By letter dated thirty one Jan, 1946, equipage Command requested qualified makers to submit proposals for the event of an outsized experimental eggbeater. This rotary-wing craft was to be capable of carrying outwardly Associate in Nursing a pair of.44m by 2.44m by 6.10m freight package consideration up to 4536kg at a high speed of 105km/h, to hover at Associate in Nursing altitude of 915m, Associate in Nursingd to possess a military science radius of 160km and an endurance of half-hour. it had been supposed to be used in transfer of ordnance, equipment, supplies, and personnel, with hundreds to be down into or raised out of areas within which even eggbeater landings were not possible. Moreover, this sky crane eggbeater had to be simply destroyed for transport on customary trailer trucks.
Advised by Friedrich von Dobhloff, the Austrian engineer UN agency throughout the war had pioneered the appliance of jet principle to helicopters at the Wiener Neustadter Flugzeugwerke and UN agency conjointly worked with McDonnell on the XH-20 and different helicopters, the AAF surface Branch recognized that achieving such capabilities would need major and risk-fraught technological advances and, consequently, it inspired bidders to think about mistreatment (1) a way of rotor construction aside from standard steel tube spar and wood; (2) gas-turbines and jet-driven rotors; and (3) servo controls, blade ailerons, or different devices to cut back the high management forces inherent within the use of a rotor that was expected to possess a diameter of twenty-two.86 to 24.38m. Finally, to attenuate prices, the surface Branch counseled that the body and different non-critical parts of this flying test-rig be created within the simplest type doable.
As requested, the bidders submitted proposals for a two-phase programme with the primary part consisting of a style study and therefore the second part, which might be undertaken solely when the AAF approved the look study, vocation for the fabrication of a flying test-rig. when proposals analysis, Kellett craft Corporation of higher Darby, Pennsylvania, was notified on a pair of might, 1946, that it had won {the style|the planning|the look} competition and shortly when a contract for the primary part design study was negotiated.
The annual style study part disclosed that technical issues would be even harder than anticipated, notably because the results of the necessity to use a rotor of a lot of larger diameter, and thus harder to manufacture and management. Powerplant choice conjointly verified arduous as, though accordant with AAF personnel at Wright Field that the employment of gas-turbine and rotor-tip combustion was doubtless to supply the simplest answer, Kellett was eventually forced to suggest a twin-turbine installation rather than the only rotary engine favoured by the AAF. This and different technical recommendations were supported by the Air equipage Command at the tip of the look study part and on twenty seven August, 1947, Kellett was awarded Contract AC15011 to make a ground test-rig for the XR-17 (which became the XH-17 in June 1948 once the new created U. S. Air Force adopted a revised designation system). Provision was incorporated within the contract for the modification of the bottom rig into a flying test-stand at the Air Force choice.
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