|McDonnell Model 78 / XHCH-1|
The McDonnell Model 86 was the first helicopter specially designed for the Navy vert-rep (vertical replenishment) mission - carrying supplies and ammunition between ships—and for the Marine logistic support mission—carrying heavy loads for short distances from ship-to-shore or from marshalling areas ashore to front-line units.
Emphasis was placed during its design on extreme simplicity, ease of maintenance, and good flying characteristics while carrying underslung loads of up to 6804kg when operating at normal gross weight, or 9979kg when operating at overload gross weight. The powerplant installation, derived from that developed for the XHRH-1, consisted of two 3750eshp Allison XT56-A-2 turbines mounted atop the fuselage and providing compressed-air to the 726kg thrust McDonnell 12JP20 pressure jet at the extremity of each rotor blade. The crew of two consisted of a pilot on the starboard side and an aft-facing winch operator to port. There was no provision for carrying loads internally. Loads were to be carried externally on a sling, in a net, or in a specially-developed pod. This pod was to be fitted with a detachable tail unit to stabilize the load in flight and with large wheels to enable it to be towed on uneven ground after it had been delivered to forward bases. Consideration was also given to using the Fairchild pod which had been designed for the XC-120 twin-engined cargo aircraft.
Three XHCH-1 prototypes (BuNos 138654/138656) were ordered on 11 April, 1952, under Contract NOa(s)52-947 and a mock-up was inspected on 22 and 23 May, 1953. However, the programme was later cut back due to lack of funds. No prototypes were completed but a much revised mock-up was inspected on 15 and 16 November, 1956, and a full-scale rotor was tested on a hot-whirling bench beginning in December 1957. Additional budget cuts forced the Navy to terminate the contract on 18 January, 1959, before completion of a prototype. Nevertheless, McDonnell kept working on the Model 86 sky crane until June 1961.
Rene J. Francillon "McDonnell Douglas Aircraft since 1920: Volume II", 1997