Bell P-39 development.

[blackkite]

「At the beginning of the development, P-39 was planned as high altitude interceptor with turbocharger.
The XP-39 made its maiden flight on 6 April 1938.
However, the XP-39 was found to be short on performance at altitude.
Flight testing had found its top speed at 20,000 ft (6,100 m) to be lower than the 400 mph (640 km/h) of the original proposal.
In June 1939 the prototype was ordered to be evaluated in NACA wind tunnels to find ways of increasing its speed, by reducing parasitic drag.
Tests were carried out, and Bell engineers followed the recommendations of NACA and the Army to reduce drag such that the top speed was increased 16%. NACA wrote, "it is imperative to enclose the supercharger within the airplane with an efficient duct system for cooling the rotor and discharging the cooling air and exhaust gases." In the very tightly planned XP-39, though, there was no internal space left over for the turbo. Using a drag-buildup scheme, a number of potential areas of drag reduction were found. NACA concluded that a top speed of 429 mph (690 km/h) could be realized with the aerodynamic improvements they had developed and an uprated V-1710 with only a single-stage, single-speed supercharger.

At a pivotal meeting with the USAAC and NACA in August 1939, Larry Bell proposed that the production P-39 aircraft be configured without the turbocharger.

The Army ordered 12 YP-39s (with only single-stage, single-speed superchargers) for service evaluation and one YP-39A. After these trials were complete, which resulted in detail changes including deletion of the external radiator, and on advice from NACA, the prototype was modified as the XP-39B; after demonstrating a performance improvement.

The production P-39 retained a single-stage, single-speed supercharger with a critical altitude (above which performance declined) of about 12,000 ft (3,700 m). As a result, the aircraft was simpler to produce and maintain. However, the removal of the turbo destroyed any chance that the P-39 could serve as a high-altitude front-line fighter. When deficiencies were noticed in 1940 and 1941, the lack of a turbo made it nearly impossible to improve upon the Airacobra's performance. The removal of the turbocharger and its drag-inducing inlet cured the drag problem but reduced performance overall.」

Bell P-39 Airacobra - Wikipedia

en.wikipedia.org

P-39 engine protection

I would imagine the engine will be more susceptible to rear gun attacks due to it being in the middle of the plane. Is there any evidence for or against this. Maybe there is extra armor? Thanks guys.

forum.il2sturmovik.com

38-326 | This Day in Aviation

 

[blackkite]

Bell P-39 Airacobra - Aeroplane - avia.wikisort.org

avia.wikisort.org

「XP-39Bell Model 11, one prototype 38–326 first flown 6 April 1938 or 1939. Powered by a 1,150 hp (860 kW) Allison V-1710-17 (E2) engine and was fitted with a General Electric B-5 turbosupercharger, creating a two stage supercharging system similar to the P-38 (engine-mounted mechanical supercharger, remote exhaust-driven turbo-supercharger as a second stage for high-altitude). Aircraft remained unarmed. Later converted to XP-39B.」

https://twitter.com/x/status/1756288138232656299

View: https://x.com/ian_bott_artist/status/1756288138232656299/photo/3

 

[Antonio]

Development of US fighters in the 30's is interesting.
Most early monoplane designs, under funded, resulted in 2nd class performers. The subsequent USAAC reaction was to ask for unreal performance, encouraging manufacturers to adopt immature or even bet for still non-existent technology. As a result they got 2nd class performers again.

 

[riggerrob]

As an aside, does anyone sell a plastic scale model of a P-39 or P-63 that can be built with the forward cowling open to display the cannon?

 

[tomo pauk]

At the beginning of the development, P-39 was planned as high altitude interceptor with turbocharger.
The XP-39 made its maiden flight on 6 April 1938.
However, the XP-39 was found to be short on performance at altitude.
Flight testing had found its top speed at 20,000 ft (6,100 m) to be lower than the 400 mph (640 km/h) of the original proposal.

Unfortunately, the top speed was not just 'lower than the 400 mph of the original proposal', it was badly under that figure. NACA says that the XP-39 as-is was capable for just 340 mph at 20000 ft (see pg. 85 of the 'Vee's for victory' book).
Reason for the awful top speed was the similarly awful drag of the aircraft, the coeficient of the drag at zero lift (ie. at max speed) was 0.0329; compare with eg. Spitfire V at around 0.022.

