# Ending the Argument



## DogMD11 (Oct 20, 2017)

Hello everyone! First time posting here, but long time lurker. Lots of great info on this forum; I have learned so much about a subject I _thought_ I knew pretty well!

In June 1990, the EAA's magazine Sport Aviation published an article called "Flight Test Comparison...Ending the Argument" by John Ellis and Christopher Wheal. The article was a modern-day performance comparison between a P-47D Thunderbolt, P-51D Mustang, FG-1D Corsair, and F6F-5 Hellcat. This was not an analysis of WWII-era data but rather an actual flight test of the four aircraft which compared their performance and flight characteristics. 

It's an interesting article and thought everyone here would enjoy reading/discussing it. I recently obtained a copy of it through EAA's archive and can provide scans of the article if requested. I did a search for this article on this forum but did not find anything; if it has been discussed before then I apologize and ask if someone could provide a link to the appropriate thread.

You can find an online copy of the article at www.coursehero.com but you have to sign up to be a member (don't know if it costs anything or not). I'd be happy to post scans of the article here, but I'm not sure how to do it and don't want to get into any trouble with copywriting or anything like that. Some help would be appreciated!


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## soulezoo (Oct 20, 2017)

How about a reader's digest conclusion in the mean time?


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## pbehn (Oct 20, 2017)

No argument is ended that easily. No aircraft is as they were in WW2, did they have guns ammunition armour and all the other gubbins.


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## vikingBerserker (Oct 20, 2017)

and the same fuel, same oil etc etc


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## pbehn (Oct 20, 2017)

vikingBerserker said:


> and the same fuel, same oil etc etc


Paint preparation, radiosssssszzzzzzzzzzzzzzzzzzz


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## soulezoo (Oct 20, 2017)

Of course, for all those reasons and many, many more, there will never be an "Ending Argument"

Look at all the fun we'd be missing here amongst ourselves were that so!

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## Elmas (Oct 20, 2017)

Ground control, Pilot's skill...

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## DogMD11 (Oct 20, 2017)

As far as a "readers digest" summary goes, it's a little hard to define. From the article: "...Unfortunately, the title we chose for the paper turned out to be rather ambitious as the test program actually raised more questions than it answered."

The performance section of the article was -in my opinion- tough to draw any meaningful conclusions. Because of the use of 100LL fuel, the radial engined fighters were required to reduce manifold pressure by 4 inches, while the Mustang was able to use full power settings. There was no explanation as to why this was (compression ratios?), and it was not stated as to whether the P-51's power was reduced accordingly to compensate. Despite this, the performance of the four aircraft was very similar and there were no real surprises in the categories tested: time to climb (10,000 feet), level acceleration (10,000 feet), turn performance, roll performance, and diving accelerations. 

The most interesting aspect of the article was an attempt to quantify handling by measuring maneuvering stability and performing "simulated mission tasks and agility testing". The later consisted of air-to-air and air-to-ground tracking, 180 degree course reversal, and target tracking. It was here that the Corsair and Thunderbolt shined, both with very nice handling near the stall limit and low control forces. The Hellcat had high stick and rudder forces throughout its envelope and the Mustangs' very high stick forces and zero stall warning/vicious departure made it difficult to fly near the limit. Lots of good stuff here about the handling of each aircraft. 

I suppose none of this is any real news to those of us who are knowledgeable about these aircraft. However, to have one person fly and try to objectively evaluate these aircraft was the most interesting part - very different from reading combat reports and memoirs with their subjective evaluations. 

Also, too bad they couldn't have tested a P-38.

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## GregP (Oct 20, 2017)

The leading world designers were striving to make the best fighter. It isn't the least bit surprising to me to see that they all got pretty close to one another with wildly different designs.

Al lot of time, when the power is similar, the performance is similar since everyone is trying to be light and fast with about equal power.


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## wuzak (Oct 20, 2017)

DogMD11 said:


> The performance section of the article was -in my opinion- tough to draw any meaningful conclusions. Because of the use of 100LL fuel, the radial engined fighters were required to reduce manifold pressure by 4 inches, while the Mustang was able to use full power settings. There was no explanation as to why this was (compression ratios?), and it was not stated as to whether the P-51's power was reduced accordingly to compensate. Despite this, the performance of the four aircraft was very similar and there were no real surprises in the categories tested: time to climb (10,000 feet), level acceleration (10,000 feet), turn performance, roll performance, and diving accelerations.



Do you know what the manifold pressures used were?

It could be that the MAP the P-47 was reduced from was for a higher grade of fuel, while the MAP used in the Mustang was for a similar grade (standard was 100/130).


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## pbehn (Oct 21, 2017)

Great to see that the test has ended all the arguments

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## DogMD11 (Oct 21, 2017)

Here is the article, I divided it into two parts. Part 1:

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## DogMD11 (Oct 21, 2017)

Part 2:


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## Dawncaster (Oct 21, 2017)

Weight and drag conditions also be considered.






P-47D : 80% of 14500 lbs gross weight, two wing pylons installed.
F6F-5 : 86% of 12480 lbs gross weight.
P-51D : 88% of 10100 lbs gross weight.
FG-1D : 92% of 12028 lbs gross weight, two stub pylons installed.

Compared to gross weight for military service condition, best condition for Thunderbolt and worst condition for Corsair.

ps. gross weight from tactical chart for Thunderbolt and Mustang and from pilot's manual for Corsair and Hellcat.


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## DogMD11 (Oct 21, 2017)

Whoops, here is the rest of Part 2:

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## pbehn (Oct 21, 2017)

Did I read correctly that the turbo had been disconnected on the P-47?

Much as I love the Merlin , as I understand it if you only want performance up to 10,000ft then an Allison powered Mustang I would be better.


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## Shortround6 (Oct 21, 2017)

Anybody notice the engine in the Mustang is listed as a V-1690-*9 *which is the engine usually associated with the P-51H?

Granted many P-51Ds were re-engined with -9 (or -9A) either near the end of the war or post war in US service.

Perhaps it is a typo and they meant the -7?

There is a difference in the supercharger gears, the -9 went _back _to the same gears as the -3 used on most of the P-51Bs & Cs.
A bit less power at low altitude but a bit more around 10,000 ft than the -7 engine in low gear?

Without pressure used in the test being given it is an unknown. The -3 and -9 could hold 60-61in to 10,000ft and that was Military power, not WER. METO _might be _2700rpm and 46in which is actually quite a change from take-off or military power. 

I would note that in the Corsair's pilots manual the chart for take-off is given at 32 degrees F (0 degrees C ) and says to _add 10% _for *every* 20 degrees F (10 degrees C) to the distance and that is at 54" of MAP. Corsair take-off (and climb?) test was done at 15 degrees hotter than the F6F and P-51, climb may have gone closer to average as the cooler air at high altitude may have been closer than the runway temperature.

The R-2800 engines, without using auxiliary superchargers (or turbo) start falling off in power between 1500-3500ft depending on the RAM and in climb that is a lot less than full speed level flight. An R-2800 was lucky it was making 1600hp at 10,000ft in low gear without ram. 
The sea level 54in for take-off had fallen to about 40in of MAP without ram. Now if you limit the engine to 50in for take off and the first 3-4000ft it doesn't change the climb much (if any) after that. 
P-47 could hold any pressure desired under the Max limit to 10,000ft with ease. F4U and F6F would have engaged the auxilary supercharger in low gear at somewhere between 4000-5000ft if making a maximum effort climb. See climb charts. 
perhaps the 100LL would not allow the higher temperatures that go with the use of the auxiliary supercharger?

