HTK / H-22 / K-225 Mixmaster
The Kaman K-225 was the world's first helicopter powered by a turbine engine. The helicopter had rotor system developed by Kaman which used two intermeshing rotor blades--called synchropter blades. The US Navy bought two Kaman K-225 and Coast Guard one for $25,000 each. The K-225 demonstrated the the benefit of the synchropter design to the US Navy and Coast Guard.
Kaman Aircraft company built three K-225s under a Navy contract (NOa(S)-10876) to test and evaluate the type and the Coast Guard purchased one of these, CG-239, in early 1950. It was delivered to Air Station Elizabeth City on 18 March 1950 where it underwent testing and evaluation.
The K-225 used two two-bladed intermeshing rotors, thereby eliminating the tail rotor. The blades were made of laminated spruce covered with fabric and dope. Control was achieved through the use of servo flaps located behind the trailing edge of each blade, actuated by a series of push-pull rods. Kaman later added a gas turbine engine to a K-225, making it the first rotary-winged aircraft so powered.
On 11 May 1950, CG-239 went into the workshops at Elizabeth City after undergoing 120 flying hours. After this, it was apparently "little used" except for pilot refresher training. CG-239 was transferred to the Navy on 22 March 1954 and was later sold into private hands. It crashed on 1 October 1955. Although there were no injuries, the helicopter was completely destroyed.
Evaluation of the K-225 by the Navy led to an order for 29 K-240s with the designation HTK-1, powered by a Lycoming O-435-4 piston engine developing 240hp.. Primary a trainer, it provided seating for a pilot, a co-pilot/student and a passenger, or in the ambulance role a stretcher; even anti-submarine duties have been performed. They served with the Navy at Pensacola until 1957.
In May 1957 a drone HTK-1 helicopter, carrying a safety pilot, operated from the fantail of Mitscher (DL 2) in the vicinity of Narragansett Bay. These tests and others, conducted in February off Key West, in which a piloted HUL-1 carried Mk 43 torpedoes in flights to and from the Mitscher, demonstrated the feasibility of assigning torpedo carrying drone helicopters to destroyers and led to the development of the Drone Anti-Submarine Helicopter (DASH) which was later embodied in the QH-50C.
In March 1954 the experimental HTK-2 was fitted with twin Boeing 502-2 engines.
Some sources claim that remaining HTK-1s were redesignated to TH-43E in 1962, but this must be an error.
The US Army evaluated one Navy HTK-1 under the designation H-22.
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