Frank Piasecki's huge twin tandem-rotor transport helicopter
By Willie Bodensyein
When on 23 October 1953 Frank Piasecki's YH-16 23.8m long transport or rescue helicopter, powered by two overlapping rotors each measuring 25m in diameter took to the air at Philadelphia International Airport, it was by far the largest helicopter then flown. Piloted by Harold Peterson and Phil Camerano, its maiden hop which lasted twelve minutes, included hovering, forward and sideways flying.
Plawecki's design was in response to a USAF requirement for a wide-ranging helicopter capable of rescuing downed strategic bomber crews. The hefty fuel capacity required to meet its specified 2250km range in part dictated its size. The YH-16 design that he penned was built in prototype form. Its capacious fuselage could accommodate forty passengers or three light trucks loaded through its clamshell rear doors and ramp.
When the U.S. Army got sight of the design, it saw in the H-16 an answer to several helicopter mission requirements of its own and joined the USAF in sponsoring further development.
Designed to be powered by two 1650hp Pratt & Whitney R-2180 radial engines, it soon became evident that it would be under powered. Turbine power, lighter, more powerful and more reliable, by then had become available. Two 1800shp Allison T38 units were accordingly installed in Piasecki's second prototype that was during the design process changed into a heavy-lift craft. This prototype, the world's first twin-turbine helicopter, again with Harold Peterson and George Callaghan at the controls, took to the sky in July 1955.
In 1956, the Allison powered prototype set an unofficial speed record of 267km/h and prospects for the H-16 program could not have looked brighter. But then tragedy struck. Returning from a test flight in December 1956, the YH-16A broke apart in the air and crashed near the Delaware River, killing Peterson and Callaghan. Investigators determined that the rear rotor shaft had failed, allowing the blades to desynchronize and wobble into the plane of those of the forward rotor.
By then, the Air Force that in June 1949 had placed an order for two service test and evaluation aircraft decided against procuring the H-16 for operational use and in 1955 had turned the YH-16 over to the Army for evaluation. The US Army continued evaluations, but ultimately judged the YH-16 to be unsuited to sustained operations under field conditions and in mid-1956, terminated the H-16 test programme.
This tragic accident was the final nail in the coffin of the H-16 and the program was scrapped, pre-empting the sixty-nine-passenger YH-16B Turbotransporter (a conversion of the YH-16 then in progress), which would have flown with two 3700shp Allison T56 engines. Piasecki's plans to produce variants capable of transporting large exterior cargo pods, equipped with variable-height landing gear legs in order to accommodate pods of varying sizes, also only remained on the drawing board.
Crew: 3 (2 pilots and flight engineer)
Capacity: 47 troops or 38 stretchers and 5 attendants
Length: 77 ft 7 in (23.65 m)
Height: 25 ft 0 in (7.62 m)
Empty weight: 25,450 lb (11,544 kg)
Gross weight: 45,700 lb (20,729 kg)
Powerplant: 2 ◊ Allison T56-A-5 turboshafts, 2,100 shp (1,600 kW) each
Main rotor diameter: 2◊ 82 ft (25 m)
Main rotor area: 10,562 sq ft (981.2 m2)
Performance Maximum speed: 156 mph (251 km/h, 136 kts)
Cruise speed: 125 mph (201 km/h, 109 kts)
Range: 216 mi (348 km, 188 Nm)
Service ceiling: 15,600 ft (4,800 m)