Bell P-39 Airacobra & P-63 Kingcobra (2024)

* In the years before World War II, the Bell Aircraft Company developed ahigh-performance fighter of innovative design, the "P-39 Airacobra",featuring a mid-mounted engine. The P-39 would be produced in large numbers,though it would be most prominently used by the USSR; the same was true ofthe P-39's improved successor, the similar "P-63 Kingcobra". This documentprovides a history and description of the Airacobra and the Kingcobra.

[1] P-39 ORIGINS

* Larry Bell had been born in Indiana in 1894, but his family moved toCalifornia when he was 13. In 1912, he went to work for aviation pioneerGlenn L. Martin, rising to the vice-president position of the Martin firmby 1920. Martin wasn't the easiest person to work for, and Bell knew he'dnever get into a partnership position with the company -- so Bell quit in1925. He couldn't steady work for three years, but then he landed a job atConsolidated Aircraft in Buffalo, New York, rising to become general manager.

When Consolidated moved its operations to California, Bell decided to stay inBuffalo along with a cadre of like-minded individuals, forming Bell Aircraftin 1935. Later Bell would admit that naming the company after himself wasn'ta good idea, since it made it more difficult to delegate authority andlearned that "when your name's out front, you have to do a lot of things thatare a terrible bore."

The first product built by Bell was an extremely innovative machine, designedby a team under Bell chief engineer Robert Woods, named the "Airacuda", thename rhyming with "Barracuda". It was a "bomber destroyer", powered by twinAllison V-1710 water-cooled vee-12 engines, one mounted in a pusher fashionon each low-mounted wing. There was a glassed-in position in front of eachengine nacelle, accommodating a gunner with a 37 millimeter cannon. Therewere two more 7.62-millimeter (0.30-caliber) Browning fixed machine guns ineach nacelle, as well as a flexibly-mounted 12.7-millimeter (0.50-caliber)Browning machine gun in a blister position on each side of the rear fuselage,and the capability of dropping small parachute bombs or "aerial mines" toknock out enemy aircraft flying below.

The Airacuda was very whizzy-looking by the standards of the time, very muchfitting pulp science fiction concepts of the day -- and indeed it did make apopular splash, appearing on magazine covers, and even being duplicated as adie-cast toy. From a later perspective it looks pretty silly, which may bedue to the benefit of hindsight -- but a TIME magazine article from 1943called it "freakish-looking", suggesting the idea seemed dubious early on.The initial "XFM-1" prototype performed its first flight on 1 September 1937;it was followed by 12 "YFM-1" evaluation machines, with early examplesfeaturing taildragger landing gear and later ones featuring tricycle landinggear. The Airacuda's performance was poor, its role unclear, while it wasovercomplicated and unreliable; all of them were scrapped in 1942.

* In the meantime, Bell had been working on a single-seat fighter, the "BellModel 3", in response to a 1936 US Army Air Corps (USAAC) requirement. Asthe design emerged, it was a low-wing monoplane with tricycle landing gear,then an unusual feature, with the engine unconventionally mounted inmid-fuselage, turning the propeller through a driveshaft. This arrangement,which had been used in a few earlier experimental aircraft, was seen asenhancing agility by placing the engine at the machine's center of gravity(CG), as well as permitting installation of heavy armament in the nose.There was some thought of putting the co*ckpit behind the engine, close to thetail -- but that was quickly judged unrealistic, with the co*ckpit movedforward of the engine, this revision being designated the "Model 4".

The Bell proposal was submitted to the Air Corps in May 1937, with the USAACawarding a contract for a single prototype of what had by then become theBell "Model 12", more formally "XP-39", in October of that year. Initialflight of the XP-39 prototype was on 6 April 1939, with test pilot JamesTaylor at the controls. The machine was named "Airacobra" -- note that thename was "Air-A-Cobra", not "Air-Cobra" as it is easily miswritten, the nameclearly being assigned to echo the Airacuda name. In any case, this machinewas powered by an Allison V-1710-17 engine with a turbocharger system, theAllison providing 860 kW (1,150 HP). The aircraft featured a scoop on eachside of the engine for the turbocharger system. Armament was envisioned astwo 12.7-millimeter and two 7.62-millimeter Brownings in the nose and a T-137-millimeter cannon firing through the prop hub -- though the XP-39 wasn'tarmed.

On the basis of satisfactory initial test flights, the Air Corps awarded Bella contract to produce a dozen "YP-39" evaluation machines -- with the orderthen augmented with a 13th machine that was originally planned as the"XP-39A" -- to feature changes recommended in light of studies by the USNational Advisory Committee for Aviation (NACA). While work went on to buildthese machines, the XP-39 was rebuilt to the "XP-39B" configuration, theprimary change being that the turbocharger system was deleted, with theAllison engine reverting to its standard single-stage supercharger. TheXP-39 was the only Airacobra to be fitted with a turbocharger system.

Sources are very confused as to why the decision to delete the turbochargerwas made; one common claim is that the Air Corps didn't believe high-altitudeperformance was important to their requirements, and had concerns over theadmitted complexity of the turbocharger. It seems a bit hard to believe thatthe Air Corps wouldn't have wanted good high-altitude performance if theycould have got it, and they had no problems with the use of the sameturbocharger on the P-38 Lightning; it appears that NACA wind tunnelexperiments showed the XP-39 turbocharger installation was so aerodynamicallycluttered that it did more harm than good. The XP-39B deleted the scoops forthe turbocharger, and instead featured a small but distinctive carburetorintake on the spine of the aircraft. The re-born XP-39B performed itsinitial flight on 25 November 1939.

