HSL [Model 61]
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. Thus in 1950, the US Navy launched an industrywide competition for a new helicopter to be designed specifically for the ASW role. In the following June, Bell won this competition and was awarded a contract calling for the building of three prototypes of its Model 61, to be designated XHSL-1.
This four-seat machine was the first and would be the only Bell helicopter using the tandem-rotor layout. Nevertheless each of 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. Despite the fact that the US Navy would have preferred a twin-engined machine, the Model 61 was powered by a single 2.400hp Pratt & Whitney R-2800-50 engine installed in the centre fuselage 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. With a crew of four, comprising a pilot, a co-pilot and two sonar operators, and a maximum gross weight of over 11700kg, the Model 61 was then the biggest helicopter to be ordered into production in the United States.
For the development and production, the Bell Helicopter Division was moved from Buffalo to Fort Worth. The first XHSL-1 flew on 4 March, 1953, but development of the HSL-1, was to be long and difficult. The helicopter suffered many teething troubles, the worst being vibration. After these 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 in July 1955. A follow-on contract for sixteen more 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. Nevertheless 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.
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