Bell P-39 Airacobra

Single-Seat, Single-Engine Fighter / Fighter-Bomber Aircraft

United States | 1941

"The Bell P-39 Airacobra was one of the more unique piston-engine American fighters of World War 2 - seating its engine aft of the pilot while driving the propeller unit at the nose."

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Authored By: Staff Writer | Last Edited: 04/29/2021 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site; No A.I. was used in the generation of this content.

The Bell P-39 Airacobra is yet another in the long line aircraft studies stemming from World War 2 in the "what-might-have been" category. The system had all the looks of a top performer, armament that could go head-to-head with any contemporary and a design philosophy that could have brought about a whole new era is aircraft engineering. Unfortunately for the aircraft, several key requirements effectively doomed the Airacobra as a subjective failure - never quite living up to expectations. Still, the system served well enough, save for its intended role of high performance fighter, and went on to become a steady performer in the low-level attack role (excelling in combat under 10,000 feet). She was sent en masse to the Soviets via Lend-Lease and shunned by the British altogether - the latter finding that the aircraft (as advertised) possessed none of the capabilities being marketed by the Bell prototype.

P-39 Quick Glance

Generally a very pleasing aircraft to look at, the P-39 design came about at a time when streamlining aircraft shapes were just coming into their own. The P-39 was a vast departure from most aircraft being conceived of at the time and featured several design elements that distinguished the type from her contemporaries. Chief among these was in the internal layout, the Allison series engine mounted in the middle of the fuselage just aft of the cockpit. Engineers ran an extended shaft from the engine through a center bearing underneath the pilots feet to the front fuselage section where the three-blade propeller and reduction gear were mounted. As a result of this engine placement, the engine had to be fed through intakes mounted along the fuselage as opposed to a conventional placement in the nose. In early P-39 forms, this meant intakes were added to the sides of the fuselage just aft of the cockpit. Other forms mounted these intakes along the wing roots and the most identifiable form saw the intake affixed to the top of the fuselage. Wings were low-mounted monoplane assemblies and the empennage featured a traditional "T-style" arrangement with a single vertical fin. The P-39 also featured a powered tricycle landing gear system, a relatively new concept in the art of aircraft design for the time.

In what turned out to be effectively an early form of the "bubble" canopy, the Airacobra featured a complex canopy design which offered up unparalleled vision over the entire design. The pilot sat in a very ergonomically-minded cockpit that featured two automotive-style "swing" doors to either side of his seat. The windows in these doors were fully retractable and done so through a car-like crank handle. Upon having to exit his aircraft in the event of damage or power loss, the pilot simply jettisoned the doors via lever and rolled out one side or the other, eventually slipping off the edges of the respective wing. If enough time was allotted, he could even make his way to the wings edge and make a controlled jump.

Cockpit design was simple and similar in scope to the P-38 Lightning and P-40 Warhawk. Control levers were dominated by the throttle lever, easily the largest of the group. Most of the main control gauges were held in a center column running from knee-to-face height and offering up easy access. The throttle and other controls were held off to the lower left in a separate assembly that included the gun controls. Space-wise, the cockpit fit the build of a standard 5'8" pilot (standard for the time at least) and offered up limited comforts for sorties that could very well last several hours. Beyond that, however, many-a-veteran would curse the system's limited conveniences on longer trips. Internally, nothing was spared in constructing a cockpit worthy of any pilots own life. The cockpit featured air-tight sections to keep deadly fumes from the nose-mounted armament out and deadly fumes from the engine from creeping in from the rear. All vital systems were held in this area of the fuselage, which itself featured rugged and sturdy construction practices that would become synonymous with Bell Aircraft for a time.

A Changing World - For the Worse

The Bell P-39 design came about at a time when the world was turning increasing hostile on both sides of the United States. Troubles in Europe were readily apparent with the political and military movements occurring in Germany and Italy. Expansionism by the Empire of Japan in Asia were another area of real concern and forced an internal evaluation of American military power and might as it then stood. Systems then in service were found to be wholly inadequate for the new methods of war and attempts were now in motion to rectify the critical situation. Enter Larry Bell - president of the Bell Aircraft Corporation.

