The Lockheed XF-90, a jet fighter prototype developed by Lockheed Corporation, is a remarkable piece of aviation history. This swept-wing aircraft, which first took to the skies in 1949, was later subjected to nuclear blast tests during Operation Upshot-Knothole in 1953, surviving a 1-kiloton detonation. Despite its pioneering design and resilience, the XF-90 was ultimately canceled due to underperformance after only 14 test flights.
Development and Design Origins
The XF-90 project was initiated in 1948 by Lockheed’s Skunk Works team, led by chief engineer Russ Lightfoot. The team’s goal was to create a high-altitude interceptor capable of Mach 0.92 speeds in response to U.S. Air Force requirements. The design incorporated a 49-degree swept-wing configuration, a concept inspired by German wartime research.
The aircraft featured an all-metal semi-monocoque fuselage, primarily constructed from aluminum alloys for weight savings. Measuring 41 feet 6 inches in length with a wingspan of 40 feet, the XF-90 included a pressurized cockpit for the pilot. Early wind tunnel tests at Lockheed’s Burbank facility in 1948 validated the design’s stability at transonic speeds, leading to the construction of two prototypes.
Maiden Flight and Early Testing
The first XF-90 prototype conducted its maiden flight on May 23, 1949, piloted by Lockheed test pilot Joe Towler. The aircraft reached an altitude of 35,000 feet and a top speed of 675 mph during initial evaluations. However, subsequent test flights in 1949 and 1950, totaling 14 sorties, revealed issues with engine performance. The J34 turbojets failed to deliver promised thrust, limiting acceleration and climb rates.
Flight testing was primarily conducted at Edwards Air Force Base by Air Force pilots from the Air Materiel Command. These tests included evaluations of the aircraft’s handling with its tricycle landing gear and hydraulic controls.
Performance Limitations and Cancellation
Despite design intentions for a service ceiling of 52,000 feet and a range of 1,200 miles, actual tests showed the XF-90 struggling to exceed 40,000 feet and Mach 0.79. This underperformance was attributed to aerodynamic drag from the wing-root air intakes. In 1950, the U.S. Air Force canceled the XF-90 program after determining it did not meet interceptor requirements, reallocating funds to more advanced designs like the F-94 Starfire.
Post-cancellation analysis by Lockheed engineers highlighted the need for afterburners, which were absent in the J34 engines. This lack of afterburners contributed to the aircraft’s underpowered state, a key factor in the program’s cancellation.
Nuclear Testing at Nevada Test Site
During Operation Upshot-Knothole in 1953, the XF-90 prototype was placed 3,500 feet from ground zero for the “Annie” shot, a 16-kiloton airburst. The purpose of this test was to assess aircraft survivability against nuclear effects. The XF-90 endured the blast’s overpressure and thermal radiation without structural failure, sustaining only minor damage to its canopy and control surfaces.
Following the test, the XF-90 was decontaminated at Indian Springs Air Force Base and later preserved. This demonstrated its robust construction against blast waves equivalent to 1 psi overpressure, highlighting the aircraft’s resilience in extreme conditions.
Legacy as a Design Pioneer
The XF-90’s swept-wing and area-ruled fuselage influenced later Lockheed projects, including the F-104 Starfighter. The XF-90 provided early data on transonic drag reduction, contributing to the development of more advanced aircraft designs. Despite its cancellation, the XF-90’s design principles left a lasting impact on the field of aviation.
Today, the surviving prototype is displayed at the National Museum of the United States Air Force in Dayton, Ohio. Restored in 2005, the aircraft serves as a testament to its role in Cold War aviation development. Archival footage and documents from the 1950s underscore the XF-90’s forgotten status, overshadowed by jet advancements like the F-86 Sabre, yet pivotal in proving aluminum structures’ resilience to nuclear environments.