Boeing-Vertol 179 / 237 / YUH-61A
In 1971 the US Department of Defense issued a requirement for a new UTTAS (Utility Tactical Transport Aircraft System) helicopter to replace the Bell UH-1 in service with the US Army.
The specification called for an aircraft capable of lifting an entire eleven-man infantry squad, or an equivalent weight in cargo, to medium altitudes at a minimum cruising speed of 323kph, and at considerably higher ambient temperatures. All designs proposed in response to the specification were required to use two General Electric T700-GE-700 turboshaft engines, and were to have wheeled landing gear, duplicate or heavily armored critical mechanical components, manual rotor blade folding, and only minimal avionics.
In August 1972 the two leading contenders for UTTAS hardware were Sikorsky, with its S-70 ordered for evaluation as the YUH-60A, and Boeing Vertol, with the Boeing Vertol Model 179 (YUH-61A).
The Model 179 was the first Boeing Vertol design with a single main rotor, designed round a similar type of hingeless semi-rigid main rotor of composite construction from the company's licence-produced MBB BO.105.
Powerplant was a pair of the specified General Electric YT700 turboshafts, located in two pods on the sides of the fuselage beside the transmission unit, above the rear of the cabin. The cabin could accommodate 11 troops (in addition to the three crew), or its area of 8.3sq.m could accommodate freight. Alternatively, a slung load of 3175kg could be lifted. The fuselage was of frame-and-stringer construction, with glassfibre and honeycomb being used for strength and to reduce maintenance. The conventional pod-and-boom fuselage had a four-blade glassfibre tail rotor and a large tail-plane with incidence varied automatically with airspeed for improved control. The landing gear was fixed tricycle, with single main wheels and a twin-wheel nose unit.
Boeing Vertol 179
Three model number 237 military prototypes were completed (serials 73-21656 through -21658), the first (73-21656) flying on 29 November 1974.
A competitive evaluation of the YUH-60A and YUH-61A was conducted from 1975, and the Sikorsky entrant was judged the winner in December 1976. All three YUH-61A prototypes were returned to Boeing-Vertol shortly after.
Of the three prototypes built, one was modified for the LAMPS III programme as a 'navalized' version of the Model 237 in the Navy's LAMPS II competition for a ship-based multi-purpose helicopter, but again lost out to the Sikorsky H-60. It had a four-blade rotor of composite material.
Boeing Vertol completed a fourth prototype as the Model 179 civil demonstrator, with accommodation for between 14 and 20 passengers. A 14/20-passenger civil transport (N179BV), it failed to gain commercial interest. Failure to win the Army contract made its production uneconomic, and as a result only the prototype was built. Development of both types was later abandoned.
YUH-61A prototypes 73-21656 & 58 were on display at Army Aviation Museum, Ft. Rucker, AL.
Boeing-Vertol Model 179
Engine: 2 x General Electric YT700-GE-700 turboshaft, 1146kW
ain rotor diameter: 14.93m
Length with rotors turning: 18.13m
Max take-off weight: 8481kg
Empty weight: 4302kg
Max speed: 290km/h
Cruising speed: 216km/h
Hovering ceiling: 1722m