Bell Aircraft

If change was what the United States military was after, then change is what it found in this visionary. Bell had already made a splash on the aircraft design scene with their failed - yet incredibly interesting - first attempt with the Bell FM-1 "Airacuda". This "bomber-destroyer" was to have been the military answer for an ultimate bomber interceptor with the most distinct design feature being the 37mm cannons mounted in engine nacelles on each wing (including their respective gunners as well). Engines were of a "pusher" type (Allison brand) but the aircraft proved to be simply too heavy for the intended role. The aircraft did go on, however, to field an entire squadron before production ended.

In any case, development of the Airacuda (beginning the company tradition of using a naming convention featuring the word "air" in official designations) forced Bell's team to tackle the seemingly impossible. The experience garnered in the creation of the XFM-1 Airacuda was priceless and convinced the promising team that they could develop an aircraft for the US Army's new requirement - an interceptor. Besides the Curtiss P-36s, P-40 Warhawks and Seversky P-35s then in service, the US Army had very little to go on in the way of tangling with Japan's best fighters and bombers. She fielded no such aircraft to effectively seek out attacking bomber formations at night, no aircraft to threaten the new crop making up Japanese fighter command and no aircraft to efficiently bomb or cannon ground targets in any way with repeated success. The canvas was generally a blank one and Bell and his team set to work.

Birth of a Cobra

Bell's engineers took some new information to heart. First and foremost, armament of contemporary American fighters at the time was generally inadequate for use against the new generation of bombers. Aircraft were still being fielded with a World War 1-style gun arrangement featuring just two rifle-caliber (7.62mm) machine guns. Bell engineers took a radical approach to arming their prime fighter design and made the centerpiece of the aircraft a powerful - though slow-firing - Oldsmobile-brand 37mm cannon. This alone brought the new design leaps ahead of anything then service. The 37mm cannon would be supplemented with heavy caliber machine guns for additional punch in the form of 12.7mm (.50 caliber) types mounted in the wings. The design crew's optimism was not in question as such an aircraft would surely be reckoned with in any skies around the world but it did present several speed bumps in the thought process. A large caliber weapon as requested by the design team meant that there would have to be proper and adequate placement for the system somewhere in the fuselage. As a result, the P-39 was basically a design set around the position of this cannon - effectively being that the Airacobra was an aircraft designed around its own primary armament.

From one point of view, the addition of the 37mm cannon forced a design that was highly unorthodox while on the other it provided the aircraft a solid center of gravity for which to fire such a powerful weapon. Being centered in the fuselage and firing through the front, the aircraft could be of such high containment that eventual weight changes within the structure would generally have very little effect in the way of the aircraft's overall performance specifications. The weapon was hence mounted in the upper forward portion of the fuselage nose with the barrel protruding and firing out through the propeller hub. Two 12.7mm machine guns were also added to the upper-forward portion of the fuselage to compliment the cannon arrangement with more concentrated direct fire. These systems were synchronized to fire through the spinning propeller blades and had their rate-of-fire affected to a point but not wholly detrimental. Additional 12.7mm machine guns were added to either wing - one to a wing - for an impressive overall armament capability. The resulting aircraft, with the powerful and turbosupercharged (the turbosupercharger was mounted on the port side of the fuselage)Allison V-1710-17 liquid-cooled engine of 1,150 horsepower, was now designated officially as the XP-39.

