I stand corrected on the number of 37mm shells. 60 is the number of a P-400´s 20mm shells. And I meant the cal.30-06 machine gun had 1,000 rounds each. IMO the ideal number of guns and amount of ammo depends on what the plane is supposed to do. Your four-gun proposal would probably be the better choice for an interceptor.
Could you have designed a better P-39?
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I stand corrected on the number of 37mm shells. 60 is the number of a P-400´s 20mm shells. And I meant the cal.30-06 machine gun had 1,000 rounds each. IMO the ideal number of guns and amount of ammo depends on what the plane is supposed to do. Your four-gun proposal would probably be the better choice for an interceptor.
Hey Guys, sorry for the delay getting back to you on the P-39A (aka XP-39) but I'm up to my ears in finishing a Statement of Work to add an additional 10 C-130 aircraft to our on going avionics upgrade to the C-130H and L100 aircraft.
As soon as possible I will put my info out...I have computer modeled the performance and have exact weights.
Der Dog
As soon as possible I will put my info out...I have computer modeled the performance and have exact weights.
Der Dog
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Ottawageezer
Recruit
As a newcomer, I find the P 39 re-design discussion civil, well-informed, friendly and fun. Here are some thoughts on the subject: possible changes in design that might have improved the P 39 performance as a fighter or attack aircraft. Though perhaps bending the original challenge, it seems interesting to consider changes that could have been made in later years (items 1 and 2 below) as well as in 1938.
1. Revisit the airframe structural design to have it conform to the adequate British (or German) stress limits rather than the more conservative American values. Relaxed stress limits contributed from the start to the fine performance of the F8F Bearcat and substantially improved the already excellent P 51 Mustang. The empty weight of the P51F, for example, was 5635 lbs. compared to 7125 lbs. for the P 51 D, a huge 20.9% improvement. Similar weight saving in the P 39 would improve, in probable order of value, rate-of-climb, range, maneuverability, top speed, landing speed and take-off run and would allow some latitude for weight-increasing modifications. Admittedly there would seem almost no chance of the Air Corps agreeing to this until well into the war.
The extremely rugged (sometimes over-rugged) construction of U.S. fighters seems to have been the common cause of rates-of-climb lower than they should have been.
1.1. As part of the airframe re-think, add armor, but make it part of the load-bearing structure of the airplane as was done with the IL 2 Shturmovik and the Fairchild A 10. The compact grouping of the pilot, cooling system and engine make the P 39 well suited to protection from below by one undersurface sheet of armor. A particularly thick sheet would be a nice feature of a ground attack version of the plane
2. I agree with several of you that, especially for the fighter role, the engine should be changed to a Merlin. There seems little chance, though, that this could be considered before September 1940 when it was agreed that Packard would produce the Merlin in the United States.
3. Increase the size of the leading-edge air intakes, ducts, and, if need be, radiators, to provide satisfactory cooling. The intakes have always LOOKED too small, noticeably smaller in fact than the leading-edge intakes on the radial air-cooled F4U Corsair. By all means keep the intakes on the leading-edge, however, because they are an asset there. As with intakes right at the nose, such as on the P 47 and F6F, they avoid airflow shear or turbulence from upstream surfaces, but do so without increasing the drag-producing cross-sectional area. In may opinion, leading-edge intakes, sometimes used only for the oil-cooler or carburetor, likely contributed to the good performance of aircraft such as the B 17, Mosquito, F4U Corsair, F8F Bearcat, Hawker Tempest and Fury, Yak 3 and 9, and the promising Westland Whirlwind.
3.1. Optimize ducting to fully exploit the 'Meridith effect' (1934), the jet thrust of heated air from the radiator, as was done with the Spitfire and Mustang..
3.2. Remove the carburetor air-intake from behind the canopy and incorporate it into a leading-edge intake. This would slightly reduce drag and accommodate the change to the Merlin which, unlike the Allison, has an updraft carburetor.
4. Remove the nose wheel. The Airacobra has always seemed too small to afford the luxury of a tricycle landing gear and performance in the air should take precedence over landing and ground handling. (The Bf 109 clearly followed this precedence a bit too far.) Removing the nose wheel frees valuable space in the nose (expensively bought by the unorthodox engine location), saves weight, and means less to go wrong or to maintain. As demonstrated by the Airacobra's tail-dragging naval cousin, the Airabonita, the main wheels can be attached to the front spar and stowed on retraction between the front and main spar. With the Airabonita, however, the radiators and ducts were moved backwards, out of the way, to the undersurface of the wing. In my opinion this should not be done. Instead, the wheels should be attached further out on the wing even if this requires reinforcement of the front spar. Alternatively, they might be retracted directly backwards as on the F4U. With the latter option, a notch would be needed in the main spar to accommodate the landing gear strut and the spar would need reinforcement at the notch.
