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Republic XF-91 Thunderceptor


The design evolved to compete with the XF-92 was the Republic XF-91 Thunderceptor. This was based on the F-84F Thunderstreak swept-wing derivative of the F-84 Thunderjet straight-winged tactical fighter.

Ordered in 1946, the wing was of the variable-incidence type to permit a higher angle of attack for take-off and landing, but this feature was combined with a planform of inverse taper and thickness, together with leading-edge slots. Thus the chord and thickness of the wing increased from root to tip, producing more lift at the tip than at the root, and this arrangement dictated that the main landing gear units retract outward into the thick tips rather than inward into the thin roots.

The XF-91 was built to test the use of rocket power to boost a jet fighter in combat. In addition to a 2359kg / 5200-lb thrust General Electric J47-GE-3 turbojet, the two XF-91s each employed four 680kg thrust Reaction Motors XLRII-RM-9 rocket motors mounted two-each above and below the jet exhaust. With all five powerplants burning, the XF-91 was supersonic in level flight, attaining 1812km/h.

The first XF-91 made its initial flight on 9 May 1949 on jet power alone. By late 1949, evaluation of the rocket boost powerplant began. In December 1952 the type exceeded Mach 1.

The first XF-91 was refitted with a nose radome housing APS-6 radar above the engine intake. The second machine was retrofitted with a V-shaped butterfly tail and tested with this configuration after it was determined, in 1951, that the XF-91 would not be placed into production.

This second airframe was eventually destroyed while the first has been retained by the Air Force Museum in Dayton, Ohio.


Wingspan: 9.53 m / 31 ft 3 in
Length: 13.18 m / 43 ft 3 in
Height: 5.69 m / 19 ft 8 in
Wing area: 29.73 sq.m / 320.01 sq ft
Max take-off weight: 10800 kg / 23810 lb
Empty weight: 7190 kg / 15851 lb
Max. speed: 1812 km/h / 1126 mph
Ceiling: 14000 m / 45950 ft
Range: 1600 km / 994 miles


Republic XF-91 Thunderceptor



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