The XP-39

The XP-39 was, at least outwardly, very similar to the final P-39 models soon to reach production. However, several elements soon became apparent with the program that would forever change the destiny of the aircraft - and effectively tarnish its rather impressive image. Despite production already beginning on several YP-39s, the US Army involved itself evermore in the Airacobra's design. With several old hands still holding power for this branch of service, the US Army decided to modify the Airacobra design to make it more ideal for use as a close-air support platform capable of operating under the control of ground forces instead of being its own independent aerial entity. As such, the P-39 was now being asked to provide better performance under a 10,000 foot ceiling limit. This meant the deletion of the ultra-important turbosupercharger - a requisite component in the aircraft's design that was all necessity when performing against the specifications found in the new German and Japanese fighters. It was thought that the deletion of the component would assist in making the P-39 a more stable and better-performing low-level system. What it did, however, was rob the aircraft of its performance gains that so wowed interested purchasing parties. The air intake was now moved to the upper portion of the fuselage (the more identifiable "look" to the P-39 that we recognize today) and another Allison engine was selected for production that would provide better low-level performance akin to what the US Army was looking for.

P-39 Production

The initial production P-39 systems became the P-39C models and were quickly followed by the P-39D series. The aircraft almost took on the designation of P-45 due to the radical list of changes from the original proposal through it was eventually settled that the P-39 designation was sufficient in detailing the significant changes and additions. P-39C models had a pair of 7.62mm (.30 caliber machine guns) mounted in between the existing 12.7mm heavy machine guns. Sixty examples of the ordered P-39C models effectively removed the 12.7mm heavy caliber wing-mounted machine guns and replaced them with 4 x 7.62mm types (two machine guns to a wing with 1,000 rounds each) and became P-39D designations while still retaining their nose-mounted 12.7mm heavy machine guns (200 rounds each). The 37mm cannon (30 rounds) was still in place. The completed P-39C and D models initially went to war with the 31st Pursuit Group (later becoming "Fighter" Group). It was also found later that the P-39 made for a stable bombing platform, particularly in the dive-bombing role, and had a single 500lb bomb affixed to the centerline fuselage underside.

Miscast Girl - the Airabonita

In an attempt by the Bell company to widen the interest of the P-39 design, the XFL-1 "Airabonita" was devised to showcase a modified P-39 form to the United States Navy as a carrier-borne aircraft alternative to the aging models being fielded. This model - of which only a single prototype was ever constructed - was a slightly revised P-39 with the most noticeable change to the system being the use of a traditional "tail dragging" undercarriage. The aircraft was powered by the Allison V-1710-6 series engine and flew for the first time on May 13th, 1940. As might be expected, this version failed to win over the naval audiences and went down in Airacobra lore as yet another failed design attempt. Additionally, the Airacobra was successfully mated with a radio-control feature that made her a popular remote-controlled target drone for some time. Additional variations also included a bizarre modification that produced the dual-seat trainer version which saw the fuselage extended to include a forward seating placement instead of the nose armament. These appeared in limited form from existing F- and Q-models and took on the designation of TP-39.

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P-39 Operators

Among early users of the type were the British which, with Germany pressing up against their door, were in desperation of finding legitimate fighter contenders for which to arm their fighter squadrons in place of their aged Hawker Hurricanes. P-39s in service with Britain took on the designation of "Airacobra Mk I" and, despite the shortcomings inherent in a turbosupercharger-less aircraft, were nonetheless thrown into the fray. To add to the mix, these P-39s began to show signs that the aircraft was not intended for use in the unforgiving sea-borne British Isle elements. The aircraft were prone to breakdowns and mechanical failures particularly in their landing gears. The rugged airfields of Britain were nothing in comparison to the smooth test-bed runways found in the United States. The mechanical service records of the Airacobra Mk I's got progressively worse over time and made the aircraft a much-hated breed on the island. To add insult to injury, it was soon found that dangerous fumes were being pumped into the cockpit after the firing of the 37mm cannon, fume levels deadly enough to kill a man. As a result, orders were issued that all RAF pilots use their oxygen masks from the point of engine ignition to the point of engine shutoff for their own safety. Whatever surplus P-39s on order the Brits had, they gladly passed them on to the hard-pressed forces of the Soviet Union (eventually to receive P-39N and P-39Q models in quantity by war's end). Any remaining P-39s after that were returned to America which, in turn, shipped them off for use to Australia (these as the P-400) - another hard-pressed nation at war or under threat.

