| Boeing-Vertol 179 / 237 / YUH-61A 1955 |  |
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| Boeing-Vertol 179 / 237 / YUH-61A 1955 | |
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Competitor in the UTTAS programme to choose a utility helicopter for the US Army (won by the Sikorsky UH-60). Of the three prototypes built (1974), one was modified for the LAMPS III programme. It had a four-blade rotor of composite material. G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
Army experience with assault transport helicopters in Vietnam led, during the early 1970s, to the formulation of a requirement for a new Utility Tactical Transport Aircraft System (UTTAS) helicopter intended to eventually replace the UH-1 Iroquois in the assault transport, general utility, and aeromedical evacuation roles. The UTTAS specification issued in January 1972 called for a simple, robust, and mechanically reliable 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. 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 Boeing-Vertol and Sikorsky were selected as finalists in the UTTAS competition, and each firm was awarded a contract for the construction and initial flight testing of three prototype aircraft. Boeing-Vertol's UTTAS entry carried the company model number 237, and the first of the three prototypes contracted for by the Army made its maiden flight in November 1974. The YUH-61A, as the Army designated the Boeing-Vertol machine, featured a four-bladed hingeless main rotor made of composite materials, had built-in work platforms that allowed easy access to all critical mechanical components, and was somewhat smaller and some 540kg lighter than Sikorsky's competing YUH-60A. All three YUH-61A prototypes (serials 73-21656 through -21658) were delivered to the Army in March 1976, and the UTTAS 'fly-off was conducted over the next eight months. In December 1976 Sikorsky's entry was named the winner of the competition, and all three YUH-61A’s were returned to Boeing-Vertol shortly thereafter. The firm subsequently entered 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 and eventually ceased further development of the type. S.Harding "U.S.Army Aircraft since 1947", 1990
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 requirement called for much the same capacity as that available with the UH-1, but this payload had to be maintained up to much greater altitudes and at considerably higher ambient temperatures. 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, and this profited from the company's licence-production of the MBB BO.105 utility helicopter, for the Model 179 was designed round a similar type of hingeless semi-rigid main rotor of composite construction. Powerplant was a pair of the specified General Electric YT700 turboshafts, located in two pods on the sides of the fuselage beside the shallow transmission unit above the rear of the cabin. This latter could accommodate 11 troops (in addition to the three crew), or its area of 8.3m2 could accommodate freight; alternatively, a slung load of 3175kg could be lifted. The fuselage was of frame-and-stringer construction, a considerable quantity of glassfibre and honeycomb being used for strength and to reduce maintenance. The conventional pod-and-boom fuselage terminated in a four-blade glassfibre tail rotor and a large tail-plane with incidence varied automatically with airspeed for improved control. The landing gear was of fixed tricycle type, with single main wheels and a twin-wheel nose unit. Three military prototypes were completed, the first 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. Boeing Vertol completed a fourth prototype as the Model 179 civil demonstrator, with accommodation for between 14 and 20 passengers. Subsequent development of both types was later abandoned. D.Donald "The Complete Encyclopedia of World Aircraft", 1997
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