Bell FL Airabonita
by Jack McKillop
The Bell Aircraft Corporation was formed in Buffalo, New York, on 10 July 1935 with Lawrence “Larry” Bell as president. Bell had a long and distinguished career in aviation having worked for the Glenn L. Martin Company, where he rose to vice-president and general manager, and the Consolidated Aircraft Corporation, where he became general manager. By 1935, Reuben Fleet, the founder of Consolidated Aircraft, had decided to move the company from Buffalo to San Diego, California, and Bell advised him he wanted to stay in Buffalo and form his own company. Fleet promised Bell that he would give him sub-contract work to help in establishing the new company and as promised, Fleet gave Bell orders for over US$900,000 (over US$11 million in year 2001 dollars) for wing panels for PBY-2 and -3 Catalinas, q.v.
These orders gave the company a chance to get organized but Larry Bell wanted to design and build aircraft. Robert Woods, the Chief Engineer of Bell Aircraft, had considerable experience with the liquid-cooled engine and all of Bell’s future piston-engine aircraft were powered by these engines. Bell’s first opportunity to design a new aircraft came in 1936 when the U.S. Army Air Corps (USAAC), superseded by the U.S. Army Air Forces (USAAF) on 20 June 1941, issued an operational requirement for a long-range escort fighter to protect bombers. Bell’s design, the Bell Model 1, was accepted and a development contract was signed for one XFM-1 Airacuda on 4 June 1936; this was later followed by a development contract in May 1938 for thirteen YFM-1s but only nine were built. This twin-engine aircraft was innovative but its top speed was less than 300 mph (483 km/h), it had poor performance, and the cost for each aircraft would have been US$219,000 (US$2.77 million in year 2001 dollars). Accordingly, the aircraft never went into production.
Bell’s second design, the Model 2, was a modification of a Consolidated A-11 re-engine with an Allison liquid-cooled engine. This new aircraft was designated XA-11A but never went into production.
In March 1937, the USAAC issued a specification for a new fighter and two months later, Bell submitted designs for their Models 3 and 4. Both were single-engine fighters with a tricycle landing gear and a liquid-cooled engine; the difference between the two was the location of the engine. The Model 3 featured an engine located ahead of the cockpit while the Model 4 had the engine behind the cockpit. The Model 4 design was accepted and a development contract for one XP-39 Airacobra was signed on 7 October 1937.
On 1 January 1938, the U.S. Navy (USN) issued a specification for a light, high-performance, carrier-based fighter aircraft to replace the biplane fighters then in service. Larry Bell was very anxious to obtain a USN contract because there was little or no profit with development contracts for aircraft like the XFM and XP-39. This was evident when realizing that the corporate profits for the years 1935 through 1937 were US$49,439 (US$602,915 in year 2001 dollars). Bell, Brewster, Curtiss, Grumman and Vought submitted proposals for the Navy fighter; some were single-engine while others were twin-engine. After considering the proposals, the USN ordered three aircraft, one Bell Model 5 as the XFL-1 Airabonita, one Grumman Model G-34 as the XF5F-1 Skyrocket and one Vought-Sikorsky Model V-166B as the XF4U-1 Corsair, q.v.
The contract for one XFL-1 for testing was signed 8 November 1938 and specified delivery of a single prototype with 300-days to Naval Air Station (NAS) Anacostia, District of Columbia; the projected delivery date was 4 September 1939. Like the Model 4, this aircraft was to be powered by a liquid-cooled engine installed behind the pilot; the use of the liquid-cooled engine was a gamble because the USN had banned the storage of highly flammable glycol coolant in ships in the 1920s. Since the XFL-1 was a navalized version of the Model 4, many modifications were required before the Model 5 could be used by the USN. Two of them mandated by the USN were (1) increasing the wing area to permit a carrier landing speed not to exceed 70 mph (112.7 km/h) and (2) the use of a conventional landing gear and tailhook rather than the tricycle landing gear of the Models 3 and 4.
One major modification was the use of a conventional tail wheel, plus a tailhook, instead of the tricycle landing gear of the Model 4. This required moving the main landing gear forward and attaching it to the front wing spar requiring a new one-piece wing instead of outer panels bolted to a center stub. The use of a conventional landing gear and the engine located far aft provided for center of gravity problems. Consideration was given to moving the wing 3-inches (7.62 centimeters) aft but this was never done leading to stability problems described below. Unlike USAAC aircraft, the wings of the XFL-1 also contained flotation bags, later deleted, that would be deployed if the aircraft was ditched. Finally, the USN also demanded that ten small bomb bays, five in each wing, be built into the underside of each wing to accommodate 5.2 pound (2.36 kilogram) bombs to be dropped over an enemy aircraft formation.
