Bearcat vs Corsair

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.

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.

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.

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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.

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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.

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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.

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.

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.

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.

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.

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.

and brings a load of stability issues with it. You keep wandering off and away from my assertion that the P-51H was a Better Airframe than the P-51D/B. With exactly the same engine the P-51H was more agile, faster, and more stable for all the reasons I stated above. The fact that bigger and better engines made each Bf 109 faster didn't make the airframe better and the German pilots will tell you the same thing - with each power upgrade, absent the airframe changes necessary to offset the weight, cg and torque changes, the airplane was less pleasant to fly - ditto the migration from P-51A through the Merlin upgrades. The P-51H had the same Basic Weight of the P-51A but structurally more sound than ALL the production P-51/A-36 models

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.

Nope - with exactly equal engines the P-51H was superior. Handling from take off to aerobatics to high speed dives, speed at all altitudes, climb and turn at all altitudes.

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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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.

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.

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.

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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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