The first of the batch of YP-39s performed its initial flight on 13 September1940, with all delivered by the end of the year. They also used asupercharger instead of turbocharger; the later YP-39 machines in theevaluation batch featured armament. Even before the first flight of YP-39,the Air Corps had ordered a batch of production machines, originallydesignated "P-45" but then designated "P-39C", their configuration being muchlike that of the armed YP-39s. The first P-39C flew in January 1941.

The P-39C really wasn't suitable for combat, lacking armor and self-sealingtanks. 80 had been ordered, but only 20 were built, combat reports fromEurope indicating that the P-39C was simply not up to combat duty. Theremaining 60 machines in the order were built with armor, self-sealing tanks,and enhanced armament as the "P-39D". The P-39C ended up being an evaluationtype, with the P-39D being the first Airacobra to go into formal service withthe Army Air Corps. It would also be the first "Cobra" variant to seeaction.

[2] P-39D DESCRIBED

* From the P-39D onward, the Airacobra family did not change radically inconfiguration, so the P-39D makes a good baseline for the type. The P-39Dwas, as mentioned, of low-wing configuration with a broadly conventionallayout -- differing from convention with the centrally-fitted Allison engineand its driveshaft (implying a transmission hump up through the co*ckpit),tricycle landing gear, and the eccentric feature that the pilot got in andout of the co*ckpit through a car-style side door, with a door on each side.The doors even had roll-down windshields. They made access to the aircrafteasy, though they also made escape a bit tricky in a pinch; apparently theywere rigged so they could be discarded to simplify bailing out.

Construction was mostly of aircraft aluminum, with some magnesium parts andfabric-covered flight surfaces. All the landing gear assemblies had singlewheels, with the nose wheel castoring and ground steering by differentialbraking. The nose gear retracted backward, and the main gear hinged in thewings to pivot towards the fuselage. The engine was a V-1710-35 Allison,also with 860 kW (1,150 HP) but with technical improvements, driving athree-bladed Curtiss Electric variable-pitch propeller. Self-sealing fueltanks were fitted in the wings; trim considerations made installing fueltanks in the fuselage problematic, the engine preventing them from beinginstalled on the CG, and the relatively small size of the wing tanks meantmodest range. Armament consisted of:

• One M4 37-millimeter cannon -- "M4" being the service designation for the T9 -- with 30 rounds of ammunition. The P-39C had only 15 rounds of ammunition.
• Two 12.7-millimeter Browning guns on top of the nose, firing through the prop arc with interrupter gear, with 300 rounds per gun (RPG). The P-39C also had two 7.62-millimeter Brownings on the bottom of the nose, but they were deleted from the P-39D.
• Four 7.62-millimeter Brownings, two in each wing, with 1,000 RPG.

There was a centerline stores rack, capable of handling stores of up to 225kilograms (500 pounds). Although the P-39D was used for trials of variousconfigurations of belly tanks for ferry flights, it is unclear if the P-39Dever carried a belly tank in service.

 ___________________________________________________________________ BELL P-39D: ___________________________________________________________________ wingspan: 10.36 meters (34 feet) wing area: 19.79 sq_meters (213 sq_feet) length: 9.19 meters (30 feet 2 inches) height: 3.61 meters (11 feet 10 inches) empty weight: 2,475 kilograms (5,460 pounds) MTO weight: 3,720 kilograms (8,200 pounds) max speed: 580 KPH (360 MPH / 315 KT) service ceiling: 10,000 meters (33,000 feet) range: 960 kilometers (600 MI / 520 NMI) ___________________________________________________________________

* A total of 429 baseline P-39Ds was built, followed by 336 "P-39D-1"machines, the primary difference being replacement of the M4 37-millimeternose cannon with a 20-millimeter Hispano Mk.404 cannon with 60 rounds ofammunition. It appears the substitution was due to production difficultieswith the 37-millimeter cannon. The P-39D-1 also featured a small fillet onthe front of the tailfin where it merged with the top of the fuselage;sources are a bit unclear as to whether the fillet was actually fitted to thebaseline P-39D, but it certainly didn't appear on the P-39C.

Following the P-39D-1, Bell built 158 "P-39D-2" machines, much the same asthe P-39D-1 but with very minor tweaks. In addition, a total of 26P-39D-series aircraft was converted to a photo-reconnaissance configuration,the "P-39D-3", by placing two cameras in the aft fuselage and adding a bit ofarmor. It is unclear if they retained full armament. They were followed by11 similar "P-39D-4" conversions. Total production of the D-series was 429 +336 + 158 = 923 aircraft.

[3] P-39 VARIANTS: EXPORT P-400, XP-39E THROUGH P-39Q

* Roughly in parallel with P-39D production, Bell manufactured a total of 675"P-400" Airacobras for export. The French had bought a batch of P-400s inApril 1940; the order was taken over by the British after the fall of Francea few months later, with the British then substantially increasing the buy.The P-400 was very similar to the P-39D-1, with the 20-millimeter Hispanocannon, but instead of 7.62-millimeter Brownings in the wings, it featured7.7-millimeter (0.303-caliber) Brownings for compatibility with Britishammunition.

