Republic XF-91

Republic XF-91 Thunderceptor
Republic XF-91 at Edwards Air Force Base , 1951
Type:	Interceptor
Design country:	United States
Manufacturer:	Republic
First flight:	May 9, 1949
Commissioning:	Flight tests canceled in 1954
Production time:	Was never mass-produced
Number of pieces:	2

The Republic XF-91 Thunderceptor was an experimental interceptor fighter for the US aircraft manufacturer Republic . It is a single-seat, all-metal aircraft with a hybrid propulsion system consisting of a jet and a rocket engine . The basis for the middle-decker was the Republic F-84 .

history

First investigations by Alexander Kartweli (who had also designed the P-47 and F-84) on the XF-91 began in 1946. The machine was the first aircraft developed for interception that could fly faster than sound , the conception saw an application for object defense. Several unusual designs were chosen for this. For example, the profile depth at the wing root of the wing, which was swept at 35 °, was less than at the wing tips (it had a width of 3.92 m there), and its angle of incidence could be adjusted in flight (especially for take-off and landing) by hydraulic jack screws between - 2 ° and + 5.65 ° can be changed continuously. This idiosyncratic wing shape resulted from the little experience at the time with swept wings, the flight characteristics of which were not yet sufficiently constructively mastered, especially in slow flight. For structural reasons, it was also necessary to position the main landing gear far outwards - this resulted in the floor plan of the wing. To accommodate the main landing gear, the wing had to be sufficiently thick, which explains the greater depth and thickness of the outer wing. This also reduced the wing's susceptibility to vibrations and improved the stability of the machine, especially in slow flight. As a side effect of this design, the engineers expected the thin wings near the fuselage to reduce drag in this critical area. The two landing gear struts to be drawn into the wings each had two small running wheels in tandem, the nose wheel retracted back into the fuselage. A J47 jet engine with an afterburner was provided to achieve the planned flight performance . Since such an afterburner was not available, Republic developed it itself. The output of the afterburner was adjustable, although the automatic system proved to be unreliable and so, curiously, the control was carried out remotely from the ground according to the pilot's instructions. Another problem with the afterburner operation was the short life of the inner exhaust fairing of just five hours. Since a supersonic flight and the planned climb rate could not be achieved with this either, two Curtiss-Wright XLR-27 rocket engines were also planned. Since these were not available, four XLR-11 rocket engines from Reaction Motors were installed instead , two above and two below the jet engine.

46-680 and 46-681

The American military showed interest in the design and ordered two prototypes still known as XP-91. The first machine left the factory in Farmingdale Long Island on February 24, 1949 . The first flight of the XF-91 (relocated to Edwards Air Force Base for safety reasons) with Republic chief test pilot Carl Bellinger at the controls took place on May 9, 1949. A number of amazingly smooth flight tests were carried out, during which the machine became the first type of fighter aircraft developed in the USA to reach supersonic on December 9, 1952.

The reason for the delay was the late installation of the rocket engines, which did not take place until late 1952. The second prototype (46-681) flew with a V-tail unit and a radar bow similar to that of the F-86D, but had an accident as early as 1951 after an engine failure.

However, there was no series production of the planned XF-91A (normal) and XF-91B (all-weather version similar to the second prototype), as the flight time was limited to only 25 minutes. So it ultimately stayed with the two prototypes after the Air Force discontinued the project in 1954. Overall, the construction, especially the wing, turned out to be too heavy and the intended tactical performance was not achieved.

Technical specifications

Three-sided view of the XF-91

• Length: 13.21 m
• Span: 9.52 m
• Height: 5.51 m
• Wing area: 29.73 m²
• Empty weight: 7,181 kg
• Takeoff weight: 8,424 kg
• Max. Takeoff weight: 13,600 kg
• Engine: a General Electric J47-GE-3 with 23.2 kN thrust without and 35.24 kN with afterburner
  • additional four rocket motors Reaction Motors XLR11-RM-9 with 6.67 kN thrust each
• Top speed: 1584 km / h (according to other sources 1191 or 1812 km / h)
• maximum range: 1,870 km
• Service ceiling: 16,750 m
• The planned armament of the serial version: two to four 20 mm automatic cannons, two air-to-air guided missiles
• Crew: 1 man

Received aircraft

46-680 in the National Museum of the United States Air Force

The first prototype (USAF serial number 46-680) is on display at the National Museum of the United States Air Force .

Web links

Commons : Republic XF-91  - Collection of pictures, videos and audio files

• Information from the USAF Museum on the XF-91 ( Memento from September 3, 2014 in the Internet Archive )

Individual evidence

1. ↑ History Milestones (US Air Force) ( Memento from July 17, 2012 in the web archive archive.today )
2. ↑ FlugRevue January 2010, pp. 84–87, Inverted World - Republic XF-91 Thunderceptor