McDonnell XHJD-1 Whirlaway
Platt-LePage Aircraft PL-9
McDonnell Aircraft Co had invested in Platt-LePage Aircraft in mid-1942, in exchange for having McDonnell personnel learn helicopter design. In 1943 McDonnell authorized Constantine M. Zakhartchenko and a small group of engineers to undertake research on design and construction of rotors. He was appraised of Platt-LePage's preliminary work on a twin-engined, twin-rotor helicopter to meet Army requirements. Although that PL-9 design eventually proved unsuccessful in the Army competition (the AAF selected the Kellet XR-10), it fared better in a different guise as McDonnell, in return for an increase in his investment as finalized in June 1944, obtained Platt-LePage's agreement allowing the McDonnell Aircraft Corporation to initiate the parallel development of the twin-engined, twin-rotor concept.
On the strength of both this agreement and the work accomplished by Zakhartchenko's team, McDonnell proposed a helicopter of this design to the Navy to serve either as a testbed or as an anti-submarine warfare platform. As a testbed, the proposed Model 65 was intended to be used for the study of the effects of rotor diameter, disk loading, variations in rotor blade flap and lag angles, and other variables. In the ASW role, it was to be able to carry an adequate load of detection gear and weapons.
Considering the side-by-side rotor arrangement proposed by McDonnell to be a most suitable configuration for large helicopters capable of operating in the ASW role, the Bureau of Aeronautics issued a Letter of Intent on 15 May, 1944, covering the design, construction, and testing of one XHJD-1. This Letter of Intent was confirmed on 23 March, 1945, when Contract NOa(s)-3703 was awarded.
At the time of contract award, design of the Whirlaway, entrusted to a team led by Constantine Zakhartchenko, was well underway and ground testing was begun early in 1946. Piloted by Charles R. Wood Jr, the XHJD-1 made its first hover flight at Lambert Field, St Louis, on 27 April, 1946.
Designed to carry up to ten occupants but normally flown as a two-seater with up to 816kg of test instrumentation, the Whirlaway was fitted with twin side-by-side rotors mounted on pylons extending outboard of the engine nacelles. The nacelles, each housing a 450hp Pratt & Whitney R-985-AN-14B seven-cylinder radial engine, were attached to short wings which supported approximately 10 per cent of the gross weight during cruise and as much as 30 per cent of the weight in power-off autorotation, with consequent substantial improvement in overall performance efficiency. This feature, combined with the ability to transmit power from either engine to both rotors by transmissions and gear boxes, enabled the XHJH-1 to maintain level flight at full gross weight on the power of only one engine.
From April 1946 until June 1951, the XHJD-1 was used for numerous flying research tests including the evaluation of performance, stability balance and vibration characteristics peculiar to its twin-rotor configuration. In the process, the Whirlaway had its original 15.24-m diameter rotors replaced by rotors of varying diameters and had a braced tailplane with externally balanced control surfaces added before translation flights began. Once vibration and resonance problems with its unsynchromzed three-blade rotors were alleviated through the use of shock-absorbing rotor mounts, the XHJD-1 was considered to handle well and was flown some 250 hours without serious mishap. It was flown not only by McDonnell and Navy pilots but after being fitted with a rescue winch, was also evaluated in November 1949 by USAF pilots from the Arctic Rescue Helicopter Board.
As helicopter technology had made significant progress since development of the Whirlaway had been initiated, neither the XHJD-1 nor its proposed Model 65C development was put into production. Upon completion of its trials programme, the XHJD-1 - the first helicopter to bear the McDonnell name and the world's first successful twin-engined, twin-rotor helicopter was donated to the National Air and Space Museum.
Engine: 2 x Pratt & Whitney R-985-AN-14B Wasp Junior, 336kW / 450 hp