North American F-107 Ultra Sabre
North American Aviation's F-107A, informally called the Ultra Sabre, was a Mach 2 tactical fighter-bomber developed from the F-100 Super Sabre for a U.S. Air Force competition. Its variable-area engine intake sat on top of the fuselage, leaving the belly free for a semi-recessed weapon. Only three prototypes were built; the Air Force chose Republic's F-105 instead, chiefly because it had a full internal bomb bay. The prototypes finished their careers as research aircraft with NACA and NASA, and two survive in museums.
Why It Mattered
The F-107A was North American Aviation's entry in a U.S. Air Force competition for a new tactical fighter-bomber, and only three prototypes were ever built. It lost that contest to Republic's F-105 Thunderchief, a decision that the Pima Air & Space Museum attributes primarily to the F-105's full internal bomb bay, which the F-107 lacked. The type is remembered for an intake arrangement that Smithsonian Magazine describes as a configuration no jet had used before or since. Its standing remains contested: the magazine writes that, depending on who is talking, it was either the best fighter the Air Force failed to buy or a flawed loser from the outset. All three aircraft ended their flying lives as research aircraft rather than in squadron service.
Design Notes
The design began as a development of the F-100 Super Sabre and was at first designated the F-100B. So much changed that the designation became F-107A before the first prototype flew. Its engine intake sat on top of the fuselage, above and behind the cockpit, and fed a Pratt & Whitney YJ75 turbojet. The Pima Air & Space Museum explains the position: the overhead intake left the belly free to carry a weapon partially submerged in the fuselage. The intake was a variable-area duct that adjusted the airflow reaching the engine automatically. The flight controls were equally unusual: Smithsonian Magazine records roll control by spoilers instead of ailerons, and NASA notes an all-moving vertical fin and a sophisticated stability augmentation system. The intake's position came at a price, since the magazine observes that a pilot would have had difficulty checking behind him. North American also proposed a two-seat version with both crew members under a single canopy, but none was built.
Operational History
North American received a contract in August 1954 for three prototypes, with six further aircraft ordered for pre-production. The first prototype, serial 55-5118, flew on 10 September 1956 from Edwards Air Force Base, with company test pilot Robert Baker at the controls. It reached Mach 1.03 on that flight, but the landing went wrong when the brake parachute failed to deploy and the nose-gear strut broke. The type reached Mach 2 in tests on 3 November 1956. The second prototype flew on 28 November 1956 and went on to weapons testing with conventional and atomic bombs. The third prototype made its first flight on 10 December 1956. After testing, Tactical Air Command ran a fly-off against the F-105; the contest was close, but the F-105 was chosen as the standard tactical fighter. The pre-production order was cancelled, and the three prototypes became test aircraft. In late 1957 the first and third prototypes were loaned to the National Advisory Committee for Aeronautics (NACA) for high-speed research. Pima records that NACA also used them to test the control system intended for the X-15 rocket plane. NASA found the first aircraft mechanically unreliable, and it flew only four times before the agency grounded it. The third aircraft flew forty times for NACA and NASA before a takeoff accident on 1 September 1959 ended its flying, without injury to its pilot. It was never repaired, and it was eventually used for firefighting training before being destroyed in the early 1960s.
Afterlife
The second prototype never flew for NACA and went instead to the Air Force's museum at Wright-Patterson Air Force Base, flown there on 25 November 1957. Smithsonian Magazine tells how that delivery flight nearly went wrong: the aircraft had no navigation radios and no cockpit or instrument lights, and its pilot, Clyde Good, checked his instruments by the light of a cigarette lighter after dark. The first prototype, after its brief research career and years in storage, was loaned to the Pima Air & Space Museum in June 1974. NASA confirms that it is now on display at Pima, in Tucson, Arizona. Two of the three prototypes are therefore held by museums today, the first at Pima and the second by the National Museum of the U.S. Air Force in Ohio.