However, British expectations of the "Airacobra I" -- as it was designated inRoyal Air Force (RAF) service -- had been set by performance figuresestablished by the unarmed and unarmored XP-39 prototype. On evaluation, theP-400 turned out to be about 10% slower than advertised, and of course itshigh-altitude performance was pathetic. It should be noted, however, thatBell engineers were correct in believing the mid-mounted engine was good formaneuverability, the RAF report concluding that an Airacobra could easilyout-turn a Messerchmitt Bf 109.

Only a portion of the P-400 order was delivered to the UK, serving for ashort time with RAF Number 601 Squadron, "City Of London". The remainder ofthe batch was shipped to the USSR or was taken into US Army Air Forces(USAAF) service -- the "Air Corps" having been superseded by the "Air Forces"in June 1941. The P-400s saw combat in the South Pacific; it is likely theywere fitted with 7.62-millimeter Brownings for ammunition compatibility,though sources are unclear on the matter.

* The P-39D left something to be desired in service, suffering from a rangeof teething problems such as gear that was unreliable or froze up and otherdeficiencies. Deficiencies were addressed in subsequent variants, initiallywith a confusing list of P-39 variants built in small or relatively limitednumbers:

• The "XP-39E", which was a substantially modified experimental machine, with a 53-centimeter (21.3-inch) fuselage stretch, more fuel capacity, and wider wings plus tailplane. All flight surfaces had squared-off tips, with the tailfin fitted with a prominent leading-edge fillet later in development. It was supposed to have been used to evaluate the Continental V-1430 engine, but non-availability of such meant it was powered by an Allison V-1710-47 engine with a two-stage supercharger instead. Three were built; despite all the changes, its performance was no better than that of the P-39D, and so that line of investigation was abandoned.
• The "P-39F" was almost identical to a P-39D with the M4 37-millimeter cannon, but had an Aeroproducts three-bladed prop, since Curtiss was having problems making deliveries. 210 were built, with 27 given minor improvements and redesignated "P-39F-2".
• There was an intent to build a "P-39G" variant, but the aircraft planned for that build ended up getting other designations. There was no "P-39H" nor "P-39I"; the USAAF didn't like to use the "I" suffix because it was too easy to confuse with a "1" and end up with "P-391", but what happened to the P-39H designation is unclear. That means the P-39F series was followed in production by the "P-39J", which was much like the P-39F, but had a slightly improved Allison V-1710-59 engine. 25 P-39Js were built.
• The "P-39K" featured the further improved V-1710-63 engine. 210 were built, all under the designation of "P-39K-1", there apparently not being a P-39K (no block number) subvariant. Six were slightly modified as "P-39K-2" machines, with one P-39K-1 altered as the "P-39K-5" testbed, with a V-1710-85 engine, a wider Aeroproducts prop, and other changes.`
• The "P-39L" was much the same as the P-39K, except for fit of a Curtiss Electric propeller with a diameter of 3.15 meters (10 feet 4 inches). 250 were built under the designation of "P-39L-1" -- again, there was no P-39L subvariant -- with 11 modified to "P-39L-2" reconnaissance machines.
• The "P-39M" was similar to the P-39L, but had a V-1710-67 engine with improved high-altitude performance. 240 were built under the designation of "P-39M-1", with 8 converted to "P-39M-2" reconnaissance machines. It appears that the P-39M was the first Airacobra to carry a centerline external tank as a normal fit, tank options being either 284 liters (75 US gallons) or 662 liters (150 US gallons).

* All these variants were simply a warmup to the "P-39N", with almost as manyP-39Ns built as the sum of all earlier variant production. The baselineP-39N featured a V-1710-85 engine and a 3.18-meter (10 foot 4 inch)Aeroproducts prop; a P-39K was modified as the series prototype. 500 ofP-39Ns were built, with all but the first 160 featuring elimination of threeinternal fuel cells to reduce weight. The P-39N could of course carry anexternal tank to compensate for the smaller internal fuel load, and serviceunits that wanted the full internal fuel load back could install a fieldupgrade kit to restore the deleted fuel cells. Several further P-39Nsubvariants were built:

• The "P-39N-1" featured a wider 3.51-meter (11 foot 7 inch) Aeroproducts propeller. 900 P-39N-1s were built.
• The "P-39N-2" was a photo-reconnaissance conversion of 128 P-39N-1 machines.
• The "P-39N-3" was a photo-reconnaissance conversion of 35 baseline P-39N machines.
• The "P-39N-5" was a P-39N-1 with armor plate replacing the co*ckpit rear armor glass. 695 were built for a total P-39N production of 500 + 900 + 695 = 2,095 aircraft.

* The actual definitive Airacobra variant, however, was the "P-39Q", with more P-39Qs built than the rest of P-39 production put together. Subvariantsincluded:

