First flight of a gas-turbine powered helicopter on Dec. 11, 1951
December 11 marks a watershed moment in helicopter history, for on this date in 1951, the transition from reciprocating — or piston — engines to more powerful gas turbine engines began.
Reciprocating engines are relatively inexpensive and simple to operate and are used on smaller helicopters and training aircraft, but the engines can be heavy, noisy and less efficient at higher altitudes.
On Dec. 11, 1951, the Kaman K-225, powered by a Boeing B502-2 gas turbine engine, became the first such helicopter in the world after making its first flight at the Bloomfield, Connecticut, headquarters of Kaman Aircraft Company — founded on Dec. 12, 1945 by 26-year-old aeronautical engineer, Charles Kaman, who had earned his stripes working for the legendary Igor Sikorsky.
Like Sikorsky, Kaman was committed to revolutionary advances in vertical flight. The Kaman company history includes a quotation from Kaman that reads, "One of the first steps in any endeavor is overcoming the discouraging advice of those who say it can't be done."
In 1949, two years before the first gas turbine-engine powered K-225 flight, Kaman built the first K-225 commercial model, powered by a Lycoming piston engine, for use as a crop duster. The Navy then ordered two of the models to examine the advantages of the K-225's intermeshing rotor system and the Kaman blade-mounted servo-flap control system.
Instead of the now-common tail rotor to cancel the torque effect of the main rotor, the K-225 used two counter-rotating, intermeshing rotors — a "synchropter" design by Anton Flettner for the Fl 265 experimental anti-submarine warfare and the Fl 282 "Kolibri" (hummingbird) reconnaissance helicopters for Nazi Germany's Kriegsmarine and the Luftwaffe.
Flettner's right hand man in the design work was Kurt Hohenemser, the son of the blind German Jewish musicologist Richard Hohenemser and his wife, Alice, both of whom committed suicide by turning on the gas in their Berlin apartment in 1942 when faced with deportation to the concentration camps by the Nazi SS.
Flettner and Kurt Hohenemser, who survived the war years living in Silesia and then a monastery in West Germany with his wife and children, were among the first German emigrants to the United States after World War II.