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## pbehn (Oct 22, 2017)

I have a feeling that if this test was done for real during the period 1943 to 45 it still wouldn't answer any questions. Any aircraft that was available to test was already scheduled to have changes and improvements if they weren't already being done on the production lines.

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## pbehn (Oct 22, 2017)

For my two pence there were and always will be serious issues with any such test. 

Firstly the planes took off and landed from land. Two of the aircraft were specifically designed for carrier operations. Operating from a carrier means a lot of penalties in weight and structure so the Hellcat and Corsair should get some credit for that.

Stall speed, as an absolute minimum in level flight is of great interest for carrier operations but for little else. Stall at other speeds was important for pilots as was how predictable and controllable the stall was. The P 47 gets no marks in the test for its stall speed, but it could out turn a 109 at 30,000ft because of its wing loading and the power generated at that height by its turbo engine, that is another expression of "stall characteristics"

The P 51D was not a peak performance aircraft in 1944, it was just a very good aircraft that could carry a huge internal an external load of fuel and so project a good performance over most of Europe. If ultimate performance was the aim then the P51 would have been fitted with a Griffon, as later racers were. However a Griffon engine P51 wouldn't have reached Berlin and returned to base. The US air force could have coped with a lower top speed rate of climb etc on the P51 they could not have coped with a reduced range. 

If you ask me to choose, I will have one of each thank you. A Tempest for Fridays a Spitfire for Saturdays and a Mosquito to go to church on Sundays.


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## Shortround6 (Oct 22, 2017)

pbehn said:


> I have a feeling that if this test was done for real during the period 1943 to 45 it still wouldn't answer any questions. Any aircraft that was available to test was already scheduled to have changes and improvements if they weren't already being done on the production lines.




It would answer more questions than this test. At least they might have written down what boost pressures were actually used on the Mustang? Comparing climbs using unknown power settings and somewhat less than gross weights doesn't really give good answers.

I understand the constraints of the test. No 100/130 fuel, which may have hurt the radial engines more than the Mustang, radials being a bit more sensitive to fuel _usually. 
_Getting combat equipped aircraft is almost impossible at this point in time (or in the 90s) so gross weights are going to be lower and trying to ballast borrowed aircraft up to WW II weights in a short space of time and have the ballast stay in place and not damage the aircraft was probably out of the question. How close they could get by juggling the fuel load (and stay in CG) I have no idea. But having one aircraft operating at 80% of gross and another operating at 92% is going to skew the results as you noted earlier.
Cutting the manifold pressure by about 4in in the case of the radials due to the fuel is understandable but allowing the Mustang to use full boost until rough running forced a reduction in throttle doesn't seem right? Mustang should have been cut by 4 to 4.5in to keep things in proportion? 
Max continuous is stated as being used for the other parts of the test but this varies with altitude considerably for the radials also. Their superchargers are NOT going to hold a given pressure in the manifold at a reduced RPM anywhere near 10,000ft while it is not a great trick for the 2 stage supercharger in the Mustang to do so. In fact the Mustang might be able to hold the 2700rpm/46in max continuous to 15,000ft or better? (at least in level flight?) 

Maybe the loss in power matches the lighter weight to some extent?


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## wuzak (Oct 24, 2017)

pbehn said:


> The P 51D was not a peak performance aircraft in 1944, it was just a very good aircraft that could carry a huge internal an external load of fuel and so project a good performance over most of Europe. If ultimate performance was the aim then the P51 would have been fitted with a Griffon, as later racers were. However a Griffon engine P51 wouldn't have reached Berlin and returned to base. The US air force could have coped with a lower top speed rate of climb etc on the P51 they could not have coped with a reduced range.



Not sure about the range.

Certainly the endurance would be reduced, but the cruise with the Griffon should be faster, which would offset the time factor to some degree.

Rolls-Royce were keen to put the 2-stage Griffon in the Mustang, but NAA said there would be too much rework involved (at that stage of the war - 1942).


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## BiffF15 (Oct 24, 2017)

Does anyone have forecast data for what a Griffon powered Mustang might have done range / performance wise? The powers that be would have known we would be on the continent eventually, but then again the war in the Pacific required serious range for land based forces.

Cheers,
Biff


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## pbehn (Oct 24, 2017)

wuzak said:


> Not sure about the range.
> 
> Certainly the endurance would be reduced, but the cruise with the Griffon should be faster, which would offset the time factor to some degree.
> 
> Rolls-Royce were keen to put the 2-stage Griffon in the Mustang, but NAA said there would be too much rework involved (at that stage of the war - 1942).


M opinion was based on the Griffon being bigger and heavier and having a larger swept volume. All of these tend to increase fuel consumption. It may be true that a Griffon engine P 51 would consume approximately the same while cruising to rendezvous. Personally I doubt it. However much of a P51s mission was on escort where consumption was in gallons per hour and the speed dictated by the bomber formation. On this part of a mission and in combat it would definitely consume more.


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## Shortround6 (Oct 24, 2017)

It shouldn't consume a lot more while cruising. Power required it pretty much dependent on drag. Yes the extra weight will cause a bit of extra drag ( higher angle of attack for wing at same speed) but that is going to be rather small. Larger radiator scoop? but airflow _through _the radiator will be in proportion to the power being made. 

That leaves the actual fuel economy of the engine. The Griffon is 36% bigger in swept volume to be sure but it runs approximately 10% slower. It also has about 22% more scrubbed area of cylinder wall and pistons scrubbing cylinder walls are roughly 75-80% of the friction in an engine. Fiction goes up with the square of the speed soooo.......
Running an engine even 200rpm slower can make a difference in friction losses (one big reason for dropping the revs and using high boost (relatively) for cruising.
A clean Mustang (tanks gone) can cruise at over 300mph true at 1850, boost not given, at 25,000ft using 59 gallons an hour. I don't know what the power is but is seems to be well under 700hp. (2400rpm and 36in/3lb is 775hp at 22,500ft) 

I have no idea what settings are needed to get 5-600hp out of a Griffon at 22-25,000ft.

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## wuzak (Oct 24, 2017)

Shortround6 said:


> It shouldn't consume a lot more while cruising. Power required it pretty much dependent on drag. Yes the extra weight will cause a bit of extra drag ( higher angle of attack for wing at same speed) but that is going to be rather small. Larger radiator scoop? but airflow _through _the radiator will be in proportion to the power being made.
> 
> That leaves the actual fuel economy of the engine. The Griffon is 36% bigger in swept volume to be sure but it runs approximately 10% slower. It also has about 22% more scrubbed area of cylinder wall and pistons scrubbing cylinder walls are roughly 75-80% of the friction in an engine. Fiction goes up with the square of the speed soooo.......
> Running an engine even 200rpm slower can make a difference in friction losses (one big reason for dropping the revs and using high boost (relatively) for cruising.
> ...



Cruise settings all seem to refer to maximum cruise. Which is at 2,400rpm and over 1,200hp @ 25,000ft for a Griffon 65.

Regarding drag, I don't think the engine itself would lead to an increase in drag, for while it is bigger in area than the Merlin it is not bigger than the P-51's fuselage.

It would require larger oil coolers, intercooler radiator and engine coolant radiators, as you have noted. This would probably require a larger scoop, which would impact the drag slightly.

Also, with the escort duty the P-51s may not have escorted the B-17s for the entire journey. Rather, escorts were done in relays, with other aircraft, such as P-47s, providing the initial cover. This would allow the P-51s to get to the rendezvous at their optimum speed.


