“Flight Manual ” p-39 Airacobra PILOT’S FLIGHT OPERATING INSTRUCTIONS ARMY MODEL P-39Q-1 AIRPLANE This publication shall not be carried in aircraft on combat missions or wnen there is a reasonable chance of its falling into the hands of the enemy. NOTICE: This document contains information affecting the National Defense of the United States within the meaning of the Espionage Act, 50 U.S. C., 31 and 32, as amended. Its transmission or the revelation of its con- tents in any manner to an unauthorized person is prohibited by law. THE “AIRACOBRA” STORY by Leo J. Kohn All photos from Collect-Air Photos Bell P-39D-1-BE, AAC 41-28360, was the first standardized A/racobra in squadron service. This particular airplane has an unusually long cannon muzzle. INTRODUCTION “A projectile within a projectile” best delineates the vague notion held by a small group of visionary aeronautical engineers. Theirs was no more than an illusory idea about a particular feature of a particu- lar piece of equipment, and stemmed from a state- ment made in 1918 by the famous French engineer, Marc Birkigt, who said: “...the best place for an anti-aircraft gun was in an airplane.” Theirs was a feeling that an explosive-shell gun, as large as possi- ble, should be put into the air. It would not require any larger bullets to put a man out of action in 1937 than in 1918. But when the engineering staff of the fledgling Bell Aircraft Corp. began developing the concept of their new fighter airplane they envisioned something that would be able to do more than kill or injure unprotected individual enemy soldiers. What they had in mind was an airplane capable of cannonading explosive shells powerful enough to attack suc- cessfully an armored division or a fleet of mosquito (PT) boats and, last but not least, to vanquish the biggest and highest flying bomber. Members of the Bell staff were invited observers at a series of tests conducted by the Army Air Corps and Army Ordnance Corps at the Aberdeen, Mary- land Ordnance Proving Grounds in 1935. The tests were conducted to determine the destructive force of various types of ammunition particularly as to their effect on actual aircraft structures. The out- come of these tests proved that the American-devel- oped 37-mm. cannon was far superior to any of the other guns tested. In fact, the 37-mm. cannon was already the pre-eminent feature of their radically new multi-engine, multi-place fighter, the XFM-1 Airacuda — a concept well ahead of its time. And so, Bell engineers began with a 37-mm. can- non and built an airplane to act as a gun platform. Unlike most designs then, it was built around its main armament rather than building an airplane and then arming it. The Bell Aircraft Corp. was an outgrowth of a now commonplace phenomenon in the business world — the relocation of a manufacturing facility. The Consolidated Aircraft Corp. was long located in Buffalo, New York, but in 1935 moved its entire operation to San Diego where they could continue development and production of their long-range flying boats. Remaining behind were some of the key members of its management and engineering staff, the latter particularly having been associated with Consolidated’s single-engine fighter programs. So Lawrence D. Bell, Robert J. Woods, O. L. Woodson, and Roy Whiteman, all Consolidated ex- ecutives, remained behind. They pooled their tal- ents, resources and efforts to form the Bell Aircraft Corp. Bell became President, and Woods became the Chief Design Engineer. The fledgling company was kept alive financially with some patronage from Consolidated in the form of some leftover contracts for a Navy biplane dive bomber and subcontract work for flying-boat wings. In essence, it was not burdened with the old “tradi- tions” and “philosophy” of its predecessor or, for that matter, the industry as a whole. Consequently, if the company was to establish itself as a force in the aviation industry it would have to do it in a bold and masterful way. The only way to do this was to strike out in a different and untried direction. That they were capable of doing just that struck the avia- tion world like a lightning bolt with the Airacuda. In describing the design philosophy of the Airacobra, Larry Bell said “we went back to funda- mentals!” Their idea, before beginning the building of a fighter airplane was to analyze and understand the philosophy and set the reason for fighter aircraft, and then go about the task of designing and building an airplane worthy of the “fighter” name. They actually looked far back into the history of warfare and weaponry, and tried to think of the airplane they wanted to build in military terms rather than aeronautical terms. Where other manu- facturers may have thought in terms of the airplane as a vehicle, the Bell group thought instead in terms of firepower. Since the victory invariably — or almost always so — goes to the side with the greatest firepower, they asked themselves what a fighter