Origin of McDonnell F-15 Eagle

Last revised February 20, 2000


The McDonnell Douglas F-15 Eagle is today one of the world's most formidable interceptor fighters. Although largely designed in the late 1960s and early 1970s, it still remains the primary air-superiority fighter serving with the USAF, and will remain so well into the first decade of the 21st century. In service with the United States, Israeli, and Saudi Arabian air forces, the Eagle has scored an impressive number of air-to-air kills, perhaps approaching 100, with NO known air-to-air losses.

The McDonnell Douglas F-15 Eagle has its origin back in the mid-1960s, when the US aircraft industry was invited to study US Air Force requirements for an advanced tactical fighter that would replace the F-4 Phantom as the primary fighter aircraft in service with the USAF. Such an aircraft needed to be capable of establishing air superiority against any projected threats in the post-1975 period. Without compromising the primary air-to-air combat role, the aircraft was to be capable of performing a secondary air-to-ground mission.

Throughout much of the Vietnam War, the primary fighter in service with the USAF was the McDonnell F-4 Phantom, a large, twin-engined, two-seat aircraft. The Phantom had originally been designed back in the 1950s to Navy requirements for a two-seat multi-role fighter, intended to destroy enemy aircraft at beyond-visual-range (BVR), using a powerful fire control radar to detect threats and to direct Sparrow semi-active radar guided missiles against them. No cannon was provided, since the received wisdom of the late 1950s was that the internal gun was an obsolete holdover from the pre-missile age. However, the North Vietnamese air force was equipped with MiG-17s and MiG-21s, small, relatively unsophisticated aircraft designed for close-in dogfighting. In the years 1965-68, the kill-ratio in air battles against the North Vietnamese Air Force was only 1.5 to one, much poorer results that those obtained in Korea by the F-86 Sabre against the MiG-15. One of the reasons for this rather poor record was the rather restrictive rules of engagement over North Vietnam, which required a close-in positive identification of the enemy before missiles could be fired, negating the advantage of the Phantom's powerful radar and long-range Sparrow missiles. In a close-in knife fight against MiG-17s and MiG-21s, the Phantom was considerably less maneuverable and was at a relative disadvantage in these types of encounters. Another reason was the fact that most USAF pilots had never been trained for air-to-air combat, and did not know how to exploit the strengths of their own aircraft against the weaknesses of the enemy's planes.

As a result of the experience over North Vietnam, the Air Force concluded that they had better pay more attention to the possibility of close-in air-to-air fighting in the design of their future fighter aircraft, and not simply rely on superior radars and long-range missiles to ensure victory. At first, the Air Force was rather uncertain of just what kind of aircraft they wanted to replace the Phantom, and their initial requests for proposals were rather vague and tentative, relying more on the industry telling them what they should be buying rather than issuing any specific requirements.

On October 6, 1965, the Air Force issued Qualitative Operational Requirement (QOR) 65-14F, which defined what later came to be known as the F-X (Fighter-Experimental) project. A Request For Proposals (RFP) was issued to the industry on December 8, 1965. The Air Force initially pictured the F-X as being a close-support multirole aircraft powered by a pair of advanced turbofan engines and equipped with variable-geometry wings. Boeing, Lockheed, North American, Grumman, and McDonnell all wanted a piece of the action and got to work on initial concept studies.

After looking over the initial concept studies, in March of 1966 the USAF issued Concept Formulation Study (CFS) contracts for these requirements to three manufacturers--Boeing, Lockheed, and North American. Although Grumman and McDonnell had not been awarded any Air Force contracts, they nevertheless continued to fund their own studies on the same requirements.

However, none of the submitted designs were considered any further by the Air Force, mainly because the aerodynamic configurations and the bypass ration of the turbofans were considered inadequate. Nothing was ordered by the Air Force, and work on the F-X proceed at only a slow pace from mid-1966 to the autumn of 1967. On April 28, 1967, McDonnell merged with the Douglas Aircraft Corporation, becoming McDonnell Douglas. However, all of the work on the company's F-X proposal continued to be carried out at the St Louis facility.

In July of 1967, the Soviet Union unveiled a new generation of combat aircraft at an airfield at Domodedovo near Moscow. Among these was the Mikoyan MiG-25 Foxbat, a twin-engined, twin-tailed fighter capable of a Mach 2.8 performance. The capabilities of the Foxbat sufficiently alarmed Air Force officials that work on the F-X was assigned a higher priority, and in August of 1967, a second Request for Proposals for a CFS of the F-X was issued. This time, the Air Force had a clearer idea of what they wanted. The general emphasis this time was to be on a fighter rather than on ground support. The conception of the FX as being a 60,000-pound variable-geometry multirole aircraft was abandoned in favor of a 40,000-pound fixed-wing dedicated fighter.

