P-40 Performance - Allison versus Merlin

[wuzak]

1. P-40B: top speed 352 mph on 1,040 HP (1710-33), climb rate 14.5 m/s initial.
2. P-40E: top speed 360 mph on 1,150 HO (1710-39), climb rate 10.7 m/s initial.
3. P-40F: top speed 364 mph on 1,300 HP (1650-1), climb rate averaged 83.8 m/s to 6,100 m (wish they gave initial climb rate!)
4. P-40N: top speed 378 mph in 1,200 HP (1710-81), climb rate 11.4 m/s initial.

Wow..the P-40F had a climb rate 8 times that of the P-40E!

Since the 1650-1 was a single-stage Merlin, what difference was expected?

The -1 was a single stage 2 speed Merlin. It had the improved supercharger of the Merlin XX, so its performance would theorteically be moved higher in altitude. Because ofthe 2 speed supercharger the loss of performance at lower altitudes would have been minimised.

If they had used a 2-stage, multi-speed Merlin .... maybe it would have been interesting. Of course, then, to be fair, they'd have to fit an Allison with a competitive system (aux stage or turbo). That might have needed a different airframe ...

Certainly a turbo system or the Allison 2 stage system would have required a lot of work on the P-40 airframe. The 2 stage Merlin was not much longer than the original Allison, but quite a bit heavier. Some weights would have to have been readjusted, and extra cooling would have been required.

I see that some of this has been commented on by others but, really, the Merlin-powered P-40F was no better than the Allison-powered one, unless a 2,000 foot ceiling difference was being deemed important. I doubt seriously that anyone wanted to fight a P-40 at 30,000+ feet anyway. the real question of interest would be a comparison at 10,000 - 15,000 feet, where it was employed in combat.

It would appear that the P-40F had roughly the same performance as the E at the E's best altitude, but the F's best altitude was about 8000ft higher. (P-40E 342mph @ 11,400ft, 340mph @ 15,300, P-40F 350.5mph @ 12,800ft, 364.5mph @ 19,270ft).

http://www.wwiiaircraftperformance.org/P-40/P-40E_40-384_PHQ-M-19-1300-A.pdf
http://www.wwiiaircraftperformance.org/P-40/P-40F_41-13601_PHQ-M-19-1440-A.pdf
P-40 Performance Tests

Since they installed a single stage Merlin, I'm pretty sure nobody expected it to be better by any significant amount. Maybe that was the point of the exercise ... to demonstrate the equivalence of the two installations. That it certainly did.

The point of the exercise was to use the V-1650-1s that the USAAF were getting under the terms of the Packard agreement (1/3 of Packard production was to go the the USAAF).

 

[wuzak]

1. P-40B: top speed 352 mph on 1,040 HP (1710-33), climb rate 14.5 m/s initial.
2. P-40E: top speed 360 mph on 1,150 HO (1710-39), climb rate 10.7 m/s initial.
3. P-40F: top speed 364 mph on 1,300 HP (1650-1), climb rate averaged 83.8 m/s to 6,100 m (wish they gave initial climb rate!)
4. P-40N: top speed 378 mph in 1,200 HP (1710-81), climb rate 11.4 m/s initial.

What is the source for these figures Greg?

 

[GregP]

Boy Kreighund, are your numbers for the Allisons in post # 16 somewhat misleading or what?

You picked 2-stage engines in the -93, -109, -117, and -121. The first three are E motors (driveshaft engines) and are P-63 engines. The last one is an F28 (F motors had propellers mounted) and only 4 were built for the XP-40Q, so it was an oddball. The real numbers are as follows:

E11 (1710-93): 1,325 HP for TO; 1,180 HP @ 21,500 feet; 1,800 HP WER. 2,521 built.
E22 (1710-109): 1,425 HP for TO; 1,100 HP @ 28,000 feet; 1,750 HP WER. 222 built.
E21 (1710-117: 1,325 HP for TO; 1,000 HP @ 25,000 feet; 1,800 HP WER. 2,237 built.
F28 (11710-121): 1,425 HP for TO; 1,100 HP @ 28,000 feet; 1,700 HP WER. 4 built.