5. Change the armament. The elimination of the nose wheel allows the general sentiment of Piper106, Shortround6, Markus, kreighund and delcyros to be taken further. With no nose wheel, a pure fighter version of the Airacobra would benefit from removing the 37mm cannon and going to 5 or 6 closely grouped guns in the nose, all 50 caliber with a common trajectory. A bomber interceptor might similarly be armed with, say, five identical 20mm cannon. Also, with no 37mm gun and no nose wheel to contend with, what the British claimed was extremely poor armament accessibility could be improved. A ground attack Airacobra, however, should retain the 37mm cannon and combine it with, say, four 20 mm cannon in the nose, even if this means fairing over unavoidable bulges.
6. On a fighter version of the plane, change the seating to give the pilot a much more reclining posture as in the Bf 109. This is effective and important in reducing drainage of blood from the brain in a tight turn or zoom. In the Airacobra, it also makes more space available for fuel,under the pilot. With no the 37 mm cannon, there would be room forward for the pilots feet. On a ground attack P 39, the original seating should be kept.
7. I agree with delcyros that automatic wing slats should be added to improve maneuverability and lower the stalling and landing speeds (as on the Bf 109) and perhaps mitigate, or even eliminate, the tendency of the Airacobra to tumble and go into a flat spin. The disadvantage, as experienced on the Bf 109, is possible disruption in aim when the slats suddenly deploy.
8. I agree that getting rid of the automobile doors is a very sensible idea. This would save weight and would simplify and improve both fuselage and canopy structure. A further minor point, if the new canopy slides, an antenna mast could still be avoided, as on the FW 190, with a pulley/spring arrangement inside the canopy.
1. Revisit the airframe structural design to have it conform to the adequate British (or German) stress limits rather than the more conservative American values. Relaxed stress limits contributed from the start to the fine performance of the F8F Bearcat and substantially improved the already excellent P 51 Mustang. The empty weight of the P51F, for example, was 5635 lbs. compared to 7125 lbs. for the P 51 D, a huge 20.9% improvement. Similar weight saving in the P 39 would improve, in probable order of value, rate-of-climb, range, maneuverability, top speed, landing speed and take-off run and would allow some latitude for weight-increasing modifications. Admittedly there would seem almost no chance of the Air Corps agreeing to this until well into the war.
The extremely rugged (sometimes over-rugged) construction of U.S. fighters seems to have been the common cause of rates-of-climb lower than they should have been.
1.1. As part of the airframe re-think, add armor, but make it part of the load-bearing structure of the airplane as was done with the IL 2 Shturmovik and the Fairchild A 10. The compact grouping of the pilot, cooling system and engine make the P 39 well suited to protection from below by one undersurface sheet of armor. A particularly thick sheet would be a nice feature of a ground attack version of the plane
2. I agree with several of you that, especially for the fighter role, the engine should be changed to a Merlin. There seems little chance, though, that this could be considered before September 1940 when it was agreed that Packard would produce the Merlin in the United States.
3. Increase the size of the leading-edge air intakes, ducts, and, if need be, radiators, to provide satisfactory cooling. The intakes have always LOOKED too small, noticeably smaller in fact than the leading-edge intakes on the radial air-cooled F4U Corsair. By all means keep the intakes on the leading-edge, however, because they are an asset there. As with intakes right at the nose, such as on the P 47 and F6F, they avoid airflow shear or turbulence from upstream surfaces, but do so without increasing the drag-producing cross-sectional area. In may opinion, leading-edge intakes, sometimes used only for the oil-cooler or carburetor, likely contributed to the good performance of aircraft such as the B 17, Mosquito, F4U Corsair, F8F Bearcat, Hawker Tempest and Fury, Yak 3 and 9, and the promising Westland Whirlwind.
3.1. Optimize ducting to fully exploit the 'Meridith effect' (1934), the jet thrust of heated air from the radiator, as was done with the Spitfire and Mustang..
3.2. Remove the carburetor air-intake from behind the canopy and incorporate it into a leading-edge intake. This would slightly reduce drag and accommodate the change to the Merlin which, unlike the Allison, has an updraft carburetor.
