The Republic XF-91 Thundercepter was a single-place fighter-type airplane powered by a General Electric J47-GE-17 turbojet engine. The wing had a sweep angle of 40 degrees at the 50% chord line and had inverse taper and variable incidence. The root chord (airplane center line) had a dimension of 95 inches while the wing tip chord measured 154.5 inches. The wing incidence was variable in flight through a range from -2 degrees to 5.65 degrees.
The Republic XF-91 Thundercepter appears in a 1951 NACA photograph and two NACA technical reports (research memoranda), but not in the flight records of the NACA High-Speed Flight Research Station (now NASA’s Armstrong Flight Research Center in Edwards, California). Access by the NACA research staff to the XF-91 could have resulted from the proximity of the Republic and NACA hangars at the South Base (Edwards Air Force Base) over most of the time period from 1946 to 1954. One NACA technical report dealt with testing performed by the NACA and Republic using the inflight variable wing incidence capability, while the other report looked at wing aileron effectiveness.