airplane should be able to do. Then they studied the best of the then current fighters, both American and foreign, to determine their shortcomings. It was easy to see that three qualities were necessary: 1) Sufficient fire- power; 2) Improved landing and ground handling characteristics; 3) Greater pilot vision. The Spanish Civil War brought home the fact that fighter aircraft would have to in the future operate under less than “ideal” conditions than those which could be found at improved bases. The fighter had to be able to get in and out of improvised fields and possibly even highways, take off in cross winds if necessary, and operate at night without the aid of million-candlepower floodlights. Fighter pilots were also often fatigued from the strain of combat, and this could be relieved somewhat if they didn’t have to fight the airplane back onto the ground. Being a new company, the Bell people didn’t delude themselves about being able to build an airplane so much faster than anyone else. They knew full well that with horsepower, size, and wing loading the same, there was no reason why any of the more capable aircraft manufacturers couldn't build fighter planes that would have about the same top speed, ceiling, rate of climb, maneuverability, and other performance characteristics. The power- plants, airfoil sections, and other standard compo- nents were available to other manufacturers too. Unless Bell came up with superior features, they couldn’t have much to sell the military when they bid for contracts. Bell P-39Q-20-BE, AAF 44-3572, with a drop tank and the underwing armament pods. DESIGN PHILOSOPHY All thinking was brought to bear on that 37-mm. cannon, which in turn presented problems never previously encountered, one of which was that the weapon and its ammunition were extremely heavy compared to the smaller bore .30 and .50-cal. machine guns. In order to install this gun a con- siderable amount of space at right angles to the line of flight was required. It was also felt that the gun should be mounted rigidly, preferably on the aircraft’s centerline, so that the recoil could be taken up by the mass of the engine. Invariably starting with a picture of the 37-mm. piece and its shell charges, preliminary sketches were put down. To be included also were all of the other components normally found in a single- engine fighter. It wasn’t long before it became ob- vious that it wouldn’t work, and some other ar- rangement would be necessary to accommodate the large bore of the cannon. The trend in Europe had been toward equipping liquid-cooled engines with an offset propeller reduction gear which permitted a relatively small 20 or 23-mm. bore cannon to be installed in the vee be- tween the cylinder banks and to fire through a hollow propeller hub. This arrangement was con- sidered practicable and was included in the pre- liminary design sketches. However, no such engine existed in the United States, at least of sufficient power, that would permit the installation of such a cannon. Obviously the air-cooled radial engine was not feasible, and the only American liquid-cooled engine at the time was the still relatively new 1150- hp 12-cylinder Allison. On the basis of this particular “‘state of the art,” Bell proposed to place the engine farther back in the fuselage and install the cannon and ammunition ahead of the engine. With this arrangement power was to be transmitted to the propeller through an extension shaft about five feet long, taking power from the front end of the engine crankshaft to an offset gear-reduction unit in the nose. A streamlined bullet-like nose was now attainable, and which was later found to be essential if a speed of 400 m.p.h. was to be reached. This nose design permitted adaptation to a tri- cycle landing gear, one requirement of which was that it have a reasonably long fore and aft wheel base to provide stability and good handling qualities on the ground. Because of this, the engine could be lo- cated nearer the center of gravity, and this central location of the engine promised reduced polar movement of inertia which gave improved maneuverability and permitted a most economical structural design from a strength/weight standpoint. In these preliminary designs, current practices lo- cated the pilot in a cockpit behind the engine. In this position the pilot would occupy a station about two-thirds of the length down the fuselage. From the standpoint of installation it offered certain ad- vantages, but it was obvious that even with the tri- cycle gear the pilot’s field of vision forward and downward would be greatly impaired. The demand for more and more speed resulted in bigger engines which robbed the fighter pilot of a vital need — good visibility. They had already ruled out the radial engine for this reason, and they were not much further ahead with their engine installation so far. They had to devise a new arrangement so that visibility forward, downward, aft, and to the sides would