The Bell P-39 Airacobra was one of the United States’ principal fighter aircraft in service at the start of World War II. The P-39N was a major production variant, focusing on structural lightening and using an upgraded engine. The aircraft’s highly unconventional design placed the engine behind the pilot, driving the propeller through a long shaft.
While the P-39’s performance was considered poor by US and British pilots for high-altitude interception due to the absence of an effective turbo-supercharger, its heavy nose-mounted cannon armament and excellent low-to-medium altitude performance made it highly successful when operated by the Soviet Air Force on the Eastern Front, primarily in the tactical fighter and ground-attack roles.
Unique Design and Key Features
Mid-Engine Configuration and Drivetrain
Engine Placement: The Allison V-1710 V-12 liquid-cooled engine was mounted in the fuselage center, behind the pilot. This novel layout was intended to shift the center of gravity and free up the nose.
Driveshaft: The propeller was driven by a long extension shaft that ran beneath the cockpit floor to a gearbox in the nose, a distinguishing engineering feature.
Armament Bay: The space vacated by the engine in the nose allowed for the mounting of the aircraft’s powerful primary weapon, a large-caliber cannon, to fire through the propeller hub.
Structural and Operational Characteristics
Landing Gear: The P-39 was the first American fighter to feature a tricycle landing gear configuration, which provided excellent visibility and easier ground handling.
Cockpit Entry: Uniquely, the pilot entered the cockpit via automobile-style doors with roll-down windows on either side, rather than a sliding canopy.
Altitude Limitation: The production P-39s were limited to a single-stage, single-speed supercharger. The lack of an efficient turbo-supercharger severely handicapped its performance above 15,000 feet (4,500 m), rendering it unsuitable for high-altitude air combat over Western Europe.
P-39N Variant Specifications and Armament
P-39N Specifics
The P-39N series (including N-1 and N-5 sub-variants) were the most numerous production run, incorporating efforts to reduce weight (sometimes by reducing internal fuel capacity) and installing the more powerful V-1710-85 engine. The P-39N-1 introduced a wider 11 ft 7 in (3.53 m) Aeroproducts propeller.
Armament (Typical P-39N Configuration)
Weapon Type
口径
場所
Purpose/Note
Cannon (M4)
37 mm
Nose (firing through propeller hub)
Primary anti-aircraft/ground attack weapon (low rate of fire, high impact)
Machine Guns (Synchronized)
2 × .50 cal (12.7 mm)
Nose (firing through propeller arc)
Heavy machine guns for close-range fighting
Machine Guns (Wing)
4 × .30 cal (7.62 mm)
Wings
Additional firepower (sometimes replaced by two .50 cal guns in the later Q-model)
Performance Data (P-39N)
仕様
Detail
メーカー
Bell Aircraft Corporation
Engine Power
1,200 hp (Allison V-1710-85)
Max Speed
Approx. 385 mph (620 km/h) at optimal altitude
Service Ceiling
Approx. 35,000 ft (10,670 m) (though effective performance was lower)