The XF-108 was expected to be able to reach altitudes of 80,000 feet, which would have made the Rapier one of the highest-flying aircraft ever built.
The North American XF-108 Rapier was a proposed interceptor aircraft, designed to defend the United States from incoming supersonic Soviet strategic bombers. While work on the XF-108 progressed through the 1950s at the height of the Cold War, the program was ultimately cancelled in 1959—both on account of project costs and the fact that the Soviets had adopted ballistic missiles as their primary method of launching a nuclear attack, rendering the XF-108 moot. When the program was cancelled, only one wooden mock-up had been built—the closest the XF-108 had come to fruition.
In the 1950s, the U.S. Air Force wanted to replace their early Century Series interceptors, the F-102 Delta Dagger and the F-106 Delta Dart. Specifications for a replacement were established in 1955, calling for an interceptor that could achieve a service ceiling of 60,000 feet, a top speed of Mach 1.7, and a range of 1,000 miles. The Air Force wanted the interceptor to operate with a two-man crew and two engines.
North American was eventually issued a contract for two prototypes. Designing the prototypes was a complicated process, as aerospace technology was improving so rapidly; keeping the project on the cutting edge required constant revisions to the design, in part because the Air Force kept revising their specification requirements.
Ultimately, the XF-108 was to feature a “cranked” delta wing. A cranked delta wing has a kink or bend on either the trailing edge or trailing edge, which can improve an aircraft’s stability at high speeds and at high angles of attack. Other features, like forward canards, were discarded during the intricate design phase.
When the design was finally settled upon, the XF-108 featured two fuel tanks in the fuselage and five fuel tanks in the wing, giving the interceptor a combat radius of about 1,100 nautical miles. The XF-108’s top speed was estimated at 1,980 miles per hour, approximately Mach 3. Notably, the XF-108 was expected to be able to reach altitudes of 80,000 feet, which would have made the Rapier one of the highest flying aircraft ever built—comparable to the U-2 Dragon Lady, and later the much more advanced SR-71 Blackbird.
To simplify production, North American migrated the General Electric J93 turbojet engines from their XB-70 Valkyrie bomber program over to the XF-108. Each J93 offered a whopping 28,800 pounds of thrust. But given the XF-108’s gross weight of 76,000 pounds, the high-thrust engines were necessary. Offering a 0.77 thrust-to-weight ratio, the XF-108 was expected to climb at 45,000 feet per minute.
But the XF-108 never progressed further than the construction of a wooden mock-up. As noted, the program’s expenses quickly added up, and given the abundance of other Century Series fighters under development or in service, the Air Force determined that the XF-108 was no longer necessary. It helped that the Soviet Union appeared to be recalibrating their to rely on ballistic missiles rather than strategic bombers.
So the XF-108 got the axe. Yet its basic fuselage and weapons package lived on, in the North American A-5 Vigilante, a Mach 2-capable carrier-based nuclear strike bomber that many viewed as a scaled down version of the forgotten plane.
About the Author: Harrison Kass
Harrison Kass is a senior defense and national security writer with over 1,000 total pieces on issues involving global affairs. An attorney, pilot, guitarist, and minor pro hockey player, Harrison joined the U.S. Air Force as a Pilot Trainee but was medically discharged. Harrison holds a BA from Lake Forest College, a JD from the University of Oregon, and an MA from New York University. Harrison listens to Dokken.
Image: Wikimedia Commons.