be guaranteed. A proposed design by Koolhoven of Holland was studied and analyzed for possible application of its cockpit arrangement which afforded the pilot greater visibility. In the Koolhoven design the pilot was seated behind the armament with the engine lo- cated near the trailing edge of the wing aft of the pilot. Actually, the Koolhoven design was never de- veloped, but its location of the engine, pilot, and cannon did offer excellent possibilities to attain the pilot vision they sought. The detailed design of the airplane itself disclosed some disadvantages. The company’s first attempt to locate the pilot ahead of the engine didn’t look too promising. The requirements for maximum speed and performance and minimum weight led them temporarily to abandon the forward pilot location. Instead, a preliminary design was prepared reverting to the aft pilot location. This was submitted to the Materiel Division at Wright Field where it was carefully studied by the engineers who informally reported the design as being generally suitable. Bell was also told that within a few weeks the Army Air Corps would be requesting intercep- tor/pursuit design proposals for evaluation, and the Wright Field people wanted them to enter their design in that competition. Back in Buffalo the Bell team began more intensive study of the detail design. Shortly they received the promised invita- tion to submit their design. They were still not satisfied that what they had on the drawing board achieved their engineering objec- tives, which were to be over and beyond ordinary fighter characteristics such as speed, maneuverabil- ity, and pilot protection. These were the fundamen- tal “fundamentals” they wanted to build into their airplane as a matter of course with no special effort to achieve them. BREAKTHROUGH It was only a matter of time that the breakthrough — the “over and beyond” — was achieved in a single engineering innovation. Simply, the engine would be located behind the pilot, transmitted its power through a drive shaft to a gear box in the nose and then to the propeller. This was the difference — the gear box in the nose rather than attached to the engine. The key to achieving the three fundamentals was the extension shaft. Hardly new — even the Wright brothers employed them. Most aircraft manufac- turers didn’t want to risk the effort and expense in this direction, but Bell already had some experience with extension shafts. The design concept now offered firepower to spare. It would allow room for the 37-mm. cannon and two .50-cal. guns besides in the nose, plus what- ever additional guns might be installed in the wing. It provided for excellent visibility. With the engine behind and below the pilot’s head level, he The Bell XP-39B, AAC 38-326, was the revised XP-39, and here has a strut cover on the nose gear and small wheel-well doors. The air intake in the wing is lipped and further out from the root, and a special probe is mounted outboard of the right main landing gear and was probably for test. The reason for the propeller cuffs is not known, considering the bullet-like nose. was left with a commanding view in all directions with few obstructions. | Not the least to be gained, it was not necessary to engineer the retracting nose wheel into the engine compartment with no engine now in the way. Without question, now Bell’s engineering staff had something on which they could build. The remote-drive installation was the most obvious design characteristic, and Larry Bell and Bob Woods, along with Harland M. Poyer, Director of Engineering, all mustered their own and their staff's brilliant talents to rest on developing this compo- nent alone. So in 1937 Bell submitted two designs to the Air Corps for the fighter design competition. One was essentially the Airacobra with the ten-foot exten- sion shaft, and the other was a more conventional model with the engine located in front of the pilot. To the credit and vision of the Air Corps, it chose the Airacobra and acknowledged that it was truly an outstanding design and engineering achievement from stem to stern. Bell was awarded a contract to build an experimental model and assigned the fighter designation XP-39. Whereas other manufacturers heretofore built a fighter airplane and attached armament to it, Bell now had the opportunity to show the aviation world that it would and could first build an arma- ment system and wrap an airplane around it. The weight of the cannon was 106 lbs. The 37- mm. projectile had a muzzle velocity at aircraft speed of 2000 ft./sec. at a firing rate of 120 shells/ min., each shell bursting into about 100 fragments. The gun and cannon mount itself was not a new concept but merely a variation of an original SPAD idea. Placing the engine behind the pilot and moving the reduction gear, usually an integral part of an engine itself, forward into the nose directly behind the propeller with the power transmitted from the engine spelled one thing — WEIGHT! Bell’s