• The "P-39Q-1" was much like the P-39N, retaining the V-1710-85 engine, but replaced the two 7.62-millimeter machine guns in each wing with an underwing fairing stowing a single 12.7-millimeter machine gun -- for total armament of four 12.7-millimeter guns plus the 37-millimeter cannon. Pilots had complained the 7.62 millimeter guns were ineffectual, with Soviet pilots mocking them as "paint scratchers". 150 P-39Q-1 machines were built.
• The "P-39Q-2" was a photo-reconnaissance conversion of 5 P-39Q-1 machines.
• The "P-39Q-5" was much the same as the P-39Q-1 but restored the deleted fuel tankage. 950 were built.
• The "P-39Q-6" was a photo-reconnaissance conversion of 148 P-39Q-5 machines.
• The "P-39Q-10" was similar to the P-39Q-5 except for various minor tweaks, for example improved winterization -- presumably at Soviet request, the bulk of P-39Q production going to the USSR. 705 were built.
• The "P-39Q-11" was a photo-reconnaissance conversion of 8 P-39Q-10 machines.
• The "P-39Q-15" was similar to the P-39Q-10 except for minor tweaks, such as reducing the number of oxygen bottles from 4 to 2. 1,000 were built.
• The "P-39Q-20" was in turn similar to the P-39Q-15 but with further minor tweaks. Most were delivered to the USSR, with the wing guns deleted from these machines; the Soviets thought that two 12.7-millimeter guns and the 37-millimeter cannon provided perfectly adequate armament, and wanted the wing guns deleted to save weight. In fact, they had been yanking the wing guns from earlier P-39Q machines after delivery. The wing guns were similarly deleted from later P-39Q subvariants sent to the Soviet Union. 891 P-39Q-20 machines were built.
• The "P-39Q-21" was similar to the P-39Q-20, but had a four-bladed Aeroproducts propeller. 109 were built.
• The "P-39Q-25" was similar to the P-39Q-21, but had a reinforced rear fuselage and tailplane. 700 were built.
• The "P-39Q-30" was similar to the P-39Q-25 but reverted to the three-bladed propeller; it also featured minor tweaks. 400 were built, for total P-39Q production of 150 + 950 + 705 + 1,000 + 891 + 109 + 700 + 400 = 4,905 aircraft.

The list below summarizes Airacobra variants and production:

• XP-39 (1 built): turbocharged initial prototype
• YP-39 (13 built): evaluation machines
• XP-39B (1 upgrade): rebuilt initial prototype
• P-400 (675 built): with 20-mm cannon for RAF, most flown by USAAF
• P-39C (20 built): preproduction machines
• P-39D (923 built): initial full production variant
• XP-39E (3 built): heavily modified experimentals
• P-39F (229 built): like P-39D, but with Aeroproducts prop
• P-39J (25 built): V-1710-59 engine
• P-39K (210 built): V-1710-63 engine
• P-39L (250 built): like P-39K, but with wider Curtiss prop
• P-39M (240 built): V-1710-67 engine
• P-39N (2,095 built): V-1710-85 engine, other changes
• P-39Q (4,905 built): quadruple 12.7-millimeter guns, other changes

That gave total production of 9,589 Airacobras.

[4] AIRACOBRA IN SERVICE / SOVIET COBRA "CLONES"

* The US was abruptly thrown into World War II on 7 December 1941, and spentmuch of 1942 simply trying to stave off disaster while preparing to take theoffensive. The P-39 was one of the weapons available at the time, seeingservice in the South Pacific, in the Aleutians, and in North Africa andItaly.

In USAAF hands, its record was mixed: it was sturdy and well-armed, but itshigh-altitude performance was poor and its centrally-mounted engine led tohandling problems. The difficulty was that after ammunition was expended,the aircraft's CG shifted back so that the aircraft was inclined to flytail-first, throwing it into a flat spin from which recovery was problematic.Bailing out under such conditions was also troublesome, because the pilot hada tendency to hit the tail. Even if recovery were possible, the spin had atendency to warp the aircraft's tail, rendering the controls useless, whichis why the P-39Q-25 introduced a reinforced rear fuselage.

Still, the aircraft's firepower was impressive. Many sources say the37-millimeter cannon was inclined to jams, but the significance of thatproblem is disputed; nobody disputes that any enemy target that took a solidhit from the cannon wasn't going anywhere but down. The Airacobra'slow-altitude performance was also good, being regarded as a peppy littleaircraft at the low level -- and certainly nobody could fault it for looks,with its elegant curved lines. One USAAF pilot, Lieutenant Bill Fiedler,became an ace in the Airacobra, while several other USAAF pilots scored killswith it. However, to the Army Air Forces the Airacobra was an "also-ran";the P-39 was ultimately relegated to training and other rear-area roles inUSAAF service.

* There were several minor export users:

• As mentioned, the British RAF flew one squadron of P-400 Airacobras, but only performed a single combat mission with the type before withdrawing it from service.
• The Australians obtained a number of hand-me-down Airacobras from the USAAF early in the Pacific fighting to help protect Darwin and other targets in northern Australia. The Aussie P-39s never saw action, and they were quickly withdrawn from service.
• The Free French obtained almost 250 Airacobras from mid-1943 in the Mediterranean theater, but they were phased out in favor of the Republic P-47 by late 1944.
• After the surrender of Italy to the Allies in 1943, the country was split between Allied-aligned and Axis-aligned factions. From 1944, the pro-Allied Italian government obtained almost 150 P-39s, which were used against the pro-Axis Italian forces and the Germans. The Italians continued to fly their P-39s into the postwar period.
• The Portuguese interned a number of P-39s that performed forced landings in Portugal during the war, going so far as to pay the Americans for them. Without training in flying or maintaining the P-39s, not to mention no supply of spares, they weren't all that useful, and were ultimately scrapped.

* It was the Soviet Union that made the most of the Airacobra, obtainingroughly half the P-39s built, over 5,500 -- over a quarter of the number ofLend-Lease aircraft sent to the USSR, more than any other type. While earlyon they came in through a variety of routes, eventually they were generallyair-ferried from the USA through Alaska and Siberia, generally by Sovietpilots, many of them women.