The Russians found particular favor with the P-39 as a close-air support fighter. It proved to be quite a stable gunnery platform and the 37mm cannon was enough to give German soft armor a run for its money. Being that all of the powerful armament was basically concentrated in the nose section, this allowed for relatively easy targeting of slow-moving enemy ground units. This also provided for a very effective recoil-absorbing airframe to further the aircraft's inherent capabilities. It got to the point that some Russian P-39N and P-38Q models deleted all wing armament altogether to have concentrated firepower in the nose. In any case, the Airacobra proved its worth as a fighting platform via Lend-Lease, though still - in some respects - they remained outmoded by the German fighter offerings on the whole.

France initially ordered the P-39 early in the war but was forced to delay delivery of these units due to the country's capitulation to the German invasion. However, they would be one of the last operators of the machine by war's end and for a time afterwards. The P-39 would also be fielded in limited quantities by Allied Italian forces for a time but did little to show for their Airacobra use. Portugal interned some eighteen wayward P-39s that landed on their soil, ultimately applying payment to the United States for these captured systems at the end of the war. Regardless, the nation was glad to add some modern fighters to its stable. The Royal Australian Air Force received a mix of D- and F-models pending the Japanese invasion of the Australian mainland. These were returned to the United States when the threat officially subsided.

The P-39 as a Dogfighter

Not to say that the P-39 was a completely useless dogfighting platform - it should be noted that the aircraft could provide a fair fight in the hands of a skilled pilot knowing the limitations of his system. If the Airacobra could drag an opponent down below 10,000 feet, it stood a definitive chance to overtake an enemy through ingenuity and firepower (controlled friendly war games with even the fabled Vought F4U Corsairs showed this to be true). Performance-wise, however, the P-39 was devoid of any truly exceptional qualities when compared to the fighter types that were purpose-built for the role including the heavy Republic P-47 Thunderbolts.

However, the P-39 made many-an ace for the Soviet Air Force where air-to-air battles along the East Front typically unfolded under the optimal 10,000 feet ceiling limit of the Airacobra. Aleksandr Ivanovich Pokryshkin, the third highest scoring Allied ace, earned 60 Luftwaffe victims flying in his P-39. Similarly, Grigori Rechkalov - the second top scoring Soviet ace - earned 44 such victories piloting a P-39. Initial P-39 deliveries to the Soviet Union arrived with the British-selected 20mm Hispano-Suiza nose cannon while later models came with the more potent American-endorsed M4 37mm cannon - the latter adjustment making quite a difference. It is of note here that the United States did not deliver the M80 AP round for these autocannons through Lend-Lease. In their place came 1.2 million rounds of M54 HE rounds, proving useful for air and soft ground targets. As such, the Soviet P-39s were not used in the dedicated "tank-busting" role.

American P-39s in Europe

The USAAF fielded the P-39s in limited force across European operations. The 31st Fighter Group was set up and comprised of the 307th, 308th and 309th Fighter Squadrons. These men and their mounts arrived in England in July of 1942. Seeing prompt action, the Airacobra proved no match for the Luftwaffe. In one such fighter sweep, six of the twelve P-39s were lost to enemy action. It was not long after that the USAAF pulled the Airacobra form the theater, replacing the 31st Fighter Group P-39s with tried-and-true Supermarine Spitfires. Still, P-39s saw combat actions in support of the Operation Torch landings over North Africa and then over Italy. These primarily flew under the 10,000-foot ceiling limit, used in the close-support role and escorted by fighters. No German column, troop concentration or supply depots were safe.

P-39s in the Canal Zone

The P-39 was set into service in the Panama Canal zone under fear that the area was ripe for an attack from either ocean from Japanese or German submarine groups.