suc- cessful undertaking of the design and installation of this power train was materially aided by never-end- ing counsel and help from the Air Corps Engineer- ing Section and Allison Division of General Motors Corp. When it was done the cost in weight of this innovation was precisely 50.7 lbs. — the drive shaft weighed only 40 lbs. and the single supporting center bearing was only 10.7 lbs. The weight of the gear box would have been about the same on either end of the shaft. A tremendous advantage gained from this arrangement permitted speedy removal of the engine for servicing reasons without having to remove the propeller, gear box, cannon, or drive shaft. A revised version of the XP-39 as of November 20, 1939 showing a single intake in the starboard wing and a larger one on the port. Propeller cuffs are also employed, and the sleek filled finish is evident here. STRUCTURAL DESIGN This arrangement also provided for a fuselage comprised of two sections known as the “forward” and “aft” fuselages. The forward section was the structural focal point of the aircraft and where the aircraft’s design philosophy took concrete form. In- tegrally it comprised a major portion of the whole fuselage and included the center wing section, engine bed, extension shaft, propeller gear-reduc- tion assembly mounting, principal armament mounts, nose-wheel attachment fittings, and sup- ports and brackets for all the accessories. Indeed, it had the general appearance of a truck chassis and in all probability could have functioned equally well in that mode if it were mounted on wheels and oper- ated on the ground. To this unit would attach the outer wing panels, the pilot’s cabin which was really a capsule, the engine and accessories, the extension shaft and gear box, heavier armament and ammunition magazines, coolant system, landing-gear assembly, and the aft fuselage. The Allison V-1710 engine was mounted on four Fabreeka pads, joined to the gear box by the exten- sion shaft operating at crankcase speed. The shaft ran through the forward fuselage beam under the pilots seat, connected by a flanged coupling and supported by a center bearing. A three-bladed Cur- tiss Electric propeller with a hollow hub went on the nose. An electric inertia-type starter was employed, activated by a pedal on the floor. On top of this was superimposed the pilot’s cabin, but it was designed as an integral part of the fuselage just forward of the engine compartment, and tailored to fit a man no taller than 5 ft. 10 in. Fume- tight bulkheads were provided between the engine compartment and the cabin, and between the cabin and the armament bay forward. Also attached to this was the aft fuselage section which supported the complete tail unit and con- tained the radio installation. Ordinary semi-mon- ocoque construction with eight bulkheads was em- ployed. The Bell Airacobra I, here in RAF camouflage and markings, shows a larger spinner opening for the 20- mm. cannon, but does not show any guns in the wing. Wherever possible lighter materials were used to reduce weight and the XP-39 was probably the most advanced effort in this country to use lighter materials at that time. The end result was that the Airacobra came out extremely light at a gross weight of merely 6044 lbs., a contributing factor toward the outstanding performance of the proto- type, and important for later production models to add equipment and warload. Extruded aluminum-alloy sections were used for the main fuselage beam, tied together virtually solid with heavily reinforced aluminum webbing. Two cast steel bulkheads were located where the center section joined to the beam to become an integral part of the center section. Further adding to this An Arracobra I struts its stuff above the clouds show- ing the guns in the wing and the cannon port. rugged construction was a heavy-gauge stamped aluminum deck plate riveted to the tops of these bulkheads and extending the full length of the beam. A sturdy forged angle member was mounted to the rear beam to form the engine bed. The outer skin of the forward section was of formed aluminum sheet riveted to the bulkheads. Two main longitudinal beams were held parallel and rigid to make for a self-contained unit prin- cipally by tubular spreader bars, forward bulkheads, former members, and the aft splicing bulkhead. Also acting as tying members were the coolant- radiator brackets for the high-temperature Prestone system, and the cabin which was attached later. The wing itself utilized the NACA 0015 airfoil section at the root, tapering to an NACA 23009 sec- tion at the tip. Construction was of stamped alumi- num ribs and built-up spars for a full-cantilever wing. All control surfaces were fabric covered. The entire airplane was flush riveted and filled with a special compound to produce an ultra-smooth sur- face. This whole arrangement of sub-assemblies was extremely adaptable to high-speed production through the use of a relatively small