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## Koopernic (Oct 25, 2017)

wuzak said:


> Not sure about the range.
> 
> Certainly the endurance would be reduced, but the cruise with the Griffon should be faster, which would offset the time factor to some degree.
> 
> Rolls-Royce were keen to put the 2-stage Griffon in the Mustang, but NAA said there would be too much rework involved (at that stage of the war - 1942).



If North American said the P-51 required too much modification to take the Griffon they meant it would be better and faster to start an all new aircraft. The P-51B had vast amounts of panel changes over the P-51A while the P-51H was new again.

Of course North American could have built a Griffon powered P-51H given the effort involved in the H but would that have yielded a better aircraft? Larger certainly but faster than 487 mph?

The reason Supermarine shoe horned the Griffon into a hybrid of the Spitfire IV and Spitfire VIII is because brute power was the only way to overcome the limitations of the early 1930s airframe and aerodynamic technology. A Merlin Mustang was as fast if not faster than Griffon Spitfire. A Griffon mustang may not be much faster.


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## wuzak (Oct 25, 2017)

Koopernic said:


> If North American said the P-51 required too much modification to take the Griffon they meant it would be better and faster to start an all new aircraft. The P-51B had vast amounts of panel changes over the P-51A while the P-51H was new again.
> 
> Of course North American could have built a Griffon powered P-51H given the effort involved in the H but would that have yielded a better aircraft? Larger certainly but faster than 487 mph?
> 
> The reason Supermarine shoe horned the Griffon into a hybrid of the Spitfire IV and Spitfire VIII is because brute power was the only way to overcome the limitations of the early 1930s airframe and aerodynamic technology. A Merlin Mustang was as fast if not faster than Griffon Spitfire. A Griffon mustang may not be much faster.



The Griffon had similar power at 20-25,000ft with 100/130 grade fuel and +18psi boost (67inHg MAP) as the V-1650-9 did with 90inHg MAP and ADI.

The Griffon-Mustang discussion was occurring when the Mustang X and P-51B programs were in their initial stages. The Griffon Mustang would have predated the P-51H by a year or so. Certainly the 100 series Merlins (of which the V-1650-9 was one) had yet to be developed at that time.

The Griffon Spitfire (XIV) was 30-40mph faster than the equivalent Merlin Spitfire (VIII), depending on the sub type (F, LF, HF) and the Merlin variant used (63, 66, 70). Certainly the Mustang was as fast as the Griffon Spitfire, but it was quite a bit faster then the Spitfire with the same engine.


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## pbehn (Oct 25, 2017)

From what I have seen of the P51 production line it was true mass production, you cannot make small changes to such a system, any modification means in effect a new aircraft.


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## Shortround6 (Oct 25, 2017)

Another problem was the Griffon itself, _where_ were hundreds or thousands of 2 stage Griffons going to come from in 1942? 
I mean this form a planning perspective. First squadron with Spitfire MK XIVs didn't become operational until Dec of 1943. 
To build Griffon powered Mustangs instead of Merlin Mustangs in 1943 (and Packard couldn't build Merlins fast enough in the Spring/summer of 1943) you need a source of 2 stage Griffons at a rate of hundreds per month by the middle of 1943.

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## drgondog (Oct 25, 2017)

AFAIK the Griffon was never considered for the Mustang at NAA or AAFMC. As noted above there were major changes required to both the airframe as well as Packard (or new source) tooling and start up. The Merlin 100 was a candidate but deemed too late for B/D and too early in the development/refinement stage in late 1943. It was installed in NA-105B XP-51G with excellent results in 1944, but by that time the 1650-9 was selected.

The political forces at the AAFMC/GM Board of Directors were also a hidden hindrance to any 'new' engine coming from England, as Allison frantically striving to replace the Packard Merlin with a new two stage/two speed V-1710 installed in the XP-51J.

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## BiffF15 (Oct 25, 2017)

Bill,
As a CROT (crude rule of thumb) could one compare the equivalent Spitfires with Merlin / Griffon engines for fuel flow differences to get a "rough" hack at what a Griffon Mustang would have burned? And from that extrapolate a "rough" hack at it's range with or without external fuel tanks?
Cheers,
Biff


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## YF12A (Oct 25, 2017)

pbehn said:


> From what I have seen of the P51 production line it was true mass production, you cannot make small changes to such a system, any modification means in effect a new aircraft.


Agree. This reminds me of the B-29 "Battle of Kansas" situation.


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## tomo pauk (Oct 25, 2017)

Koopernic said:


> ...
> The reason Supermarine shoe horned the Griffon into a hybrid of the Spitfire IV and Spitfire VIII is because brute power was the only way to overcome the limitations of the early 1930s airframe and aerodynamic technology. A Merlin Mustang was as fast if not faster than Griffon Spitfire. A Griffon mustang may not be much faster.



Since the Spitfire 'swallowed' the 2-stage Griffon without breaking a sweat, looks like the supposed early 1930s airframe have had more stretch than it's designer team ever reckoned. Modifications nothwitsanding.
Spitfire's aerodynamic technology was unmatched by many design tems in years to come. By 1944, the only thing that was aerodynamically probelmatic was layout of it's big radiators. Other people also went with brute power when available (including NAA, Republic, Hawker, Focke Wulf), so that point is moot.


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## Juha2 (Oct 25, 2017)

Hello
if somebody has enough info on CAC CA-15, that might give a clue on "Griffon P-51" consumption.


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## pbehn (Oct 25, 2017)

Shortround6 said:


> Another problem was the Griffon itself, _where_ were hundreds or thousands of 2 stage Griffons going to come from in 1942?
> I mean this form a planning perspective. First squadron with Spitfire MK XIVs didn't become operational until Dec of 1943.
> To build Griffon powered Mustangs instead of Merlin Mustangs in 1943 (and Packard couldn't build Merlins fast enough in the Spring/summer of 1943) you need a source of 2 stage Griffons at a rate of hundreds per month by the middle of 1943.


Simply re write history. Give the plans for the Griffon to Napier and tell them to make it instead of the Sabre.. Give the plans to the P51 to Hawkers and say make it with a Griffon. No more Typhoons or Tempests but a lot of different P1s and Mustang XIVs for a variety of roles.

It means re writing commercial relations between UK and USA plus 20/20 hindsight though.


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## davparlr (Oct 25, 2017)

pbehn said:


> he P 51D was not a peak performance aircraft in 1944, it was just a very good aircraft that could carry a huge internal an external load of fuel and so project a good performance over most of Europe.


? From mid 44, to the end of the war the P-51D with high octane fuel, was a class A fighter easily contesting the skies over Germany and Japan. Not until late 1944 did Germany generate any aircraft that could challenge the Mustang but never had the quantity to do it.

The report is somewhat confusing to me. I had never heard that the control forces for the P-51 could be very high. Indeed the Fighter Conference in late '44 never mentioned high control forces and selected the P-51 as second best all around fighter above 25k feet slightly behind the P-47, and also second best all around fighter below 25k feet almost equal to the F8F. Only one person rated the P-51 elevator forces poor while none rated the aileron forces as poor.


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## GregP (Oct 25, 2017)

I'm not sure I read all of this thread yet, but fuel consumption shouldn't be too hard to get. It'll be the same as for a Griffon in a Spitfire at the same power level. Might be a different speed. but the gal/hour should be about the same. Speed at power level will be different, but fuel consumption should be for a Griffon engine more or less in a fighter airframe, and the Spitfire was very close.

From the Pilot's Notes for the Spitfire XIV:

Spitfire XIV has 4 tanks. They total 111 gallons. It consumed 22.5 gallons climbing to 20,000 feet, leaving 88.5 gallons.


