AAF and RAF escorts.

I will trace Eaker's struggles to gain critical mass in ETO as North Africa/MTO continued to drain resources from the 8th AF build up, neutralizing Eaker's ability to get to the '600 inventory/300 daily mission' total the he stated was required to conduct a Strategic Campaign. This will involve examining Arnold-Eaker on primary stage with Spaatz, Doolittle, and Brits in the background, and Arnold-Giles back in the US jump starting combat tank development, increasing internal fuel in existing fighters and looking at the near fatal XP-75 decision.

There will be a section detailing comparative performance between the May-1943 LW primary single and twin engine fighters and US P-51A, P-38G and P-47C. For each, derived from flight tests at, or close to, operational flight conditions. It will chart out Top speed at existing power ratings of MP for P-38/47 and 51 and 1.32 ata for FW 190A6/7, Bf 109G-6, Me 110G-2, Me 410B. Airspeed comparisons will be at SL, 5,000 feet, 20,000 feet, 25,000 feet and 30,000 feet, as well as ROC at those same. Ditto for February, 1944 to illustrate Bf 109G6-AS and FW 190A8 introduction as the P-51B/C and P-38J emerged with increased MP, P-47D-11 gained WI and Paddle Blade prop. No charts using 44-1 (150octane) fuel as that didn't exist until after D-day.

There will be a section detailing timelines for the critical development features for the P-38/47 and P-51 in 1943 which set the stage for Big Week finally starting the Strategic CAMPAIGN leading to D-Day. For the Mustang, the key features include: Installation of Merlin 2S/2S engine, increasing internal fuel by nearly 50%, installing the Bubble canopy and six gun wing, installing increased O2/combat tank pressurization, sealed ailerons. Introduce Malcolm Hood as a driver for bubble canopy . P-51D not part of the narrative otherwise as the first deliveries in ETO to Fighter Groups was barely prior to the timeline of the story.

Pro's and Con's of each of AAF primary fighters as Long Range Escort fighter.

A section to present Combat units in ETO and MTO for 8th, 9th, 12th and 15th by equipment and combat record air to air from May, 1943 to the eve of D-Day.

A section to look at the Prelude, the USAAF failure to develop single engine Long Rang Escort prior to 1942-1943.



I have toyed with notion of inserting F4U-1 as a 'what if", but it only makes sense if I can get valid cruise data to develop Combat radius comparing to ETO AAF boundary conditions for Combat Radius. Opinion, it would have been at least as effective as the P-47C because it had 56 more gallons of internal fuel, but it has to be compared at 25,000 feet - not USN profiles of 15,000 feet.

There will

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## FLYBOYJ (Aug 27, 2017)

Zipper730 said:


> I'll do a search if you'd like


PLEASE do!

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## Shortround6 (Aug 27, 2017)

drgondog said:


> The new book will be "Long Range Escort - How the Bastard Stepchild Mustang saved the 8th AF" or words to that effect.
> 
> I have toyed with notion of inserting F4U-1 as a 'what if", but it only makes sense if I can get valid cruise data to develop Combat radius comparing to ETO AAF boundary conditions for Combat Radius. Opinion, it would have been at least as effective as the P-47C because it had 56 more gallons of internal fuel, but it has to be compared at 25,000 feet - not USN profiles of 15,000 feet.



It sounds like a most interesting book.

The big question on the F4U-1 is what the performance was like between 25,000 and 30,000ft as it's engine was loosing power as altitude increased. Engine was down to 1450hp at 25,000ft Military power and a bit over 1200hp at 30,000ft also military power.
I believe but could be wrong, that the Corsair had more drag than the P-47 and the engine charts do show an advantage for the P-47. Like 1625hp max continuous being available at 25,000ft (or below) at 2550rpm and 42in manifold pressure while the F4U-1 to get 1625hp max continuous at below 24,000ft needs the same 2550rpm but needs 49.5in manifold pressure from low gear of the auxiliary supercharger. The extra 7.5in ( 3 3/4lbs) pressure making the power needed to drive the aux supercharger?
Max lean ratings seem to show as much as a 10% advantage for the P-47 in HP made per gallon of fuel burned? 

While the internal 361 gallons of the F4U (wing tanks protected by CO2?) so a roughly 20% advantage over the early P-47 305 gallons if the F4U needs even 10-15% more fuel to fly the same speed/altitude than any advantage disappears pretty quick. Using a Navy plane for less than a 10% increase in range? perhaps only 0-5% increase?

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## swampyankee (Aug 27, 2017)

Shortround6 said:


> It sounds like a most interesting book.
> 
> The big question on the F4U-1 is what the performance was like between 25,000 and 30,000ft as it's engine was loosing power as altitude increased. Engine was down to 1450hp at 25,000ft Military power and a bit over 1200hp at 30,000ft also military power.
> I believe but could be wrong, that the Corsair had more drag than the P-47 and the engine charts do show an advantage for the P-47. Like 1625hp max continuous being available at 25,000ft (or below) at 2550rpm and 42in manifold pressure while the F4U-1 to get 1625hp max continuous at below 24,000ft needs the same 3550rpm but needs 49.5in manifold pressure from low gear of the auxiliary supercharger. The extra 7.5in ( 3 3/4lbs) pressure making the power needed to drive the aux supercharger?
> ...




Even if the P-47 had the same Cdcl=0​​ as the Corsair, the P-47 had a smaller wing. Up-close-and-personal, the P-47 is a surprisingly small aircraft.


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## GregP (Aug 28, 2017)

If you think a P-47 is surprisingly small, I'd ask if you never saw one up close to another WW2 single-engine fighter.

We have a P-51A, two P-51Ds, an F4U-1a, a Seversky AT-12, a Boring P-26, a P-40N, an A6M5 M<odel 52 Zero, an Aichi D4Y-3, a J2M-3, an Fw 190A, a Pilatus, P-2, an Me 163, A Bf 109, a Hispano Ha.1112, an He 280, a full size replica He 100D, an SBD, several AT-6s, a P-39 and, lately at least, a Spitfire Mk IX.

The P-47 is very easily the largest aircraft in that list. The P-47 is more than 2 feet longer than an F4U-4, has equal wingspans, and can take off about 8,000 lbs heavier. It isn't greatly larger than the Corsair, but is more massive and will easily be picked out as the larger aircraft when side by side.

A Corsair fuselage is mostly empty space from the firewall back and a P-47 is mostly completely filled with a turbo system.

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## Peter Gunn (Aug 28, 2017)

drgondog said:


> The new book will be "Long Range Escort - How the Bastard Stepchild Mustang saved the 8th AF" or words to that effect.
> 
> *SNIP*



I'm sure you have it covered but if you are in need of a good proofreader, I happily volunteer my services. Before my current stint, I spent eight years in PR both writing copy and proofing coworkers output.

As I said, I'm sure you have it taken care of but I'm always happy to help if needed and good luck. Either way, put me down for a signed copy as well.

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