P-39 and P-63 Data

[thunderbird]

Being a fan of the P-39, i also am a realist. There were many missed opportunities that are hard to understand in hindsight. i wonder these days why the Rolls Royce two stage two speed aftercooled supercharger from the Merlin 61 couldn't be adapted to the Allison V-1710? Why couldn't Allison get ahold of a Packard Merlin Mk 61 and reverse engineer its supercharger? Why didn't the British consider dropping the Merlin Mk 61 into the P-39 or even the P-40? Certainly the experiment of dropping the Merlin XX into the P-40 showed that there was no improvement switching one single stage motor for another.

Of course, part of the secret to the P-51's success was actually its build quality. I saw a P-39 static display in a mall in Buffalo, NY, and was apalled at the workmanship of the external skins. I don't know whether they all came out of the factory looking like they'd fallen off the truck, but i have a suspicion that they did. Maybe the British were also appalled at the build quality of their P-39s and immediately gave up on them.

The fascinating thing about both British and German engineering is that both actively looked for and implemented improvement on their aircraft, and quickly enough to get the improved aircraft into combat.

Another case of American ineptitude, the Chance Vought turbocharged F4U-3. C-V never got it to work, and yet, why couldn't they tear apart a P-47 to see how to make it work? They would have had F4U-5 type performance in early 1943 if they had.

 

[FLYBOYJ]

I saw a P-39 static display in a mall in Buffalo, NY, and was apalled at the workmanship of the external skins. I don't know whether they all came out of the factory looking like they'd fallen off the truck, but i have a suspicion that they did. Maybe the British were also appalled at the build quality of their P-39s and immediately gave up on them.

A few things - a static display is an extremely poor platform to make any real world comparisons. Many times static display aircraft have been tossed around and reclaimed from discarded hulks and are put together just good enough to have a talking point.

Now when you talk about "workmanship," what are the specifics? Riveting? Buckled skins? Dents?

 

[Shortround6]

i wonder these days why the Rolls Royce two stage two speed aftercooled supercharger from the Merlin 61 couldn't be adapted to the Allison V-1710?

I don't know how much adopting it would take. It took Allison almost a year to switch from the 8.80 supercharger gears to the 9.60 supercharger gears because there wasn't enough space inside the accessories drive case for the larger (thicker) gears the higher gear ratio needed to handle the higher power needed. The way the Allison was designed they needed to redo the crankcase casting to make the room as the space for the gears were contained in a recess in the block casting.
Supercharger drives need to transmit hundreds of horsepower and when you get to the impellers themselves they are running, in the case of the 9.6 gears at 28,800 rom which calls for very careful mounting.
Allison was also working on their own two stage system.
AND what many people tend to forget, it just wasn't the supercharger casings and impellers. You need room for the intercoolers and their ducts.
You also need larger radiators/oil coolers for the two stage engine. If you are making another 200 or more HP in the cylinders to drive the bigger supercharger to get the same HP to the propeller shaft thousands of feet higher you need to provide cooling for the extra power being generated. You also have to figure out how to provide the cooling air needed in the higher, thinner air (more cubic feet per minute needed)

Certainly the experiment of dropping the Merlin XX into the P-40 showed that there was no improvement switching one single stage motor for another.

Well, the Merlin XX did improve the altitude capability of the P-40 by about 5,000ft if not more, depending on the gear ratio in the Allison.

Another case of American ineptitude, the Chance Vought turbocharged F4U-3. C-V never got it to work, and yet, why couldn't they tear apart a P-47 to see how to make it work? They would have had F4U-5 type performance in early 1943 if they had.

A couple of things. They knew how a P-47 worked, it used a very large fuselage full of ducts and a very large intercooler. It also used a GE turbo and it used several generations of turbo (later ones could turn higher rpm without throwing blades/self destructing) and different turbo controllers.
GE turbos did not like to mounted close to the engine, they liked being 5-8 feet away to let the exhaust cool off before hitting the turbine blades to avoid the turbine blades overheating and failing. P-47 used a much longer pathway in part because they didn't run the exhaust pipes on the outside of the plane for cooling.

