Spitfire V Versus P-40E

[Mike Williams]

Sadly I've never found original performance test data for a P-40K

These are all the test reports I'm seeing for the P-40K fwiw:

Memorandum Report on P-40K-1, A.A.F. No. 42-9761: Speed Tests - Normal and Smooth Camouflage
Memorandum Report on P-40K-1, A.A.F. No. 42-9761 (addendum): Speed Tests

 

[Schweik]

Yeah I've seen those, except the second page on the addendum, which is interesting (and better than nothing) but still doesn't tell us very much and apparently done at military power. All they were looking at there was what difference smoothing the paint made.

There must be a proper evaluation of the K model both by the USAAC, RAF, and probably the Soviets too. I know there is a document on WWIIaircraftperformance.org where they used a P-40K in some tests against a Zero and another where they used it against some Allied aircraft but I couldn't find them, they aren't in the P-40 section.

 

[Mike Williams]

Fwiw, more on the Spitfire V, P-40E/Kittyhawk comparison. These P-40s were just not good climbers. Too much weight and not enough power I suppose.

 

[Schweik]

No they weren't, though it helped to boost the power by 15-20% which was just a matter of pushing the throttle forward, and / or drop the weight a bit.

 

[varsity07840]

Yeah I've seen those, except the second page on the addendum, which is interesting (and better than nothing) but still doesn't tell us very much and apparently done at military power. All they were looking at there was what difference smoothing the paint made.

There must be a proper evaluation of the K model both by the USAAC, RAF, and probably the Soviets too. I know there is a document on WWIIaircraftperformance.org where they used a P-40K in some tests against a Zero and another where they used it against some Allied aircraft but I couldn't find them, they aren't in the P-40 section.

A P-40K and a P-43 were test flown against an A6M2 captured by China after it crashed landed on a beach in 1941. In 1942 it was rebuilt by Chinese and American technicians and tested in early 1943.

 

[Schweik]

A P-40K and a P-43 were test flown against an A6M2 captured by China after it crashed landed on a beach in 1941. In 1942 it was rebuilt by Chinese and American technicians and tested in early 1943.

I think that test is on world warIIaircraft performance.org somewhere

 

[Mike Williams]

No they weren't, though it helped to boost the power by 15-20% which was just a matter of pushing the throttle forward, and / or drop the weight a bit.

Was there some kind of cooling issues during climb? Oil temps high? It would have helped if 3000 R.P.M. could have been used as well as the same boost as with level flight, for example 44" Hg. while climbing. I was hoping I could work up a 44" Hg./3000 rpm curve extrapolated from the Australian test but the 2600 R.P.M. used sort of complicates that notion.

 

[Mike Williams]

A P-40K and a P-43 were test flown against an A6M2 captured by China after it crashed landed on a beach in 1941. In 1942 it was rebuilt by Chinese and American technicians and tested in early 1943.

Oh yea, good one, here you go: General Technical Data and Flight Characteristics of the Japanese Zero Fighter Plane

 

[Mike Williams]

Three comments on that -

1. That would 14 mph faster than the P-40E in the Australian test we've been looking at.
2. I would agree with you that what you mentioned there probbaly represents takeoff power of 1,325 Hp, which is achieved at 51" Hg
3. However the normal WEP rating (not overboost) for the P-40K-15 was 60" Hg for 1,550 hp. So that would be 15% more power.

My source for that is Shamburger, Page & Christy, Joe. The Curtiss Hawks. Wolverine Press, 1972. Library of Congress No. 79-173429 , page 231

That's a significant power increase. That 60" must be mentioned in a P-40K Pilot's Notes or Operating Instructions sheet somewhere? Was the radiator or oil cooler improved from the P-40E to the P-40K or N to accommodate the increase in power?

 

[varsity07840]

Oh yea, good one, here you go: General Technical Data and Flight Characteristics of the Japanese Zero Fighter Plane

I recall reading that years ago along with critiques of the report. Given the statement that the engine could produce 900 HP, it's obvious that the engine/aircraft was not in service condition. A favorable comparison of the P-36A to the Zero confirms that. Pilots that flew the P-36A against the Zero on Dec. 7th would have disagreed with that report.

 

[Schweik]

That's a significant power increase. That 60" must be mentioned in a P-40K Pilot's Notes or Operating Instructions sheet somewhere? Was the radiator or oil cooler improved from the P-40E to the P-40K or N to accommodate the increase in power?

