Kaman
K-225
#

Photo: Robert Deering 10/23/2006
Smithsonian National Air and Space Museum
Chantilly, Virginia

The K-125 was Charles Kaman's first helicopter, which utilized intermeshing rotors and Kaman's patented servo-flap stability control.  The K-125 first flew on 15 January 1947.

The K-190 and K-225 were an improved versions of the K-125, which first flew in April and July 1949 respectively. The U.S. Navy bought two and the Coast Guard one for $25,000 each. Later, they received the H-22 designation.

A modified K-225 equipped with a Boeing 502 (YT50) engine became the world's first gas turbine powered helicopter in December 1951. This aircraft is now at the Smithsonian.

This Kaman K-225 was the first helicopter to fly with a gas turbine driven transmission. Turbines offered important advantages for helicopters including reduced weight, improved reliability, easier maintenance and higher power-to-weight ratios, which allowed for larger useful loads, increased safety and lower operating costs. In 1949, Kaman built the K-225 commercial model, primarily for use as a crop-duster. The Navy ordered two to evaluate the advantages of the intermeshing rotor system and the novel blade mounted servo-flap control system.

In 1951, Kaman replaced the reciprocating engine that originally powered this K-225 with a Boeing 502-2 gas turbine to demonstrate the potential of jet-powered helicopters to the Navy. The K-225 served as the prototype for Kaman's successful HOK series of military helicopters, which incorporated a cabin in place of the open cockpit. The engine currently on the aircraft is not original.
Dimensions:
Rotor diameter 38 feet, height 14 feet 2 inches, length 38 feet.

Physical Description:
2-seat tandem experimental helicopter with intermeshing twin rotor, steel-tube fuselage, turbine engine, tricycle landing gear.

Source: Wikipedia and the Smithsonian Air & Space Museum