The XFL-1 Airabonita was an experimental shipboard version of the land-based P-39 Airacobra which was developed in parallel with the Army version. However, the Airabonita had the misfortune to be in direct competition with the Vought Corsair for Navy orders, and only one example was built.
In February 1938, the US Navy had issued a specification for a high-speed, high-altitude fighter. Bell submitted a navalized version of the Airacobra in response to this request. At the same time, Chance Vought submitted a design which was eventually to emerge as the superlative F4U Corsair. A US Navy contract for one XFL-1 prototype was placed on November 8, 1938. The BuAer Number was 1588.
The XFL-1 was powered by a 1150 hp Allison XV-1710-6 (E1), the first in-line engine to be fitted to an American naval fighter since 1928. The use of a liquid-cooled engine in itself was quite a gamble for Bell, since in 1927 the Navy had explicitly excluded liquid-cooled engines from aircraft carriers, fearful of storing the flammable glycol coolant aboard ship.
The XFL-1 differed from its land-based counterpart primarily in having underwing radiators and a tailwheel undercarriage. The main undercarriage members were transferred to the front wing spar, and an arrester hook was fitted. The relocation of the main undercarriage members to the forward part of the wing necessitated the relocation of the wing-root radiators to exterior points under the rear of the central section of the wing. The fuselage was shorter than that of the P-39, the vertical tail surfaces were redesigned, and the airframe was stressed for carrier operations. The canopy was of a higher profile than that of the P-39, and the pilot sat higher in the cockpit. The wing was of larger span with greater chord. The dorsal intake was smaller and shallower than that on the YP-39. Armament was to have been two 0.30-inch machine guns in the fuselage nose, plus a 0.50-inch machine gun or a 37-mm cannon firing through the propeller hub, although no armament was actually ever fitted to the XFL-1 prototype.
The XFL-1 flew for the first time on May 13, 1940, with test pilot Brian Sparks at the controls. The aircraft was painted overall Navy grey, except for the upper wing surfaces which were chrome yellow. It was transferred to NAS Anacostia in Washington, DC for further testing in July of 1940. During tests, the XFL-1 achieved a maximum speed of 307 mph at sea level, 336 mph at 10,000 feet, and 322 mph at at 20,000 feet. Initial climb rate was 2630 feet per minute, and an altitude of 20,000 feet could be attained in 9.2 minutes. Service ceiling was 30,900 feet. Weights were 5161 pounds empty, 6651 pounds loaded, 7212 pounds maximum. Dimensions were span 35 feet 0 inches, length 29 feet 9 1/8 inches, height 12 feet 9 2/3 inches, wing area 232 square feet.
Since the use of an in-line, liquid-cooled engine as a powerplant for carrier-based aircraft had for many years run counter to Navy thinking, the project was regarded with disfavor by many. Longitudinal stability proved to be marginal, and the vertical tail surfaces were enlarged after a series of wind-tunnel tests. Difficulties with the Allison engine delayed delivery of the XFL-1 to the Navy until February of 1941. The XFL-1 failed its carrier qualification trials due to problems with the undercarriage. The aircraft was returned to the manufacturer for modifications. Shortly thereafter, the superior performance of the F4U Corsair against which the Airabonita was competing led the Navy to decide on May 12, 1941 that the XFL-1 was unsuitable for further development and the project was abandoned with only one example ever being built.
The Navy later did operate a couple of Airacobras, but they acquired them directly from the Army and never used them from carriers. Towards the end of the war, the US Navy acquired a pair of P-39Qs from the Army (Ser No 42-20807 and 19976) for use as target drones. They were delivered to NAS Cape May, New Jersey in February of 1946 and used for test work fitted with smoke generators. They were initially designated XTDL-1, but their designations were later changed to F2L-1K. Their BuAer numbers were 91102 and 91103.