Bf-109 vs P-40

[Shortround6]

In my reading, the P-40 was never designed to fly higher than 15,000ft.
Quite often pilots admit it was used in situations it wasn't designed for, aka, taking on A6M or 109s from 27,000ft.

I think this is one of those often repeated myths. Can anybody come up with any documents from the late 30s (1937-1939) that say that the USAAC didn't want planes that could fly higher than 15,000ft?

Achieving peak speed at 15,000ft and not being designed to fly higher that 15,000ft are not at all the same thing.

In 1938-early 1939 the USAAC was very interested in Turbo supercharged aircraft, they had been for years. From their experience they judged that turbo equipped aircraft would not be ready for about two years from the spring of 1939 when they placed the initial contract for P-40s. The P-39 and P-40 without turbos were supposed to ready in just one year.

What helped kill P-40 altitude performance was a steady and large weight growth.

Planes at the 1939 fighter trials included not only the P-40 but a YP-37 with a turbo-charger, a Hawk 75R ( P-36 with a TWO-stage supercharger). the XP-39 and the Seversky AP-4 ( P-35 with inward retracting landing gear and the SAME two-stage supercharged P&W engine and the Hawk 75R). The P-40 was judged the winner, in part because it would be available (in production) the quickest.

Getting back to the weight growth. The XP-40 weighed 5,184 pounds empty and had a normal gross (not max) of 6280lbs. the First production versions went to 5,376lbs empty and 6,787lbs gross (normal), the P-40B (Tomahawk IIA) went to 5,590lbs empty and 7,325lbs gross and the P-40C (Tomahawk IIB) went to 5,812lbs empty and 7,549lbs gross (normal). A 20% increase in weight can do serious things to both rate of climb and ceiling. The P-40E gained some power low down (little or none at 15,000ft) but weight went to 6069lbs empty and 8290lbs Clean (max internal fuel but no external fuel or bombs). Again, it is easy to see why the P-40 did not perform at altitude, and it has little to do with the initial design requirements in 1938. It has something to do with a lack of engine development and the lack of effective light weight guns. Swapping in a DB601 would have done little or nothing until you get to the 601E. The 109 got it's altitude performance, not from a better supercharger or trick supercharger drive but from being almost a ton lighter.

 

[tomo pauk]

If it was only about output they would've just installed 2nd stage/geared superchargers, no?

The only two-stage in-line engine available for USAAC early enough was the Packard Merlin V-1650-3, and it was duly installed into a best airframe available. By the time US have had both 2nd stage Allisons and Merlins in quantity, P-39 -40 were being phased out.

Aside from wing loading, the wing has other factors that contribute to performance characteristics, aspect ratio and lift to drag to name a couple.
More power is usually the way to circumvent an inadequate wing design.

Good points.

 

[Ratsel]

Again, it is easy to see why the P-40 did not perform at altitude, and it has little to do with the initial design requirements in 1938. It has something to do with a lack of engine development and the lack of effective light weight guns. Swapping in a DB601 would have done little or nothing until you get to the 601E. The 109 got it's altitude performance, not from a better supercharger or trick supercharger drive but from being almost a ton lighter.

Well the Me 109G-6 was 1/2 ton lighter (normal flying weight) then the P-40E and killed the P-40E performance wise (even at empty weight). In the case of the DB 605A along with its props and gear reduction, it was a much much better settup the the P-40's Allison/prop/g-r. That big chin hanging low out front of the P-40D up had alot to do with its lack of level flight speed. The P-40A/B/C had a much cleaner nose areodynamically speaking. Why Cutriss decided to go with a 10" lower crankshaft centerline is beyond this reporters mind.

 

[Shortround6]

Where are you getting that?

I read the radiator at the front of the plane was a higher drag location than the rear scoop position.
In part because it disrupts the boundary layer over the wing, multiplying drag.
This was based on a 1976 publishing.

I am getting this from a number of sources. Any good history of the P-40 will tell you that the XP-40 was much slower with the radiator in the rear position than when moved to the front. According to the sources it varied from 299mph to 324mph. there were two other changes that could have affected speed. One was the change to ejector exhaust stubs with the XP-40 did not have and the other was moving the air intake forward a number of feet. After the changes the Plane got into the 340mph region. The Army wanted a Guaranteed speed of 350mph and later upped it to 360mph. Curtis promised they could meet the speeds. Failing to meet the guaranteed speeds would have meant a penalty for each and every aircraft made that did not reach the guarantee speed ( or an agreed upon tolerance). Moving a radiator and increasing drag to please the marketing dept would have been a very stupid thing to do. Curtiss lost over $14,000 on the P-46 contract because the second prototype to fly would not reach the guaranteed speed.