4. Remove the nose wheel. The Airacobra has always seemed too small to afford the luxury of a tricycle landing gear and performance in the air should take precedence over landing and ground handling. (The Bf 109 clearly followed this precedence a bit too far.) Removing the nose wheel frees valuable space in the nose (expensively bought by the unorthodox engine location), saves weight, and means less to go wrong or to maintain. As demonstrated by the Airacobra's tail-dragging naval cousin, the Airabonita, the main wheels can be attached to the front spar and stowed on retraction between the front and main spar. With the Airabonita, however, the radiators and ducts were moved backwards, out of the way, to the undersurface of the wing. In my opinion this should not be done. Instead, the wheels should be attached further out on the wing even if this requires reinforcement of the front spar. Alternatively, they might be retracted directly backwards as on the F4U. With the latter option, a notch would be needed in the main spar to accommodate the landing gear strut and the spar would need reinforcement at the notch.
5. Change the armament. The elimination of the nose wheel allows the general sentiment of Piper106, Shortround6, Markus, kreighund and delcyros to be taken further. With no nose wheel, a pure fighter version of the Airacobra would benefit from removing the 37mm cannon and going to 5 or 6 closely grouped guns in the nose, all 50 caliber with a common trajectory. A bomber interceptor might similarly be armed with, say, five identical 20mm cannon. Also, with no 37mm gun and no nose wheel to contend with, what the British claimed was extremely poor armament accessibility could be improved. A ground attack Airacobra, however, should retain the 37mm cannon and combine it with, say, four 20 mm cannon in the nose, even if this means fairing over unavoidable bulges.
6. On a fighter version of the plane, change the seating to give the pilot a much more reclining posture as in the Bf 109. This is effective and important in reducing drainage of blood from the brain in a tight turn or zoom. In the Airacobra, it also makes more space available for fuel,under the pilot. With no the 37 mm cannon, there would be room forward for the pilots feet. On a ground attack P 39, the original seating should be kept.
7. I agree with delcyros that automatic wing slats should be added to improve maneuverability and lower the stalling and landing speeds (as on the Bf 109) and perhaps mitigate, or even eliminate, the tendency of the Airacobra to tumble and go into a flat spin. The disadvantage, as experienced on the Bf 109, is possible disruption in aim when the slats suddenly deploy.
8. I agree that getting rid of the automobile doors is a very sensible idea. This would save weight and would simplify and improve both fuselage and canopy structure. A further minor point, if the new canopy slides, an antenna mast could still be avoided, as on the FW 190, with a pulley/spring arrangement inside the canopy.
Lighthunmust
Banned
I wonder if the Red Air Force would agree that it needed to be re-designed. They appeared to believe it a great plane only needing a few tweaks.
- Thread starter
- #85
That doesn't mean they wouldn't have appreciated an even better P-39.
michaelmaltby
Colonel
.... called the P-63 KING COBRA 
.
MM
.MM
- Thread starter
- #87
Lighthunmust
Banned
It also doesn't mean that they would. The tweaks I mentioned were about the equipment the Soviets removed not adding or changing equipment. From what I have read the Soviets did not have too many complaints about the P-39 for air to air. They understood the limitations and strengths of the design and used it accordingly. As I recall Chuck Yeager thought the Airacobra was a pretty good plane within its limitations.
.... called the P-63 KING COBRA
MM
A day late and a dollar short
The P-63 was not so much the product of a redesign as an entirely new aircraft that just looked similar to a P-39. Sorta like the difference between a P-51D and P-51H. I don't think you really could redesign the P-39 to be much better because of the inherent limitations of its size and layout.
Even with the benefit of experience they still didn't get a P-63 with the capability of a P-51 or P-47 in altitude or range. However if the fight was below 10K both of those would be in trouble against a P-63.
What is remarkable about the P-39 is how beautiful it is, what a great racer it was after the war, and how effective it was when flown by American and Soviet pilots who knew how to use it.
My primary source is "Cobra!" by Birch Matthews
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- Thread starter
- #90
Oooohh, I like this. Can we start a pool and build our own?
- Thread starter
- #92
Maybe having 3-4 hull HMGs 'stead of 2?
A low-to-mid altitude companion to P-38, the DoubleCobra. Two x 37mm, 4 x .50cals (or 6 x .50cals only), 2 x 75 plus a 150-gal drop tanks, additional fuel cells in outer wings (2 x 90 gals?), plus fuel cells in inner wing (60 gals?). Perhaps 390-400 mph by 1943?
A low-to-mid altitude companion to P-38, the DoubleCobra. Two x 37mm, 4 x .50cals (or 6 x .50cals only), 2 x 75 plus a 150-gal drop tanks, additional fuel cells in outer wings (2 x 90 gals?), plus fuel cells in inner wing (60 gals?). Perhaps 390-400 mph by 1943?
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Shortround6
Major General
I think that kind of sums it up.
some other thoughts on this subject.