The Cd0 of the XP-39 was worse than what the biplanes had, the main culprits being the coolers, turbo, intakes and similar.

Using a drag-buildup scheme, a number of potential areas of drag reduction were found. NACA concluded that a top speed of 429 mph (690 km/h) could be realized with the aerodynamic improvements they had developed and an uprated V-1710 with only a single-stage, single-speed supercharger.

NACA was expecting 402 mph at 13200 ft from the XP-39 without a turbo and with the other improvements they suggested.
(per the chart on the same pg. of the same book)

The production P-39 retained a single-stage, single-speed supercharger with a critical altitude (above which performance declined) of about 12,000 ft (3,700 m). As a result, the aircraft was simpler to produce and maintain. However, the removal of the turbo destroyed any chance that the P-39 could serve as a high-altitude front-line fighter.

P-39C, as tested by USAAC, was good for 379 mph at 16000 ft (see the test report available here). Excellent for 1941, still good for 1942.

Installation of better engines was a surefire way to improve the performance even better for all the fighter aircraft, while still being without a turbo. See here for P-39C with just two guns and some nip and tuck, but with the V-1710-35 that has a faster-turning impeller than the ordinary -35s, making 406 mph at 18300+ ft.
See here (same link as the 1st one) for the different P-39s (-M, -N, -Q) making 375-400 mph with a better V-1710 installed.

Issue with the P-39 was the same as with the P-40 and the V-1710-powered P-51s: the engine-making company (Allison in this case) was slow on the ball wrt. outfitting their product with the better S/C in a timely manner. Better S/C is crucial on a small engine that the V-1710 was.

 

[DermotODyna]

As an aside, does anyone sell a plastic scale model of a P-39 or P-63 that can be built with the forward cowling open to display the cannon?

The old Monogram (later Revell) 1/48 P-39 kit had that option. I remember leaving that open made it difficult to balance the completed plane on its landing gear since there was no room to put lead weights in the nose. The kit included a clear plastic stand to prop the tail up.

Mind you, that's a memory from thirty years ago, so accuracy is not guaranteed!

 

[pathology_doc]

IMHO there is not a single V-1710-powered fighter that would not have been improved by the substitution of 60-series Merlins.

 

[southwestforests]

As an aside, does anyone sell a plastic scale model of a P-39 or P-63 that can be built with the forward cowling open to display the cannon?

Yes.
Kitty Hawk has a 1/32 scale plastic model with cockpit, engine, and gun bay, interiors.

Access panels to gun bay, engine, gun bays in wings, and 2 equipment bays in aft fuselage can be left open.
It has no pilot.

Instructions PDF can be downloaded from this model kit history and review website,

P-39Q/N Airacobra, Kitty Hawk KH32013 (2015)

One place to purchase kit is this outfit up by where my parents live.
Being 1/32 scale with over 300 parts it will relieve you of $80 to $100, depending.

ZIMKH32013 1:32 Zimi Model Kitty Hawk P-39Q P-39N Airacobra

spruebrothers.com

 

[Foo Fighter]

Bell P-39F Airacobra English

MONOGRAM/PRO MODELLER 1/48 5924 P-39Q AIRACOBRA Model Kit

Monogram/pro Modeller 5924 P-39q Airacobra Model Kits. KingKit are UK specialist suppliers of new and used Aircraft model kits.

www.kingkit.co.uk

 

[P-STICKNEY]

As an aside, does anyone sell a plastic scale model of a P-39 or P-63 that can be built with the forward cowling open to display the cannon?

Monogram used to in 1/48 Scale. I think one of the Retrokit manufacturers has re-issued it.

 

[hesham]

From the book,the American Fighter.

 

[blackkite]

XP-39E Bell Model 23. three P-39Ds modified for ground and flight testing first flown 21 February 1942. Intended for 2,100 hp (1,600 kW) Continental I-1430-1 engine but only flown with 1325 hp Allison V-1710-47 engine. Used to test various wing and vertical tails. Fuselage lengthened by 21 in (530 mm) and used in the development of the P-63. The production variant, with the Continental engines was to be designated P-76; there was no Bell XP-76 as such.