IAS at 20,000 feet cruise (MAP not stated) at various rpm were as follows:

1800 rpm, 240 mph, 88.5 gallons: 4.65 air miles per gallon --> 411.5 miles --> 1.71 hours --> 51.8 gal/hour

2000 rpm, 240 mph, 88.5 gallons: 4.6 air miles per gallon --> 407 miles --> 1.70 hours --> 52 gal/hour

2200 rpm, 240 mph, 88.5 gallons: 4.45 air miles per gallon --> 394 miles --> 1.64 hours --> 54 gal/hour

2400 rpm, 240 mph, 88.5 gallons: 4.3 air miles per gallon --> 380 miles --> 1.58 hours --> 56 gal/hour


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## Shortround6 (Oct 25, 2017)

Most of these engines burned from 0.45lbs to 0.50lbs of fuel per horsepower hour in cruise settings (lean mixture) . Some settings (or combinations) were better than others. But as Greg's illustration shows, the Spitfire MK XIV varied about 8% from 1800rpm to 2400rpm (boost may have gone inverse. like -2lbs at 2400rpm and +4lbs at 2400rpm) 
Without knowing the power required it gets increasingly into guess work as to the settings required for a particular aircraft to cruise at a given speed. 

If you are depending on a 10% or less difference in fuel consumption to make to a particular target or group of targets on a regular basis (not a one off raid) then you are probably cutting things too fine. AN unexpected head wind could leave your planes just a few miles short of returning.


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## MycroftHolmes (Oct 25, 2017)

It's a bit of a myth that the Mustang was significantly faster than a Spitfire with the same engine. The oft-quoted statement that the Mustang was '20-30 mph faster' applied to an early Spitfire IX with the Merlin 61 (nominally capable of 403 mph). By contrast the Spitfire HFIX with normal wing-tips and the Merlin 70 could do 419 mph, which suggests that a P51B would be ~10 mph faster if both aircraft were in pristine condition. Of course, the Mustang's wing was much more sensitive to dirt and dents and after a few missions the speeds would probably be more-or-less identical. The top speed of about 430 mph for the P51 is also quoted in Bowyer and Sharp's _Mosquito_.


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## tomo pauk (Oct 25, 2017)

Hope that you don't mind butchering the post a bit 



MycroftHolmes said:


> It's a bit of a myth that the Mustang was significantly faster than a Spitfire with the same engine. The oft-quoted statement that the Mustang was '20-30 mph faster' applied to an early Spitfire IX with the Merlin 61 (nominally capable of 403 mph). By contrast the Spitfire HFIX with normal wing-tips and the Merlin 70 could do 419 mph, which suggests that a P51B would be ~10 mph faster if both aircraft were in pristine condition.
> The top speed of about 430 mph for the P51 is also quoted in Bowyer and Sharp's _Mosquito_.



The V-1650-3 engine was equivalent of the high-alt Merlins produced in the UK. The Mustang III (ie. P-51B) with that engine was good for 450 mph. data sheet ; chart (67 in Hg max boost on 130 grade fuel)

We also have a comparison between Spitfire V and Mustang II - on a worse engine the Mustang II was 30++ mph faster.



> Of course, the Mustang's wing was much more sensitive to dirt and dents and after a few missions the speeds would probably be more-or-less identical.



I'll politely ask for surces about this sentence.

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## davparlr (Oct 25, 2017)

My data, mostly from Spitfireperformance, shows a max speed of the P-51B (-3) at sea level (which I think is the best measurements for aerodynamic performance) is 370 mph at 67" (max speed of the -7 engine at 67" was 360 mph). Fastest speed I found for the Spitfire IX, the Merlin 66, was 336 mph (18 lbs boost, equivalent to 67" US). This supports the claim that the Mustang was 20 - 30+ mph faster than the equivalently powered Spitfire, at SL.


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## pbehn (Oct 25, 2017)

davparlr said:


> My data, mostly from Spitfireperformance, shows a max speed of the P-51B (-3) at sea level (which I think is the best measurements for aerodynamic performance) is 370 mph at 67" (max speed of the -7 engine at 67" was 360 mph). Fastest speed I found for the Spitfire IX, the Merlin 66, was 336 mph (18 lbs boost, equivalent to 67" US). This supports the claim that the Mustang was 20 - 30+ mph faster than the equivalently powered Spitfire, at SL.


I would say a Griffon P51 would maintain that advantage because the Spitfire was limited by its propeller diameter.


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## pbehn (Oct 25, 2017)

Shortround6 said:


> It shouldn't consume a lot more while cruising. Power required it pretty much dependent on drag. Yes the extra weight will cause a bit of extra drag ( higher angle of attack for wing at same speed) but that is going to be rather small. Larger radiator scoop? but airflow _through _the radiator will be in proportion to the power being made.
> 
> That leaves the actual fuel economy of the engine. The Griffon is 36% bigger in swept volume to be sure but it runs approximately 10% slower. It also has about 22% more scrubbed area of cylinder wall and pistons scrubbing cylinder walls are roughly 75-80% of the friction in an engine. Fiction goes up with the square of the speed soooo.......
> Running an engine even 200rpm slower can make a difference in friction losses (one big reason for dropping the revs and using high boost (relatively) for cruising.
> ...


Great post S/R shouldn't there be an additional BHP loss through the added output of the supercharger.?


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## pbehn (Oct 25, 2017)

davparlr said:


> ? From mid 44, to the end of the war the P-51D with high octane fuel, was a class A fighter easily contesting the skies over Germany and Japan. Not until late 1944 did Germany generate any aircraft that could challenge the Mustang but never had the quantity to do it.
> 
> .


That was exactly my point posted before. As an escort the P51 did not have to out perform the enemy, even with the Me262 it could still have an affect simply by making sure it kept at close to maximum speed to avoid combat not the best speed to hit the bombers. In absolute performance it was behind the Tempest at low level and many LW aircraft at high level, about on par in speed but not allround performance with Griffon Spitfires. The jet age had already arrived but in terms of propeller driven aircraft the P51 was not the best, it was quite obviously good enough though to do the job that was asked of it, over Berlin and Poland.

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## Shortround6 (Oct 25, 2017)

pbehn said:


> Great post S/R shouldn't there be an additional BHP loss through the added output of the supercharger.?



might depend on the cruise settings? 
again the supercharger power required is somewhat proportional to the sq of the speed of the impeller (or it's tips). 


Griffon 61 used 13.4 and 11.3 in impellers and 5,84 and 7.58 gears. 
Merlin V-1650-3 used 12 and 10.1in impellers and 6.39 and 8.095 gears. 

Using 2000rpm cruise for the Merlin the impeller tips are moving at 847fps on the big impeller in high gear and using 1800rpm for the Griffon the the tips are moving 797fps on the big impeller in high gear if I have done the math right. The Griffon will be moving more air per revolution of the impeller so it isn't tip speed alone but at cruising speeds the supercharger isn't sucking up anywhere near the power they do at full speed. For example the supercharger will use 2.25 times the power at 2700 engine rpm as it does at 1800 engine rpm. 

If the Griffon is making 25-33% more power at a given rpm (using the same manifold pressure) then it doesn't need to turn as many rpm to make "cruising power" in a low drag airframe. 

