Piasecki 16H Pathfinder
The Piasecki Aircraft Corporation has been engaged since the early 1960s on a series of compound helicopter research designs known by the name Pathfinder. The concept first took material form at the Model 16H-1 Pathfinder prototype (registration N616H). This aircraft was developed as a private venture and flew for the first time on 21 February 1962, undertaking this flight as a 'pure' helicopter without using the 3-blade ducted tail fan. No wings were fitted at that stage, the cabin was unfaired, and the retractable landing gear was fixed in the extended position. Small stub-wings, which could be folded, and a fully-enclosed cabin to accommodate a pilot and 4 passengers, were added later in the year. The Pathfinder also mounted a retractable landing gear.
Powered by a 550shp UACL PT6B-2 turboshaft engine, the Pathfinder had a l2.50m diameter 3-blade rotor, a fuselage length of 7.62m and a gross weight of 2,565kg. In all, it amassed a total of 185 flying hours, during which speeds of up to 273km/h were attained. Piasecki subsequently received a joint US Army/US Navy contract to develop a compound helicopter capable of providing data on flight by such aircraft at speeds of up to 370km/h. As part of this programme the original aircraft was redesigned to become the Model 16H-1A Pathfinder II, in which form it made its second ‘first’ flight on 15 November 1965. Modification work had begun in 1964, ground tests snd tethered test ascents were carried out in in October 1965, and initial hovering trials were completed by the end of the year.
The principal design changes in the Pathfinder II were the enlargement of the fuselage, lengthened to accommodate 8 persons; the installation of a 1,250shp General Electric T58-GE-5 engine; and the adoption of a three-foot larger-diameter rotor at 13.4m, a new drive system and a new tail fan. The gross weight of the 1A model was 1037kg heavier than the first model. By May 1966 the Pathfinder II had flown some 40 hours, during which it had achieved level speeds of up to 361km/h (compared to 287 with the first version), had flown sideways at up to 55km/h and backwards at 52km/h, and had made 20 auto-rotative flights. For the final phase of the Army/Navy programme, in the summer of 1966, it was refitted with a 1,500shp T58-GE-5 engine, having new-design air intakes ahead of the wing leading edges, and received the new Model designation 16H-1C.
Joint Army-Navy sponsorship of the 16H-1A ended in late 1966, at which time the craft was returned to Piasecki for further company-funded research.
Piasecki announced several designs based upon the Pathfinder configuration, although up to 1972 none of these had been built. In 1968 it announced the Model 16H-3F Pathfinder III, a twin-turbine design using the 16H-1A fuselage with two T58-GE-10'S and 4-blade rotor and tail fan, for search and rescue, ASW and military utility applications. The 16H-3H Heli-Plane project, for an 8-passenger executive transport with twin PT6 or TPE 331 engines, was superseded in 1969 by the 9/15-seat 16H-3J commercial transport project; this in turn was redesignated 16H-3K in 1971, following the proposal to install more powerful PT6B engines. In 1972 Piasecki was reported to be working on a high-performance development of the original Pathfinder, designated 16H-1HT, to seat a pilot and 4 passengers. Intended to be powered by a 986shp Turbomeca Astazou XVI engine, it was planned to have a maximum speed of 325km/h and a range of 708km.
Piasecki 16H-1A Pathfinfer II