I really can't understand this mania for trying to turn a pig's ear into a silk purse.
The P-39 had a lot of limitations due to it's initial design and no amount of minor "tweaks" were going to do more than help a bit.
many of the "tweaks" proposed in this thread (and others) are not really "tweaks" but designing a whole new airplane that just sort-of looks like a P-39.
P-39 was built the way it was because at the time it was ordered the only other game in town was the P-40. It was first ordered in the Summer of 1939 and first deliveries were in the Dec of 1940 (not combat capable) in 1941 it not only was the second most produced US fighter but it beat the production of the next 4 or 5 types put together. In 1942 it was still the second most produced fighter although other were catching up. Spend a number of months "dinking" with the P-39 design and you wind up with hundreds fewer fighters in 1942.
The P-39 was limited in it's small size (for an american fighter), there is only so much room to put stuff. P-40s had a bigger wing and a narrower track. While the landing gear folded back the landing gear legs were housed in a protruding fairing under the wing. the wing was longer front to back than it would be further out with a wider track and the wing is thicker top to bottom which gives more room to house the wheels without resorting to lumps and bumps on the wing.
It is all very well to talk about "just use the Meredith effect" but getting it to actually do what you want may be another story. While the 'idea' was fairly well known, having been put in a paper and read to a society in 1935 turning the formula or equation into practice took a lot more work. Look at a P-51 and see how much volume (cubic feet) they used to get the radiator/oil cooler duct to expand and contract in the right way and to fit the proper sized radiator to get the results that they got. Were do you find that kind of volume in the P-39?
The P-39 was handicapped by an American obsession with heavy gun armament. Not only was the plane designed around the gun rather than around the engine but the inclusion of the wing .30s and a totally foolish amount of ammo fished things off. (one of the "tweaks" the Russians used, dump the wing guns and ammo).
A P-39 carried about 886-890lb worth of guns and ammo, not including ammo boxes , gun mounts, gun heaters, chargers and other bits and pieces.
A Spitfire MK V with belt fed Hispanos carried about 620lbs worth of guns and ammo. Try bolting 270lb worth of lead ballast into the Spitfire and then limiting it's throttle so it gives about 200-300hp less than it really did and then compare it's performance to the P-39.
I have no idea why the USAAC thought you could jam that weight of armament into an 1150hp fighter and get something that was going to perform.
- Thread starter
- #95
That's a misundestanding that happens alot with these what-if threads.
Usually when I start one of these what-if threads, I'm imagining a redesign of the aircraft from day one with the magic of hindsight, not tweaks of an existing aircraft.
Shortround6
Major General
That's a misundestanding that happens alot with these what-if threads.
Usually when I start one of these what-if threads, I'm imagining a redesign of the aircraft from day one with the magic of hindsight, not tweaks of an existing aircraft.
I can understand some "what-ifs" and also "this would have been a neat plane if" but when the what-if wants to rewrite history "if they had just done "so and so" they could have/would have WON the battle of Upper Wenslydale or dominated the sky over Pago-Pago without ever considering what negative effects the modifications would have on either performance or production it gets a little strange.
As I have said before one of my personal "what if's" is a MK II Whirlwind (without Merlins) if not a MK III so I am not immune to the idea
I have no illusion that it would change the course of the war, at least not by much.
Lighthunmust
Banned
Ditch the wing guns and 37mm cannon. Use a 20mm or .50 in the nose. Tell your pilots to do what Hartmann said "Stick your nose in their cockpit".
Shortround6
Major General
Belt fed 20mm guns for starters, at least two if not 3 installations were mocked up and 1 or two flown? That is no stretch.
Set up fuel system to cross fed so if one engine goes out you can fed the remaining engine with both fuel tanks.
Fit full feathering propellers.
Fit fuselage fuel tanks. again already schemed/drawn up.
Fit an under fuselage hard-point to go along with a hard point under each wing. Plumb hard-points for drop tanks.
Engines is were it gets a little bit tricker
Fit a two speed gear box to the supercharger so you have sort of a Peregrine X engine like the Merlin X. Won't do much for altitude but should increase take-off and low level power by around 100hp per engine. Increase boost to 12lbs.
MK III gets a Merlin XX style supercharger or Merlin 46 style supercharger with 2 speed drive. Sized for the Peregrine engine. Might be able to get just under 1000hp per engine for take-off instead of historic 775hp which would help with under wing loads. low level climb should get a good boost. Might get 860hp at 18,500-19,000ft instead of 885 at 15,000ft. A useful increase if not amazing. Cuts into Typhoon territory quit nicely.
Messy1
Master Sergeant
Sure, 60 years of hindsight is a marvelous tool.
