The first XF-91, 46-680, after the addition of a fairing at the tailplane-fin junction, during early flight tests.
The Republic XF-91 Thunderceptor was a compromise between the pure jet and the rocket-powered interceptor. Although it never entered large-scale production, It provided a glimpse of the fighter of the future.

46-680 during its press debut at Farmingdale, Long Island, on February 24, 1949, with its underbelly dive brake in evidence and an unfaired fin-tailplane junction.

The second XF-91, 46-681, shows off its extraordinary planform. The extension of the rocket housing under the jetpipe is evident.

Despite its ungainly appearance, the butterfly-tailed XF-91 proved to have a better performance.

The first XF-91, 46-680, after the F-86D-style nose radome had been fitted, probably to represent the “XF-91B” all-weather interceptor.

Taken at Edwards Air Force Base, these two studies show 46-681 after its new rear fuselage with the butterfly tail had been fitted. Note the extended rocket housing and small underwing drop tanks.

46-680 at Edwards Air Force Base on January 23, 1950, when the Phase One flight tests had been completed.

The XF-91 takes off for its trouble-free maiden flight on May 9, 1949. Note the tandem main wheels.

A 1/24-th scale model of the “F-91” showing the butterfly tail originally planned but only fitted belatedly to the second prototype.

Republic XF-91 Thunderceptor