Designed by Scaled Composites as a testbed and demonstrator aircraft for Willams' new FJX-1 turbofan engine. Although the aircraft was not meant for production, the frame drew a lot of interest and it evolved into the Eclipse 500. The prototype flew with a variant of the FJX-22, but they did not give the desired performance and the design was changed to use the PW610F engine. The aircraft (the one and only) was donated to the EAA museum at Oshkosh in 2001.