The Red Air Force put the Airacobra to very good use. In fact, in hindsightthe P-39 could almost be regarded as a Soviet aircraft that the Americans hadcontracted to build for the USSR; at one point, Soviet dictator Josef Stalinwrote a personal letter to US President Franklin Roosevelt asking for moreP-39s.

While a myth has persisted that the Red Air Force used the P-39 for closesupport, it was actually employed as an air combat machine. The Soviets hada much better close-support aircraft, the brutish Il-2 Shturmovik; the USonly supplied the Red Air Force with high-explosive 37-millimeter rounds, notarmor-piercing rounds. The tale of the P-39 as a close-support aircraft inthe war on the Eastern front appears to have been promoted by references toits use in "tactical support" -- which in Soviet usage simply meant it wasflown in association with ground force operations, not necessarily implyingclose-support duties.

Many of the top Soviet aces flew the "Kobruschka (Sweet Little Cobra)",including Grigory Rechkalov, who scored 57 victories, most of them inflictedby the P-39, and the well-known Aleksandr Pokryshin, with 53 victories, againmost being obtained with the P-39. One Red Air Force pilot, Mikhail Baronov,scored one of his 28 total "kills" by chopping off the tail of a Bf-109 overStalingrad with the prop of his P-39. Some claim the P-39 was the best-likedof all Western aircraft obtained by the Red Air Force.

Why the dramatic difference between the US and Soviet experience with theP-39? It wasn't a question of the Red Air Force being up against a weakeropponent; the German Luftwaffe was never a pushover for any Allied airforces. Part of the reason was that the Red Air Force was a tactical airarm, its primary mission being battlefield support of Red Army ground forces,and as a result air combat tended to be at low altitudes. Under suchconditions, the P-39 could fight on at least equal terms with the Luftwaffe'sMesserschmitt Bf 109F and its successor variants, as well as the Focke-WulfFw 190 -- which was not noted for its high-altitude performance either.

Another reason was that the Red Air Force thoroughly evaluated the Airacobrabefore putting it into service, finding out the hard way about its viciousspin characteristics, with several test pilots killed. The faults weredocumented, however, with rules for flying the aircraft written up foroperational pilots -- they were warned to never perform aerobatics if theyhad expended their ammunition -- and training implemented to make sure P-39pilots knew how to avoid spins and, when possible, head them off before thepoint of no return. Procedures had to be devised for maintenance in extremecold conditions. Bell engineers went to the USSR to assist the Soviets inqualifying the P-39, obtaining feedback for refinements to the design.

* Some late-model P-39s supplied to the USSR remained in service into theearly 1950s, a testimony to Soviet fondness for the machine. Some wererefitted with Soviet armament of a single Berezin 20-millimeter cannon andtwin Berezin 12.7-millimeter UBS machine guns; a few were even fitted withthe Klimov M-105P vee-12 engine, which had a similar form-factor to theAllison V-1710.

Before America began supplying Airacobras to the USSR, the Soviets eventhought of copying it, finding the reports on its design of great interest.The first concept for doing so was proposed in 1939, with well-known aviationdesigner Pavel O. Sukhoi sketching out a concept much along the lines of theP-39. That came to nothing, but in 1940, another aircraft designer namedMikhail I. Gudkov came up with his design for what would now be called anAiracobra "clone", the "Gu-1".

The Gu-1 had the exact same general layout as the P-39 -- mid-mounted vee-12engine, tricycle landing gear, a cannon firing through the prop hub, twoheavy machine guns in the nose, and four light machine guns in the wing. Itslines and details were distinctly Soviet, however, one major difference beingthat it didn't have the P-39's car-style doors. A prototype was actuallybuilt after an extended development, performing its first flight on 12 June1943 -- with the flight ending in a crash that killed the pilot, Aleksey I.Nikashin. That was the end of the program, though Gudkov also proposed a"Gu-2" interceptor along the same lines, featuring very heavy armament,including a 45-millimeter Shpital'niy cannon firing through the prop hub. Itdidn't happen.

In 1941 yet another Soviet aircraft designer, Viktor N. Belyayev, came upwith a design for a "twin Airacobra", the "OI-2", the configuration matingtwo P-39 clones together with a center wing section, though only the rightfuselage had a co*ckpit. The basic configuration looked much more like a P-39than the Gu-1, even featuring the car-style doors. It was to be powered bytwin vee-18 Klimov M-120UV engines with 1,340 kW (1,800 HP) each, with aTaubin 23-millimeter cannon firing out each prop hub, four UBS12.7-millimeter machine guns firing through the prop arc in the leftfuselage, four ShKAS 7.62-millimeter machine guns in the wing center section,and a capability for external loads of up a total of 500 kilograms (1,100pounds). It was certainly an interesting idea and impressively capable onpaper -- but it didn't get off the drawing board.

[5] P-39 MODIFICATIONS / BELL XFL-1 AIRABONITA

* Given some of the Airacobra's vices, it wasn't surprising that the servicesflying the machine thought a two-seat trainer would be useful in teachingnovice pilots how to fly the machine. Bell responded by modifying a P-39Q-5to "TP-39Q-5" configuration by removing the armament, adding a forwardco*ckpit with a side-hinged canopy up front for a flight instructor, andadding a ventral strake under the tail and an extended forward tailfin filletto deal with aerodynamic changes. It was rolled out in September 1943.