Fitting the P-47 system into the smaller F4U airframe using the available 1942/early 43 parts was going to be more difficult than using 1944-46 parts.

For some reason the Navy went with the Birmann turbo. Supply issues with GE?
And again GE changed the rpm limit of the turbo from 18,250rpm to 22,000rpm by the time you get to the P-47D so make sure you are basing the comparison on the available components.

 

[tomo pauk]

Why didn't the British consider dropping the Merlin Mk 61 into the P-39 or even the P-40?

Merlin Mk.61 will not fit on the P-39, not least because a Merlin will be needing the new crankcase without a reduction gear so the extension shaft does not go through the pilot.
There was not enough of Merlin 61s for the Spitfire anyway, and there was a lot of much better airframes (Mustang, Spitfire, Mosquito, Lancaster...) for a 2-stage supercharged Merlin than it was the P-39, that was represented in the UK by token number anyway.

Certainly the experiment of dropping the Merlin XX into the P-40 showed that there was no improvement switching one single stage motor for another.

I'm not sure what kind of experiment that was. There was a real-world effort to produce a better-performing fighter than the P-40E, and P-40F was exactly that.
One-stage supercharged Merlin of the day was a much better engine than contemporary an one-stage supercharged V-1710, much because the Merlin's superchargers were bigger.

Of course, part of the secret to the P-51's success was actually its build quality. I saw a P-39 static display in a mall in Buffalo, NY, and was apalled at the workmanship of the external skins. I don't know whether they all came out of the factory looking like they'd fallen off the truck, but i have a suspicion that they did. Maybe the British were also appalled at the build quality of their P-39s and immediately gave up on them.

P-39 was a sleeker aircraft than the Spitfire or P-40, even if it was not as sleek as P-51. Problem with P-39 was that it's engine was sub-par. Note that racer P-39s were winning the races.
British gave up on P-39s because these were over-sold and under-performing.

The fascinating thing about both British and German engineering is that both actively looked for and implemented improvement on their aircraft, and quickly enough to get the improved aircraft into combat.

British and Germans were very close to the actual fighting, so their improved (and many times troublesome, like the Fw 190 or Typhoon, or Panther tank) kit was being thrown in the battles very fast. American ww2 started later, they were not as pressured as the European militaries, and it took months for their gear to arrive to the front lines for the reasons the Americans can't be held accountable.
Americas were also looking for the improvement of their aircraft, let's not sell them short.

Another case of American ineptitude, the Chance Vought turbocharged F4U-3. C-V never got it to work, and yet, why couldn't they tear apart a P-47 to see how to make it work? They would have had F4U-5 type performance in early 1943 if they had.

Why should, in early 1943, the turbocharged F5U-3 gain the performance of the F4U-5?

 

[GregP]

At Yanks Air Museum in Chino, CA, we have a P-39. The workmanship is excellent.

There is another air museum at Chino, the Planes of Fame. They have a static P-39 and it looks like it was ridden hard and put up wet. The difference is basically one is fairly beaten up and has corrosion issues and the other was never really mistreated.

I don't agree Tomo's assertion that the Allison was so much worse than the Merlin. The Merlin WAS better at the time, but not a LOT better. Yes, the Merlin had a bigger supercharger wheel, but the basic Allison engine was a decently good one with a couple of faults that were rectified decently quickly. However, most of the early Allisons were never really pushed very hard. Early P-39s were operated at some 39.5" of MAP, while the Soviet Union pushed theirs to 60", 70" or 75". I'm talking -39 or -73 Allisons.

