The F-107 Ultra Sabre should have become one of America’s greatest Cold War fighters. Faster than Mach 2, armed for nuclear strike missions, and packed with cutting-edge technology, it was the radical successor to the legendary F-100 Super Sabre.
Its most distinctive feature—a massive dorsal air intake mounted above the cockpit—gave it an appearance unlike any other fighter of its era and earned it a reputation as one of the most unusual jets ever built. Yet despite impressive performance, the F-107 found itself locked in a battle for survival against the Republic F-105 Thunderchief while, across the Iron Curtain, the Soviet Su-7 was fighting its own struggle to become the USSR’s next great fighter-bomber.
This is the story of the F-107 Ultra Sabre, the daring design that pushed American aviation to its limits, the Cold War rivalry that doomed it before it could enter service, and the question that still lingers today: did the U.S. Air Force cancel the wrong aircraft?
The North American F-107 is a prototype aircraft that was North American Aviation’s entry in a United States Air Force tactical fighter-bomber design competition of the 1950s, based on the F-100 Super Sabre. It incorporated many innovations and radical design features, notably the over-fuselage air intakes. The competition was eventually won by the Republic F-105 Thunderchief, and two of the three F-107 prototypes ended their lives as test aircraft. One is on display at the National Museum of the United States Air Force and a second at Pima Air and Space Museum.
Design and Development
In June 1953, North American initiated an in-house study of advanced F-100 designs, leading to proposed interceptor (NAA 211: F-100BI denoting “interceptor”) and fighter-bomber (NAA 212: F-100B) variants. Concentrating on the F-100B, the preliminary engineering and design work focused on a tactical fighter-bomber configuration, featuring a recessed weapons bay under the fuselage and provision for six hardpoints underneath the wings.
Single-point refueling capability was provided while a retractable tailskid was installed. An all-moving vertical fin and an automated flight control system were incorporated which permitted the aircraft to roll at supersonic speeds using spoilers. The flight control system was upgraded by the addition of pitch and yaw dampers.
The aircraft’s most distinguishing feature is its dorsal-mounted variable-area inlet duct (VAID). While the VAID was at the time a system unique to the F-107A, it is now considered to be an early form of variable geometry intake ramp which automatically controlled the amount of air fed to the jet engine.
Although the preliminary design of the air intake was originally located in a chin position under the fuselage like the Vought F-8 Crusader, the air intake was eventually mounted in an unconventional position directly above and just behind the cockpit. The VAID system proved to be very efficient and NAA used the design concept on its A-5 Vigilante, XB-70 Valkyrie and XF-108 Rapier designs.
The air intake was in the unusual dorsal location as the Air Force had required the carriage of an underbelly semi-conformal nuclear weapon. The intake also severely limited rear visibility. Nonetheless, this was not considered very important for a tactical fighter-bomber aircraft at that time, and furthermore it was assumed that air combat would be via guided missile exchanges outside visual range.
In an emergency, the ejection seat was designed to blast directly through the non-jettisoning canopy and bring the pilot swiftly clear of the air intakes. In non-emergency operation, the canopy opened by sliding vertically upwards via guide mechanism, rather than the typical arrangement of a hinged or horizontally sliding canopy.
The first F-107A 55-5118 with its vertically sliding canopy in open position.
A two-seat version of the F-107 was proposed by North American, which seated both crewmembers under a single canopy in an extended forward fuselage, but none were built.
In August 1954, a contract was signed for three prototypes along with a pre-production order for six additional airframes.
In the end however, the United States Air Force decided to purchase the Republic F-105 Thunderchief after heavy consideration for the F-107 program.
Top Photo: North American Aviation XF-107A “Ultra Sabre”, developed from the F-100
Sources: YouTube: Wikipedia