That experiment proving satisfactory, Bell converted 12 P-39Q-20 machines toa similar "RP-39Q-22" configuration, the "R" indicated "restricted", as innot suitable for combat. A few were supplied to the USSR; the Red Air Forcethought it a good idea, and so cooked up a few Airacobra trainer conversionsof their own, designated "UTI P-39"; they had a different forward canopyarrangement.

Two P-39Qs were actually obtained by the US Navy for use as radio-controlleddrones, being initially designated "XTDL-1" and then "XF2L-1K". SomeAiracobras ended up on the civilian racing circuit for a time after the war.A fair number of P-39s still survive on static display, and one or two areeven still flying.

* Bell was enthusiastic enough about the Airacobra to develop a prototypeof a carrier-based variant in response to a US Navy request, resulting in theconstruction of a single "XFL-1 Airabonita" -- first flight being on 13 May 1940, with test pilot Brian Sparks at the controls.

The Airabonita was clearly a member of the Airacobra stable, the maindifference being that it had taildragger landing gear and an arresting hook,forward of the tailwheel. All landing gear assemblies retracted, the maingear being placed closer to the wing leading edge than on the P-39. TheAirabonita also had a raised co*ckpit to improve field of view for carrierlandings. The prototype was unarmed. The Navy began trials on theAirabonita in July 1940, revealing severe balance problems; the problems wereaddressed, with testing not resuming until the early spring of 1941.

By that time, the Navy had settled on the Vought F4U Corsair to meet theservice's requirement for an advanced fighter. The Navy had never likedwater-cooled engines much in the first place, and so the Airabonita programwas canceled in May 1941, with the aircraft judged "unsatisfactory as acarrier fighter". It was scrapped the next year.

[6] P-63 KINGCOBRA

* During 1941, the Bell company began to rethink the P-39 design, with one ofthese rethinkings emerging as the unsuccessful XP-39E. Another line ofinvestigation resulted in a USAAF contract for two "XP-63" prototypes awardedin June 1941.

Getting the XP-63 into the air proved troublesome, however; Bell wasdistracted by producing the P-39 in volume, and the initial XP-63 designturned out to be badly overweight, demanding a redesign. The first XP-63flew on 7 December 1942, a year to the day after Pearl Harbor, though the aircraft was lost in a crash a few weeks later. The second prototype took tothe air in February 1943, but was lost in a crash in May. Fortunately forthe program, a third prototype had been ordered in mid-1942, and wasflying in late April 1943. Even before the flight of the first prototype theUSAAF had ordered the type into production, with the first "P-63A Kingcobra"machines rolled out in October 1943.

As it emerged, the P-63 was similar enough to the P-39Q to be mistaken forit, the P-63A being a low-wing aircraft with tricycle landing gear,mid-mounted Allison engine, car doors on each side of the co*ckpit, andarmament consisting of a 37-millimeter cannon firing through the prop hub,two 12.7-millimeter Brownings on top of the nose, and a single12.7-millimeter Browning in a fairing under each wing, for a total of fiveguns.

The P-63 was, however, a generally new design, featuring little partscommonality with the P-39. The P-63 was slightly longer than the P-39, withthe most distinctive recognition feature being that the trailing edge of therudder on the P-63 was straight, while it was rounded on the P-39; the P-63'stailfin was also taller. Another distinctive recognition feature was afour-bladed prop.

Other changes were subtler. The wingspan and wing area were increased, andthe wing featured the new "laminar" airfoil configuration established byNACA. More importantly, the P-63 was powered by an Allison V-1710-93 enginewith a second supercharger stage -- not a turbocharger, as indicated in somesources -- giving it good high altitude performance. It appears that theP-63, just as with the XP-39E, was originally slated to be powered by theContinental V-1430 engine, which as noted was a nonstarter.

 ___________________________________________________________________ BELL P-63A KINGCOBRA: ___________________________________________________________________ wingspan: 11.68 meters (38 feet 4 inches) wing area: 23.04 sq_meters (248 sq_feet) length: 9.96 meters (32 feet 8 inches) height: 3.84 meters (12 feet 7 inches) empty weight: 2,892 kilograms (6,375 pounds) MTO weight: 4,763 kilograms (10,000 pounds) max speed at altitude: 660 KPH (410 MPH / 355 KT) service ceiling: 13,100 meters (43,000 feet) range: 725 kilometers (450 MI / 390 NMI) ___________________________________________________________________

USAAF evaluation of the Kingcobra was positive, but the service felt noparticular need for the aircraft as a frontline fighter, and so it was builtprimarily for Soviet use -- indeed, much of the tweaking of the P-63 designwas performed in response to Red Air Force inputs.

[7] P-63 VARIANTS

* A total of 50 initial production P-63A-1 machines was built. They were followed by improved subvariants:

• The "P-63A-5" was much the same as the P-63A-1, but featured some minor detail changes and new radios. 20 were built.
• The "P-63A-6" added a stores attachment under each wing for an external tank or bomb. 130 were built.
• The "P-63A-7" was a minor change on the P-63A-6, featuring a modified tailplane with wider span, revised mountings for the nose machine guns, and other fixes. 150 were built.
• The "P-63A-8" featured an Allison engine with water-methanol injection, which permitted several minutes of combat power under redline operation, further improving the P-63's performance. Ammunition supply for the wing guns was cut from 250 to 200 rounds per gun. 200 were built.
• The "P-63A-9" was similar to the P-63A-8, but featured more co*ckpit armor. 445 were built.
• The "P-63A-10" replaced the old M4 37-millimeter cannon with the improved M10 model, and also raised the cannon's ammunition supply from 30 rounds to 58 rounds; the small ammunition supply for the cannon had been a persistent pilot complaint. In addition, the P-63A-10 featured an N-9 lead-computing gunsight. 730 were built.

