Hiller YROE-1 Rotorcycle

In 1953, Hiller Helicopters developed the Rotorcycle to meet a U. S. Marine Corps requirement for a single-person collapsible helicopter that could support special operations missions or be air-dropped to pilots trapped behind enemy lines. Hiller built the prototype, and the British firm, Saunders-Roe built ten production models, including the five YROE-1s requested by the Marine Corps, including this one. The first flight of a Rotorcycle occurred in 1956.

The Rotorcycle was so stable a non-pilot could fly it after only eight hours of instruction. However, The Marine Corps did not accept the YROE-1 for military service because of its slow speed of 84 kph (52 mph), its minimal range of 64 km (40 miles), its vulnerability to small-arms fire and the lack of visual references on the structure, which could cause the pilot to experience spatial disorientation at all but very low altitudes.

Rotor Diameter:5.64 m (18 ft 6 in)

Length:3.81 m (12 ft 6 in)

Height:2.29 m (7 ft 6 in)

Weight:Empty, 140 kg (309 lb)

Gross, 255 kg (562 lb)

Engine:Nelson YO-65-2 four-cylinder, two-cycle engine, 43 hp

Manufacturer:Saunders-Roe for Hiller Helicopters, United Kingdom, 1961

Hiller YROE-1 Rotorcycle

The Korean War experience taught the U.S. Marine Corps a number of lessons, including the fear that pilots downed behind enemy lines had very little time to escape. Too often the helicopters sent to rescue the aircrew were themselves damaged and shot down, or the aircrew was captured before the rescue flight arrived. The Marine Corps saw a solution in an easily-flown lightweight helicopter useful that would be for escape and in small-unit tactical operations. Hiller Helicopters responded to this proposal with the remarkable ROE-1 Rotorcycle. This small one-place helicopter more than met its performance requirements, but ultimately the idea proved to be flawed and the type did not enter operational service.

Stanley Hiller had established a successful business by developing novel helicopter designs, with an experimental research division within his company devoted to the development of innovative vertical flight aircraft such as the ramjet-powered HOE-1 and the Model 1031 Flying Platform (see NASM collection for both). This group had an excellent opportunity to demonstrate their engineering skill in 1953 when the U.S. Navy announced a requirement on behalf of the Marine Corps for a one-man helicopter that was easily transportable and simple to fly for use in rescue, escape and evasion, and special tactical missions. Thirty firms competed for the contract, but only two, Hiller and Gyrodyne, were selected. Gyrodyne's coaxial YRON-1 design was not adopted by the Marine Corps, but later became the Navy's Drone Anti-Submarine Helicopter (DASH), which served on destroyers whose deck area was insufficient to mount a full-scale helipad.

Hiller's design took form as the XROE-1. This remarkable machine weighed only 132 kg (290 lb), and came in a 70 cm (27 in) diameter package that could be assembled in the field in only five minutes without any specialized tools. Most of the assembly was hinged together so that the parts could simply be unfolded and locked into place with pins. Only the tailboom was packaged separately. The unassembled Rotorcycle fitted into a streamlined container that could easily be dropped by parachute from the under-wing bomb racks of tactical aircraft. Its conventional single rotor with anti-torque tail rotor configuration was as easy to fly as it was to put together, largely due to the incorporation of Hiller's patented "Rotormatic" gyro-stabilization system. The cyclic stick was mounted in an overhead position to reduce the number of control linkages and to facilitate the folding of the aircraft. Otherwise, the controls were similar to those of most other contemporary helicopters.

The Rotorcycle was so stable and simple to operate that Hiller expected a non-pilot to be able to solo the ROE-1 after only 8 hours of instruction. For its diminutive size, the helicopter had excellent performance. However, the 9.1 liter (2.4 U.S. gal.) fuel tank gave it a range of only 64 km (40 miles) in calm wind conditions at its cruise speed of 84 kph (52 mph). The tripod landing gear could be exchanged for a float arrangement for operations on calm water. The center-of-gravity range was limited, so that if a light-weight pilot operated the aircraft, then ballast had to be placed in a little bucket on the front gear leg to balance the Rotorcycle properly.

Hiller constructed a flight test prototype along with a non-flying structural model. The first flight of the XROE-1 took place in November 1956. The Marine Corps was impressed with the Rotorcycle's performance and ordered 5 YROE-1 evaluation models. Unfortunately, Hiller could not afford to produce the aircraft, because its manufacturing capability was dedicated to the UH-12/H-23 program. British manufacturer, Saunders-Roe, built the five Marine Corps Rotorcycles under license along with an additional five aircraft for sale overseas, all of which were completed by 1961.

Marine Corps testing revealed that the aircraft performed well, but also uncovered several flaws in the ultra-light helicopter concept. The most serious problem that haunted the Rotorcycle, and most of the other lightweight vertical takeoff projects of the 1950s, was the lack of an adequate horizon reference when flying out of ground effect. Unlike larger aircraft, the Rotorcycle did not have any protruding structures that could be visually aligned with the horizon, which made an inadvertent loss of control more likely. The situation made the Rotorcycle unsuitable for operation at night and low-visibility conditions and this seriously diminished its usefulness in escape and covert operations. Even without this problem, the advent of turbine-powered helicopters in the late 1950s, and improved search and rescue techniques, made the Rotorcycle's capability redundant and resulted in the cancellation of the program.

Over the years, several inventors have attempted to imitate the Rotorcycle as a sport aircraft, but the same problems, which were encountered during the ROE-1's development, have kept the concept from becoming popular.

A number of Rotorcycles still survive, and at least one was still flying with a private owner at the end of the twentieth century. The second YROE-1 was donated to the Smithsonian Institution after completion of its testing in 1961.

Rotor Diameter: 5.64 m (18.5 ft)

Length: 3.81 m (12.5 ft)

Height: 2.29 m (7.5 ft)

Weight: Empty, 139.9 kg (308.5 lb)

Gross, 254.9 kg (562 lb)

Engine: Nelson YO-65-2 four-cylinder, two-cycle engine, 43 hp

References and Further Reading:

Labermont, Paul. Helicopters and Autogyros of the World. Cranbury, NJ: Cassell and Company, Ltd., 1970.

Spencer, Jay P. Whirlybirds: A History of the U.S. Helicopter Pioneers. Seattle:

University of Washington Press, 1998.

YROE-1 curatorial file, Aeronautics Division, National Air and Space Museum

R. D. Connor