I am not saying the Griffon is better than the Merlin in fuel consumption but the automatic assumption that it is a fuel hog _when cruising_ may need a lot closer look. 
Obviously once you go to power settings over 2400rpm and 7lbs boost (max lean) fuel consumption can skyrocket

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## pbehn (Oct 25, 2017)

Shortround6 said:


> If the Griffon is making 25-33% more power at a given rpm (using the same manifold pressure) then it doesn't need to turn as many rpm to make "cruising power" in a low drag airframe.
> 
> I am not saying the Griffon is better than the Merlin in fuel consumption but the automatic assumption that it is a fuel hog _when cruising_ may need a lot closer look.
> Obviously once you go to power settings over 2400rpm and 7lbs boost (max lean) fuel consumption can skyrocket


My argument in this case is that there isn't a free lunch. In my opinion the Griffon would have used at least as much fuel if not more when cruising and would certainly have used more while on station and in combat. Against this the Griffon is heavier while the P51 was pushing the boundaries of safe take off weights with a Merlin.


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## Koopernic (Oct 25, 2017)

tomo pauk said:


> Since the Spitfire 'swallowed' the 2-stage Griffon without breaking a sweat, looks like the supposed early 1930s airframe have had more stretch than it's designer team ever reckoned. Modifications nothwitsanding.
> Spitfire's aerodynamic technology was unmatched by many design tems in years to come. By 1944, the only thing that was aerodynamically probelmatic was layout of it's big radiators. Other people also went with brute power when available (including NAA, Republic, Hawker, Focke Wulf), so that point is moot.



The Spitfire did break a sweat with the Griffon. It essentially became impractical and unsafe to loop in realistic circumstances and its handling deteriorated. The spitfires 1930s NACA 4 digit airfoils came at a cost fitness could not overcome.

The Spitfire was made possible by the maturity of the PV12 Merlin, it’s superchargers and 100/130 fuel. If it had of been forced to operate with Allison V-1710 or DB601/605 it would have given away so much speed, climb and sustained turn its legend would probably not have been made.

It required the Me 109G1 and the DB605A of 1942 to match the 1310hp the Spitfire had in 1940.

The Griffon Spitfire did climb like the clappers and above 25000ft.

The Tempest with Griffon probably would have been a faster aircraft.


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## Shortround6 (Oct 25, 2017)

A P-51D with wing racks empty could do about 5.5 miles to the US gallon at 25,000ft while doing 335mph which is a bit higher than they used/planned for cruising. I don't have the pilot's manual at hand to show the charts with underwing loads. 
I do believe a Griffon engine versions would use a bit more gas but since the Mustang was using under 700hp hp (maybe way under) I don't see why the Griffon engine would use that much more while cruising? Once you go to combat settings where the Griffon is making hundreds of horsepower more than the Merlin it is going to use fuel in proportion the power made. If the Griffon is making 20% more power it is reasonable to assume it will use 20% more fuel. 
The B-17s cruised about 180mph and the P-51s "while on station" were doing 305 or above and essing above them. They were going to esse regardless of engine or version of engine. 

Max take-off for a P-51D included either a pair of 1000lb bombs or a pair of 165 gallon drop tanks. You can use 110 gallon drop tanks and save 710lbs worth of fuel and tanks (the 110 gallon tanks weigh less than the 165 gallon tanks) . 
Granted this may not have been the best idea from ALL air fields but on the other hand, the Griffons would not have been installed by units in the field. Proper bracing and upgraded landing gear would have been part of the package. 

Please note I am not advocating such a conversion. It would not have been available in enough numbers to do anything until well into 1944 and only at the cost of shorting other programs of Griffons unless you can magic up a completely new engine factory.

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## Koopernic (Oct 25, 2017)

MycroftHolmes said:


> It's a bit of a myth that the Mustang was significantly faster than a Spitfire with the same engine. The oft-quoted statement that the Mustang was '20-30 mph faster' applied to an early Spitfire IX with the Merlin 61 (nominally capable of 403 mph). By contrast the Spitfire HFIX with normal wing-tips and the Merlin 70 could do 419 mph, which suggests that a P51B would be ~10 mph faster if both aircraft were in pristine condition. Of course, the Mustang's wing was much more sensitive to dirt and dents and after a few missions the speeds would probably be more-or-less identical. The top speed of about 430 mph for the P51 is also quoted in Bowyer and Sharp's _Mosquito_.



The P-51B had in essence the Merlin 61.
The P-51D had in essence the more powerful Merlin 66 whose supercharger was set to a lower altitude but because of greater boost and power was almost as fast as the P-51B despite its loss in high altitude power.
A P-51B/C/D with a high altitude Merlin 70 would have been extremely fast. I’m guessing 450mph.

Although the mustangs wing easily lost laminarity due to bugs, dirt and dings the very same gradual positive pressure distribution designed into it also greatly delayed compressibility and shock drag. At Mach 0.66 it made a difference. Eastman Jacobs, who designed the wing mathematically knew of this. Jacobs was designing a transonic aircraft called jakes Jeep.


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## Koopernic (Oct 25, 2017)

Juha2 said:


> Hello
> if somebody has enough info on CAC CA-15, that might give a clue on "Griffon P-51" consumption.


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## Shortround6 (Oct 25, 2017)

Koopernic said:


> The Spitfire did break a sweat with the Griffon. It essentially became impractical and unsafe to loop in realistic circumstances and its handling deteriorated. The spitfires 1930s NACA 4 digit airfoils came at a cost fitness could not overcome.
> 
> The Spitfire was made possible by the maturity of the PV12 Merlin, it’s superchargers and 100/130 fuel. If it had of been forced to operate with Allison V-1710 or DB601/605 it would have given away so much speed, climb and sustained turn its legend would probably not have been made.
> 
> It required the Me 109G1 and the DB605A of 1942 to match the 1310hp the Spitfire had in 1940.



Not quite right, the DB601E could pretty well match the 1940 Merlin III. if not exceed it handily at high altitudes. The 1310hp the Spitfire had in 1940 was at 9000ft and power faded to the normal 1030hp at 16250ft, ram not included. the MerlinX XIIin the Spitfire II was only coming into service in small numbers at the end of the BoB. 
There was NO 100/130 in the Bob. more like 100/115. A Spitfire I with a -33 Allison would have performed almost the same. A Spitfire MK I with a DB601A-1 wouldn't have been much different either. 1020ps at 4500meters (14850ft just 1,400ft below the Merlin) isn't going to show a huge difference. 
and strangely enough, the Spitfire, with it's 1930s airframe and old airfoil was faster than the 109E that was smaller and lighter but had almost the same power.


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## wuzak (Oct 25, 2017)

Koopernic said:


> The Spitfire did break a sweat with the Griffon. It essentially became impractical and unsafe to loop in realistic circumstances and its handling deteriorated. The spitfires 1930s NACA 4 digit airfoils came at a cost fitness could not overcome.



Never seen that before. Where did you get that information.

From what I have read the Spitfire XIV had much the same handling as Merlin versions, and was rated as more manoeuverable because of the extra power.


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## Stig1207 (Oct 26, 2017)

GregP said:


> Spitfire XIV has 4 tanks. They total 111 gallons. It consumed 22.5 gallons climbing to 20,000 feet, leaving 88.5 gallons.



Including warmup? 22.5 gallons from start to 20.000 ft seems to be low fuel consumption in comparison with other numbers I have seen.

Forgot to specify that I haven't seen other numbers for the Spitfire. I have read, somewhere, figures giving fuel consumption of 28 gallons from start to 5.000 ft for a P-40.