P-39s in the Pacific

After the surprise attack on Pearl Harbor (December 7th, 1941) the P-39 was pushed into the Pacific Theater of War and saw its first recorded combat with the 8th Pursuit Group. This occurred with the crews being short of spare parts and even shorter mechanical know-how. Following the initial P-39C and P-39D models were the P-39F and P-39G model series sporting an Aeroproducts-brand propeller system. Several more variations ensued for the type but most revolved around differing engines. P-39s (and her crews for that matter) were subjected to the harsh tropical environment that was the Pacific region

The Airacobra aircrews and ground crews surely showed their mettle in multiple combat actions basically doing much with a relatively limited set. It became evermore apparent that the P-39 in the Pacific Theater would soon need to be addressed and was - for the most part - properly done so with the addition of the Lockheed P-38 Lightnings delivered en masse to the region. Over the vast open spaces of the Pacific, the little P-39 was soon found to lack the needed range of a protracted island-hopping conflict so its replacement was warranted. The environment proved a nightmare for maintenance and reliability of the mechanical components as well. The Airacobra crews fought on, however, with their beautiful little ugly machines and played a key role in the protection of Australia from Japanese invasion, defending Port Moresby with a certain level of ferocity.

P-39s Across the Aleutians

Japan mounted an invasion across the Aleutian island chain off of Alaska in an effort to setup submarine replenishment points for actions in the Northeast Pacific. P-39s were thrown into the fray and mounted a valiant and pivotal defense against imposing odds. The weather in the region played poorly on the hapless American pilots, forced to wear layers of clothing and contend with the P-39s ill-suited cabin heaters. Mechanical issues were plenty and poor weather resulted in many accidents. When opportunity presented itself, however, these airmen and their P-39 mounts rained hell on the Japanese that were attempting to establish a foothold on the island chain. Targets of opportunity became flying boats, shipping vessels, airfields and depots. In all, 20 enemy aircraft were destroyed for the loss of just one P-39.

Conclusion

In the end, the P-39 was very much of what was not intended for the design. It lacked true fighter performance thanks to the US Army decision to take out the turbosupercharger and fit in a lower-rated Allison. The aircraft was specifically and primarily constructed for the role of a high-performance fighter but much of this was lost when the system was relegated to the close-air support role. The primary 37mm armament was the systems true saving grace as the down-graded wing machine guns did not match well against contemporary aircraft mounting multiple heavy caliber systems with a combination of cannon.

And a fighter design intended to be the American answer, she essentially became nothing more than a temporary solution for air forces around the globe. The landing gear issues and general mechanical reliability did not endear the system to most though the aircraft was still well-regarded for those pilots that saw beyond her deficiencies. In the end, the Airacobra was a snake that truly lacked a poisonous bite in her intended role but seemed to make for it in other ways - internally and externally. In any case, the P-39 is regarded as a modest success in most circles but only her pilots know her true value.

Some 9,584 P-39 examples were produced during her tenure at the cost of $50,666 dollars per unit in 1944 money. Production ran from 1940 to May of 1944. Formal introduction of the series began in 1941.

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Power & Performance
Those special qualities that separate one aircraft design from another. Performance specifications presented assume optimal operating conditions for the Bell P-39M Airacobra Single-Seat, Single-Engine Fighter / Fighter-Bomber Aircraft.

1 x Allison V-1710-83 water-cooled inline engine developing 1,200 horsepower and driving a three-bladed propeller at the nose.
Propulsion

386 mph
621 kph | 335 kts
Max Speed

35,991 ft
10,970 m | 7 miles
Service Ceiling

650 miles
1,046 km | 565 nm
Operational Range

3,333 ft/min
1,016 m/min
Rate-of-Climb

Structure
The nose-to-tail, wingtip-to-wingtip physical qualities of the Bell P-39M Airacobra Single-Seat, Single-Engine Fighter / Fighter-Bomber Aircraft.

1
(MANNED)
Crew

30.2 ft
9.19 m
O/A Length

34.0 ft
(10.36 m)
O/A Width

11.8 ft
(3.61 m)
O/A Height

5,611 lb
(2,545 kg)
Empty Weight

8,400 lb
(3,810 kg)
MTOW

Armament
Available supported armament and special-mission equipment featured in the design of the Bell P-39 Airacobra Single-Seat, Single-Engine Fighter / Fighter-Bomber Aircraft .

