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Kellett XR 8

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Top speed
  
160 km/h

Length
  
6.9 m

Weight
  
1,052 kg

First flight
  
August 7, 1944

Wingspan
  
11 m

Cruise speed
  
136 km/h

Engine type
  
Franklin 6 series

Kellett XR-8 Kellet XR8 Eggbeater by Piotr Dmitruk LF Models 172

Kellett xr 8 1945


The Kellett XR-8 (later redesignated XH-8) was a helicopter built in the United States during World War II. 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.

Contents

Kellett XR-8 wwwaviastarorgfotokellettxr82jpg

Early us army helicopters kellett xr 8 and bell model 30 1944


Design and development

Kellett XR-8 Kellett XR8 Wikipedia

The successful demonstration of the Sikorsky VS-300 had the USAAF favoring the helicopter over the autogiro as an approach to rotary-winged flight. Realizing this, the Kellett Autogiro Corporation 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.

Kellett XR-8 Kellett XR8 helicopter development history photos technical data

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

Kellett XR-8 Kellett XR8 helicopter development history photos technical data

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.

Kellett XR-8 XR8

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.

Kellett XR-8 Kellet XR8 7250 3200 LF Models Eshop Produced resin kits

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)

    Data from National Air and Space Museum. "Kellett XR-8". Accessed on 2 September 2008.

    General characteristics

  • Crew: 2
  • Length: 22 ft 7 in (6.9 m)
  • Main rotor diameter: 2× 36 ft 0 in (10.9 m)
  • Height: 11 ft 0 in (3.4 m)
  • Empty weight: 2,320 lb (1,052 kg)
  • Gross weight: 2,975 lb (1,349 kg)
  • Powerplant: 1 × Franklin O-405-9, 245 hp (183 kW)
  • Performance

  • Maximum speed: 100 mph (160 km/h)
  • Service ceiling: 6,700 ft (2,050 m)
  • References

    Kellett XR-8 Wikipedia