The Kellett XR-8 (later redesignated XH-8) was a

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...

built in the United States during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

. It was a two-seat machine intended to demonstrate the feasibility of a twin-rotor system and, while it accomplished this, it also demonstrated a number of problems that prevented further development of this particular design.

Design and development

The successful demonstration of the Sikorsky VS-300 had the

USAAF The United States Army Air Forces (USAAF or AAF) was the major land-based aerial warfare service component of the United States Army and ''de facto'' aerial warfare service branch of the United States during and immediately after World War II ...

favoring the helicopter over the autogiro as an approach to rotary-winged flight. Realizing this, the

Kellett Autogiro Corporation The Kellett Autogiro Corporation was an American aircraft manufacturer from 1929 based in Philadelphia, named after founder W. Wallace Kellett. History The Kellett Aircraft was formed by W. Wallace Kellett and C. Townsend Ludington and their b ...

made a proposal to the USAAF on 11 November 1942 for the development of a twin-rotor helicopter that would eliminate the need for a tail rotor and its attendant loss of power. Initially discounted on theoretical grounds, the proposal was re-examined in the light of tests done with models by the Army's Experimental Engineering Section, and was accepted on 7 January the following year. This was followed on 11 September with a contract for nearly $1,000,000 to build two prototypes with the three-bladed rotors contained in Kellett's proposal, along with an alternative two-bladed system. The resulting aircraft had a stubby, egg-shaped fuselage with a single tail-fin and tricycle undercarriage. Two seats were enclosed side-by-side behind an extensively-glazed nose and the two rotors intermeshed with one another, offset by 12½°. The fuselage construction was of steel-tube, skinned in sheet metal and fabric, and the rotor blades were built of plywood ribs and skin attached to steel tubes. The intermeshing rotors quickly earned it the nickname " eggbeater".

Operational history

The first flight took place on 7 August 1944 with Kellett chief test pilot Dave Driscoll at the controls. A lack of directional stability was discovered, and was corrected by the addition of two extra tail fins. A far more serious problem was discovered on 7 September, when it was found that a blade from each rotor had collided while the aircraft was in flight. The Air Force therefore ordered Kellett to design a new, rigid rotor system for the XR-8. In the meantime, the two-bladed rotor system was trialled on the second prototype, beginning in March 1945. This proved immediately unworkable, with severe vibration that was prohibitively difficult to resolve. Similarly, it became apparent that the rigid rotor system was going to require extensive redesign of the aircraft, and this effort was dropped as well. On 23 January 1946, the XR-8 was accepted for service trials with its original, non-rigid rotors in place. However, the program was canceled almost immediately, and the prototype was eventually handed over to the National Air and Space Museum where it remains in 2008.

Variants

* XR-8 – initial version (1 built) * XR-8A – version with two-blade rotor system (1 built) * XR-8B – version with rigid rotor system (not built)

Specifications (XR-8)

References

Bibliography

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External links

Smithsonian Air and Space Museum page on the XR-8
{{USAF helicopters 1940s United States experimental aircraft 1940s United States helicopters R-08 United States military helicopters Aircraft first flown in 1944 Single-engined piston helicopters Synchropters