Allison P-40 vs Merlin P-40 (or 1 speed vs 2 speed)

[wuzak]

And the P-40F/L didn't have better performance than the ASllison P-40. The difference between them was within the airspeed indicator error.

In terms of outright speed, perhaps not.

But where the performance was achieved was different.

Here are tests of the P-40E and the P-40F
http://www.wwiiaircraftperformance.org/P-40/P-40F_41-13601_PHQ-M-19-1440-A.pdf
http://www.wwiiaircraftperformance.org/P-40/P-40E_40-384_PHQ-M-19-1300-A.pdf

Note that this test shows a maximum speed of 342mph @ 11,400ft and 340mph @ 15,300ft.

A source like Joe Baugher (Curtiss P-40E (Kittyhawk IA)) quotes 362mph @ 15,000ft (Curtiss P-40E (Kittyhawk IA)). This must have been for ones with later engines - the E in the test had the V-1710-39 with 8.8:1 supercharger drive ratio, rather than the later 9.60:1 gears.

Baugher quotes speeds of:
335mph @ 5000ft
345mph @ 10,000ft
362mph @ 15,000ft

Time to climb to 20,000ft of 11.5 minutes.
Service ceiling was 29,000ft.

For the F, Baugher (Curtiss P-40F Warhawk) quotes speeds of:
320mph @ 5000ft
340mph @ 10,000ft
352mph @ 15,000ft
364mph @ 20,000ft

Time to climb to 20,000ft of 11.6 minutes.
Service ceiling was 34,400ft.

The test report from http://www.wwiiaircraftperformance.org only has two all out level speeds listed where the engine was flat out (3,000rpm), and two more with reduced rpm:
320mph @ 9,800ft (2,650rpm)
350.5mph @ 12,800ft (3000rpm)
336.5mph @ 16,700ft (2,650rpm)
364.5mph @ 19,270ft (3000rpm)

Time to climb to 20,000ft of 10.2 minutes.
Service ceiling as listed by Joe Baugher.

The test report for the E shows a time to climb to 20,000ft of 11.82 minutes. The earlier (and lighter) D has a time to 20,000ft of 10.0 minutes in a separate test.

The E has a higher peak climb rate (2,400fpm @ 10,000ft vs 2,210fpm @ 9,600ft). By 15,000ft the E's RoC has dropped to 1,370fpm (F: 1,860fpm), 20,000ft it is 880fpm (F: 1,480fpm) and 25,000ft it is 480fpm (F: 1,000fpm).

The P-40E and P-40F were in different condition in the tests so far listed.

The F had the gun ports taped over, while the E did not. The F had wing racks with shackles and stays, the E was set up for use with a belly tank (though the tank was removed for all-out level speed tests).

A later test of the F (http://www.wwiiaircraftperformance.org/P-40/P-40F_41-13635_FS-M-19-1578-A.pdf) showed performance at differing rpm and 18,100ft. Why 18,100ft, I do not know.

The speed was 374 without belly tank and sway bars removed (369.5mph with sway bars in place).

RoC was 2,185fpm @ 18,100ft and 1,380fpm @ 25,000. Quite an improvement over the earlier F.

The later N used the V-1710-81 with the 9.6:1 gears.
http://www.wwiiaircraftperformance.org/P-40/P-40N-5_42-105241_Eng-47-1685-A.pdf

Max speed is shown as 350mph @ 16,400ft. The increased altitude rating of the engine comes at the cost of low altitude climb rates. The RoC at 10,000ft is 1,935fpm compared to the E's 2,400fpm, the RoC at higher altitudes is improved: 1,365fpm vs 880fpm @ 20,000ft and 760fpm vs 480fpm @ 25,000ft. The service ceiling is also improved to 31,000ft.

So, you can see that the F definitely moves the performance up about 4-5,000ft. Without losing too much down low.

The N loses performance down low, compared to the E, in order to improve altitude performance. That is the trade-off in using a single speed engine.

