The Lockheed XF-90 “penetration fighter” was the first US-built, swept-wing jet to be equipped with afterburners and wingtip fuel tanks as standard equipment and to have fully adjustable vertical and horizontal stabilizers.
The Lockheed XF-90 was one of the most striking experimental fighters ever built, although it never entered production. It was notable for being the first American-made, swept-wing jet to feature afterburners and wingtip fuel tanks as standard, as well as fully adjustable vertical and horizontal stabilizers. The use of Fowler flaps and leading-edge slats enhanced wing airflow, positioning the F-90 as a leader in 35-degree swept-wing design. During test flights, the XF-90 achieved speeds exceeding Mach 1.15.
According to James C. Goodall in his book 75 Years of the Lockheed Martin Skunk Works, following World War II, the USAAF sought a “penetration fighter” that could escort bombers on their missions to and from targets. In 1945, the USAAF issued a call for a fighter with a combat radius of approximately 900 miles. The contenders for this contract included McDonnell’s XP-88A, North American’s XP-86C, and Lockheed’s XP-90. On June 20, 1946, Lockheed was awarded a contract to build two prototype XP-90 aircraft.
Although Chuck Yeager broke the sound barrier on October 14, 1947, this achievement came too late to influence the XF-90’s development. The prototype was stress-tested to destruction at the National Advisory Committee for Aeronautics Lab in Cleveland, Ohio, and ended up as scrap. The second prototype was sent to the Nevada Proving Ground to participate in nuclear weapons testing, where it withstood three atomic detonations. The blasts tore off its tail, ripped the landing gear from the wings, and left the main wing section warped and scorched.
Despite its streamlined design, the XF-90 performed poorly. The main issue was that it was heavily built yet lacked sufficient power. The XF-90 was originally expected to break the sound barrier, but little was known about supersonic flight at the time. To prepare for the unknown, engineers made the aircraft’s aluminum skin from extra-strong 75ST aluminum instead of standard 24ST alloy and also increased its thickness, making it four times more resistant to stress than standard aircraft. As a result, the XF-90 was heavier than a DC-3 and engineered to handle 12g forces, making it 80 percent heavier than the F-86. However, it was underpowered, with its two Westinghouse J34 engines generating only 6,000 pounds of thrust to move an aircraft weighing 27,200 pounds.
On May 17, 1950, during a series of test flights aimed at pushing the aircraft toward breaking the sound barrier, the plane performed a low-altitude dive and vanished into the haze. At that instant, observers on the ground heard a loud boom and initially assumed the aircraft had exploded. However, much to their relief, it had actually reached Mach 1.12 during the dive, and everything was unharmed.
The XF-90 successfully broke the sound barrier multiple times and showed no structural issues during its flights. Serving as an early model before the F-104 Starfighter—often called a “missile with a man in it”—the XF-90 stood out for its stylish design, capturing the public’s imagination and being used in eye-catching Westinghouse engine advertisements. Its popularity was further cemented by its appearance on the cover of the September 1953 Blackhawk comic book. Afterward, the emerging baby boomer generation became fascinated by jet technology and followed the adventures of Blackhawk and his co-pilot, Chuck. Growing up in the atomic era, when children practiced hiding under desks during nuclear drills, these stories provided both excitement and reassurance as Blackhawk and his squadron of six sleek F-90Bs stood guard against the threat of “Red” enemies.
In the late 1980s, the second XF-90 prototype was recovered and cleaned for preservation. It was set to be displayed at the National Museum of the United States Air Force near Dayton, Ohio, where it would be shown exactly as it looked after spending fifty years in the desert.
75 Years of the Lockheed Martin Skunk Works is published by Osprey Publishing and is available to order here.
Photo by U.S. Air Force
