Why The Air Force Still Flies U.S. F-15s After Nearly Fifty Years (Even with F-35s in The Air)

Kyle Mizokami

Key Point: In a world still dominated by fourth-generation fighters, the F-15 is an aging—but still formidable—fighter.

For nearly three decades, the F-15 Eagle fighter was considered the undisputed king of the skies. Until the debut of its replacement, the F-22 Raptor, the F-15 was the U.S. Air Force’s frontline air superiority fighter. Even today, a modernized Eagle is still considered a formidable opponent, and manufacturer Boeing has proposed updated versions that could keep the airframe flying for the better part of a century.

The F-15 traces its roots to the air war in Vietnam, and the inauspicious showing of American Air Force and Navy fighters versus their North Korean counterparts. Large, powerful American fighters, designed to tackle both air-to-air and air-to-ground missions, were performing poorly against their smaller, less powerful—but more maneuverable—North Vietnamese counterparts. The 13:1 kill ratio American fliers enjoyed in the Korean War dropped to an abysmal 1.5 to 1 kill ratio in Vietnam.

Contemporary fighters, such as the F-4 Phantom, had been designed under the assumption that the air-to-air missile had rendered dogfights obsolete, and with them the need for superiority maneuverability and a gun for air combat. The U.S. Air Force decided it needed a dedicated air superiority fighter, one that combined two powerful engines, a powerful radar, a large number of missiles and a gun. Above all, it had to be maneuverable enough to win a dogfight.

The Air Force issued a request for proposals for the new FX fighter in 1966, and no fewer than six companies submitted competing paper designs. No prototypes were built. The air service selected McDonnell Douglas (now a part of Boeing) in 1969, ordering 107 full-scale development planes.

The F-15 was a formidable aircraft. Early versions were powered by two Pratt & Whitney F100-PW-100 afterburning turbofan engines, producing 14,500 pounds of static thrust—23,500 with afterburners. This gave the aircraft a thrust-to-weight ratio of greater than one, making it so powerful that it was the first fighter to exceed the speed of sound in vertical flight. The F-15 had so much thrust it could climb to sixty-five thousand feet in just 122 seconds. In horizontal flight, the F-15 could reach speeds of Mach 2.5, and cruise at speeds of Mach 0.9.

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