Although the P-63 was never used in combat by the USAAF, the service did useit as a piloted gunnery target, the "RP-63". Five P-63A-9s were initiallybuilt as "RP-63A-11" targets, with armor but no armament. They featured therear co*ckpit glazing faired over, a modified carburetor scoop, and werefitted with a light on the prop spinner and on each side coupled to an arrayof sensors that would cause the lights to flash when the aircraft was hit byspecial "frangible" ammunition broke up on impact. The primary rationale wasto train gunners on bombers to counter fighter attacks.

The RP-63A-11s were followed by 95 "RP-63-12" targets based on the P-63-10.The RP-63s were painted bright orange and were nicknamed "Pinballs".Sometimes they towed target sleeves instead of being used as targetsthemselves. Including the Pinballs, a total of 50 + 20 + 130 + 150 + 200 +445 + 730 + 5 + 95 = 1,825 P-63A machines was built.

* A "P-63B" variant with a Rolls-Royce Merlin engine was considered but neverbuilt, and so the next Kingcobra variant was the "P-63C". It was similar tothe P-63A-10 but featured an improved V-1710-117 engine, wingspan clipped by25 centimeters (10 inches) and, after early production at least, a prominentventral fin to improve yaw stability; it is unclear if the fin helped reducethe aircraft's propensity to spin. The "P-63C-1" was the initial productionsubvariant, with 215 built; they were followed by 1,012 "P-63C-5" machineswith minor improvements. 200 more P-63C-1 machines were manufactured as"RP-63C-2" Pinball targets, for a total of 215 + 1,012 + 200 = 1,427 P-63Cmachines built.

Only one "P-63D" -- technically a "P-63D-1" -- was built. It was similar tothe P-63A-10, with no ventral fin, but featured a bubble canopy and thecarburetor intake moved back, presumably to allow the canopy to be slid backto open. The wingspan was increased over that of the P-63A, to 11.94 meters(39 feet 2 inches); the P-63D was powered by an Allison V-1710-109. Theaircraft was lost in a crash due to an engine fire that claimed the life ofpilot Bob Borchardt.

The P-63D was followed by the "P-63E", which was along the lines of theP-63C-10, with the ventral fin and the M10 cannon, but with the widerwingspan, stepped-back carburetor intake, and V-1710-109 engine of the P-63D.It retained the old car-door co*ckpit scheme; it featured more fuel capacityand a new Aeroproducts propeller. Only 13 "P-63D-1" machines were built;there was thought of a "P-63D-5" variant with the bubble canopy, but with theend of the war P-63 production was wound down. A single "P-63F-1" was builton an experimental basis, being essentially a P-63E with a number of tweaks,most prominently a substantially taller tailfin.

The final production version of the Kingcobra was the "RP-63G" Pinballtarget, with 32 built, for a total of 100 + 200 + 32 = 332 Pinballs. ThePinballs lingered on in service after the war, but were generally retired in1947. There was work towards a "P-63H" with a new Allison "Turbo-Compound"V-1710 with both two-stage supercharging and a turbocharger, but the jet ageovertook it, and it never happened.

* The following list summarizes Kingcobra production:

• XP-63 (3 built): initial prototypes
• P-63A (1,725 built): initial production machines
• RP-63A (100 built): initial Pinball targets
• P-63C (1,227 built): ventral fin, V-1710-117 engine, clipped wings
• RP-63C (200 built): Pinball targets
• P-63D (1 built): bubble canopy, wide wing, V-1719-109 engine
• P-63E (13 built): like P-63D but with old co*ckpit scheme
• P-63F (1 built): experimental machine with tall tailfin, etc
• RP-63G (32 built): final production Pinball machine

That gave total production of 3,302 Kingcobras.

[8] KINGCOBRA IN SERVICE / P-63 MODIFICATIONS

* As mentioned, the Soviets were the primary users of the P-63, obtainingabout 2,400, ferried by air over the Siberia route. P-63s shipped to theUSSR never saw combat against the Nazi Reich; the Soviets had plenty offighter aircraft at the time, and being intent on performing a thoroughevaluation of the Kingcobra before putting it into service, did not provideit to frontline units before the Nazi surrender in May 1945. Some Red AirForce pilots recollected seeing P-63s in service against the Germans, but norecords confirm this.

The P-63 did, however, see action in the brief Soviet campaign against theJapanese before Japan's surrender in August 1945, primarily being used forescort and ground attack; there was little air-to-air conflict in that fight,because the Japanese didn't have many fighters left to send up against theRed Air Force. Soviet pilots liked the Kingcobra, seeing it as a bigger andbetter Airacobra, though it retained the nasty spin characteristics of theP-39.

After the war, the P-63 remained in first-line Red Air Force service. It wasseen as very useful in helping pilots convert to new jet fighters as theycame into service, since the jets generally had tricycle landing gear, andthe P-63 was an exception among Red Air Force piston fighters in that it hadtricycle landing gear as well. The Kingcobra lingered on the flightlinesinto the early 1950s. There are tales that US pilots encountered them duringthe war in Korea, but no documentation confirms that notion.