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## Koopernic (Oct 26, 2017)

Shortround6 said:


> Not quite right, the DB601E could pretty well match the 1940 Merlin III. if not exceed it handily at high altitudes. The 1310hp the Spitfire had in 1940 was at 9000ft and power faded to the normal 1030hp at 16250ft, ram not included. the MerlinX XIIin the Spitfire II was only coming into service in small numbers at the end of the BoB.
> There was NO 100/130 in the Bob. more like 100/115. A Spitfire I with a -33 Allison would have performed almost the same. A Spitfire MK I with a DB601A-1 wouldn't have been much different either. 1020ps at 4500meters (14850ft just 1,400ft below the Merlin) isn't going to show a huge difference.
> and strangely enough, the Spitfire, with it's 1930s airframe and old airfoil was faster than the 109E that was smaller and lighter but had almost the same power.



You are misled about the fuel grade during the BoB, as I was earlier.

http://www.newcomen.com/wp-content/uploads/2012/12/Chapter-11-Marshall.pdf
I also invested in an SAE paper
A Short History of Aviation Gasoline Development, 1903-1980


The USAAC decided to convert to 100 octane fuel in 1935 after Shell and Standard had delivered useful quantities. The US specification steadfastly focused on the lean ON octane number and was indifferent to rich mixture response. The process used was polymerisation of isobutylene to create iso-octane and the feedstock was in short supply. This was a far sighted decision. Without the US decision of 1935 it there would be no plant to produce 100 octane of any type for the RAF for 1939.

As a result of the guaranteed orders the US oil industry developed and invested in the following production capacity.
1 addition of tetraethyl lead
2 synthesis of iso octane
3 catalytic cracking with regenerative catalyst (Houdry process)
4 Acid alkylation of butane and propane (a British patent, it improved both lean and rich mixture response, it hadn’t been developed but was serendipitous). US invested purely to increase lean response.

This ensured that when the UK required 100/130 it was merely a matter of blending from the above options which were all coming on line in 1938.

(So jimmie Doolittle did win the BoB)

The Germans started construction of alkylation plants in 1940 but only one was ever completed and that was in 1943. It takes that long to build plant. Britain’s 1937 work on 100 octane would be too late for the BoB were it not for the 1935 US decision. The Germans were suck with synthesis of iso octane because cracking didn’t work well with synthetic fuel and alkylation plant s took too long to build.


Although there were initial British experiments with US 100 ON octane they had for years had an appreciation of rich mixture responses.

The Schneider Trophy races with the Rolls Royce R-type (early Griffon) used fuels consisting of acetone, benzol(benzene & toluene), methanol which had a massive charge cooling and rich mixture anti knock effect)

The initial 1937 air ministry specification still lacked a performance number but it did have a work instruction for blending cuts of fuel that would produces fuel that would have a ON/PN of around 100/130. The actual 130PN requirement came later when the test engines had been developed and manufactured to prove this from samples taken from production. There was no such PN test engines in the USA till 1942.

The British specification for blending however produced a fuel of 100/130 from the very beginning. Initially it relied on exotic Caribbean fuels or of Borneo from its overseas possessions and colonies.

US 100 octane was 100 ON but the specification was indifferent to the rich mixture. In reality it was probably around 100/120, same as pure octane The US was interested in sustained economical sustained power.

The BoB 100 octane was 100/130 from the beginning. It was controlled but not as tightly as it was from 1942 and it’s possible they used 100/125.
===========

The fuel Britain and France used in WW1 was approx 75ON. It was distilled from crudes taken from the Caribbean and Asia. American crude is inferior and aviation fuel X supplied in WW1 was only 45 to 55 ON ran well in the well designed Liberty engine but not in Nieupoerts or Sopwiths.
============


The Spitfire always had 200-300 more horse power
Me 109E v Spitfire I-III. 1050 to 1310
Me 109F v Spitfire V. 1200 to 1460
Me 109G1 1.3 ata v Spitfire IX. 1300 v 1560 two stage Merlin 61
Me 108G6 1.42 ata V Spitfire IX. 1420 v 1700 two stage Merlin 66

Even with the 1800hp to 2000hp 1.8 to 1.98 ata DB605DB/DC the Merlin on 100/150 seemed 200 hp more powerful.

However when the Me 109 had close to the same power it seemed much faster than the Spitfire.

Power = improved manouverbillity and speed.

A 1320 hp Me 109 would beat a 1100 hp Spitfire but it was infact the other way around.

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## Milosh (Oct 26, 2017)

The R-R R engine is not directly related to the 1939 Griffon. There was a derated R known as the Griffon tested in 1933.


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## tomo pauk (Oct 26, 2017)

Koopernic said:


> The Spitfire did break a sweat with the Griffon. It essentially became impractical and unsafe to loop in realistic circumstances and its handling deteriorated. The spitfires 1930s NACA 4 digit airfoils came at a cost fitness could not overcome.



The 1st sentence is your opinion. 2nd sentence is hard to comprehend for a non-original speaker.



> The Spitfire was made possible by the maturity of the PV12 Merlin, it’s superchargers and 100/130 fuel. If it had of been forced to operate with Allison V-1710 or DB601/605 it would have given away so much speed, climb and sustained turn its legend would probably not have been made.



??
Spitfire became a legend already in 1940, when there was no 100/130 grade fuel, DB 605, and V-1710s were produced in penny packets.
It is not a fault of the Spitfire that RR came out with ever better engines, it is to it's credit that it was able to accept those engines in timely manner and without problems.
Shove the DB 601A on the Spitfire I or DB 601E on the Spit V and difference will be barely felt.



> It required the Me 109G1 and the DB605A of 1942 to match the 1310hp the Spitfire had in 1940.



Wrong on year stated, engine stated and Bf 109 version stated.
It also seems like the altitude where power is attained ceased to be relevant for ww2 aircraft.


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## tomo pauk (Oct 26, 2017)

Koopernic said:


> <snip>
> (So jimmie Doolittle did win the BoB)



Hugh Dowding won it, if we really want to pick a person.



> The Spitfire always had 200-300 more horse power
> Me 109E v Spitfire I-III. 1050 to 1310
> Me 109F v Spitfire V. 1200 to 1460
> Me 109G1 1.3 ata v Spitfire IX. 1300 v 1560 two stage Merlin 61
> Me 108G6 1.42 ata V Spitfire IX. 1420 v 1700 two stage Merlin 66



For such a Luftwaffe fanboy, I don't know why posting wrong data?
DB-601E: 1450 PS
DB 601A restricted: 1400
DB 605A full: 1540



> Even with the 1800hp to 2000hp 1.8 to 1.98 ata DB605DB/DC the Merlin on 100/150 seemed 200 hp more powerful.
> 
> However when the Me 109 had close to the same power it seemed much faster than the Spitfire.



Bf 109 was far smaller aircraft, with limitations involved due to the size. Spitfire was rarely out-climbed, from 1941 on usually carried twice the cannons, and was capable for carrying much greater fuel tankage and bigger & much more powerful engines. Also better visibility.



> Power = improved manouverbillity and speed.
> 
> A 1320 hp Me 109 would beat a 1100 hp Spitfire but it was infact the other way around.



It was not.
Curiously enough, there was no recon Bf 109s flying 600+ miles and back, free from interception. Unlike the Spitfires.

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## Barrett (Oct 26, 2017)

Intriguing subject--thank you for bringing the article to our attention. Enjoying the skookum comments from so many knowledgable folks. I was in the antique-warbird community at the time (1990) but missed it. FWIW, the wartime joint fighter conferences held at Patuxent River and Eglin Field showed the F4U as the best fighter-bomber and in fact the best fighter in some regimes. I knew two participants. Rex Barber (of Yamamoto fame) said that if the US were to build one fighter, it should be the F4U. Grumman test pilot Corky Meyer tended to agree, though with some Hellcat reservations!


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## GregP (Oct 26, 2017)

Regarding post 42, how does propeller diameter limit a Spitfire?