So, you can see that the Allison didn't do too badly when you consider that the low HP ratings were all at altitude, where ALL WWII engine had somewhat lower ratings than at sea level.

Oh yeah, numbers from Dan Whitney's Vee's for Victory. We regularly get the sea level takeoff numbers from the the E and F engines we build and ship today (single stage, no aux stage), and can get better if anyone wants to race an Allison. Bring money; it ain't cheap. Nobody wants to fly their warbird these days IFR at 20,000 + feet; they'd rather fly VFR and play fighter pilot than waste their gas straight and level flying IFR. One last point, most of our single-stage E and F have a WER rating of about 1,600 HP @ 3,000 RPM. You can get more if you blip the RPM up to 3,200 or 3,400.

We have 5 or more tractor pullers who run them regualrly at 4,000 - 4,500 RPM. They get great HP and stomp all over the Merlin tractors in Europe. The European Tractor Pull Association tried to outlaw the Allison by limiting aircraft engine tractors to 1650 cubic inches and we simply made an Allison V-1650 and continued to beat them. They gave up and re-allowed the V-1710. We have one customer in the Netherlands who has been running our Allisons on the same tractor for 6+ years at 4,500 RPM+ with nothing but regular maintenance (oil changes, clean the screens, change plugs, etc.). He just ordered a sparre engine because he is expecting one to break. So far, it hasn't, but he wants to be covered in case.

If anybody really WANTS a two-stage Allison, we have two auxilliarly stage superchargers ready for overhaul and sale. We can even deliver a turbo setup if anyone really wants one. So far, nobody does since they stay at VFR altutudes.

 

[GregP]

Sorry Wuzak, typo as I'm sure you know. I went back and corrected it and noted that in the edit note area. The P-40F average 8.8 m/s to 6,100 m. The references didn't give an initial climb rate for the F but rather a time to 6,100 m. It would be handy if they had a standard climb test so we could campare apples to apples, wouldn't it?

Source? http://en.wikipedia.org/wiki/Curtiss_P-40_variants. I know Wiki isn't generally all that great, but a quick check with some of my other references shows the same numbers for the variants. I'm sure you can check yours, too.

Let's see, a reference for the P-40N top speed. How about Curtiss P-40N Warhawk - Manufacturer was Curtiss (USA), or Curtiss P-40N Kittyhawk, or Variants P-40N. I could go on, but three is enough, I think. Also, our museum flies a P-40N and it WILL go that fast (TAS, not IAS), even with someone like me in the back seat looking at the ASI. Faster if they go to 3,200 or 3,400 rpm! ... as they have done in the past.

They made 13,739 P-40's. If the F was so good, how come they only made 1,082 of them and phased it out for later P-40 models? Personally, I like the P-40F without the carburetor scoop on top of the cowling. But it wasn't much of an improvment over the Allison version and nobody fought P-40's at high altitude unless there was no other option. It's hard to believe there wasn't a better plane for combat at altitudes over 15,000 feet! My bet on the questiomn above is they stopped making the single-stage Merlins and concentrated on 2-stage units. if so, why didn't they try a 2-stage Merlin in a P-40?

Of course, if they had a 2-stage, multi-speed supercharged version of the Merlin in it, that might have been different, as stated above. I'd like to have seen that model built and tested. Maybe it would have lived up to Don Berlin's intentions. I'd imagine that if true, it would have been a good performer, but maybe not quite as good as high-altitude P-51's or P-47's. I'd still like to know.

I read somewhere years ago that Don Berlin had been allowed to make ONE 2-stage P-40 just so he could prove it out. But I can't find that reference again and cannot remember if it was a 2-stage Allison, a turbocharged Allison, or a 2-stage Merlin. I wasn't into the engines at the time and simply cannot recall. If anyone out there definitely knows, please post! It hardly matters if only one was made, but would be an interesting footnote for the sake of the knowledge.

 

[wuzak]

Variants P-40N.

This site has a lower top speed listed.