number of jigs. Likewise, the sub-assemblies did not require a great amount of space for their fabrication. The inward-retracting landing gear offered a generous tread of 136 in. for the rear wheels, and a long nose-wheel strut for a long wheel base. Had the engine been located in the nose the wheel base would have been short. It was also one of the first such systems to employ disc brakes. A landing-gear test vehicle was built in confor- mance with the weight, balance, tread and wheel base of the XP-39, and tested at speeds of up to 70 m.p.h. over all kinds of surfaces and obstructions, as well as hazards that might later be experienced at unimproved air bases. This resulted in a sturdy and reliable system, fully retractable by electric drive. The nose wheel was non-steerable, able to caster up to 60 degrees left or right. The fuel system consisted of two 60-gal. tanks in the outer wing panels, with the left tank including a reserve of 20 gal. A bomb rack fitted to the center section could take a droppable 75 or 150-gal. auxili- ary tank. READY TO FLY And the day arrived when the XP-39 stood in fly- ing readiness with its Allison engine, ten-foot shaft, independent gear box, hollow propeller hub, 37- mm. cannon, tricycle gear, and forward pilot loca- tion, all at a weight at least 500 lbs. less than the standard Army Air Corps single-place fighter. The wing loading was 28.3 lbs./sq. ft. The Allison field representative crawled in and fired up the engine which caught right off and ran as smooth as a sewing machine except for an ever- so-slight vibration. After the initial engine tests were flawlessly con- cluded, everyone thought the job was done and their troubles over. They were wrong. Since the whole XP-39 project was a secret one, the test flights could hardly be made from the mu- nicipal airport in Buffalo, so the ship was dis- mantled and loaded into a sealed box car, and then delivered to the Air Corps’ test station at Wright Field. It was then reassembled, inspected, and readied for flight testing when the bad news came. The Allison people had been making extensive tests on another engine to trace the cause of the slight roughness noticed during the initial start-up at Buffalo. They found a peculiar condition of tor- sional vibration occurring in the accessory-drive end rae ie of the engine at idling speed which caused the engine to lose proper timing and caused extreme deflections in a small spring-quill drive shaft within the engine. The XP-39 was grounded until this trouble could be resolved. Extreme tension and pressure was felt among the various engineers to solve this problem, but it still remained. After almost three months of round-the- clock work by Allison. engineers the trouble was tracked down to spring resonance in the small quill accessory drive shaft. The inclusion of a simple hy- draulic dampener on the quill shaft not only elimi- nated the trouble for all time, but brought a nice bonus of improved smoothness throughout the en- tire operating range. The required changes were quickly made on the XP-39’s engine and prepara- tions made to begin flight testing. Bell secured the services of Jimmy Taylor, an ex- pert civilian test pilot, to perform the intial ground and flight tests for a period of about one week. The first flight was made on April 6, 1939, and it re- quired different flight-test techniques than nor- mally used. After Taylor finished his work, the Airacobra was turned over to Homer Berry to complete the routine flight tests. The time loss caused by the engine problems made it necessary to accelerate the test program. Oil-pressure trouble developed when the oil got too hot, and it was felt that the problem was due to insufficient flow of the cooling air to the oil cooler. Greatly enlarged scoops were fitted to the side of the XP-39 to induce larger quantities of air to pass through the coolers. The scoops soon became enor- mous and out of all proportion to the sleek lines of A Bell P-39Q-20-BE, modified to an RP-39Q-20-BE, shows the improved clear cockpit canopy as well ae an inproiee ventral fin. In civilian guise as N-63813, it was formerly AAF 44-3887, and shows some damage to the wing tip. vi The YP-39 had the carburetor-air intake located just aft of the redesigned cockpit enclosure, and has two air intakes on each side of the wing root. It also has the larger vertical tail that became standard. the airplane, and the XP-39 was derisively dubbed both the Scoopacobra and the Airaducta — the names were hardly considered funny by that time. The cause was finally determined to be a standard right-angle pipe fitting at the point where the oil left the tank to flow to the engine. The fitting had an extremely high restriction of the oil flow and prevented an adequate amount of oil from reaching the engine. There were at least a dozen such problems that oc- curred during the design, construction, and testing of the XP-39. In every case the final answer proved to be simple, but it