 

[Shortround6]

Well the Me 109G-6 was 1/2 ton lighter (normal flying weight) then the P-40E and killed the P-40E performance wise (even at empty weight). In the case of the DB 605A along with its props and gear reduction, it was a much much better settup the the P-40's Allison/prop/g-r. That big chin hanging low out front of the P-40D up had alot to do with its lack of level flight speed. The P-40A/B/C had a much cleaner nose areodynamically speaking. Why Cutriss decided to go with a 10" lower crankshaft centerline is beyond this reporters mind.

They went with the change in thrust line to get the better reduction gear design. Curtiss really didn't have any choice. Allison made the engines and the reduction gears. The Long nose engines were having trouble with the gears at 1040hp, going to 1150HP (or more) with the old style gear would just be inviting trouble.
The chin radiator may not have been as bad as many people claim. P-40E could do 360mph at 15,000ft on 1150hp. That is assuming that the "RAM" lifts the FTH from 12,000ft to 15,000ft. if not then it is getting 360mph on less power. The 109F-1/2 was good for about 370-380mph at 15,000ft using about 1160hp? Now not only does the P-40 have that big chin radiator but it is a lot heavier, has about 36% more wing area and is generally bigger in General. Even if the wings had the same profile (airfoil) the P-40s larger wing would be good for about 10-12mph worth of the difference.
Without access to the flight test data of the planes (p-40s) with the various radiator installations we are just guessing. Considering that there were 7 different radiator configurations tried on the P-40 somebody must have accumulated some interesting data on radiator drag

 

[vanir]

That was where Curtiss got their French orders from you know, the French wanted dive speed which is what sold them on the P-36 originally and in turn the P-40, which they considered simply a re-engined P-36 of which there were already two radial variations. It was actually the British that requested all the extra gear in the P-40 like extra armouring and self sealing tanks but these didn't appear until the P-40B, French and initial Army orders were for the plain P-40 based off the prototype.

I read the original Curtiss marketing flight tests of the P-36, power on vertical dives to a minimum speed of 400mph etc. It actually hit 450 in the test, French made an order within the month.

The thing which strikes me though is it being fairly unusual the US level speed requirements. It sounds suspiciously competitive with the European arms race of the thirties. Top speed ratings are for brochures in the marketing department, they don't relate much to military interests. RAF requirements are things like throttle heights and loadbearing. German ones altitude, cruise and rough field performance. The high top speeds of British and German fighters was incidental, not specified as far as I can remember.

Anyways we had a lot of P-40E and P-40M with a handful of F and K in Australia (NZ got the N and we went to the Spit), I have been around these warbirds and people who've flown them. Relating mostly to the P-40M, what I've heard is marginally slower than a LF MkV Spit. Marginally.
Yeah heresay, take it for whatever it's worth.

 

[Wildcat]

Anyways we had a lot of P-40E and P-40M with a handful of F and K in Australia (NZ got the N and we went to the Spit), I have been around these warbirds and people who've flown them. Relating mostly to the P-40M, what I've heard is marginally slower than a LF MkV Spit. Marginally.
Yeah heresay, take it for whatever it's worth.

Actually Australia received 553 P-40N's, making it the most numerous of all P-40 marks to serve the RAAF in the Pacific.

 

[vanir]

The three front line sqns in PNG had MkIa and MkIII. They started transitioning to SpitXIII in 43 and I was under the impression NZ wound up with the Ns.
I've not looked it up for a year, I'm going by memory and what I read in passing. That was just what I was thinking.

Happily stand corrected.

