Kellett XR-8

__NOTOC__

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

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)

pecifications (XR-8)

aerospecs
ref=National Air and Space Museum. [http://collections.nasm.si.edu/code/emuseum.asp?style=browse&currentrecord=1&page=search&profile=objects&searchdesc=Kellett%20XR-8&quicksearch=Kellett%20XR-8&newvalues=1&newstyle=single&newcurrentrecord=3 "Kellett XR-8"] . Accessed on 2 September 2008.
met or eng?=eng

crew=2
capacity=
length m=6.9
length ft=22
length in=7
span m=
span ft=
span in=
swept m=
swept ft=
swept in=
rot number= 2
rot dia m=10.9
rot dia ft=36
rot dia in= 0
dia m=
dia ft=
dia in=
width m=
width ft=
width in=
height m=3.4
height ft=11
height in=0
wing area sqm=
wing area sqft=
swept area sqm=
swept area sqft=
rot area sqm=
rot area sqft=
volume m3=
volume ft3=
aspect ratio=
wing profile=
empty weight kg=1,052
empty weight lb=2,320
gross weight kg=1,349
gross weight lb=2,975
lift kg=
lift lb=

eng1 number=1
eng1 type=Franklin O-405-9
eng1 kw= 183
eng1 hp=245
eng1 kn=
eng1 lbf=
eng1 kn-ab=
eng1 lbf-ab=
eng2 number=
eng2 type=
eng2 kw=
eng2 hp=
eng2 kn=
eng2 lbf=
eng2 kn-ab=
eng2 lbf-ab=

max speed kmh=160
max speed mph=100
max speed mach=
cruise speed kmh=
cruise speed mph=
stall speed kmh=
stall speed mph=
range km=
range miles=
endurance h=
endurance min=
ceiling m=2,050
ceiling ft=6,700
g limits=
roll rate=
glide ratio=
climb rate ms=
climb rate ftmin=
sink rate ms=
sink rate ftmin=

armament1=
armament2=
armament3=
armament4=
armament5=
armament6=

ee also

aircontent
see also=
related=
similar aircraft=
* Vought-Sikorsky VS-300
* Sikorsky R-4
lists=

References

*
*
*

External links

* [http://collections.nasm.si.edu/code/emuseum.asp?style=browse&currentrecord=1&page=search&profile=objects&searchdesc=Kellett%20XR-8&quicksearch=Kellett%20XR-8&newvalues=1&newstyle=single&newcurrentrecord=3 Smithsonian Air and Space Museum page on the XR-8]