Bell XP-39E Airacobra

The XP-39E was an experimental version of the Airacobra originally produced as a test bed for the Continental V-1430 engine.

www.historyofwar.org

 

[blackkite]

Bell XP-39E with laminar flow wing, 1942 | World War Photos

XP-39E with laminar flow wing

www.worldwarphotos.info

The radiator of the P-39 is cleverly designed, so it is not easy to tell from the appearance where it is installed.

 

[blackkite]

Hi! I compared P-40N and P-39Q.
P-39 was very progressive and clean.
Source are as follows.

Variants P-40N

Bell P-39Q Airacobra American World War II Single-seat Fighter

Bell P-39Q Airacobra aircraft photos

www.skytamer.com

https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/article/196306/bell-p-39q-airacobra/

 

[Foo Fighter]

There are disparate opinions of this aircraft. I cannot honestly make heads nor tails of it tbh. Obviously all aircraft have their fans and detractors but I would need more non aligned information to make a reasoned opinion.

 

[Grey Havoc]

Basically it suffered in USAAC / USAAF service from the rather ill-advised decision early on to delete its supercharger, but it got a second lease on life when the Soviet Union found it very useful indeed at the mostly lower altitude operations its air force liked to concentrate on.

 

[Antonio]

There are disparate opinions of this aircraft

My personal opinion is that it depends on considering it was developed as an interceptor (failure) , then confronted against air superiority fighters (failure) but finally found a niche as a close support aircraft (success)

 

[hesham]

My personal opinion is that it depends on considering it was developed as an interceptor (failure) , then confronted against air superiority fighters (failure) but finally found a niche as a close support aircraft (success)

That's right my dear Antonio.

 

[blackkite]

Its best speed of 368 miles per hour(592km/h) was reached at 13,800 feet(4,200m). At higher altitudes, performance began to degrade rapidly and the airplane had reached its maximum ceiling by the mid-20s range(6,000m range). Unfortunately, developing events in Europe were soon dictating air combat at altitudes over 30,000 feet(9144m).

 

[blackkite]

https://www.quora.com/Why-do-the-P-39-and-P-63-aircraft-have-such-small-radiator-inlets-The-P-40-and-later-model-P-38s-also-used-the-Allison-engines-but-had-much-larger-chin-radiators-Anyone-know-how-Bell-managed-to-keep-the-Allison

Why do the P-39 and P-63 aircraft have such small radiator inlets? The P-40 and later model P-38's also used the Allison engines but had much larger chin radiators. Anyone know how Bell managed to keep the Allison engine from overheating?

The entrance for the cooling air does not have to be huge for fast aircraft, but you'll find that the radiator behind that inlet is quite large. The way in which airflow works through the radiator is to have it enter at high speed and then expand into a larger volume which slows it down and increased the pressure. That does two good things. The airflow is slower through the radiator core providing more time to absorb heat from the water, and the increased pressure makes for a very positive airflow through that radiator, which is beneficial since as the air travelling through the core absorbs heat, it expands and make a "mobile plug" which needs some pressure to push it through the core. The outlet for the radiator is up to 20% larger in area than the inlet to allow for that expanded air volume to escape without restrictions.
In fact there is a thing called the Meredith Effect which was used to advantage in the P51 radiator ducting design where that expanded hot air (it's had energy added from the hot water) could be forced out the exit (which was adjustable in size) to actually produce a little positive thrust for the aircraft.
Air cooling has a similar story re the entry and exit arrangements. The big radials had tight fitting cowls with relatively small inlet areas behind the prop but a large volume inside the cowl in front of the cylinder fins. This slowed the air and increased the pressure. Tinware around the cylinders made sure the only exist path for the airflow was through the finning where it absorbed heat and then exited through the slots/cowl flaps behind the cylinders. The exit ducting is, once again, roughly 20% larger than the inlet area, and since airflow was low during take off and there is no water to absorb excess heat (no thermal inertia), cowl flaps were opened to increase the exit area and encourage good airflow until the aircraft was airborne and had accelerated enough to provide sufficient airflow into the cowl for good cooling, and the cowl flaps were progressively closed.
Cooling design is quite a science (with some art thrown in) for both water cooled and air cooled engines.