The difference was amazing: 1,050 to 1,150 hp at 39" MAP versus War Emergency outputs of 1,570 hp @ 3,000 rpm and 60" MAP; 1,745 hp at S.L. at 66" MAP and 3,000 rpm; and 1,780 hp at 70" MAP @ 3,000 rpm at S.L. and 3,200 rpm at low altitudes. These numbers are right there with the Merlin outputs and a bit better in some cases, depending on the boost you are talking. The single-stage Merlin DID have a bigger supercharger wheel and it WAS better at above 15,000 feet. But the real culprit in the Allison versus Merlin story is the service-recommended conservative operation of the Allison.

There is a pdf you can find with the Allison-recommendations dated Dec 12, 1942 that shows these power settings and also recommends NOT using MAP above 60" on Allison models with the 9.6 : 1 supercharger gears, while perhaps allowing higher MAP in the Allisons with 8.8 : 1 supercharger gears. The difference is the margin from detonation temperature above 120°F at the intake.

You can find the Allison pdf letter online at: http://www.wwiiaircraftperformance.org/P-40/V-1710_Service_Use_of_High_Power_Outputs.pdf

The P-39 (not the P-400) performed decently at lower altitudes and within short ranges, but that envelope wasn't all that useful in the ETO. They needed higher-altitude performance and longer ranges. As such, the P-39 simply wasn't well-suited for ETO use and, as a result, wasn't much used by the U.S.A. or the UK. The Merlin did, indeed, turn out to be a better-performing engine in the ETO, due more to the supercharger setup than any other reason, and everyone in here knows the Merlin was and IS a great engine. But the Soviet Union DID find the P-39 performance niche useful (at higher -than-recommended boost levels) and DID use P-39s to very good results in support of ground operations and in low-altitude, short-range fighter operations.

The P-63 was very much better than the P-39, though the U.S.A. didn't adopt it. The 2-stage Allison-powered P-63 would give a P-51 everything it could handle, but still wasn't exactly a long-range aircraft and it was also about 15 mph slower than the P-51 at top speed. Shorter range and lower top speed meant that even if it handled a bit better than a P-51 (subjective, at best), it wasn't going to be a step forward in capability. Lacking that "step forward," there was no real reason to put it into production for the USAAF.

But, the largest user of the P-39, the Soviet Union, still needed fighters, and it was put into production for Soviet Lend-Lease. They operated most of the 3,300 built with good results.

 

[Conslaw]

Being a fan of the P-39, i also am a realist. There were many missed opportunities that are hard to understand in hindsight. i wonder these days why the Rolls Royce two stage two speed aftercooled supercharger from the Merlin 61 couldn't be adapted to the Allison V-1710? Why couldn't Allison get ahold of a Packard Merlin Mk 61 and reverse engineer its supercharger? Why didn't the British consider dropping the Merlin Mk 61 into the P-39 or even the P-40? Certainly the experiment of dropping the Merlin XX into the P-40 showed that there was no improvement switching one single stage motor for another.

Of course, part of the secret to the P-51's success was actually its build quality. I saw a P-39 static display in a mall in Buffalo, NY, and was apalled at the workmanship of the external skins. I don't know whether they all came out of the factory looking like they'd fallen off the truck, but i have a suspicion that they did. Maybe the British were also appalled at the build quality of their P-39s and immediately gave up on them.

The fascinating thing about both British and German engineering is that both actively looked for and implemented improvement on their aircraft, and quickly enough to get the improved aircraft into combat.

Another case of American ineptitude, the Chance Vought turbocharged F4U-3. C-V never got it to work, and yet, why couldn't they tear apart a P-47 to see how to make it work? They would have had F4U-5 type performance in early 1943 if they had.

The turbocharger in the XF4U-3B worked reasonably well for an experimental program, propelling the prototype to around 480 MPH. It worked well enough that the Navy ordered 26 preproduction units, and 13 were delivered. The thing is, the turbocharger wasn't the GE model that was already in production for the P47 and was already sorted out. It was a different model from a company called TEC (Sometimes called Birman). Even if development and production went perfectly smoothly, there was little chance that a turbocharged F4U before the end of the war, and even if it was, it may not have any practical benefits over the F4U-4, since the performance improvements were over 30,000 feet, and Navy planes rarely had to go that high.

