Kellett XR-8

https://en.wikipedia.org/wiki/Kellett_XR-8

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.

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.

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".


Role
Experimental helicopter

National origin
United States

Manufacturer
Kellett Autogiro Corporation

First flight
7 August 1944

Number built
2

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.

Specifications (XR-8)

General characteristics
Crew: 1
Capacity: 1 pax
Length: 22 ft 7 in (6.88 m) fuselage
Height: 11 ft 0 in (3.35 m)
Empty weight: 2,320 lb (1,052 kg)
Gross weight: 2,975 lb (1,349 kg)
Fuel capacity: 34 US gal (28 imp gal; 130 l) normal; 81 US gal (67 imp gal; 310
l) maximum
Powerplant: 1 × Franklin O-405-9 6-cyl. horizontally-opposed air-cooled piston
engine, 245 hp (183 kW)
Main rotor diameter: 2× 36 ft 0 in (10.97 m)
Main rotor area: 1,017.5 sq ft (94.53 m2) each rotor

Performance
Maximum speed: 100 mph (161 km/h; 87 kn)
Service ceiling: 10,000 ft (3,000 m)
Hover ceiling: 3,000 ft (910 m)
Disk loading: 35.2 lb/sq ft (172 kg/m2)
Power/mass: 12.14 lb/hp (7.375 kg/kW)




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