No, apparently a change to radiator or oil cooler wasn't needed (or if it was, I'm unaware of it). Allison changed the crank shaft to first a peened and then tempered homogeneous construction, then they also strengthened the crank case too. As far as I know that is the only major difference between the V-1710-39 on the P-40E and the V-1710-73 on the P-40K

The official 60" / +15 lb boost rating is mentioned twice in the famous Dec 1942 Allison memo here:

http://www.wwiiaircraftperformance.org/P-40/V-1710_Service_Use_of_High_Power_Outputs.pdf

That memo is from Alison to the War Dept., complaining about P-40 units overboosting in the field (in the Middle East and in Australia), and warning that there will be a risk of problems when the new Allisons with higher gear ratios make it to the field (on P-40M and P-40N fighters) but we don't have to concern ourselves with overboosting.

To quote them "The engines under discussion are of the -F3R and -F4R type with 8.8:1 blower ratio 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 3000 R.P.M"

Later they say:

"In determining the 57" hg. war emergency rated manifold pressure Amendment 5 fuel was used and the detonation point was stayed away from at 120 degrees F. carburetor air temperature with the engine running at 3,000 R.P.M. The 60" war emergency rating on the 8.8 blower ratio was somewhat further from the detonation point but was limited by structural limitations of the engine to the 60" value. We therefore feel that, with the tendency to pull out a manifold pressure such as 66" to 70" on 8.8 blower, a bad precedent is being established which may cause numerous failures when the 9.6:1 supercharger gear ratio engines are received in the field."

There is another memo somewhere which talks about the changes done to the Allison, but I seem to have lost track of where any of that stuff is, I think it's on WWIIaircraftperformance as well but I'm not sure. Shortround6 might know.

The only manual I have on the P-40K is a manual for overhauling the engine. The P-40N manual mentions a WEP rating of 57" for 1480 HP (page 4 of the PDF) but it had the higher gear ratio engine that Allison was warning about.

 

[Schweik]

I assumue "Amendment 5 Fuel" means British high octane fuel but I don't remember if we ever proved that.

 

[Schweik]

The manual for the P-40F and L (merlin engines) says the WEP rating which is apparently some kind of automatic setting, is 61" Hg (page 7 of the PDF) and it says that WEP is available in both low and high gear, use low gear below 8,000 ft and high gear above 8,000 ft. Later on page 42 the Critical altitude for WEP is listed as 4,600' for low gear and 12,000 ft for high gear.

See attached

 

[Schweik]

I recall reading that years ago along with critiques of the report. Given the statement that the engine could produce 900 HP, it's obvious that the engine/aircraft was not in service condition. A favorable comparison of the P-36A to the Zero confirms that. Pilots that flew the P-36A against the Zero on Dec. 7th would have disagreed with that report.

Oh yeah I agree, it's obvious they didn't get the A6M running properly. I was only looking for the report hoping for some more data on the P-40K but there really wasn't much.

 

[Shortround6]

Problems with the P-40 are the large amount of weight they were trying to lift (when climbing) with 1150hp or less.

Standard US procedure was to use military power for the first 5 minutes of the climb (42-44in in the case of the P-40s and the full 3000rpm)

British and Australian testing may do the P-40 a disservice if they use the 2600rpm and lower boost for the entire climb.

Both countries used a 5 minute full power rating (or sometimes 3 for the British) but the British then dropped to a 30 minute rating (and used that for all climbing tests) while the Americans didn't use that time period at all, the Americans dropped to either a one hour rating or (same rating different name) max continuous which was good for as long as the fuel lasted or a temperature gauge went into the red. The British/Australian climb tests are using the max continuous rating which for the Allison In the P-40 was about 1000hp.

The P-40 would have climbed very well indeed had the supercharger been able to supply 60in (or even 56in) for more than a minute or two when climbing.
The 60 in limit on the P-40 K was all done at 2500ft no RAM or a bit over 3000ft when at climb speed. High speed level flight was good for a bit higher.

The 56in limit was good for for 4300ft NO RAM. there is little or no difference between the superchargers on an E or a K. When Climbing the the K could have had 60in at sea level (on a standard day) and held it to around 3000ft but then the pressure would decline until at something over 4300ft the pressure was down to 56in as the plane continued to climb (far into the 2nd minute or start of the 3rd?) the pressure in the manifold would continue to drop as the supercharger just cannot supply anymore air at an engine speed of 3000rpm, Until you hit the high 11s or low 12s ft at which point the supercharger, with wide open throttle is supplying 42in in the case of the K. again, sources are all over the place depending on exact manifold and backfire screens.

That's a significant power increase. That 60" must be mentioned in a P-40K Pilot's Notes or Operating Instructions sheet somewhere? Was the radiator or oil cooler improved from the P-40E to the P-40K or N to accommodate the increase in power?