One 1200 hp Allison V-1710-81 twelve-cylinder liquid-cooled engine. Maximum speed 208 mph at 5000 feet, 325 mph at 10,000 feet, 343 mph at 15,000 feet. Maximum climb rate was 2120 feet per minute at 5000 feet, 2230 feet per minute at 10,000 feet.

Perhaps the difference between the V-1710 having WEP and not?

Also, note that the P-40N is a lightweight version, with lighter structure and 2 fewer guns, and so is not directly comparable with the P-40F.

 

[wuzak]

The P-40F average 8.8 m/s to 6,100 m. The references didn't give an initial climb rate for the F but rather a time to 6,100 m.

This report has an initial climb rate of 2100ft/min (10.7m/s) at sea level and a peak climb rate of 2210ft/min (11.2m/s) at 9600ft.

Also, our museum flies a P-40N and it WILL go that fast, even with someone like me in the back seat. Faster if they go to 3,200 or 3,400 rpm! ... as they have done in the past.

Earlier P-40s with earlier V-1710s would not have had 3200rpm allowed, let alone 3400rpm. As Tomo pointed out, the N was more than a year after the F.

They made 13,739 P-40's. If the F was so good, how come they only made 1,082 of them and phased it out for later P-40 models?

Engine availability.

Personally, I like the P-40F without the carburetor scoop on top of the cowling. But it wasn't much of an improvment over the Allison version and nobody fought P-40's at high altitude unless there was no other option. It's hard to believe there wasn't a better plane for combat at altitudes over 15,000 feet!

There was....and that's why they didn't get more Merlins.

The USAAF were getting only a portion (1/3) of Packard production, and when the P-40 was coming on-line so was the P-51B.

Of course, if they had a 2-stage, multi-speed supercharged version of the Merlin in it, that might have been different, as stated above. I'd like to have seen that model built and tested. Maybe it would have lived up to Don Berlin's intentions.

Don Berlin really wanted the 2 stage Merlin for the P-40. But would it have been worth the effort?

 

[krieghund]

Boy Kreighund, are your numbers for the Allisons in post # 16 somewhat misleading or what?

I believe the question was about the engine in the XP-40Q being the same as installed in the P-63?

The data I provided gave the answer, no it was from a different series but had similar powers, I wasn't concerned about production numbers.

This is the V-1710-119 in the Mustang. This would have worked in the 'Q' as well, to bad they didn't allow the use of the ADI when flight testing this aircraft.

 

[Jabberwocky]

I don't know if I've ever seen the 378 mph figure in primary documentation, certainly not in testing data. Generally speaking, tested P-40Ns seem to max out at about 360 mph, with the lowest figures down under 350 mph and the best at about 365 mph.

Remember though that the performance of test aircraft varied wildly. The RAF and USAAF P-40F tests have top speeds as high as 374 mph in one test with a cleaned up example and as low as 342 mph in RAAF tests with a war-weary example.

The RAAF and RAF operated a lot of P-40Ns and I've got a few of their service tests on hand. The best speed data I have on hand from their testing is the following:

August 1943 RAAF data sheet:

364 mph at 17,200 feet for P-40N (unidentified sub-type, V-1710-81, MP not given)
312 mph at sea level, conditions as above

October 1943 RAF data

359 mph at 12,000 ft with P-40N-1 with V-1710-81 at 52" manifold pressure (5 minute war emergency)

March 1944 RAAF testing

344 mph at 17,000 ft for a P-40N-5 with V-1710-81 at 44" manifold pressure (15 minute military power)
352 mph at 9,200 ft for P-40N-5 with V-1710-81 at 57" manifold pressure (5 minute war emergency)

Undated RAAF data sheet

310 mph at 1000 ft, for P-40N with V-1710-81 at 55" manifold pressure (5 minute war emergency)
359 mph at 10,000 ft, conditions as above

 

[krieghund]

Referring back to my previous post #16 here is the Spec curve of the P-63 with those three referenced engines..............enjoy from WWII Performance Website

 

[Shortround6]