Low down performance could be recovered by using higher MAPs/boost with the appropriate fuels.

A multi-speed supercharger drive should enable the P-40 to retain the low down performance E while accessing the better high altitude performance of the N. There is a small weight penalty - the 2 speed Merlin gained ~75lb over its single speed brother.

 

[wuzak]

http://www.wwiiaircraftperformance.org/P-40/P-40E-Specifications_Performance.jpg

http://www.wwiiaircraftperformance.org/P-40/P-40F-Specifications_Performance.jpg

Interesting that the F's performance numbers were derived from flight test (marked with *), whereas the E's was not.

 

[Shortround6]

A difference in climb is that the Allison powered planes were tested at full power (3000rpm) for the first 5 minutes and the rest of the test done at 2600rpm. Obviously in combat the P-40E could climb faster using military power of 3000rpm.

However, the climb for the Melrin powered version was done at 2850rpm at all altitudes so it too, in combat situations, could climb a bit faster using 3000rpm.

There is little doubt that the Merlin engine allowed for a 3-4000ft higher effective ceiling.

A later test of the F showed performance at differing rpm and 18,100ft. Why 18,100ft, I do not know.

As a Guess 18,100ft was rated altitude of the engine in high gear. Or that particular plane's wide open throttle altitude as it seems to be off 50rpm and 400ft.(not uncommon for many engines).

A June 1943 dated Pilots manual for the P-40F L also gives a war emergency rating of 61 in MAP and 1300hp at both 4,800ft and 12,000ft. The Military power was 48.2in and 1240hp at 11,500ft and 1120hp at 18,500ft. Take off was 54.3in at 1300hp at sea level. At the moment I don't know when the WER rating was approved for the P-40 Merlin.

 

[P-39 Expert]

In terms of outright speed, perhaps not.

But where the performance was achieved was different.

Here are tests of the P-40E and the P-40F
http://www.wwiiaircraftperformance.org/P-40/P-40F_41-13601_PHQ-M-19-1440-A.pdf
http://www.wwiiaircraftperformance.org/P-40/P-40E_40-384_PHQ-M-19-1300-A.pdf

Note that this test shows a maximum speed of 342mph @ 11,400ft and 340mph @ 15,300ft.

A source like Joe Baugher (Curtiss P-40E (Kittyhawk IA)) quotes 362mph @ 15,000ft (Curtiss P-40E (Kittyhawk IA)). This must have been for ones with later engines - the E in the test had the V-1710-39 with 8.8:1 supercharger drive ratio, rather than the later 9.60:1 gears.

Baugher quotes speeds of:
335mph @ 5000ft
345mph @ 10,000ft
362mph @ 15,000ft

Time to climb to 20,000ft of 11.5 minutes.
Service ceiling was 29,000ft.

For the F, Baugher (Curtiss P-40F Warhawk) quotes speeds of:
320mph @ 5000ft
340mph @ 10,000ft
352mph @ 15,000ft
364mph @ 20,000ft

Time to climb to 20,000ft of 11.6 minutes.
Service ceiling was 34,400ft.

The test report from WWII Aircraft Performance only has two all out level speeds listed where the engine was flat out (3,000rpm), and two more with reduced rpm:
320mph @ 9,800ft (2,650rpm)
350.5mph @ 12,800ft (3000rpm)
336.5mph @ 16,700ft (2,650rpm)
364.5mph @ 19,270ft (3000rpm)

Time to climb to 20,000ft of 10.2 minutes.
Service ceiling as listed by Joe Baugher.

The test report for the E shows a time to climb to 20,000ft of 11.82 minutes. The earlier (and lighter) D has a time to 20,000ft of 10.0 minutes in a separate test.

The E has a higher peak climb rate (2,400fpm @ 10,000ft vs 2,210fpm @ 9,600ft). By 15,000ft the E's RoC has dropped to 1,370fpm (F: 1,860fpm), 20,000ft it is 880fpm (F: 1,480fpm) and 25,000ft it is 480fpm (F: 1,000fpm).

