Airacobra P-39Q-1-BE

Design and Development

The P-39Q Airacobra was one of the few aircraft from Bell that introduced innovative ideas and unique features. The Airacobra was essentially built around the 37mm Colt M4 cannon, designed by the Browning Arms Company. Apart from the P-39, this cannon was only mounted on the P-63 Kingcobra. Generally, pilots disliked it because of its low muzzle velocity (2000 ft/s). Nevertheless, the cannon, along with additional machine guns in the nose of the aircraft, provided very powerful armament for that time.

Due to the size and space needed for the cannon and the decision to use tricycle landing gear, Chief Designer Robert Woods chose to place the engine in the center of the airframe. This engine position required a 3-meter-long shaft and gears to run under the pilot, connecting the engine to the propeller.

The XP-39 Airacobra prototype debuted at Wright Field on April 6, 1939, and from the start, it performed exceptionally well at high altitudes. In its first run, the prototype reached a speed of 390 mph, and in subsequent tests, it nearly hit 400 mph. The fighter also had an impressive climb rate, reaching 20,000 feet in just 5 minutes. This outstanding performance was primarily due to the Allison V-1710 engine with the new B-5 turbocharger. Additionally, the prototype was unarmed and lacked armor and self-sealing fuel tanks, which contributed to its lightweight and speed.

However, the airframe had its flaws. The small fin caused problems with longitudinal stability, and the chosen aerofoil section was not ideal for the higher end of the aircraft's speed range. While the plane was undergoing tests at Wright Field, NACA (National Advisory Committee for Aeronautics) engineers determined that the air intakes created excessive drag and had them removed. The cockpit was lowered, the wings were clipped, and the fuselage was stretched. Most importantly, the original engine was replaced with a less powerful Allison engine featuring a single-stage mechanical supercharger. These modifications, along with the addition of armament, self-sealing fuel tanks, and armor, significantly degraded the fighter's performance - attempts to improve the aircraft inadvertently removed several of its original advantages.

After entering operational service, the aircraft gained a reputation as a dangerous machine, primarily due to its weight distribution. With a heavily loaded nose (full of ammunition), the weight was concentrated near the aircraft's center of gravity, resulting in excellent maneuverability at low altitudes. However, firing off all the heavy cannon ammunition altered the weight distribution, potentially causing the pilot to induce a dangerous flat spin. Additionally, gun fumes tended to collect in the cockpit, and firing all the weapons would disrupt the magnetic compass reading.

Despite these issues, the Russians were quite satisfied with the Airacobra's performance and handling. Most of the combat on the Eastern Front occurred at altitudes below 20,000 feet, which likely contributed to the decision to dispatch a large portion of the P-39s produced to that theatre.

Versions & Service

were completed for further evaluation and testing. It was not until the P-39D version that the aircraft became combat-ready. This version featured a bulletproof windshield, armor protection for the pilot, self-sealing fuel tanks, and was armed with four wing-mounted 0.30-inch machine guns, two fuselage-mounted 0.50-inch machine guns, and a 37mm cannon. Subsequent versions included the F, J, K, L, and M, but the first model produced in large numbers was the P-39N, with over 2,000 units built. The next in line was the P-39Q, the last and most produced version, with just over 4,000 units built. On July 25, 1944, P-39 production ceased, with a total of 9,558 units produced.

The Airacobra saw combat in the Southwest Pacific, Mediterranean, and Soviet theaters. In Europe, it was used by the UK, France, and later in the war, Italy and Portugal. The P-39 also served in North Africa with units of the USAAF and other countries. Initially, the UK ordered almost 400 P-39Ds. The British Airacobra was identical to the American P-39D except for the cannon, with the original 37mm replaced by a Hispano 20mm. Ultimately, only No. 601 Squadron RAF flew them. This was mainly because British expectations were based on the prototype's performance before all the changes were implemented. When it became apparent that the performance of the non-turbo-supercharged production airframe was often inferior to existing aircraft like the Hawker Hurricane or Supermarine Spitfire, most of the ordered examples were either sent to the Soviet Union or requisitioned by the USAAF. After Pearl Harbor, the USA urgently needed aircraft. The examples originally manufactured for the UK but adopted by the USA were designated P-400.