There was no real change in the radiator or oil cooler but the engine in the K used mixed water/glycol cooling instead of pure glycol like the engine in the E. This gave a better heat transfer and coped with the increase heat load.

 

[Shortround6]

The manual for the P-40F and L (merlin engines) says the WEP rating which is apparently some kind of automatic setting, is 61" Hg (page 7 of the PDF) and it says that WEP is available in both low and high gear, use low gear below 8,000 ft and high gear above 8,000 ft. Later on page 42 the Critical altitude for WEP is listed as 4,600' for low gear and 12,000 ft for high gear.

See attached

I would note that the HP ratings on the chart for WEP are in error. A simple typo I suppose.

 

[Schweik]

Problems with the P-40 are the large amount of weight they were trying to lift (when climbing) with 1150hp or less.

Standard US procedure was to use military power for the first 5 minutes of the climb (42-44in in the case of the P-40s and the full 3000rpm)

British and Australian testing may do the P-40 a disservice if they use the 2600rpm and lower boost for the entire climb.

Both countries used a 5 minute full power rating (or sometimes 3 for the British) but the British then dropped to a 30 minute rating (and used that for all climbing tests) while the Americans didn't use that time period at all, the Americans dropped to either a one hour rating or (same rating different name) max continuous which was good for as long as the fuel lasted or a temperature gauge went into the red. The British/Australian climb tests are using the max continuous rating which for the Allison In the P-40 was about 1000hp.

The P-40 would have climbed very well indeed had the supercharger been able to supply 60in (or even 56in) for more than a minute or two when climbing.
The 60 in limit on the P-40 K was all done at 2500ft no RAM or a bit over 3000ft when at climb speed. High speed level flight was good for a bit higher.

The 56in limit was good for for 4300ft NO RAM. there is little or no difference between the superchargers on an E or a K. When Climbing the the K could have had 60in at sea level (on a standard day) and held it to around 3000ft but then the pressure would decline until at something over 4300ft the pressure was down to 56in as the plane continued to climb (far into the 2nd minute or start of the 3rd?) the pressure in the manifold would continue to drop as the supercharger just cannot supply anymore air at an engine speed of 3000rpm, Until you hit the high 11s or low 12s ft at which point the supercharger, with wide open throttle is supplying 42in in the case of the K. again, sources are all over the place depending on exact manifold and backfire screens.

All true - and they wouldn't normally try to climb at high power anyway because it's very wasteful of fuel. But if for example they had to scramble to deal with an inbound attack, or if they were already flying, in combat, and needed to climb up to engage an enemy they would indeed use boost and in your scenario described above, they would still be for the first 3 minutes of a climb from sea level up to 10,000 ft at 60" down to 56" boost which is still way above what was recorded in any of those tests. After that it falls down to more or less the same as in the tests (not very good), but that is why a P-40E or K was basically a low to medium altitude aircraft. If the fight wasn't going well at 15,000 or 20,000 ft they could drop down to 8,000 or so in less than a minute.

The P-40F or L as you can see in my previous post was able to make 61" boost certainly up to 12,000 ft., and as you can see here on the P-40N ...

http://www.wwiiaircraftperformance.org/P-40/A29-412-climb-WEP.jpg

...climb at (57") WEP started at over 3,100 ft per minute, got up to about 3,370 (at 6,800 ft) and was still pretty decent at 15,000 ft (2300), up to about 18,000' where falls below 2,000 fpm.

Of course, that is at the maximum steepest climb rate at 150 mph, which is not going to happen around enemy aircraft, so realistically they would be zoom climbing or doing a high speed climb, but the extra power would help regardless.

For speed it gives a WEP full throttle height of 9200' for the P-40N and still some power all the way up to about 20 or 22,000

There was no real change in the radiator or oil cooler but the engine in the K used mixed water/glycol cooling instead of pure glycol like the engine in the E. This gave a better heat transfer and coped with the increase heat load.

That's interesting I wasn't aware of that.

 

[Schweik]

I would note that the HP ratings on the chart for WEP are in error. A simple typo I suppose.

Yeah that seems to be the number they always throw around for the P-40F, it should be 1430 or something right? That confused me for a long time when I was first researching the P-40F / L. How is that calculated precisely? Or is it based on a bench test or something?

 

[PAT303]

Where is all the drag coming from?

Cannon barrels, undercarriage, tail wheel, windscreen angle, exhaust stacks, fit and finish. I have a report on paint condition and it's relevance to speed done on a squadron sourced Spit XIV, repainting and polishing added 14mph to it's speed, many of the MkV's in use were getting tired after giving years of loyal service.

 

[Mike Williams]

Googled this P-40K specific engine flight chart that shows 60" emergency boost.