The P-40E and P-40F were in different condition in the tests so far listed.

The F had the gun ports taped over, while the E did not. The F had wing racks with shackles and stays, the E was set up for use with a belly tank (though the tank was removed for all-out level speed tests).

A later test of the F (http://www.wwiiaircraftperformance.org/P-40/P-40F_41-13635_FS-M-19-1578-A.pdf) showed performance at differing rpm and 18,100ft. Why 18,100ft, I do not know.

The speed was 374 without belly tank and sway bars removed (369.5mph with sway bars in place).

RoC was 2,185fpm @ 18,100ft and 1,380fpm @ 25,000. Quite an improvement over the earlier F.

The later N used the V-1710-81 with the 9.6:1 gears.
http://www.wwiiaircraftperformance.org/P-40/P-40N-5_42-105241_Eng-47-1685-A.pdf

Max speed is shown as 350mph @ 16,400ft. The increased altitude rating of the engine comes at the cost of low altitude climb rates. The RoC at 10,000ft is 1,935fpm compared to the E's 2,400fpm, the RoC at higher altitudes is improved: 1,365fpm vs 880fpm @ 20,000ft and 760fpm vs 480fpm @ 25,000ft. The service ceiling is also improved to 31,000ft.

So, you can see that the F definitely moves the performance up about 4-5,000ft. Without losing too much down low.

The N loses performance down low, compared to the E, in order to improve altitude performance. That is the trade-off in using a single speed engine.

Low down performance could be recovered by using higher MAPs/boost with the appropriate fuels.

A multi-speed supercharger drive should enable the P-40 to retain the low down performance E while accessing the better high altitude performance of the N. There is a small weight penalty - the 2 speed Merlin gained ~75lb over its single speed brother.

Always wondered about that 362mph on December 1, 1941. All the other tests before and since have shown the P-40E to be a 340mph airplane.

 

[Schweik]

The British also clocked the P-40F at 370 mph at 20,400' per this memo of 9/9/42


One of the things which changes the numbers a lot on the P-40E (or later models like the K especially) is the boost setting. WEP for the E was listed as 45" Hg in the manual if I remember right and that is usually the setting they used in official tests, but in the field a 60" setting was apparently routine enough that Allison officially agreed to it, according to this infamous memo about overboosting Allison engines.

The way they put it was:

"In the past week we have received reports from both the Middle East and Australia indicating the use for considerable periods of time of very high manifold pressures on V-1710-F3R and F4R engines, (AAF models -39 and -73)"

and

"The engines under discussion are of the -53R and -F4R tyhpe with 8.8:1 blower ration on which this company has agreed to the war emergency operation at 60" manifold pressure (15 lbs. / sq.in. boost) and approximately 1570 H.P. at 3,000 R.P.M."

V-1710-39 ./ F3R is the engine in the P-40E

The main point of the article was about overboosting in combat conditions to 66" and even supposedly near 70", and why it wouldn't work in the later model engines. but lets put that aside for a moment. Allison admitted here that they agreed to a 60" boost setting - that will for sure increase speed at least at certain altitudes. As you can see that part was actually underlined in the memo. But most of the reports I have seen (I admit I haven't looked through all of them) show 'Military power' ratings in the 40's or at the most 50's for the P-40E, if they indicate it at all.

S

 

[Schweik]

But most of the reports I have seen (I admit I haven't looked through all of them) show 'Military power' ratings in the 40's or at the most 50's for the P-40E, if they indicate it at all.

This test for example linked by Wuzak upthread indicates 43.9" Hg which is way below the real settings they were using in combat. This test was pretty early (Sept 1941) so it's quite possible they didn't know how far they could push the engine yet. By the time the P-40K came out the standard official WEP setting was 57" but that was just the War Department following along with standard practice. Unofficially it was apparently already 60" including with the older -39 engines.