 

[Ratsel]

They went with the change in thrust line to get the better reduction gear design. Curtiss really didn't have any choice. Allison made the engines and the reduction gears. The Long nose engines were having trouble with the gears at 1040hp, going to 1150HP (or more) with the old style gear would just be inviting trouble.
The chin radiator may not have been as bad as many people claim. P-40E could do 360mph at 15,000ft on 1150hp. That is assuming that the "RAM" lifts the FTH from 12,000ft to 15,000ft. if not then it is getting 360mph on less power. The 109F-1/2 was good for about 370-380mph at 15,000ft using about 1160hp? Now not only does the P-40 have that big chin radiator but it is a lot heavier, has about 36% more wing area and is generally bigger in General. Even if the wings had the same profile (airfoil) the P-40s larger wing would be good for about 10-12mph worth of the difference.
Without access to the flight test data of the planes (p-40s) with the various radiator installations we are just guessing. Considering that there were 7 different radiator configurations tried on the P-40 somebody must have accumulated some interesting data on radiator drag

The P-40-CU ( Tomahawk II) did 360mph with a Allison V-1710-33 making 1,090hp. Max ceiling was 33,000ft and climbed at 3,080ft/min. Seems the 'E' went the opposite direction with that big old chin

 

[vanir]

worth it for the sharks teeth pal

 

[Ratsel]

worth it for the sharks teeth pal

Some Tomahawks had the Shark-teeth too. Both in the Pacific N.Africa.

 

[vanir]

okay I fail at facetious

 

[Shortround6]

The P-40-CU ( Tomahawk II) did 360mph with a Allison V-1710-33 making 1,090hp. Max ceiling was 33,000ft and climbed at 3,080ft/min. Seems the 'E' went the opposite direction with that big old chin

I think you are confusing the cause and effect of that big old chin and the 1500lb (22%) weight gain.
Considering that the Tomahawk IIB (P40-C) was down to 345mph, ceiling of 29,500ft and initial climb of 2650fpm with exactly the same radiator and engine as the P-40-CU ( Tomahawk I). And considering that the Allison V-1710-33 was good for 1090hp at 13,200ft compared to the 1150hp at 12,000ft for the P-40E and knocking off 2% for the adjustment in altitude means that the "E" had a whopping 35-40 more HP in the 15,000ft area than the P-40-CU.

 

[Wildcat]

The three front line sqns in PNG had MkIa and MkIII. They started transitioning to SpitXIII in 43 and I was under the impression NZ wound up with the Ns.
I've not looked it up for a year, I'm going by memory and what I read in passing. That was just what I was thinking.

Happily stand corrected.

Hi Vanir. Delivery's of P-40N's for the RAAF began in July 1943. 75, 76, 77, 78, 80, 82, 84, 86 and 120(NEI) squadrons were all eventually equipped with, and saw combat with, the N model. No 80 Wing (79, 452 457 sqn's) were the Spitfire MkVIII equipped units you might be thinking about.
HTH

 

[Njaco]

That was where Curtiss got their French orders from you know, the French wanted dive speed which is what sold them on the P-36 originally and in turn the P-40, which they considered simply a re-engined P-36 of which there were already two radial variations. It was actually the British that requested all the extra gear in the P-40 like extra armouring and self sealing tanks but these didn't appear until the P-40B, French and initial Army orders were for the plain P-40 based off the prototype.

I read the original Curtiss marketing flight tests of the P-36, power on vertical dives to a minimum speed of 400mph etc. It actually hit 450 in the test, French made an order within the month.

The thing which strikes me though is it being fairly unusual the US level speed requirements. It sounds suspiciously competitive with the European arms race of the thirties. Top speed ratings are for brochures in the marketing department, they don't relate much to military interests. RAF requirements are things like throttle heights and loadbearing. German ones altitude, cruise and rough field performance. The high top speeds of British and German fighters was incidental, not specified as far as I can remember.Anyways we had a lot of P-40E and P-40M with a handful of F and K in Australia (NZ got the N and we went to the Spit), I have been around these warbirds and people who've flown them. Relating mostly to the P-40M, what I've heard is marginally slower than a LF MkV Spit. Marginally.
Yeah heresay, take it for whatever it's worth.

I'm not so sure. The reason many early LW bombers had minimum defensive weapons was because they believed that the speed of the bomber was faster than the defending fighters. So speed was a military consideration at some point although it may have not been a major consideration.

 

[post76]

What helped kill P-40 altitude performance was a steady and large weight growth.

Exactly, weight growth.
Is that not an opposing design feature to "design to fly higher"?

 

[vanir]

I'm not so sure. The reason many early LW bombers had minimum defensive weapons was because they believed that the speed of the bomber was faster than the defending fighters. So speed was a military consideration at some point although it may have not been a major consideration.