The P-40N designation actual covered a variety of aircraft depending on block number. The 378mph speed MAY apply to a very early block number (200 made?) with 4 guns, restricted ammo, one fuel tank taken out, hand starter only, small battery, one bomb fuel rack(?) and some other tricks and suing WER at 10,000ft. Later block numbers with 6 guns, electric starters and other "luxuries" but back back in and three bomb racks (even if empty) were down to the 343mph figure at 15,000ft. Supercharger would not provide any WER at that height UNLESS the engine was OVER revved. Engines capable of over revving to any significant extent without drastic shorting of life were the so called 12 counter weight crankshaft engines. Some late P-40Ns may have gotten these crankshafts from the factories, some may have gotten them at overhaul. Greg would know much better than I but many restored warbirds may use these crankshafts now. They will fit in most of the older blocks (?).

As Jabberwockey has said, a lot depends on aircraft condition. a good putty job and sanding, a good coat of "gloss" paint and a good wax job could be worth 10-15mph vrs even a decent flat camo standard factory finish let alone a well worn front line aircraft.

Basically the US was getting 1/3 of the Merlin production, they needed some way to use them. Sticking them in the P-40 was one way and at the time, very late 1941 to mid 1942, the Allisons in production
were topping out at 12,000ft and under. The Merlin in high gear offered 5-8,000 more altitude. At 20,000ft an F was 20-25mph faster than an E. Unfortunately the enemy fighters improved even more.

 

[Mike Williams]

The following reports should shed some light on P-40N performance and go some way to explain the varying data noted:

Memorandum Report on P-40N, No. 42-9987: Flight Tests.
Memorandum Report on P-40N, No. 42-105241: Performance Tests

 

[GregP]

Thanks you Jabberwocky! The performance of individual aircraft DID vary quite a bit. And the only people who much ever saw the absolute maximum speed were test pilots. NOBODY flew them at that speed, except in a dive, when away from the home airfield since they wanted to get back in one piece. The "combat speed" was generally about 50 - 80 mph slower than maximum straight and level speed. To me, "combat speed" is the cruise speed plus any acceleration produced after combat was joined, until combta broke off. Of course, they went faster if they dived out of combat, but then ... it broke off, didn't it? Unless someone followed, and that did happen on a few occasions.

I don't much care of the P-40N was a year later; it was in the P-40 family and counts. Any of the E, F, or G Allisons could easily get to 3,200 or 3,400 rpm. Any of our E, F, or G models can and sometimes do. The earlier models could, but the nosecase would overheat if it stayed there for very long since it wasn't designed for it. The F and G were and the E didn't have a nose case at all; it turned a driveshaft.

Personally, I think the real bread and butter combat P-40's of WWII started with the E. The earlier ones, about 1,723 or so ... possibly a few more ... of over 13,000 built, were somewhat developmental. Just my opinion.

 

[oldcrowcv63]

A&AEE test I have for a Kittyhawk II (V1650-1) at 8,910 lb and at 2,990 rpm indicates:

28,000 feet in 18.5 minutes
30,000 feet in 21.8 minutes
32,000 feet in 26.7 minutes
34,000 feet in 35.8 minutes

Thanks, GM, That's pretty much what I was looking for.

 

[GregP]

Yeah, if you're only turning 39" of MAP and 2,600 rpm, the P-40 flies fine but doesn't sparkle at all. 3,250 feet per minute is WAY better than 1,900 fpm, huh? Try climbing at 65" and 3,200 rpm. The climb rate will be just fine and right there with a P-51.

57+" MAP and 3,000 rpm makes a BIG difference. Either way, it still rolled better than most US aircraft in WWII.

Also, almost any late Allison can pull 75+" of MAP if needed and can get to 3,600 rpm without trouble. The prop may have some stress, but the engine can DO it. Ours do, today ... right now, and anytime. Heck, we even have the props, hubs, and brush assemblies for the Curtiss Electric prop! Want to race? We can get you 120+" of MAP with an Aux stage supercharger (G6) and you can make some serious HP in your P-40! We even have the gun synchronizer assemblies if required ... and they WORK. Of course, it is tough these days to find P-40 engine mounts. We have them, too. Heck, the P-40 is more rare today than the P-51, and probably worth more money.