 

[Schweik]

The later N used the V-1710-81 with the 9.6:1 gears.
http://www.wwiiaircraftperformance.org/P-40/P-40N-5_42-105241_Eng-47-1685-A.pdf

Max speed is shown as 350mph @ 16,400ft. The increased altitude rating of the engine comes at the cost of low altitude climb rates. The RoC at 10,000ft is 1,935fpm compared to the E's 2,400fpm, the RoC at higher altitudes is improved: 1,365fpm vs 880fpm @ 20,000ft and 760fpm vs 480fpm @ 25,000ft. The service ceiling is also improved to 31,000ft.

The N loses performance down low, compared to the E, in order to improve altitude performance. That is the trade-off in using a single speed engine.

Low down performance could be recovered by using higher MAPs/boost with the appropriate fuels.

A multi-speed supercharger drive should enable the P-40 to retain the low down performance E while accessing the better high altitude performance of the N. There is a small weight penalty - the 2 speed Merlin gained ~75lb over its single speed brother.

And yet, I'm not sure what the gear ratio on it was, but the early 'Interceptor' block P-40N seems to have a very good climb rate all the way up to 10,000 feet, and still "decent" at 15,000:

" Sea Level 156.5 3000 1400 3520 0
5,000 168.5 3000 1450 3640 1.39
*8,000 174 3000 1480 3720 2.21
10,000 175.5 3000 1340 3440 2.77
15,000 180.5 3000 1105 2680 4.41
*Critical altitude for war emergency power in climb.
3. Climb data, cowl flaps open, mixture control in the autorich position. Throttle set for 57 inches Hg. at 3000 RPM or wide open when below."

Also says it's still got 1,125 hp by 17,300' which it says is the critical altitude for Military Power, but by 26,000 feet it's sputtering along at 706 hp.

It also says 1480 hp at 10,000' with 57" Hg and 3,000 RPM where it makes a respectable 378 mph. Shouldn't 1480 be considered the power rating for that engine? usually it's listed in the ~1350 hp range.

And shouldn't we presume roughly similar power for the older V-1710-39 if it was being used at 57"?

S

 

[Shortround6]

The use of over boosting by the P-40 is a complicated and messy story. We have a lot of threads that discuss this or at least touch on it.

However a few points;

There are 3 critical altitudes, the No Ram critical altitude, pretty much established in a ground test chamber, this is for comparing the engine to itself (other models) or to different engines. The critical altitude in high speed level flight in which the speed of the aircraft rams air into the intake scoop/opening and provides higher pressure air to the inlet of the supercharger than a stationary engine would have. and the climbing critical altitude which uses the best climb speed of the aircraft in question to RAM the air into the engine inlet.
Obviously any aircraft that is moving gets at least some RAM effect unless the inlet design is a total failure (one 1920s racing airplane had such a disaster).
Using ram gets a bit tricky as even the Spitfire and Hurricane had different critical altitudes due to their different top level speeds. Now please note if a plane performs a hard turn and bleeds off speed it has also bled off ram effect and will not have fullpower coming out of the turn if above "critical" hight for whatever speed it is going.
You have a similar problem with climbing, obviously the speed is much less which shows up in the lower critical ceiling heights, but since not all planes have the same climbing speed using the same engine in different planes is going to show differences there too.

With that out of the way you had two basic supercharger gears in the P-39,P-40 and P-51, not including the A-36. However you also had a few minor changes to the supercharger along the way. You also had differences in the strength of engine parts and even changes in the engine/cylinder blocks.
The Allison seems to have been a pretty sturdy engine and tolerate abuse fairly well. The search for longer engine life also increased tolerance for abuse.

To get back to the question. " And shouldn't we presume roughly similar power for the older V-1710-39 if it was being used at 57"?

Some of the -39 engines were built before the change over to the nitrided crankshaft and the new casting techniques for the engine/cylinder blocks. You might make the power, the question seems to be how many times/how long.

