F 15 Eagle

The McDonnell Douglas (now Boeing) F-15 Eagle is a twin-engine, all-weather tactical fighter designed to gain and maintain air superiority in aerial combat. It is considered among the most successful modern fighters with over 100 aerial combat victories. Following reviews of proposals, the United States Air Force selected McDonnell Douglas' design in 1967 to meet the service's need for a dedicated air superiority fighter. The Eagle first flew in July 1972, and entered service in 1976. The F-15 is expected to be in service with the U.S. Air Force until 2025.

Since the 1970s, the Eagle has also been exported to Israel, Japan, and Saudi Arabia. Despite originally being envisaged as a pure air superiority aircraft, the design proved flexible enough that an all-weather strike derivative, the F-15E Strike Eagle, was later developed, and entered service in 1989.

Development

Origins

Following studies in 1964-1965, the U.S. Air Force developed requirements for an air superiority fighter in October 1965. Then on 8 December 1965, the Air Force issued a request for proposals (RFP) for the new fighter. The request called for both air-to-air and air-to-ground capabilities. Eight companies responded with proposals. In the following study phase, four of these companies developed some 500 design concepts. Typical designs featured variable-sweep wings, weighed over 60,000 lb (27,200 kg), included a top speed of Mach 2.7 and a thrust-to-weight ratio of 0.75. The designs were not accepted by the Air Force as they compromised fighter qualities for ground attack qualities. Acceptance of the Energy-Maneuverability (E-M) theory by the Air Force led to a change in requirements for improved maneuverability by the spring 1967. The design mission weight was reduced to 40,000 lb (18,100 kg), top speed reduced to Mach 2.3-2.5 and thrust-to-weight ratio increased to 0.97.

In 1967 U.S. intelligence was surprised to find that the Soviet Union was building a large fighter aircraft, the MiG-25 'Foxbat'. It was not known in the West at the time that the MiG-25 was designed as a high-speed interceptor, not an air superiority fighter, so its primary asset was speed, not maneuverability. The MiG-25's huge tailplanes and vertical stabilizers (tail fins) hinted at a very maneuverable aircraft, which worried the Air Force that its performance might be better than its U.S. counterparts. In reality, the MiG's large fins and stabilators were necessary to prevent the aircraft from encountering inertia coupling in high-speed, high-altitude flight.

The F-4 Phantom II of the USAF and U.S. Navy was the only fighter with enough power, range, and maneuverability to be given the primary task of dealing with the threat of Soviet fighters while flying with visual engagement rules. As a matter of policy, the Phantoms could not engage targets without positive visual identification, so they could not engage targets at long ranges, as designed. Medium-range AIM-7 Sparrow missiles, and to a lesser degree even the AIM-9 Sidewinder, were often unreliable and ineffective at close ranges where it was found that guns were often the only effective weapon. The Phantom did not originally have a gun, but experience in Vietnam led to the addition of a gun. An external gun pod was tried and later the M61 Vulcan was integrated internally on the F-4E.

F-X program

There was a clear need for a new fighter that overcame the close-range limitation of the Phantom while retaining long-range air superiority. After rejecting the U.S. Navy VFX program (which led to the F-14 Tomcat) as being unsuited to its needs, the U.S. Air Force issued its own requirements for the Fighter Experimental (F-X), a specification for a relatively lightweight air superiority fighter. The requirements called for single-seat fighter having a maximum take-off weight of 40,000 lb (18,100 kg) for the air-to-air role with a maximum speed of Mach 2.5 and a thrust to weight ratio of nearly 1 at mission weight. Four companies submitted proposals, with the Air Force eliminating General Dynamics and awarded contracts to Fairchild Republic, North American Rockwell, and McDonnell Douglas for the definition phase in December 1968. The companies submitted technical proposals by June 1969. The Air Force announced the selection of McDonnell Douglas on 23 December 1969. The winning design resembled the twin-tailed F-14, but with fixed wings. It would not be significantly lighter or smaller than the F-4 that it would replace.