Grumman, Lockheed, North American Rockwell, the Republic Division of Fairchild Hiller, General Dynamics and McDonnell Douglas all submitted proposals for the CFS. In December of 1967, both General Dynamics and McDonnell Douglas were given contracts for a second CFS, with Fairchild-Republic, Grumman, Lockheed, and North American Rockwell having to proceed at their own expense.

During this period, the industry vacillated between considering a large, twin-engined aircraft with advanced radar and long-range missiles and a small, MiG-21-sized, single-engined aircraft with minimal electronics systems but with an emphasis on maximum performance and high maneuverability. However, guided by the Air Force's unhappy experience with the Lockheed F-104A Starfighter, a single-engined high-performance aircraft with minimal electronic systems which the USAF had found that it did not need, the twin-engined, advanced electronics option seemed more attractive.

This second CFS was completed in May of 1968, and in early September the FX Concept Development was authorized. Requests for Proposals for the Project Definition Phase (PDP) were requested from eight different manufacturers on September 30, 1968. These companies were McDonnell Douglas, Boeing, Fairchild-Republic, General Dynamics, Grumman, Lockheed, Ling-Temco-Vought, and North American Rockwell. This time, the RFP was much more specific. It specified that the new fighter should have low wing loading with buffet-free performance at Mach 0.9, a high thrust-to-weight ratio, long-range pulse-Doppler radar with look-down/shoot-down capability, a ferry range sufficient to permit deployment to Europe without midair refuelling, and a maximum speed of Mach 2.5. A twin-engine format was preferred because of its higher reliability. The RFP also specified that a one-pilot cockpit was to be used, the development of more advanced computer systems, radar and electronics being thought to make the radar intercept officer unnecessary. The gross weight was not to exceed 40,000 pounds. The aircraft was to superior in air combat to any present or projected Soviet fighters, both in close-in visual and in beyond-visual-range air-to-air combat.

PDP contracts were awarded to Fairchild-Republic, McDonnell Douglas, and North American Rockwell on December 30, 1968. The North American Rockwell and Fairchild-Republic proposals both had single tail fins. The Fairchild-Republic proposal had its engines hanging out from the fuselage underneath a blended lift surface. The McDonnell Douglas proposal was a large, single-seat aircraft with twin-fins and a pair of turbofan engins.

By now, the FX was known as the F-15, and all three contenders were hard at work.

On December 23, 1969, the McDonnell Douglas proposal was named the winner of the contest, and the company was authorized to proceed with the design and development phase, to build and test twenty Full Scale Development (FSD) aircraft, and to manufacture 107 single-seat F-15s and two-seat TF-15s.

Principal engineering work on the F-15 was overseen by George Graff, who was head of the design team. Program manager Don Malvern organized the effort and moved it forward. Very early on, the McDonnell Douglas team rejected the idea of using a variable-geometry wing as being too complex, too heavy, and too expensive. The team selected instead a large-area, fixed-geometry wing with 45 degree sweep at the leading edge. The use of advanced avionics and electronics made it possible to use the single-seat configuration favored by the Air Force. The engines were to be a pair of Pratt & Whitney afterburning turbofans fed by lateral intakes. Armament was to consist of four AIM-7 Sparrow semi-active radar homing missiles mounted on the lower corners of the fuselage and four AIM-9 Sidewinder infrared-homing air-to-air missiles carried on wing stations. A 20-mm M61A1 cannon cannon was to be installed in the starboard wing leading edge. Provision was incorporated for the carrying of three 610-gallon drop tanks or up to 9000 pounds of air-to-ground stores, although the air-to-ground role was only secondary for the F-15.

The F-15 was ordered "off the drawing board", and there was to be no prototype as such and no competitive flyoff against other manufacturer's aircraft. This raised quite a bit of controversy, many people in the press fearing another cost overrun debacle. However, in response to criticism from Congress and the press over cost overruns and lengthy delays that had occurred in both the C-5A Galaxy and F-111 programs, the USAF had introduced a set of demonstration milestones which the contractor had to meet before the next stage of funding could be issued. For the F-15 project, the milestones began with the preliminary design review which was to be held by September 1970, and ended with a requirement that the first aircraft were to be delivered for test to the Air Force in November of 1974.

Sources:


  1. McDonnell Douglas Aircraft Since 1920, Volume II, Rene J. Francillon, Naval Institute Press, 1990.

  2. Combat Aircraft F-15, Michael J. Gething and Paul Crickmore, Crescent Books, 1992.

  3. The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.

  4. The World's Great Interceptor Aircraft, Gallery Books, 1989.

  5. F-15 Eagle, Robert F. Dorr, World Airpower Journal, Volume 9, Summer 1992.