Please note that the engine in the N used the 9.60 gears and the older engines with the 8.80 gears were actually allowed to use 56in of MAP and got 1490 hp when running that pressure. The no ram rating was only 4300ft however.
The P-40K got the -73 engine which still had the 8.80 gears but with the stronger parts and some other changes t was allowed to go to 1325hp for take-off and made 1150hp at 12,000ft on 42in map instead of 1150hp at 11,700ft using 44.6in (backfire screens and intake manifold differences?) however with the strongler parts in was also officially allowed 60 in of map which produced 1580hp but only until 2500ft. above which (without ram) it dropped to pretty much the same ratings as the older engine. Many of these engines were over boosted in service although exact numbers are hard to figure out. Many P-40s had pressure gauges which did not go anywhere near 70 inches. These high boost ratings could only be achieved at very low altitudes and pressures getting to 70 inches required more than RAM, they often required overspeeding the engine. Flying at 300mph at only a few thousand feet above sea level (and groundhight was what?) in a combat situation I would say that few pilots were sparing the boost gauge more than a passing glance.

The 9.60 gears take more power to turn, they heat the intake charge more and push the engine closer to the detonation limits even at boost pressures slightly lower than than the 8.80 gear engines did. Allison was a lot more insistent in the warnings about overboosting on the later engines.

The Critical altitudes of the older engines with the 8.80 gears are going to around 3000ft lower than the same/similar pressure using the 9.60 gears.
Please remember that supercharger performance is in relation to the square of the speed of the impeller so the difference in power consumed (and heat in the supercharger) and the difference in pressure out is closer to a 19% increase than the 9% difference in gear ratio.

 

[Schweik]

The use of over boosting by the P-40 is a complicated and messy story. We have a lot of threads that discuss this or at least touch on it.

Most of these points are pretty clear from the Allison memo, although from some of the stats it looks like they were still boosting at 57" and getting plenty of horsepower up to 10,000 feet or more.

60" or even 66" Hg at low altitude does correlate with one of the standard escape maneuvers described so often in the letters and first hand accounts of P-40 pilots - Split S or a power dive down almost strait down to low altitude (or until the speed gets too high), followed by a full throttle level-flight trip back toward friendly lines (or their squadron mates if they knew where that was).

If pursued, turn around and make a head on pass at the enemy aircraft and take it from there. I have read several accounts exactly like this from the Med Theater.

Another common scenario and technique described specifically with P-40Ks, (often when flying at low altitude because of strafing or dropping bombs) was:

• Detect enemy aircraft attacking from behind
  
• Skid to avoid being hit until the enemy aircraft overshoots
• Apply full boost to catch enemy A/C in a climbing turn and get a shot into them.

Both of these would work well with the 1580 hp I think. And be a nasty surprise for the Germans if they weren't expecting it.

From reading that Allison memo it sounds like it may require overspeeding (especially if you want the HP at higher altitudes) and increasing RPM is something the Russian pilots like Golodnikov mentioned specifically as a way to get more power from the P-40. The interviewer said something like "any problems with the P-40?" and Golodnikov answered "a little slow, so we increased RPM, then it's normal.".

Interesting how this puzzle seems to be coming together. I wonder if the Russians did any overboosting of the P-39s? I know they had slightly different versions of V-1710 so I'm not sure if it worked the same way. It might explain a lot.

The Allison memo also makes it clear that overboosting is safer with the higher quality fuel.

S

 

[wuzak]

Interesting how this puzzle seems to be coming together. I wonder if the Russians did any overboosting of the P-39s? I know they had slightly different versions of V-1710 so I'm not sure if it worked the same way. It might explain a lot.

The core engine were the same as used in the contemporary P-40*. Differed mainly in having the remote gearbox.

* Early E models were based on the C model that early P-40s used (with the long nose reduction gear). Later E models were based on the F model V-1710s used by the majority of Allison powered aircraft. The last E models were based on G model V-1710s, or shared components with them.

