Bell 61 / HSL
At the end of the 1940s, it became apparent that the helicopters in the Navy's inventory were not of the size to accomplish anti-submarine warfare (ASW) missions and in 1950 the US Navy launched an industrywide competition for a new helicopter to be designed specifically for the ASW role.
Bell's only twin-rotor helicopter, the HSL-1 was the largest US helicopter of the day and was the first helicopter designed from the outset for the submarine hunter/killer role with the Fairchild Petrel air-to-underwater missile.
In June 1941, Bell won this competition in June 1950, and was awarded a contract calling for the building of three prototypes of its Model 61, to be designated XHSL-1 (BuNos 129133/129135).
The two rotors were of the basic Bell two blades and automatic stabilising bar. The fore and aft rotors were interconnected and could be folded for carrier operations but the HSL was too large even with its rotors folded, to fit on the elevators of the aircraft carriers. The Model 61 was powered by a single 2.400hp Pratt & Whitney R-2800-50 engine installed in the centre fuselage and driving a transmission shaft to the front pylon, and total fuel capacity was 425 US gal providing a flight endurance of nearly four hours. Armament was intended to include air-to-surface missiles such as the Fairchild AUM-2 Petrel, as well as a dipping ASDIC. The HSL-1 was equipped with a Bell-developed autopilot which permitted motionless hovering for long periods.
For the development and production, the Bell Helicopter Division was moved from Buffalo to Fort Worth.
Powered by a 2400hp Pratt & Whitney R-2800-50 engine, the first of three prototypes flew on 4 March 1953.
After the vibration had been cured, carrier tests were made aboard the escort carrier USS Kula Gulf (CVE-108) in March 1955. Even if the HSL performed well in the air, its large size, even with rotor blades folded, was not compatible with the carrier's elevator. Even worse, was its very high level of noise while in stationary flight and this limited the sonar operator's capability of identifying contacts. Due to these shortcomings the first production contract calling for seventy-eight HSL-1s, including eighteen machines under MAP destined for Britain's Fleet Air Arm, was cut back to fifty (BuNo 129154/129168, 129843/129877) in July 1955. A follow-on contract for sixteen more (BuNo 140414/140429) was cancelled. The Navy ordered the Sikorsky HSS-1 "Sea Bat" instead.
Deliveries to Squadron HU-1 began in January 1957. Production models differed from the prototypes in having stabilising fins at the rear of the fuselage. The HSL-1 programme was not a complete failure because the Bell helicopter demonstrated interesting capabilities in the mine-sweeping role. Six HSL-1s were modified to do this and were operated by the Navy Mine Defense Laboratory in Panama City (Florida), until the end of 1960. The remaining aircraft were used for training or as spares.
The HO4S, which the HSL-1 had been intended to replace, remained in service until the appearance of the HSS-1 antisubmarine version of the Sikorsky S-58.
A civil variant, the D-116, and two derivatives of the HSL-1 were considered under design numbers D-216 and D-238 but they remained as projects.
No HSL-1 seems to have survived.
Engine: 1 x Pratt & Whitney R-2800-50, 1415kW
Rotor diameter: 15.70m
Fuselage length: 11.90m
Width (rotors folded): 3.5m
Loaded weight: 12020kg
Maximum speed: 185km/h
Cruising speed: 155km/h
Fuel capacity: 425 US gal
Warload: 800 kg
Payload: 1814 kg