The Reno racers are all running propeller smaller than stock because they don't want the prop tip to exceed something near Mach 0.85 (actual number a team secret). And the two or three fastest ones are all over 530 mph top speed at 5,000 feet. All you have to do is move to coarse pitch and you go faster, assuming you have the power to keep spinning the prop at whatever rpm you are turning.

It isn't quite that simple, but the speed record planes of today all use smaller props than wartime stock.


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## Shortround6 (Oct 26, 2017)

GregP said:


> Regarding post 42, how does propeller diameter limit a Spitfire?
> 
> The Reno racers are all running propeller smaller than stock because they don't want the prop tip to exceed something near Mach 0.85 (actual number a team secret). And the two or three fastest ones are all over 530 mph top speed at 5,000 feet. All you have to do is move to coarse pitch and you go faster, assuming you have the power to keep spinning the prop at whatever rpm you are turning.
> 
> It isn't quite that simple, but the speed record planes of today all use smaller props than wartime stock.



Modern racers at operating at 5-7,000ft? with Reno temperatures that is equivalent to what at sea level on a "standard" day? even higher? but a far cry from the prop needed at 25,000ft. 

and prop optimized for speed is different than a prop optimized for climb. 

Fighter props are almost always going to be a compromise between different requirements.


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## pbehn (Oct 26, 2017)

GregP said:


> Regarding post 42, how does propeller diameter limit a Spitfire?
> 
> The Reno racers are all running propeller smaller than stock because they don't want the prop tip to exceed something near Mach 0.85 (actual number a team secret). And the two or three fastest ones are all over 530 mph top speed at 5,000 feet. All you have to do is move to coarse pitch and you go faster, assuming you have the power to keep spinning the prop at whatever rpm you are turning.
> 
> It isn't quite that simple, but the speed record planes of today all use smaller props than wartime stock.


The Spitfire went to multi blade and contra props because they couldn't go any bigger on diameter.


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## BiffF15 (Oct 26, 2017)

This is such a well named thread! Or not...

Cheers,
Biff

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## YF12A (Oct 26, 2017)

Nothing is Over until I SAY it's Over! Oops, belongs on IMDB.

My bad, I couldn't help myself.


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## pbehn (Oct 26, 2017)

BiffF15 said:


> This is such a well named thread! Or not...
> 
> Cheers,
> Biff


Well I think we have made a good start resolving the difficult issues, now we are on the fine detail.

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## GregP (Oct 26, 2017)

They didn't HAVE to go to more blades. 

They could have increased blade chord, like the Germans did, quite successfully. I don't think anyone would call the Fw 190 or Ta 152 slow, and they had a wide-chord, 3-blade prop because the Germans preferred fuselage-mounted weapons and needed the rate of fire. The Me 209 set a world record that stood for decades with a 3-blade prop of no surprising diameter.

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## pbehn (Oct 26, 2017)

GregP said:


> They didn't HAVE to go to more blades.
> 
> They could have increased blade chord, like the Germans did, quite successfully. I don't think anyone would call the Fw 190 or Ta 152 slow, and they had a wide-chord, 3-blade prop because the Germans preferred fuselage-mounted weapons and needed the rate of fire. The Me 209 set a world record that stood for decades with a 3-blade prop of no surprising diameter.


But Greg you answer your own post. The Germans chose a broad chord 3 blade prop because of the aircrafts armament. I have flown on many turboprop planes, none had three broad blade prop. It is not my field of expertise but I suspect a short but broad blade is much more likely to run in a stalled condition. The Griffon Spitfires had an 11ft diameter prop while the P47 was introduced with a 12ft diameter later replaced with the 13ft paddle blade props. The F4U Corsair had a three blade 13ft 4 in prop from the start.


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## wuzak (Oct 26, 2017)

pbehn said:


> The Griffon Spitfires had an 11ft diameter prop while the P47 was introduced with a 12ft diameter later replaced with the 13ft paddle blade props. The F4U Corsair had a three blade 13ft 4 in prop from the start.



The Spitfire XIV had a prop diameter of less than 10'6". 

I believe the standard prop for a Spitfire IX was 10'9" in diameter.

The difference being that the Griffon was angled down to give better pilot view.


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## Aozora (Oct 26, 2017)

Shortround6 said:


> might depend on the cruise settings?
> again the supercharger power required is somewhat proportional to the sq of the speed of the impeller (or it's tips).
> 
> 
> ...


Here are the Pilot's Notes for the Spitfire IX (1946), Spitfire VII/VIII (Merlin 63 or 64, 1943) and Spitfire XIV/XIX:

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## pbehn (Oct 26, 2017)

wuzak said:


> The Spitfire XIV had a prop diameter of less than 10'6".
> 
> I believe the standard prop for a Spitfire IX was 10'9" in diameter.
> 
> The difference being that the Griffon was angled down to give better pilot view.


Wuzak, I did a search on griffon engine Spitfires and got this from wiki
"The Rolls-Royce *Griffon* engine was designed in answer to Royal Naval specifications for an ..... The *Griffon* engine drove an 11 ft (3.35 m) diameter five-bladed *propeller*, some 7 inches (17.8 cm) larger than that fitted to the Mk XIV."

But when I read the article it states what you say 10ft 5in 5 blade Rotol.
Supermarine Spitfire (Griffon-powered variants) - Wikipedia


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## wuzak (Oct 26, 2017)

pbehn said:


> Wuzak, I did a search on griffon engine Spitfires and got this from wiki
> "The Rolls-Royce *Griffon* engine was designed in answer to Royal Naval specifications for an ..... The *Griffon* engine drove an 11 ft (3.35 m) diameter five-bladed *propeller*, some 7 inches (17.8 cm) larger than that fitted to the Mk XIV."
> 
> But when I read the article it states what you say 10ft 5in 5 blade Rotol.
> Supermarine Spitfire (Griffon-powered variants) - Wikipedia



That was for the 20-series Spitfires, which had a new wing and extended undercarriage legs.


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## Aozora (Oct 26, 2017)

For interest, attached is a Flight magazine article on Fuel Development from June 1945: of note is the comment that
"The Air Ministry had the foresight to realise the critical importance of high-duty fuels, and had issued a specification for 100 octane in March 1937 - _sufficiently before the war to enable our fighters to use it from the very start,_ _although it did not come into general use throughout the whole of the RAF until August 1940." (bottom of page 612 to 613)_
Also attached are pages from the official _Weekly Oil Position Reports (WOPRs)_: these were cabinet papers, issued to Britain's War Cabinet, outlining details of the quantities of oil and petroleum products that were being shipped to Britain, and the stockpiles of the same. Note that as of 31 August 1939, there was already 153,000 imperial tons of 100 octane aviation spirit available.


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## GregP (Oct 26, 2017)

I do not believe the Spitfire was limited by the prop at all. They chose what they chose, for reasons they believed were important, and I have no access to those limitations. ALl I can say is the two fastest piston driven planes related to WWII fighters have props that are smaller, but not substantially so, than stock.

The world's fastest propeller-driven aircraft to date, the Tu-95, has 18-foot diameter props that have the tips moving at supersonic speeds. As far as I know, it is the only such aircraft regularly flying anywhere in the world. We had some supersonic prop research planes, but they didn't seem practical to us.


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## wuzak (Oct 27, 2017)

The fact that the 20-series Spitfires with the new wings and extended landing gear got props which were 7in larger in diameter would suggest that there was a deficiency in the prop for the XIV/XVIII.