STANDARD:
1 x 37mm Oldsmobile cannon firing through the propeller hub with 34 rounds OR 1 x 20mm Hispano-Suiza cannon.
2 x 12.7mm machine guns in the upper forward fuselage with 200 rounds each.
4 x 7.62mm machine guns in wings (2 to a wing) with 1,000 rounds each.

OPTIONAL:
1 x 500 lb bomb externally mounted at fuselage centerline.

Variants
Notable series variants as part of the Bell P-39 Airacobra family line.

P-39 - Base Series Designation

XP-39 - Prototype Model Designation sans armament.

YP-39 - Prototype Preproduction Models of which 13 were produced; improved XP-39 model.

YP-39A - Preproduction XP-39 Model fitted with an Allison V-1710 engine sans turbocharger; single high-altitude test frame conversion model.

YP-39B - Based on the XP-39; fitted with new engine sans turbocharger; single unit produced.

P-45 - Initial Production Designation offered by the US Army to signify major changes to model P-39C; later dropped in favor of P-39 designation.

P-39C - Initial Production Models; 80 examples produced; 60 P-39C models became P-39D types.

P-39D - Production Model fitted with self-sealing fuel tanks and increased heavier armament (addition of 2 x 12.7mm machine guns in upper forward fuselage); Allison V-1710-35 water-cooled engine generating 1,150hp; conversion models from P-39C series.

P-39D-1 - Lend-Lease Model with Hispano-brand 20mm cannon; improved P-39D models with self-sealing fuel tanks; 863 examples produced.

P-39D-2 - Lend-Lease Model with Allison V-1710-63 (E6) powerplant; improved P-39D-1 model series; 158 on order; 1 conversion model from P-139D-1.

XP-39E - 3 examples produced with new powerplant of Continental I-1430-1 at 2,100hp; becoming the XP-63 "Kingcobra" prototype.

P-39E - Improved P-39D-1 model; though 4,000 were on order none of this type were produced.

P-39F-1 - Based on the P-39D model but fitted with Aeroproducts-produced constant-speed propeller system.

P-39F-2 - P-39F models modified for photo reconnaissance duties; 2 converted as such.

P-39G - 1,800 were ordered though eventually becoming the K, L, M and N models in the series.

P-39H - Designation Not Used

P-39J - Modified P-39D-1 model series with new engine and auto boost feature; 25 examples produced.

P-39K - Fitted with V-1710-63 powerplant and Curtiss-produced propeller system; based on P-39F model series; 210 examples produced.

P-39L - Modified P-39K series with Curtiss brand propellerand rocket rails installation; 250 examples produced.

P-39M - Fitted with V-1710-83 powerplant capable of 1,200hp and a larger propeller system; gearing changed; 240 examples produced.

P-39N - Improved P-39M series; fitted with V-1710-85 powerplant; decreased armor protection and fuel for increased weight and performance.

P-39P - Designation Not Used

P-39Q - Improved P-39N series; 1 x 37mm cannon and 4 x 12.7mm machine guns - two held in underwing gunpods and synchronized to fire through the propeller.

Bell Model 14 - French Order Model Designation; never delivered.

Airacobra Mk I - British Delivery Models

P-400 Airacobra I - Royal Air Force Designation

TP-39F - Dual-Seat Trainer Model

RP-39Q - Limit Production Dual-Seat Trainer Model

F2L - US Navy Target Drone Designation

XFL-1 "Airabonita" - Single Example Prototype Model for evaluation by US Navy; traditional landing gear array instead of tricycle type.

A-7 - Proposed Radio-Controlled Drone

TDL - US Navy Radio-Controlled Target Drone

Operators
Global customers who have evaluated and/or operated the Bell P-39 Airacobra. Nations are displayed by flag, each linked to their respective national aircraft listing.

Total Production: 9,588 Units
Contractor(s): Bell Aircraft Corporation - USA

[ Australia; France; Kingdom of Italy; Poland; Portugal; Soviet Union; United Kingdom; United States ]

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