 

[Shortround6]

With the early engines (the long noses) over boosting or over speeding was a bit of a problem. No squadron or group had enough data to really establish trends but the AVG noticed that while engines didn't fail in the flight that over boosting was used, they tended to fail in the 1st or 2nd fight after that. making this complicated was that if the engine failed while being over boosted/revved the pilot may not make it back to report it. There is one anecdote about a plane being over boosted, making it back and then the engine failed right after take off on the next flight and the plane crashed within a few miles of the runway. Maybe it would have failed anyway? The Gearing was a weak point on the long nose engines and would not stand up to high power levels very well. Complicating this was that the crankshaft tended to fail behind the the front main bearing instead of in front where the gears were.
This part of what I mean by the story being messy. British tomahawk squadrons were over boosting in the NA desert. But by how much is often not given. Or only extremes, like "up to ___ in was used at times". Over boosting could wreck an engine almost immediately if the engine started to detonate. It could cause fatigue problems in the crankshaft, gearing or other parts that could shorten the engines life considerably. Later engines had parts with longer fatigue life. Allisons by mid war had service lives of around 300 hours or more, by late war it was much longer. Russians were used to engines not lasting a hundred hours. Some engines would not last even 50 hours. Abusing an Allison repeatedly and having it last 120-150 hours would be a near miracle of longevity compared to their own engines.
Russian pilot comments have to be taken in context, their own planes, engines and guns were built to be disposable at rate much higher than the US or British aircraft, engines and guns.
Engine life was always a balance between power used and life expected with materials and heat treatment thrown in and changing.

 

[Schweik]

Russian pilot comments have to be taken in context, their own planes, engines and guns were built to be disposable at rate much higher than the US or British aircraft, engines and guns.
Engine life was always a balance between power used and life expected with materials and heat treatment thrown in and changing.

The Russians had a lot of other problems - keeping their oil sufficiently clean for Anglo-American engines being one of the main ones, also fuel (sometimes American fuel was available, sometimes apparently it wasn't) and squadron mechanics being forced to improvise methods to drain out all fluids from every system that had fluids in it - oil, prestone, batteries, fuel of course, hydraulics, etc. Everything had to be drained out every night during winter and Anglo-American planes weren't originally designed for that (I think some later model P-39s had this provision).

So whatever crude method some enlisted mechanic came up with in the field had to suffice, with whatever consequences for the systems.

The original batch of P-40's they got had no spare engines or spare parts beyond basic stuff like spark plugs shipped with them either, so spare engines and a lot of other part just had to be cannibalized from other planes. Additionally, no Russian language manuals meant everything had to be figured out by trial and error. By far the greatest loss rate for P-40s in Russia had to do with mechanical issues. From "The P-40 in Soviet Aviation" article referring to their first use of Tomahawks:

"On 38 occasions radiators burst due to freezing temperatures. To provide for repairs all the silver forks had to be confiscated in neighboring villages to be used for soldering. Tires cracked and batteries burst; generators frequently broke and engines seized up. Because the 126th IAP was the first "happy owner" of the Tomahawks, it fell to that unit's maintenance personnel to attempt to rectify this "avalanche" of defects, albeit with the assistance of specialists from the VVS Scientific Research Institute. The generators and tires were changed out for Soviet-produced items and the hydraulic fluid, engine oil, and cooling systems were modified with special petcocks through which the fluids could be completely drained at night. But by the time these specialists had learned how to deal with all the defects, a large portion of the aircraft were already combat incapable. There was a total lack of spare parts and engines (no spare engines had been sent) and even cartridges for the British and American machine guns. Only nine aircraft were in flyable condition by mid-January 1942 "

and

"But the primary source of losses was mechanical failures. Practically not a single combat sortie was flown without some kind of problem. It was a common practice to land with a dead engine. Not all of these flights were completed successfully. On 17 February 1942, one of the best pilots of the regiment, HSU Senior Lieutenant S. G. Ridnyy (Tomahawk AK325) suffered an engine failure on takeoff and was killed in crash. Despite this abundance of accidents and incidents, the general impression of the pilots of 126th IAP regarding this aircraft remained good. The Tomahawk had qualities that were lacking in aircraft of Soviet production."