The only other serious export user of the Kingcobra was the French Armee del'Aire, which received 114 P-63Cs at the end of World War II. They served incombat as ground-attack aircraft in the French war in Indochina, beingfinally retired in 1951 in favor of US-supplied Grumman F8F Bearcat pistonfighters. Some P-63s lingered in liaison and other secondary roles for a fewyears after that.

* There were a number of special versions and modifications of the P-63:

• Bell considered but never built a trainer version, though the company did add a secondary co*ckpit on the rear fuselage to one P-63A and two P-63Es, the rear co*ckpit being used to seat an observer to keep an eye on trials aircraft. The Soviets did perform at least three conversions of P-63As to "TP-63A" trainer configuration, with a configuration along the lines of that of the TP-39 trainers.
• As mentioned above, a single P-63F-1 was built with a tall tailfin and other tweaks on an experimental basis.
• A P-63A was modified late in the war with a vee or "butterfly" tail, while an RP-63G was used as an experimental platform for vee tail configurations after the conflict -- with disappointing results.
• The most exotic Kingcobra special was the "L-39", used as a trials platform by the US Navy, NACA, and Bell from 1946 to investigate low-speed flight with swept wings, with two P-63As modified to that configuration. They were fitted with an instrumentation package behind the co*ckpit -- with various changes added during the course of tests, most significantly a rear fuselage plug and a prominent ventral fin. They were both scrapped in 1949.

* The Kingcobra was out of military service by the mid-1950s, but a fewsurplus P-63s did have a new career as air racers in the postwar period. Anumber of Kingcobras survive as museum displays, while a few remain flying asairshow "warbirds".

[9] FOOTNOTE: THE BELL XP-77

* Besides the Airacuda and Airacobra / Kingcobra, the only purelypiston-powered fighter developed by Bell was the "XP-77". It started life in1941 as a design to meet a military requirement for a lightweight fighterwith the general specifications of "400 HP, 4,000 pounds, 400 MPH", Bellconsequently naming their concept the "Tri-4". In the spring of 1942, theUSAAF ordered a batch of 25 Tri-4 fighters -- but development provedtroublesome, and the first "XP-77" didn't perform its initial flight until 1April 1944, test pilot Jack Woolams at the controls.

As it emerged, the XP-77 was a tidy little aircraft, made largely of wood,with a configuration patterned on prewar air racers. It had a length of6.97 meters (22 feet 10 inches), a wingspan of 8.38 meters (27 feet 6inches), an empty weight of 1,295 kilograms (2,855 pounds), and a maximumtake-off weight of 1,828 kilograms (4,029 pounds). It was built around aRanger air-cooled 12-cylinder inverted vee engine driving a two-bladed prop,with a low-mounted wing, conventional tail arrangement, canopy set well back,and tricycle landing gear. The landing gear all had single wheels, the nosegear retracting back, the main gear hinging in the wings to retract towardsthe fuselage. Armament was a single 12.7-millimeter Browning machine gun ineach wing and, optionally, a 135-kilogram (300-pound) bomb carried on thecenterline.

By the time the HP-77 flew, the USAAF had lost interest in the program, andit only went to flight test on an experimental basis. One of the problemswith the program was that air racers rarely provided a useful basis for acombat aircraft, any more than a race car provides a reasonable basis for acombat vehicle. Air racers don't need armor, armament, or maneuverability,and unless they're designed for long-distance races, they don't need rangeeither. Trying to add such features to an air racer tended to produce adesign inferior to a purpose-built combat aircraft -- and by the time theXP-77 flew, it was absolutely no match for contemporary production fighters,with a top speed of only 530 KPH (330 MPH / 285 KT).

More importantly, the requirement for which the XP-77 was built turned out tobe irrelevant, there being no useful purpose in building a "toy" fighter withminimal armament and combat capability, even if it had performed as hoped. Asecond XP-77 took to the air in July 1944, but was lost in a crash on 2October, the pilot bailing out. That was the effective end of the program,the effort being formally given the axe two months later. The secondprototype was eventually scrapped. Bell did also develop several jetfighters, as well as pioneering experimental rocket planes such as the X-1-- but the company's real future was in helicopters.

[10] COMMENTS, SOURCES, & REVISION HISTORY

* I've long been fascinated by the P-39 / P-63 -- its unorthodoxconfiguration is interesting. Was it a good aircraft? On the balance, itappears to have been a machine with many virtues that was very effective, butsaddled with some significant faults. As usual, trying to nail downproduction quantities exactly is an exercise in frustration, but the figuresgiven here can be regarded as in the ballpark.

* Sources include:

• US AIRCRAFT IN THE SOVIET UNION & RUSSIA by Yefim Gordon, Sergey Komissarov, and Dmitriy Komissarov, Midland Publishing, 2008.
• "Bell P-39 / P-63 Variant Briefing" by Robert F. Dorr, WINGS OF FAME, Volume 10, 1998.

* Revision history:

 v1.0.0 / 01 aug 11 v1.0.1 / 01 jul 13 / Review & polish. v1.0.2 / 01 jun 15 / Review & polish. v1.0.3 / 01 may 17 / Review & polish. v1.0.4 / 01 apr 19 / Review & polish. v1.0.5 / 01 feb 21 / Review & polish. v1.0.6 / 01 dec 22 / Review & polish.