 

[Wild_Bill_Kelso]

How did the turbo fit? I thought I saw an image of an F4U with a turbo, it looked pretty kludgy. 480 mph at 30k feet would make the F4U much more viable in Europe though.

 

[Wild_Bill_Kelso]

Is this the beast in question?

(Edit, I tried to post this earlier with my phone but it didn't take)

 

[GregP]

XF4U-3B diagram.

 

[ThomasP]

XF4U-3 performance data

 

[drgondog]

Being a fan of the P-39, i also am a realist. There were many missed opportunities that are hard to understand in hindsight. i wonder these days why the Rolls Royce two stage two speed aftercooled supercharger from the Merlin 61 couldn't be adapted to the Allison V-1710? Why couldn't Allison get ahold of a Packard Merlin Mk 61 and reverse engineer its supercharger? Why didn't the British consider dropping the Merlin Mk 61 into the P-39 or even the P-40? Certainly the experiment of dropping the Merlin XX into the P-40 showed that there was no improvement switching one single stage motor for another.

Multiple reasons. The RAF gave up completely on the P-400 before the first Merlin 61 was installed on a Spit V for test (and Mustang I). Second reason is that both R-R and Packard were under capacity for demand of the Merlin 60 series - and the P-51B received highest priority which cut Curtiss, Lockheed and Bell completely out of the loop. An example includes the killing of Kelsey's 'dream' for Merlin powered P-38K in late spring 1944 by 'higher authority'. Next, the Merlin 60 series a.) did not fit, b.) wold have required the same re-design of wing attach to account for aft cg as the P-63.

The P-40 cooling requirements increased for Packard 1650-1 and would have 'jumped' agin by approximately 30%+ to accomodate cooling requirements. It would have been interesting to listen to the re-design options for cooling system - almost certain to resolve to increase of frontal radiator area and susequent drag - negating signiicant improvement in top speed at high blower.

Of course, part of the secret to the P-51's success was actually its build quality. I saw a P-39 static display in a mall in Buffalo, NY, and was apalled at the workmanship of the external skins. I don't know whether they all came out of the factory looking like they'd fallen off the truck, but i have a suspicion that they did. Maybe the British were also appalled at the build quality of their P-39s and immediately gave up on them.

The build quality was fine, not as good as NA surface quality, but still good for 1930s production design and processes. P-39 parasite drag was nearly equivalent to P-51 when full scale wind tunnel testing was performed at Langley. Superior to P-38, P-40 and P-47.

The fascinating thing about both British and German engineering is that both actively looked for and implemented improvement on their aircraft, and quickly enough to get the improved aircraft into combat.

Another case of American ineptitude, the Chance Vought turbocharged F4U-3. C-V never got it to work, and yet, why couldn't they tear apart a P-47 to see how to make it work? They would have had F4U-5 type performance in early 1943 if they had.

So, what? The USN mission never included mandate for hgh altitude (>25K) performance during WWII. The superturbo charged F4U would not have superior performance over P-47D and have less Combat Radius, so never a consideration for long range escort for heavy bombers at high altitude. As to introducing a 'bug free' F4U-3 into combat ops in 1943? IMO - No chance that it replaces F4U-1 operationally and for a variety ofreasons - ever replace F4U as produced.

 

[Reluctant Poster]

XF4U-3 performance

Note that this is estimated performance not actual

Also note that the performance is not impressive

 

[Reluctant Poster]

The turbocharger in the XF4U-3B worked reasonably well for an experimental program, propelling the prototype to around 480 MPH. It worked well enough that the Navy ordered 26 preproduction units, and 13 were delivered. The thing is, the turbocharger wasn't the GE model that was already in production for the P47 and was already sorted out. It was a different model from a company called TEC (Sometimes called Birman). Even if development and production went perfectly smoothly, there was little chance that a turbocharged F4U before the end of the war, and even if it was, it may not have any practical benefits over the F4U-4, since the performance improvements were over 30,000 feet, and Navy planes rarely had to go that high.