 

[tomo pauk]

There are disparate opinions of this aircraft. I cannot honestly make heads nor tails of it tbh. Obviously all aircraft have their fans and detractors but I would need more non aligned information to make a reasoned opinion.

Depends on what people required it to do. As a high altitude fighter and/or long-range fighter, it was not good. As a low-altitude fighter where long range was not required, it was one of the better fighters.
It was probably the best fighter available en masse to the Soviets, FWIW.

Basically it suffered in USAAC / USAAF service from the rather ill-advised decision early on to delete its supercharger, but it got a second lease on life when the Soviet Union found it very useful indeed at the mostly lower altitude operations its air force liked to concentrate on.

The decision to remove one of it's superchargers (the turbosuperchager) was on point, not just because Bell botched the installation (together with the intercooler, as well as many other things, like the air intake, cooling system, oil radiator etc) - the XP-39 was about as draggy as a biplane of the day.
The other supercharger (gear-driven, on the V-1710 itself) was, well, still there.

My personal opinion is that it depends on considering it was developed as an interceptor (failure) , then confronted against air superiority fighters (failure) but finally found a niche as a close support aircraft (success)

Success of the P-39 was achieved in the Soviet hands it the role of a fighter, in the fighter units.
The close support was done by the Il-2 there.

Why do the P-39 and P-63 aircraft have such small radiator inlets? The P-40 and later model P-38's also used the Allison engines but had much larger chin radiators. Anyone know how Bell managed to keep the Allison engine from overheating?

Small radiator inlet vs. the big radiator was/is a good thing. See P-51, as well as many Soviet and Italian fighters.
On the contrary, see the big inlet on the Hurricane, Spitfire and Bf 109E contributing to the drag a lot.
P-38s never had the chin radiator for the engine coolant, it was always back in the boom.

 

[blackkite]

Hi!

The P-39 Airacobra

America’s unsung aerial hero.

warfarehistorynetwork.com

The P-39 Airacobra was a bit like Rodney Dangerfield—it “couldn’t get no respect,” especially from those who never piloted the “Flying Cannon” built by the Buffalo, New York-based Bell Aircraft Corp.

“Nothing could touch a P-39 used below 15,000-feet” contended American Air Ace Lt. Col. William A. Shomo who flew P-39s, P-40s, F-6Ds, and a P-51D in WWII. He wouldn’t have hesitated to have even taken on the vaunted P-38 at lower altitudes because of the extreme maneuverability of the “Flying Cannon.” And it could tangle successfully with a Japanese Zero, he argued, if the American pilot kept his airspeed at 300 miles per hour or better so the enemy “couldn’t turn inside you.”

The Americans in the field experimented with the aircraft throughout the war to continually gain an edge and some additional speed, eventually stripping off a chunk of belly armor under the seat that weighed some 750 pounds. With those modifications, the P-39 could “fly like a bumble bee,” asserted Shomo. He and his men especially liked the stinging power of the plane’s 37mm cannon that could, if necessary, fire off some 30 rounds in 12 seconds. The hefty warhead had a definite arching trajectory, but one could eventually learn to “drop the shell right into someone’s shirt pocket as he walked along the beach,” said the ace.

The Soviets received several models of the P-39, although most were Q-models with the Allison engine, the 37mm cannon, and four .50-caliber machine guns—two located in the upper nose and two wing-mounted. At Soviet request, the wing-mounted machine guns were later deleted.
A number of Westerners have mistakenly said the Soviets used the P-39, with its powerful 37mm cannon, as a flying tank buster. While some German tanks may have been struck on occasion by the cannon, the craft was used to its best advantage to clear the skies, silence artillery and antiaircraft batteries, and disrupt German supply lines and land-based command centers. In simple fact, the Soviet P-39s were not supplied with armor-piercing 37mm ammunition, and the standard-issue high-explosive round was not capable of knocking out armored targets.

The Soviet pilots fell in love with the fast, maneuverable, and well-armed P-39 that many found to be equal—or nearly equal—in speed to the German Bf109 and FW-190 fighters. (At Soviet request, the wing-mounted machine guns were later deleted.)Those enemy fighters could often be destroyed, the Soviets learned, with two or three short machine-gun bursts, while the strike of a single cannon shell could destroy or disable a German fighter or bomber.