Back Kellett KH-15 "Stable Mable"

Kellett KH-15

This variable stability helicopter was a flying test-bed developed with the Office of Naval Research as sponsor to study the behaviour of a small helicopter in which the significant parameters of the rotor could be altered.

This single-seater was powered by two hydrogen peroxide rocket engines mounted one at each blade tip, and fuel was stored in two spherical tanks situated to the right and left of the pilot.

The fuselage was an open steel tube structure to which was attached a fixed tripod landing gear, the main rotor, rotor controls and an open truss boom supporting the conventional variable-pitch-type tail rotor.

This helicopter was designed to test the new gyro-stabilizing system, a kind of small rotor mounted concentrically and intended to stabilize the main rotor. This stabilizer system, developed by Dr. G.J. Sissingh, should be applicable to all types of helicopter, whether having single, tandem, side-by-side or co-axial rotors. It is, furthermore, independent of the type of propulsion.

Trials were started early in 1954 to demonstrate positive dynamic stability without loss of control throughout the entire speed range, and the XH-15 in fact exhibited excellent stick-fixed dynamic stability.

P.Lambermont "Helicopters and Autogyros of the World", 1958

The open frame KH-15 used a pair of Reaction Motors rocket engines fitted at the rotor tips, and first flew under sponsorship from the Office of Naval Research on 13 May 1954. It was fitted with a patented gyro stabilisation system but, despite showing remarkable flight characteristics, it progressed no further.

R.Simpson "Airlife's Helicopter and Rotorcraft", 1998

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Technical data for KH-15

Engine: 2 x Reaction Motors XLR 32 , rotor diameter: 5.49m, gross weight: 292m

Barbara Lloyd Miles, e-mail, 16.05.2017reply

That is my dad, Norman Lloyd, testing the Stable Mable in the photograph. Unfortunately he passed away in 2009. But at the Chino Air Museum in California they loved him as he willingly shared his knowledge of the gyrocopter and the Corsair with them. We are very proud of his legacy.

Michael Shults, e-mail, 20.07.2020 Barbara Lloyd Miles

Hello Barbara Lloyd Miles,

I found this email comment from 2016 and wondered if you may have any photos or any parts from the Kellett KH-15 Stable Mable helicopter that your father worked on and flew in the early 50s. I have a KH-15 Stable Mable that is now going to a museum near Chicago. Any photos or parts for this helicopter would be very helpful in making this a display of great interest.

Best Regards,
Mike Shults
Eastern Shore Helicopters, Inc.


Devakate Sagar T., e-mail, 31.08.2014reply

Sir,i am engineering student,i trying to make my final year project.I got stuck in my project about lifting the helicopter so i want your help.
And also i want some technical data about this KH-15 helicopter.

Ricardo, e-mail, 18.08.2010reply

Please contact me.

r.d. kuehner, e-mail, 15.08.2008reply

my father, richard m. kuehner was the project engineer on this aircraft. i attended a test flight when dad was burned trying to recover the remaining hydrogen peroxide from the aircraft tank and return it to the truck where it was stored. mr. lloyd was the test pilot. i may still have some old photos

Mike Shults, e-mail, 20.07.2020 r.d. kuehner

Hello Sir,

We have a Kellett Stable Mabel Helicopter that is going to a museum near Chicago and we would greatly appreciate any photo or parts you may have of this helicopter. Anything you have will help make this a display of great interest.

Please contact me if you may have anything.

Mike Shults
Eastern Shore Helicopters, Inc.
Phone 863-885-1292


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