sure brought out a lot of short- ened tempers and blistering language. Once the Wright Field tests were completed, the XP-39 was flown to Langley Field in Virginia where it was mounted in a full-scale wind tunnel at the NACA laboratory for further tests. The airplane was then returned to Buffalo where those changes suggested by NACA engineers were incorporated together with a new engine having a higher super- charger ratio. Because the XP-39 was now no longer secret, the airplane was now thoroughly tested at Buffalo by Bell pilots, and then finally turned over to the Flight Test Branch of the Materiel Division. It was flown back to Dayton, and even before these final tests were completed the Airacobra had been so im- pressive that a contract was awarded to Bell in Sep- tember, 1940 for 80 airplanes. During this test program the XP-39 did not reach even 350 of the 400 m.p.h. claimed for it, but it had the potential. Stall speed was below 70 m.p.h., fan- tastic for such a clean airplane. Thirteen airplanes were ordered as the YP-39 for service testing. The 80-plane contract was prac- tically the YP-39 but with an Allison V-1710-35 of 1200 hp at 12,000 ft., an increase of 100 hp. The Vii empty weight was increased again up to 5042 lbs. and the gross went up to 7000 lbs. Production lines were set up at the Elmwood Avenue factory in Buffalo. Other changes were made during the Air Corps evaluation program. The original vertical tail could easily produce large angles of side slip, and rudder instability at the highest angle. Increased fin area and altered dorsal fin worked. The auto-like doors with roll-down windows were fitted with immediate quick-release hinge pins that could be operated from either inside or outside the cabin. The right-side door was normally used for entrance or emergency exit. A large baggage compartment was located behind the pilot over the engine compartment, and was ac- cessible either from outside or inside the airplane. SERVICE EXPERIENCE The first P-39’s entered service with the Air Corps in February, 1941. Parallel to the first produc- tion order was the development of the model 14, an export version intended for the French Armee de Air. These airplanes were transferred to Britain for the Royal Air Force, and another 675 were ordered by Britain. The first of these airplanes was delivered to No. 601 Squadron of the RAF. A single airplane, RAF serial AH601, mounted a 20-mm. cannon and six machine guns, and was flown experimentally in early 1941. This particular airplane had a somewhat different vertical tail with slightly more total area. It is generally assumed that these airplanes were named Caribou but this is not so, and the British kept the Airacobra appellation. These were fitted with a 20-mm. Hispano cannon in the hub, two .303-cal. Brownings in the nose, and four more of The first RAF A/racobra, serial AH601, was largely ex- perimental and had the larger area tail with a some- what straight trailing edge. The 37-mm. cannon was deleted in favor of a farther reaching .20-mm piece. Twelve exhaust stacks are visible. ; : LAA BBAOOD ioe POE inate: 2 Bell P-39C, the first model to enter Air Corps service nated as RP-39C. the same in the wings. Because the 37-mm. shell held a reduced powder charge to counteract the severe recoil of the bigger cannon, the 20-mm. pro- jectile could outrange it. The total firepower afforded the British then was 6200 rounds/min. at a weight-disposal rate of 387 lbs./min. Regardless, the British were disappointed with the Airacobra to say the least. The performance figures, based on the prototype with the bigger tur- bocharged engine, no guns, aluminum fuel tanks, no paint, etc., were never matched by the RAF version. As always, the Spitfire was “far superior” when compared to any American fighter across the board, but in this case the Airacobra did need 50-percent more runway and couldn’t operate out of many of the smaller British airfields. When 601 Squadron made its first strafing sortie across the Channel to France, it returned only six of the 12 Airacobras that went out. At the then-current operational heights it was no match for the Messerschmitt Bf 109’s, particularly in tight turns. Subsequently, the Airacobra was withdrawn from RAF service in December, 1941. Early reports following Pearl Harbor condemned the P-39, probably in good part because of the RAF rejection. Once high-altitude fighters relieved the P-39’s to operate at lower levels the type achieved an outstanding record of success. It was not as maneuverable in the air as the slower stubbier ships, These were later restricted from combat and redesig- but on ground at hastily hacked out fields it was easy to handle. As it turned out, the Army Air Corps was in dire need of getting modern airplanes as fast as possible, and the remaining RAF orders for the Airacobra were taken over by the Air Corps, complete with RAF serials, sand-and-spinach camouflage, and 20- mm. cannons. These were designated