a civil version, the model 45d was also built and flown, in anticipation of a postwar boom in aircraft sales. this differed in having the two occupants side-by-side instead of tandem as in the 45c, and was equipped with a lycoming engine. the prototype was demonstrated at the 1946 cleveland national air races. a four-seat model 50, with twin tail rotors, was also projected, but the predicted sales boom did not materialise, and firestone closed its aircraft manufacturing division.