 

[pinsog]

Yeah, if you're only turning 39" of MAP and 2,600 rpm, the P-40 flies fine but doesn't sparkle at all. 3,250 feet per minute is WAY better than 1,900 fpm, huh? Try climbing at 65" and 3,200 rpm. The climb rate will be just fine and right there with a P-51.

57+" MAP and 3,000 rpm makes a BIG difference. Either way, it still rolled better than most US aircraft in WWII.

Also, almost any late Allison can pull 75+" of MAP if needed and can get to 3,600 rpm without trouble. The prop may have some stress, but the engine can DO it. Ours do, today ... right now, and anytime. Heck, we even have the props, hubs, and brush assemblies for the Curtiss Electric prop! Want to race? We can get you 120+" of MAP with an Aux stage supercharger (G6) and you can make some serious HP in your P-40! We even have the gun synchronizer assemblies if required ... and they WORK. Of course, it is tough these days to find P-40 engine mounts. We have them, too. Heck, the P-40 is more rare today than the P-51, and probably worth more money.

What could the 1942 and 1943 Allison engines have done as far as MAP and RPM? What are you guys doing different today that they weren't doing during earl WW2 when the Germans and Japanese(especially the Japs) were giving the P40 such a bad time?

Why didn't the early Allisons try to pull as much MAP and RPM as your engines?

 

[Shortround6]

The old engines didn't have the 12 counterweight crankshaft until very late in the war.

The older engines weren't balanced as well apparently. Pistons and connecting rods not as closely matched for weight?

There may have been small but important changes to the supercharger. Changing the inlet guide vanes may be worth a few inches of MAP.

The ability to pull 72-75 in of MAP is very dependent on altitude and which set of supercharger gears are in the engine.

There is also the difference between test stand and flight. Many engines show a difference of several thousand feet of altitude between climb and level flight (high speed) pressure limits. You may be able to get 72-75in at sea level and doing 300+ mph level flight. Slowing to 140-160mph for best climb may see several in of MAP disappear.

 

[pinsog]

The old engines didn't have the 12 counterweight crankshaft until very late in the war.

The older engines weren't balanced as well apparently. Pistons and connecting rods not as closely matched for weight?

There may have been small but important changes to the supercharger. Changing the inlet guide vanes may be worth a few inches of MAP.

The ability to pull 72-75 in of MAP is very dependent on altitude and which set of supercharger gears are in the engine.

There is also the difference between test stand and flight. Many engines show a difference of several thousand feet of altitude between climb and level flight (high speed) pressure limits. You may be able to get 72-75in at sea level and doing 300+ mph level flight. Slowing to 140-160mph for best climb may see several in of MAP disappear.[/QUOTE

I guess my question is, should they have been able to get alot more out of the Allison, early in the war, with their available technology? Or did they do all they could do?

 

[bob44]

I guess my question is, should they have been able to get alot more out of the Allison, early in the war, with their available technology? Or did they do all they could do?

Possibly. But this takes development. Add a two stage supercharger, or turbocharger, intercooler/aftercooler, a pressure carb. Is a good start.
Also, you need an aircraft for this engine, something that is simple for the pilot to operate, with automatic controls, that will help manage the engine.

A problem with the Allison, from what I have read, was the uneven fuel distribution in the intake. Some cylinders too much fuel, some too little fuel. If this was known early in the engine's life, I do not know. Otherwise the Allison was a very tough engine.

 

[Shortround6]

You had several things going on at once. The early "C" engines in the P-40B&C (Tomahawks) had a problem with the propeller reduction gears. Some of the other parts may not have been the equal of even a 1941/42 manufactured engine.

Fuel was another big "IF" factor in the early part of the war. The Allisons were developed using US spec 100 octane fuel. This is different than either British 87 octane or British 100 octane. British 87 octane fuel had a fair amount of "aeromatics" in it and performed better (allowed higher boost)than than some 87 octane fuel but it was never really measured. American 100 octane fuel had very little allowable ( 2% max) "aeromatics" and while a richer mixture allowed a bit more boost there was no real jump in allowable boost pressures. In fact a few batches of US 100 octane gas performed at worse than 100 octane rating when running rich.
British 100 octane fuel at the time of the BoB and shortly after had 20% aeromatics minimum and while not tested for a while, it performed much better under rich conditions than lean. Once they did come up with test procedures and and a rating system it was found that most batches of British 100 octane had a rich mixture response of between 115-120PN. Or 100/115-120. Once they had that figured out the British began specifying 100/130 fuel. The US meanwhile shifted to a 100/125 fuel specification.