480 MPH? Is that an actual test? That number is very hard to believe and is completely contradicted by the performance calculations posted by ThomasP. 412 mph at 30,000 feet is a far cry from 480.

 

[ThomasP]

I think the 480 mph at 30,000 ft is supposed to be for the FG-3 Corsair variant. Goodyear rebuilt 13x FG-1 airframes to the XF4U-3B standard, designating them FG-3. On page 2 of the PD attached below, toward the bottom, it lists the Vmax in Clean condition as [469] mph at 33,600 ft. But it should be noted that the first flight of the FG-3 was sometime in 1945.

 

[GregP]

XF4U-3 performance data

Anyone know if these speeds are IAS or TAS?

Nevermind. Cannot be IAS!

Let's say the 412 was CAS and it is a standard day, that equates to 358 knots or 673 mph! No way. The numbers MUST be TAS mph.

 

[Reluctant Poster]

I think the 480 mph at 30,000 ft is supposed to be for the FG-3 Corsair variant. Goodyear rebuilt 13x FG-1 airframes to the XF4U-3B standard, designating them FG-3. On page 2 of the PD attached below, toward the bottom, it lists the Vmax in Clean condition as 369 mph at 33,600 ft. But it should be noted that the first flight of the FG-3 was sometime in 1945.

The best speed quoted here is 460 mph at 33,400 feet and once again it is calculated not an actual test.

 

[ThomasP]

Sorry, typo! Edited my post above. The 369 should be 469, see below:

 

[Reluctant Poster]

Sorry, typo! Edited my post above. The 369 should be 469, see below:

View attachment 674982

I would still like to see an actual test. Paper airplanes often fly much better than in reality.

 

[ThomasP]

I agree.

But the F4U airframe was pretty well understood. I ran some basic numbers using the F4U-4 data (which is from flight tests).

Normal poser for the F4U-4 was 1550 BHP at 28,000 ft. From actual flight tests the F4U-4 - with 2x pylons and a 1x 150 USgal DT - did 399 mph at 31,400 ft.

Normal power for the FG-3 was 1700 BHP at 37,800 ft. If we assume the drag for a clean FG-3 was approximately the same as for the F4U-4 with 1x 150 USgal DT, then I come up with ~460 mph at ~42,600 ft using Normal power. Since the calculated values in the FG-3 PD I posted give the Normal power Vmax as 440 mph clean at 42,600 ft and 413 mph with 1x DT at 42,200 ft, they were either using higher drag values than for the F4U-4, or they were assuming the FG-3's propeller could not utilize the power available at that altitude, or both.

 

[drgondog]

I agree.

But the F4U airframe was pretty well understood. I ran some basic numbers using the F4U-4 data (which is from flight tests).

Normal poser for the F4U-4 was 1550 BHP at 28,000 ft. From actual flight tests the F4U-4 - with 2x pylons and a 1x 150 USgal DT - did 399 mph at 31,400 ft.

Normal power for the FG-3 was 1700 BHP at 37,800 ft. If we assume the drag for a clean FG-3 was approximately the same as for the F4U-4 with 1x 150 USgal DT, then I come up with ~460 mph at ~42,600 ft using Normal power. Since the calculated values in the FG-3 PD I posted give the Normal power Vmax as 440 mph clean at 42,600 ft and 413 mph with 1x DT at 42,200 ft, they were either using higher drag values than for the F4U-4, or they were assuming the FG-3's propeller could not utilize the power available at that altitude, or both.

ThomaP - if the FTH of the Turbosupercharged engine (at 37,800 ft) was 1700BHP, the Hp would have reduced considerably by the time it reached 42K?

I suspect that the prop tip velocities would also been supersonic to add considerable drag. Uness a Cd vs RN plot is available as well as a CD vs CL for increasing pressure drag as a function of increasing altitue/lower density, more data elements are absent to estimate Vmax at that altitude which would be deep into compressibility drag rise?