The Eagle's initial versions were designated F-15A for the single-seat configuration and F-15B (originally TF-15A , but this designation was quickly dropped, as the F-15B is fully combat-capable) for the twin-seat. These versions would be powered by new Pratt & Whitney F100 engines to achieve a combat thrust-to-weight ratio in excess of 1 to 1. A proposed 25 mm Ford-Philco GAU-7 cannon with caseless ammunition was dropped in favor of the standard M61 Vulcan gun due to development problems. The F-15 retained conformal carriage of four Sparrow missiles like the Phantom. The fixed wing was put onto a flat, wide fuselage that also provided an effective lifting surface. Some questioned if the zoom performance of the F-15 with Sparrow missiles was enough to deal with the new threat of the high-flying MiG-25 "Foxbat", but its capability was eventually demonstrated in combat.

The first F-15A flight was made in July 1972 with the first flight of the two-seat F-15B (formerly TF-15A) following in July 1973.

The F-15 has a "look-down/shoot-down" radar that can distinguish low-flying moving targets from ground clutter. The F-15 would use computer technology with new controls and displays to lower pilot workload and require only one pilot to save weight. Unlike the F-14 or F-4, the F-15 has only a single canopy frame with clear vision forward. The USAF introduced the F-15 as "the first dedicated USAF air superiority fighter since the F-86 Sabre."

The F-15 would be favored by customers such as the Israel Air Force and Japan Air Self-Defense Force. However, criticism from the fighter mafia that the F-15 was too large to be a dedicated dogfighter, and too expensive to procure in large numbers, led to the Lightweight Fighter (LWF) program, which led to the USAF F-16 Fighting Falcon and the middle-weight Navy F/A-18 Hornet.

Further development

The single-seat F-15C and two-seat F-15D models entered production in 1978 with the models' first flights in February and June of that year. These new models have Production Eagle Package (PEP 2000) improvements, including 2,000 lb (900 kg) of additional internal fuel, provision for carrying exterior conformal fuel tanks and increased maximum takeoff weight of up to 68,000 lb (30,700 kg). The additional takeoff weight allows internal fuel, a full weapons load, conformal fuel tanks, and three external fuel tanks to be carried. Other improvement on the C and D models included strengthened landing gear, radar improvements, and a new digital central computer. An overload warning system was also added, which allows the pilot to fly the fighter to 9 g at all weights.

The F-15 Multistage Improvement Program (MSIP) was initiated in February 1983 with the first production MSIP F-15C produced in 1985. Improvements included an upgraded central computer; a Programmable Armament Control Set, allowing for advanced versions of the AIM-7, AIM-9, and AIM-120A missiles; and an expanded Tactical Electronic Warfare System that provides improvements to the ALR-56C radar warning receiver and ALQ-135 countermeasure set. The final 43 F-15Cs included the enhanced-capability Hughes APG-70 radar, which was developed for the F-15E. The earlier MSIP F-15Cs with the APG-63 were later upgraded to the APG-63(V)1, which significantly improves reliability and maintainability while providing performance similar to the APG-70. The improvements were retrofitted to existing F-15s.

In 1979, McDonnell Douglas and F-15 radar manufacturer, Hughes, teamed to privately develop a strike version of the F-15. This version competed in the Air Force's Dual-Role Fighter competition starting in 1982. The F-15E strike variant was selected for production in 1984.

Beginning in 1985, F-15C and D models were equipped with the improved P&W F100-220 engine. It added a digital engine control to allow for quicker throttle response, less wear, and reduced fuel burn. The original F100-100 engines were upgraded to a similar configuration with the designation F100-200E starting in 1997 and were ongoing as of 2007.

Recent upgrades include retrofiting 178 F-15C fighters with the AN/APG-63(V)3 Active Electronically Scanned Array (AESA) radar with delivery beginning in early 2009. Additionally, the Air Force also plans to upgrade other F-15s with the Joint Helmet Mounted Cueing System (JHMCS).