as P-400 rather than P-39 to keep the records straight. All were sent to the South Pacific. In March, 1942 the 67th Fighter Squadron arrived in New Caledonia and formed up with the Ameri- can Division. There sat the RAF rejects in crates. There were no erection manuals, 20 tool boxes belonging to crew chiefs, one borrowed block and tackle, and a magazine article about how the airplane was assembled. In this unlikely setting the 67th assembled, test flew, trained and created a Fighter Group with these P-400 Airacobras before entering combat at Guadalcanal in August, 1942. The first scramble of P-400’s was not sensational, as it was easy for the Japanese pilots to outmaneuver them and to avoid the deadly cannon fire. Other P-400’s reached the 35th Fighter Group at Port Moresby in New Guinea. Some of the Airacobras in the Pacific carried a pod under the fuselage which held a two-man liferaft that could be dropped to stranded airmen on viii the coral reefs where crash boats could not operate. Major Walter B. Putnam led a squadron of Airacobras in a smashing raid over Buna, New Guinea, for which he was awarded the Silver Star. Pounded by a terrific tropical rain and despite poor visibility, he and his squadron succeeded in demolishing the Japanese district officer’s head- quarters, destroyed eight or ten planes on the ground, silenced gun emplacements and set a fuel dump afire. With one cannon blast, Putnam hit the powder magazine of a Japanese transport unloading troops. Strafing four more transports he saw two planes being catapulted from a cruiser and shot down both. Before returning home he dove at another transport, gave it a couple of 37-mm. bursts, and watched it blow up as he pulled away. And that was precisely the purpose for which the Airacobra was designed. Thereafter the P-39 was used mainly in ground-support roles on various battlefields. The Airacobra fought in the South Pacific, Europe, North Africa, Australia, the Aleutians, and in Russia. The Russians valued the P-39 for its effec- tiveness in low-level support of ground troops. A total of 4773 P-39’s were sent to Russia under Lend- Lease, more than half of the total of 7800 American planes supplied to them. Red air units used them chiefly as adjuncts to the ground forces. These airplanes were stripped of armor and all other non- essentials to boost ceiling, speed, and maneuverabil- ity. In March, 1943 a regiment of the Red Air Force equipped with P-39’s claimed destruction of 43 German aircraft in three months for a loss of only three Airacobras. One Soviet P-39 had 31 swastikas painted on it! A few of the P-39’s sent to Russia were ferried to Alaska where Northwest Airlines winterized them and equipped them with survival gear. These aircraft did not see any combat service with the Soviets whatsoever. Their range made it absolutely impossible for them to be flown to Siberia via the “chain” and therefore these were turned over to the Army Air Forces for service in Alaska. The great majority of the Russian P-39’s were shipped as deck cargo to Abadan, Iran on the Persian Gulf. These were assembled and test flown at Abadan before being turned over to the Russians. It was not unknown for the P-39 to be ferried long distances over water if it carried an adequate fuel supply. In support of the invasion of North Africa, P-39’s were ferried from England over the Bay of Biscay and around the Iberian Peninsula to Gibraltar, a distance of 1095 miles. They would refuel at Gibraltar and go on to Tunisia. In one instance, 18 Airacobras — P-39D models — of the 81st Fighter Group, accompanied by two P-38F’s, were victims of a navigational error which exhausted their fuel, despite the drop tanks. All 20 of the aircraft were forced to land at Portala de Sacaven and were impounded by the Portuguese government which was neutral during World War I. Portugal was badly in need of upgrading its own air force and promptly impressed these fighters rather than intern them, and even paid the United States cash for them. The airplanes were used from 1942 to 1944 in Esquadrilla OK and were an impor- tant part of the country’s defensive forces. Awaiting the smelter after the war was this P-39D, AAF 41-6973. Twelve exhaust stacks are noticeable, unusual for a D model. Note the open radio-access hatch. P-39 LINE OF DEVELOPMENT XP-39 The single XP-39, AAC 38-326, was originally conceived with a high cockpit enclosure, a B-5 tur- bocharger on the port side of the fuselage, with cooling louvres adjacent to the engine. The fin and rudder were small and relatively narrow. Following extensive wind-tunnel tests the airplane was rebuilt as the XP-39B. The YP-39, AAC 40-27, shows the large tail now ad- ded, and double intakes in the wing leading edge. A Curtiss Electric propeller is fitted, but the cuffs have been discarded. YP-39 The Bell model 12 became the YP-39, 13 of which were ordered for service tests. These differed from the XP-39 chiefly in increased fin area which resulted