Kellett KD-1

The Kellett KD-1 was a 1930s American autogyro built by the Kellett Autogiro Company. It had the distinction of being the first practical rotary-wing aircraft used by the United States Army and inaugurated the first scheduled air-mail service using a rotary-wing aircraft.

Development
Using the experience gained in building Cierva autogyros under licence the Kellett Autogiro Company developed the KD-1 which was similar to the contemporary Cierva C.30. It had two open cockpits, a fixed tailwheel landing gear and was powered by a 225hp (168kW) Jacobs L-4 radial engine. After testing of the prototype a commercial variant designated the KD-1A was put into production. The KD-1A had a three-bladed rotor with folding blades and a number of minor detail improvements. A KD-1B which was a KD-1A with an enclosed cockpit for the pilot was operated by Eastern Airlines and inaugurated the first scheduled rotary-wing air-mail service on 6 July 1939.

In 1935 the United States Army bought a KD-1 for evaluation and designated it the YG-1, a second aircraft followed which had additional radio equipment and was designated the YG-1A. These two aircraft were followed by a batch of seven designated YG-1B. In 1942 seven more were bought for use in the observation role as the XO-60. Six XO-60s were re-engined with 300hp (224kW) Jacobs R-915-3s and re-designated YO-60. One YG-1B was modified with a constant-speed rotor and was re-designated the YG-1C, it was later re-engined with the more powerful R-915 and re-designated again as the XR-2. The XR-2 was destroyed by rotor ground resonance problems and the evaluation was continued with another modified YG-1B designated the XR-3.

Variants

 * KD-1
 * Prototype, one built


 * KD-1A
 * Commercial variant with open cockpit and a 225 hp Jacobs L-4 radial engine; three built.


 * KD-1B
 * Commercial variant with enclosed cockpit; two built.


 * YG-1
 * United States Army designation for one KD-1A acquired for evaluation.


 * YG-1A
 * One aircraft as YG-1 with the addition of radio equipment.


 * YG-1B
 * Production aircraft for the United States Army; seven built.


 * YG-1C
 * One YG-1B modified with a constant-speed rotor for evaluation, later designated the XR-2.


 * XO-60
 * Production aircraft for the United States Army with a 225 hp Jacobs R-755 radial engine, seven built.


 * YO-60
 * Six XO-60s re-engined with a 300 hp Jacob R-915-3 radial engine.


 * XR-2
 * The YG-1C re-designated after being re-engined with a 300 hp Jacobs R-915-3 radial engine.


 * XR-3
 * One YG-1B modified to XR-2 standard for evaluation.


 * Kayaba Ka-Go prototype
 * Prototype; it was an airframe which had repaired KD-1A by Kayaba.


 * Kayaba Ka-1
 * Imperial Japanese Army developed referring to KD-1A. Powered by a 240 hp Argus As 10 engine, airframe that changed engine of prototype.


 * Kayaba Ka-2
 * Imperial Japanese Army developed, referring to KD-1A. Powered by a 245 hp Jacobs L-4MA-7 engine, airframe that changed engine of Ka-1 for the same thing as prototype.

Operators

 * Eastern Airlines
 * United States Army Air Forces
 * Eastern Airlines
 * United States Army Air Forces