The Bell FM-1 Airacuda was a twin engined escort fighter developed to operate with the B-17, but that never entered service due to its poor performance and limited manoeuvrability.
In 1936 the USAAC issued an operational requirement for a long range escort fighter to operate with the Boeing B-17 Flying Fortress. At this stage that required a twin engined aircraft, and Lockheed and Bell both responded with designs. The Lockheed XPB-3/ XFM-2 lost out to the Bell XFM-1 Airacuda design, and in May 1936 Bell was given a contract to produce a prototype.
The XFM-1 was an unusual design. It was a low winged monoplane, with two Allison engines carried in nacelles mounted above the wings. The wings had straight trailing edges, and tapered leading edges outside the engines. These engines drove pusher propellers, leaving the front of each nacelle free for a gunner's position. In the first prototype each gunner had one Madsen 37mm cannon and one 0.30in machine gun. There was a fairly long and narrow Plexiglas covered cabin in the nose, containing the pilot and navigator. Further back there were blisters for a 0.50in machine gun in the sides of the fuselage. The XFM-1 could also carry twenty 30lb bombs in an internal bomb bay mounted between the wing spars. The inner wing sections contained a tunnel to allow the gunners to move into the main fuselage if needed.
Work on the prototype began in May 1936, and it made its maiden flight on 1 September 1937. This didn’t go terribly well - the port engine backfired at take off and damaged the air ducts and intercooler. During the second flight, on 24 September 1937, the starboard undercarriage collapsed while landing, causing damage to the starboard wing. This was followed by ten more successful flights, and the aircraft was accepted by the USAAC on 21 October 1937. In 1938-39 the XFM-1 underwent extensive tests at Langley Field, where it was discovered to be rather difficult to maintain.
On 20 May 1938 the War Department gave Bell a contract to produce thirteen YFM-1s for service testing, of which nine were completed. A number of changes were made to the design. The engines were given modified cowlings, superchargers and propeller spinners. The fuselage was made longer and the front redesigned. The forward firing .3in machine guns were moved to dorsal and ventral positions and the side blisters were replaced with hatches. Under-wing bomb racks were added.
The first YFM-1 made its maiden flight on 28 September 1939 and was delivered to the USAAF on 23 February 1940. The last of the nine YFM-1s was delivered on 30 July 1940.
The last three were completed as the YFM-1A, with a new nosewheel undercarriage and main wheels that retracted inward into the wings. The new undercarriage caused serious problems which required a great deal of work to fix.
Two YFM-1s were converted into YFM-1Bs but giving them 1,090hp Allison V-1710-41 engines, but this had little impact on the performance of the aircraft.
No further FM-1s were built, as the type didn't live up to expectations and performance was poor, with a top speed 30mph below that of the B-17B. It was also not manoeuvrable enough to serve as a fighter. More oddly, it couldn't actually taxi, as the engine cooling system only worked in flight, so it had to be towed around on the ground.
In January 1942 the nine surviving aircraft went to the Air Corps Technical School's 10th Air Base Squadron for use as instructional aircraft.
Engine: Two Allison V-1710-41 inline piston engines
Power: 1,090hp each
Span: 70ft 0in
Length: 45ft 11.5in
Height: 12ft 5in
Empty Weight: 13,674lb
Maximum take off weight: 19,000lb
Maximum Speed: 268mph
Cruising Speed: 200mph
Climb rate: 1,500ft/ min
Range: 1,670 miles
Guns: Two 37mm T-9 cannon in wing nacelles, dorsal and ventral 0.3in machine guns, port and starboard beam 0.5in machine guns
Bomb load: 20 30lb bombs (total 600lb)