|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. 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. Subsequently, Piasecki 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 Ďfirstí flight on 15 November 1965. Modification work had begun in 1964, ground tests were carried out in the summer of 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 larger-diameter rotor, a new drive system and a new tail fan. By May 1966 the Pathfinder II had flown some 40 hours, during which it had achieved level speeds of up to 361km/h, 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.
Since then Piasecki has 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.
K.Munson "Helicopters And Other Rotorcraft Since 1907", 1973
The Pathfinder was an interesting Compound Helicopter concept that was carried out during the 1960s by Piasecki Aircraft. Although the project never reached fruition, the concept did show promise during its flight test program. There was interest from both the Army and Navy who shared a joint development contract.
The Compound Pathfinder used a standard helicopter-style overhead rotor which was off-loaded by a small low-mounted fixed wing when the craft transitioned to high-speed horizontal flight. The three-bladed rotor was mounted on a streamlined pylon which was powered by turbine engine. The small tapered low wing was equipped with standard flaps. To the rear of the fuselage were cruciform fins which supported an annulus which contained a propeller. That rear installation performed the function of anti-torque and directional control. The model also mounted a retractable landing gear carriage.
In operation, the Pathfinder took off like a standard helicopter. Acceleration was then achieved by directing power from the rotor into the rear propeller, then as the speed increased, the fixed wings took on a larger share of the lift. It should also be noted that the Pathfinder could also be used in a STOL mode, which greatly increased its payload capability. The reverse transition for landing exactly reversed the take-off process.
There were actually two versions of the Pathfinder, the first of which was the -1 version, which first flew in 1962. The similar Pathfinder II, the 16H-1A, was completed in 1965.
The -1A version was considerably larger than the initial prototype, with a three-foot bigger diameter rotor at 13.4m, and its maximum speed was much faster at 360km/h, compared to 287 with the first version. The gross weight of the 1A model was 1037kg heavier than the first model. The two models used different powerplants; the first used a United Aircraft of Canada PT6B engine, while the later version used a General Electric T58 turbine engine.
S.Markman & B.Holder "Straight Up: A History of Vertical Flight", 2000
A high-speed compound helicopter built in 1965 as a private venture for research into fast rotary wing craft. After a two-year development period, the aircraft was modified at the request of the US Army and Navy and redesignated Pathfinder II.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
Beginning in early 1964 the Army and Navy jointly funded modifications to Piasecki Aircraft's Model 16H-1 Pathfinder compound research helicopter as part of an ongoing study of advanced high-speed rotorcraft technology. The 16H-1 had originally been developed as a company private venture and, as such, had first flown in February 1962. The modified version, designated the 16H-1A Pathfinder II by Piasecki, made its first tethered test ascents in October 1965.
Like its predecessor, the Pathfinder II was a high-speed compound rotorcraft which utilized a conventional fully articulated, three-bladed main rotor for vertical lift and a tail-mounted, dueled 'ringtail' pusher propeller for directional and anti-torque control. After takeoff, power was applied to the pusher propeller for forward propulsion, and in cruising flight the craft's small wings helped off-load the rotor and increase forward speeds.
The Pathfinder II differed from the earlier 16H-1 primarily in having a more powerful General Electric T58 shaft turbine engine, a longer and more streamlined fuselage with increased cabin accommodation, a larger main rotor, increased-span stub wings, strengthened main landing gear, redesigned engine air intakes, and upgraded electronics.
The Pathfinder II made its first free flight in November 1965, and quickly proved itself to be an extraordinarily fast and manoeuvrable machine. Forward speeds in excess of 360kph were not uncommon, and the 16H-1A was capable of flying backwards and sideways at speeds of up to 55kph. The evaluation programme provided a wealth of valuable information on compound rotorcraft technology and operations, much of which was later used in the development and testing of the AH-56 Cheyenne. 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.
S.Harding "U.S.Army Aircraft since 1947", 1990
Having left the Piasecki Helicopter Corporation, Frank Piasecki set up Piasecki Aircraft Corporation and became involved in the Agusta 101G large transport helicopter and also embarked on research under government contracts into compound helicopters. The company built a prototype of the Pathfinder 16H-1 (N616H) which first flew on 21 February 1962. This machine had an all-metal monocoque fuselage with a small low wing, a forward-swept pylon mounting a three-bladed rotor and an annular tail duct with a pusher propeller and directional vanes. It was subsequently modified with a stretched fuselage and a 1250shp General Electric T58 turboshaft engine to become the Model 16H-1A and then to Model 16H-1C Pathfinder III configuration with a 1500shp T58-GE-5. A nine-seat development, the Model 16H-3J was not proceeded with.
R.Simpson "Airlife's Helicopter and Rotorcraft", 1998
Technical data for Piasecki 16H-1A "Pathfinfer II"
Crew+passengers: 2+6, engine: 1 x General Electric T-58-GE-8 turboshaft, rated at 930kW, main rotor diameter: 13.41m, wingspan: 10.0m, fuselage length: 11.35m, take-off weight: 4870kg, empty weight: 2165kg, max speed: 370km/h, cruising speed: 280km/h, service ceiling: 5700m, range: 725-1530km