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## GregP (Oct 27, 2017)

If you say so, Wayne. I've done a LOT of prop experiments on RC planes and I can get equivalent performance with at least 4 - 6 different props, sometimes oif wildly different diameters.


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## Milosh (Oct 27, 2017)

Hard to put a larger diameter prop on a Spitfire when there is only a few inches of ground clearance. It didn't take much to get a prop strike when taking off.


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## GregP (Oct 27, 2017)

I'd think the "different" prop on a Spitfire would be a shorter one ... to avoid said groundstrike.

All my fast RC racing was with props 20% shorter than when sport flying, with considerably more pitch. You go up in pitch until you don't have the power to spin it fast enough, and back off slightly --> fast.


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## pbehn (Oct 27, 2017)

wuzak said:


> The fact that the 20-series Spitfires with the new wings and extended landing gear got props which were 7in larger in diameter would suggest that there was a deficiency in the prop for the XIV/XVIII.


It suggests to me that Supermarine wanted a bigger prop all along but were restricted by the undercarriage geometry. When the undercarriage was lengthened a bigger prop was fitted.


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## Shortround6 (Oct 27, 2017)

GregP said:


> I'd think the "different" prop on a Spitfire would be a shorter one ... to avoid said groundstrike.
> 
> All my fast RC racing was with props 20% shorter than when sport flying, with considerably more pitch. You go up in pitch until you don't have the power to spin it fast enough, and back off slightly --> fast.



With all due respect, the RC planes were operating pretty much with one air density, with changes in temperature at your flying field/s.
Trying to fly at the top of Pike's Peak with same prop you used at sea level might have somewhat different results?


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## GregP (Oct 27, 2017)

You try to optimize for conditions always. But optimizing a real prop (fixed pitch) is not about atmospheric conditions at all. You optimize for the situation (cruise, climb, top speed) you want most at standard conditions. If you have a constant-speed. you optimize for expected low and high speed (and maybe for rough fields) under standard conditions.

Then you go fly in the real air, and adjust as required.

I might fit a different prop if I were based in SIberia all the time. But if I had a number of airplanes moving around the world, I'd optimize for standard conditions and fly them.


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## Aozora (Oct 27, 2017)

pbehn said:


> It suggests to me that Supermarine wanted a bigger prop all along but were restricted by the undercarriage geometry. When the undercarriage was lengthened a bigger prop was fitted.


That's more than likely: according to Morgan & Shacklady, the new "_...oleos were lengthened and strengthened to cope with the large diameter propellers...". _The F. Mk XIV & XVIIIs used a 10ft 5in diameter Rotol R19/5F5/1, whereas on the F. Mk 21/22/24s, the propeller was a Rotol R14/5F5/2 of 11ft 10in diameter. The maximum speeds of the 20 series Spitfires increased by about 10-15 mph over the XIV/XVIII using the same Griffon 61/65s.


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## pbehn (Oct 27, 2017)

Aozora said:


> That's more than likely: according to Morgan & Shacklady, the new "_...oleos were lengthened and strengthened to cope with the large diameter propellers...". _The F. Mk XIV & XVIIIs used a 10ft 5in diameter Rotol R19/5F5/1, whereas on the F. Mk 21/22/24s, the propeller was a Rotol R14/5F5/2 of 11ft 10in diameter. The maximum speeds of the 20 series Spitfires increased by about 10-15 mph over the XIV/XVIII using the same Griffon 61/65s.


Thankyou, I pick up "stuff" from many sources but cant quote them. One of the "tricks" of the original Spitfire design came to haunt it later was the undercarriage set up it limited the prop diameter and made the later versions tricky on take off and landing, just like its only adversary the Bf109 which was also designed around a circa 1000BHP engine.

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## drgondog (Oct 31, 2017)

BiffF15 said:


> Bill,
> As a CROT (crude rule of thumb) could one compare the equivalent Spitfires with Merlin / Griffon engines for fuel flow differences to get a "rough" hack at what a Griffon Mustang would have burned? And from that extrapolate a "rough" hack at it's range with or without external fuel tanks?
> Cheers,
> Biff


Maybe. Because a.) the drag co-efficient is higher on a Spit XIV than a B Mustang, and the Griffon, as geared, dropped Hp delivered rapidly above 22K+ feet at equivalent RPM/Boost it would be hard to extract SFC at 25K+ where the Mustang was king for 8th AF escort. The RAF flew very few mission types above 15,000 feet, so the gearing was designed for a lower altitude peak performance.

If Flight tests for range, clean, existed for the Griffon/Spit accompanied by Hp as function of altitude and boost a CROT could be extracted

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## drgondog (Oct 31, 2017)

wuzak said:


> The Griffon had similar power at 20-25,000ft with 100/130 grade fuel and +18psi boost (67inHg MAP) as the V-1650-9 did with 90inHg MAP and ADI.
> 
> The Griffon-Mustang discussion was occurring when the Mustang X and P-51B programs were in their initial stages. The Griffon Mustang would have predated the P-51H by a year or so. Certainly the 100 series Merlins (of which the V-1650-9 was one) had yet to be developed at that time.
> 
> The Griffon Spitfire (XIV) was 30-40mph faster than the equivalent Merlin Spitfire (VIII), depending on the sub type (F, LF, HF) and the Merlin variant used (63, 66, 70). Certainly the Mustang was as fast as the Griffon Spitfire, but it was quite a bit faster then the Spitfire with the same engine.


Wuzak, I don't believe that a Griffon could have been adapted for first flight on or around the February 1944 timeframe without a major disruption of P-51D airframes. The XP-51F was first flying with 1650-3 in mid Feb and the first series production D also first flew in February. The modified Merlin 145 (SM 14) type was installed in the same airframe for the XP51G (with cooling and engine mount mods flew August 1944 - Just six months before production P-51H


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## wuzak (Oct 31, 2017)

drgondog said:


> Wuzak, I don't believe that a Griffon could have been adapted for first flight on or around the February 1944 timeframe without a major disruption of P-51D airframes. The XP-51F was first flying with 1650-3 in mid Feb and the first series production D also first flew in February. The modified Merlin 145 (SM 14) type was installed in the same airframe for the XP51G (with cooling and engine mount mods flew August 1944 - Just six months before production P-51H



The original discussions relating to putting a Griffon in the Mustang were taking place in late 1942. 

Any effort on that project would likely have detracted from the P-51B program. 

The main issue for production would be the supply of Griffons. There wasn't enough production historically to supply NAA as well as Supermarine and Fairey. So it would need a licence version built in the US. Maybe at the Continental plant which was originally to build the IV-1430, but ended up building Merlins (in small numbers?) instead.

Changing over to a Griffon variant would also have cost time and reduced the numbers of P-51Bs built.

I think in reality the only way a Griffon P-51 would have emerged is if they committed to it from the start, instead of the Merlin P-51. But it would have required Packard Griffons, or similar.

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## drgondog (Nov 1, 2017)

wuzak said:


> The original discussions relating to putting a Griffon in the Mustang were taking place in late 1942.
> 
> Any effort on that project would likely have detracted from the P-51B program.
> 
> ...


I pretty much agree Wuzak. That said, the gating factor that delayed delivery of P-51B-1-NA to ETO was the gestation period at Packard to tool up for the 1650-3 changes from 1650-1, then pass bench tests at Wright Pat, and subsequent production. I suspect that a.) concluding negotiations to build Griffon in US, particularly with political forces arrayed (MC/GM/Allison) against yet another Brit engine - then convert drawings, and tool up for production for Griffon, then direct NAA to redesign the P-51B/D for Griffon - would heve never made it past the sniff test when 8th AF was getting Hammered.

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