Other modifications included strengthening of the entire aircraft for carrier operations, raising the cockpit to increase visibility, and the inclusion of a small window in the belly of the aircraft just forward of the wing root to aid in carrier landings. To increase stability, the wing span, chord, and dihedral of the wing were increased, the length of the fuselage was reduced, the flaps were enlarged to reduce stall speed, and the vertical tail surfaces were modified to maintain longitudinal stability during carrier landings.
As the aircraft was
built, its gross weight increased due to the strengthening required for carrier
operations and an increase in engine weight. The Allison engine was delivered
on 4 January 1940, four months after the aircraft was scheduled for delivery,
and it was found that the long extension propeller shaft and gearbox weighed 25
percent above the original, planned weight. The Navy also insisted on the use
of improved, and heavier, equipment resulting in increased weight. Clearly, a
higher powered engine was called for to compensate for the increased weight but
the design of the airframe precluded the installation of a different power
XFL-1: One Bell Model 5
On 13 May 1940, the XFL-1 was scheduled to engage in taxi tests at Buffalo Airport, New York. While engaged in a high-speed taxi test, a gust of wind caused the aircraft to become airborne and since the pilot was running out of runway, he chose to remain in flight. After rising a few hundred feet, one of the doors for the flotation bag opened and the bag to exit the compartment; the second compartment also opened and the bag exited. After a short period, both bags were carried away by the wind.
The initial ground test in May 1940 revealed engine cooling problems which plagued the aircraft through its four year life. Another problem was inadequate directional stability, a problem that had first been determined by wind tunnel tests made at the University of Michigan. As a result of these tests, Bell had added fillets, dorsal fins and duct modifications to the XFL-1 but none cured the stability problems. Bell then tried larger horizontal and vertical tail surfaces to no avail.
After testing by Bell, the aircraft was flown to the Naval Aircraft Factory as NAS Philadelphia, Pennsylvania on 27 February 1941 for further tests. During carrier qualification tests on 12 May 1941, the landing gear failed and the aircraft was declared “to be unsatisfactory for use as a carrier aircraft or for arrested landings.” As a result of this failure and the superiority of Vought’s Model V-166B or Grumman’s Model G-34 XF5F-1, the Navy signed a contract with Vought-Sikorsky for 584 F4U-1 Corsairs on 30 June 1941.
In 1942, the XFL-1 was transferred to the Aircraft Armament Unit at NAS Norfolk, Virginia, for anti-aircraft tests. In March 1944, it was transferred to NAS Patuxent River, Maryland, and was stricken from service on 25 April 1944. After the war, the runways at NAS Patuxent River were extended into the Chesapeake Bay to accommodate jet aircraft and the XFL-1, sans engine and equipment, was used as landfill. An inglorious end to a unique aircraft.
Power Plant: One 1,150 hp (858 kW) Allison XV-1710-6 twelve-cylinder, two-bank, liquid-cooled, Vee engine driving a 10 foot 4-1/2 inch (3,16 meter) diameter Curtiss three-bladed propeller.
Wing Span: 35 feet (10,67 meters)
Length: 29 feet 9-1/8 inches (9,07 meters)
Height: 12 feet 9-1/2 inches (3,90 meters)
Wing Area: 232 square feet (21,55 square meters)
Empty Weight: 5,161 pounds (2 341 kilograms)
Gross Weight: 6,651 pounds (3 017 kilograms)
Maximum Takeoff Weight: 7,212 pounds (3 271 kilograms)
Maximum Speed: 338 mph (544 km/h) at 11,000 feet (3 353 meters)
Maximum Speed at Sea Level: 307 mph (494 km/h)
Initial Rate of Climb: 2,630 feet (802 meters) per minute
Climb to 10,000 feet (3,048 meters): 3.75 minutes
Normal Range: 965 miles (1 553 kilometers)
Maximum Range: 1,072 miles (1 725 kilometers)
Normal Fuel: 126 U.S. gallons (105 Imperial gallons or 477 liters)
Maximum Fuel: 200 U.S. gallons (167 Imperial gallons or 757 liters)
Armament: Provision for two 30 caliber (7,62 mm) synchronized machine guns in the fuselage nose and a 50 caliber (12,7 mm) or 37 mm cannon firing through the propeller hub. Armament never fitted to the aircraft.