That was the medium bomber requirement though, actually the trend started by the SB2 and taken up by dornier, blenheim, etc. The philosophy was speed over defensive armament. That was doctrine based.
I was more thinking of fighter requirements, British Air Ministry and RLM gave no speed requirements for fighters that I can think of appearing in any records, I mean I'm existentialising not making unfalsifiable claims, but the points that stood out were things like throttle height, or rough field performance, all combat related stuff. Max level speeds as you know aren't very reflective of combat performance or even what the envelope for that aircraft is like. Even the Japanese had no particular requirement for speed, or the Russians. The US which coincidentally had marketing interests and ambitions for the postwar aero industry, they're the only ones I can think of that offered a model contract on the basis of "must exceed 400mph in level flight, etc."

Hey I could be way wrong, has anybody come across anything along these lines? Some of you have much better libraries than me. Stuff I think is just a work in progress.


Oh and hey Wildcat, thanks for the info there. I lose track reading so much in passing, but really my memory retention is only good when it's very specific to a project, and on the one where I was reading Kittyhawk stuff it was for some Il2 flight remodelling of the P-40E and M in a mod I uploaded. I was trying to get accurate RAAF spec for the MkIa and MkIII and traced those stationed for a bit, it wasn't detailed research on the RAAF squadrons in total or their equipment and I can't remember how I got my impressions.

I like to get it right though, I write a little fiction with historic backdrops and it's nice to be pedantic about details I think, just good habit, write fiction like a documentarian. I tend to write matter-of-factly so it's better if the facts are correct. At some stage I planned writing something about the fighter combat over PNG, but I'm at the Eastern Front at the moment.

 

[FLYBOYJ]

A few comments here folks about the P-40 and USAAC procurement.

The P-40 design started in 1937 with the first flight occurring in October 1938. The design requirement issued at the development of the P-40 was loosely based on what the status-quo at the time really wanted in a "pursuit" aircraft (note we're not talking fighter). During that period the US was an isolationist country and its primary military doctrine was protection of US territory and interest and the thought process was just to "pursue" the forigen enemy and rid them of US territory. Additionally the US Navy saw protection of American shores as THEIR mission and there was a lot of inter-service bickering that led to many program hampered by politics and red tape.

Things changed with a NEW fighter specification issued January 25, 1939 that not only saw additional requirements placed on developing aircraft, but also introduced the specification for a fast medium bomber that would eventually bring about the B-25 and B-26, also being developed at this time. It was thought that most air combat was going to be occurring at lower altitudes 10 - 15,000 feet, 20K max. Look at the operating altitudes of the bombers of early 1939, early JU-88s had service ceilings barely reaching 30K, their best operating altitudes were going to be between 15 - 20K. A lot of the thinking was based on what was being operated over Spain just a few years earlier.

Basically American industry gave the customer what they asked for when the P-40 arrived but military planners were either stubborn or too political to see what was on the horizon. Considering the political climate of this period, the P-40 turned out to be an excellent design despite its short comings.

Read Victory Through Airpower by Serversky - he hints of this through out his book and talks about the P-40 lacking horsepower and and being void of a good cannon armament. Additionally he calls the Allison engine the "pet" of the AAC, but also remember when this book was written he was just ousted as the head of Republic. Its a good read and takes you back in time to the thinking of those who were actually involved in developing American hardware that would eventually see combat in WW2.

 

[tomo pauk]

I'd say that USAAC planers were trying to have all bases covered (hope that's the slang?), since they've ordered 13 pre-series YP-38s in April 1939, and we can be certain they knew such an airplane was to be suitable for altitudes from 20K up. The single-engined, turboed pursuit plane was to be available a year or two later compared with mech-supercharged plane, so they went for the later.

As for claims by A. Seversky that V-1710 was AAC's pet plane, that seems not to hold water - USAAC went for R-2800s for their next-gen fighter, the P-47, already in June 1940. They also looked after a 'second source of inline engines', and found that in Packard (=Merlins) - according to the 'Vee's for victory'.

 

[Shortround6]

Exactly, weight growth.
Is that not an opposing design feature to "design to fly higher"?

It is not a "design feature". It is a consequence of adapting an existing design to contemporary combat conditions. Nobody designed their planes to be heavier than they needed to be to perform the functions required of them. If the D.520 had survived another year (France not fallen in 1940) and they had added 400-500lbs worth of armor and self sealing tanks to the D.520 and it's altitude performance suffered as a result would you be claiming that the D.520 was not designed to fly at more than 15,000ft?