Sorry to be a bit long winded but it helps explain why British units in North Africa could use higher boost numbers than the US army approved for it's identical engines at the same time. While few people were using 75in of boost at the time a lot of them were running way over the "BOOK" numbers of 40-44 in MAP. Some claim ( and others say they didn't) The Flying Tigers used some rather high boost settings too, but I don't know were their fuel was coming from. British or American stocks? This fuel discrepancy carried over into the P-40E's at least and maybe into the P-40Ks. At some point in 1942 the British and Americans standardized on the 100/130 fuel specification. Trying to use 60-70 in of boost on 1940 US 100 octane fuel could be a very iffy proposition. Given ideal conditions you might get away with it. Less than ideal might mean pushing into the 50s could wreck the engine.

As far as other "technology" goes a number of parts were changed along the way, Crankshafts went from "plain" to shot peened to shot peened and Nitrided (early 1942) for an almost doubled allowable stress level, and that is before the 12 counter weight crankshaft shows up in early 1944. Other parts like connecting rods changed. Valve springs changed on the later engines. Even the way the crankcases were cast was changed.
Trying to wind an early engine AS BUILT to 3400-3600rpm could (and often did) result in disaster. Doing it to a rebuilt engine using late model internal parts could very well be a different story.

 

[GregP]

The engines we build today are mostly later series and perform to stock levels. The rated rpm is 3,000 but the design was good for a LOT more. We have some customers who run them at 4,500+ rpm, but not in airplanes.

The thing is, the American engineers and Army acceptance peoplpe were very conservative. The Allison can pull over 100" of Mercury MAP, but was rated VERY conservatively and tested conservatively. You almost can't FIND a test report at over 57" of MAP and 3,000 rpm .... but we can easily get 75"+ and 3,400 - 3,600 rpm if we want. We CAN get to 115" of MAP for a race engine. Most owners don't becasue there is almost no reason to do so.

The entire point is, when we DO, the engine handles it very well!

The Allison is tougher than the Merlin and holds a tune-up MUCH longer; MUCH more trouble-free. NOTHING wrong with a Merlin; you get what you expect to get with one, no argument there. It's just that you get so much MORE than you expect with a well-overhauled and properly-tuned Allison. We have several in Jurca Spitfire replicas and they give 95+% of the performance of the real aircaft despite having only a single stage supercharger rather than a 2-stage unit. If they had an equivalent two-stage, they'd kick-butt, and do anyway in tractor pulls where sea level performance is important.

No single-stage ALlison is great at 25,000+ feet compared with a 2-stage Merlin, but the aux-stage and turbo models were ... and ARE. ALL Alisons were VERY comparable to the single stage Merlins, particularly from a serviceability standpoint. They were VERY good engines hamstrung by a government committee that controlled the ordes. if they order a V-1710-39, thath's what you deliver ... not some BETTER engine. To do that would violate the contract.

In the post-war unlimited hydroplanes, the merlins that eventually took over from the Allisons were all 2-stage units. The single-stage Merlins mostly lost to the sinlge-stage Allisons. Guy Lombardo was the US Champion for 1946 - 1949 and won EVERY trophy on the circuit with Allisons. I have two pistons from one of his Championship-winning boats. When Merlins "took over," they were the 2-stage units and won mostly due to lack of knowledge of how to tune-up Allisons.

When they made the movie "Madison," Joe Yancey built the Allisons for the 20+ old hydroplane boats in the movie. He built them to STOCK configuration and they almost all ran 20+ mph faster than they did in "back-in-the-day" competion during the filming of the movie simply becasue the guys trying to "hot rod" the Allisons didn't know what they were doing. They ALSO put over 70+ hours on most of the boats during the filming and the engines never broke.