When the 1973 oil crisis caused petroleum price spikes in the early 1970s, interest in propfans soared, and NASA-funded research began to accelerate.[9] The propfan concept was outlined by Carl Rohrbach and Bruce Metzger of the Hamilton Standard division of United Technologies in 1975[10] and was patented by Rohrbach and Robert Cornell of Hamilton Standard in 1979.[1] Later work by General Electric on similar propulsors adopted the name unducted fan, which was a modified turbofan engine, with the fan placed outside the engine nacelle on the same axis as the compressor blades.