in a somewhat broader top to the tail. The carburetor air scoop was located immediately aft of the cockpit, the enclosure was lowered, and the tur- bocharger was eliminated. Two additional .30-cal. guns were put in the nose to go with the 37-mm. cannon and the two .50-cal. machine guns. Wing loading was 31.03 lbs./sq. ft. and the propeller diameter was 10 ft. 4.5 in. Serial numbers for the YP-39 were 40-27 through 40-39. ae tae The original XP-39, AAC 38-326, in prototype form. In an effort to solve the oil heating problem, large scoops and ducts were added to the side of the airplane, and the XP-39 was sarcastically referred to as the Airaducta or the Scoopacobra. The original cockpit enclosure was a bubble type. YP-39A One was specially ordered without the tur- bocharger but the contract was cancelled and the airplane was delivered as a YP-39. This ship was converted to a high-altitude engine and became the YP-39A. XP-39B Actually the reworked XP-39, AAC 38-326, it in- cluded modifications already made to the YP-39. The engine was changed, cockpit enclosure lowered, the turbocharger removed, the air scoop moved aft of the enclosure, and the landing gear was revised. The fin area was later increased to the broader YP-39 shape. The engine was the same as for the YP-39, and the armament the same as for the XP-39 but not yet fitted. Much experimentation work was done, resulting in various wheel fairings. This was originally ordered as the XP-45, but the P-45 model was dropped as Congress was more liberal in funding existing projects rather than new ones. The XP-39B stands in its original form with the smaller tail. P-39C This was essentially the production version of the YP-39. Twenty P-39C’s were built, and had the same fin and rudder, intakes, etc., as the YP-39, although the engine was changed. The P-39C was the first Airacobra to have camouflage, and was later redesignated RP-39C and restricted from com- bat. P-39C serials were 40-2971 through 40-2990. Sixty aircraft on this order became P-39D’s. P-400 The P-400 was the export model 14 originally or- dered by Britain, and so designated to differentiate it from the P-39 Air Corps line. The first P-400 delivered to the RAF was an experimental model, but the subsequent production models had the nor- mal P-39C tail and were called Airacobra I. These The P-39C was the first production model of the A/racobra, and was delivered in camouflage paint. kee MAAS i fi Bell P-39C shows flush intakes in the wing leading edge, with a large intake on the port side and a smaller on the starboard side. Propeller cuffs are present in this model as on the revised XP-39B. Xi had the 20-mm. cannon in place of the 37-mm. can- non, along with six .30-cal. guns — two in the nose and four in the wing. Taken over by the Army Air Forces, the P-400 retained the RAF serials, which ran AH728 through AH738, AP266 through AP383, BW100 through BW183, and BX135 through BX174, with various numbers deleted in all cases. ee see eh A special model, the P-39D Model 12, was fitted with four guns in the nose in addition to the cannon, but shows no guns in the wing. It is equipped with a Cur- tiss Electric propeller, and lacks the fillet on the ver- tical fin. P-39D As Bell’s model 15, this was the first mass pro- duced version with a contract for 863 airplanes let in 1941, and necessitating additional production facilities which were built at Niagara Falls. These airplanes incorporated self-sealing fuel cells, armor plate, and bulletproof glass. The arma- ment was increased to two .50-cal. guns in the nose with 250 rounds each and four Browning .30-cal. guns in the wing with 1000 rounds each. Included was the 37-mm. American Armament Corp. T-9 cannon with 30 shells on a continuous belt. Other- wise, the P-39D was externally similar to the P-39C. All had fittings for a droppable 75-gal. fuel tank. One known as the model 12 was fitted with four guns in the nose for test purposes. A number of P-39D’s were also used by Bell for experimental work, one being NX-BA14, being the company’s No. 14 test aircraft. P-39D serials were 40-2991 through 40-3050, and 41-6772 through 41-7115. The P-39D-1-BE, Bell’s model 14A, differed from the P-39D only in the substitution of a 20-mm. can- non. The smaller fin fitted to later P-39D’s was stan- dard on all P-39D-1-BE airplanes. This version is distinguishable only by its serials, 41-28257 through 41-28406, 41-38220 through 41-38404, and 41-38563. Another Bell 14A, the P-39D-2-BE version had a 20-mm. cannon as with the D-1, but the engine was changed to an Allison V-1710-63 of 1325 hp. Other- wise there were no external differences. P-39D-2- BE serials ran from 41-38405 through 41-38562. The P-39D-3-BE and P-39D-4-BE were in- dividual conversions of the P-39D especially adapted for ground-support duties. The oil and glycol cooling systems were armored and two cameras were fitted in the rear of the fuselage. The engine was the same as the P-39D. XP-39E In the 1941-194