Armament of F-15A/B/C/D

There are three components to the Eagle’s armament–the AIM-7 Sparrow (later the AIM-120 AMRAAM) for BVR encounters, and AIM-9 Sidewinder missiles and an internal cannon for short-range encounters.

• Sparrow:

  In the F-15, the AIM-7 Sparrow semi-active radar homing missile is carried on attachment points mounted on the lower outer edges of the air intake trunks, two on each side.

  The first Eagles to enter service with the USAF carried the AIM-7F version of the Sparrow, which introduced solid-state electronics as substitutes for the miniature vacuum tubes of the earlier versions. This miniaturization enabled the warhead to be moved forward of the wings, with the aft part of the missile being devoted almost entirely to the rocket motor. The extra space that was made available by the introduction of solid-state miniaturization made it possible to introduce a dual-thrust booster/sustainer rocket motor that enabled the effective range of the Sparrow to be essentially doubled (up to 28-30 miles) in a head-on engagement.

  The AIM-7M introduced in 1982 featured a inverse-processed digital monopulse seeker which was more difficult to detect and jam and provided better look-down, shoot-down capability.

  The AIM-7P was fitted with improved guidance electronics, including an on-board computer based on VLSIC technology. It is intended to have better capability against small targets such as cruise missiles and sea-skimming antiship missiles.

  The AIM-7M is 12 feet long and has a launch weight of about 500 pounds. The missile carries a 85-pound high-explosive blast fragmentation warhead. It has two sets of delta-shaped fins–a set of fixed fins at the rear of the missile and a set of movable fins at the middle of the missile for steering.
  
  

• AIM-120 AMRAAM:

  From 1991 onward, the Sparrow has been replaced aboard most Eagles with the Hughes AIM-120 AMRAAM (Advanced Medium Range Air-to-Air Missile), which is a “fire and forget” weapon. The Sparrow AAM had a semi-active radar guidance system which required that the target be continuously illuminated throughout the entire duration of the engagement.

  The AMRAAM is guided to the vicinity of its target by an inertial guidance unit, which can be updated if necessary by a datalink from the launching aircraft. For the final approach to the target, the AMRAAM switches over to its own high-PRF (pulse repetition frequency) active seeker and homes in on the target. Since the seeker in the nose of the AMRAAM uses active radar homing, the missile does not require that the launching aircraft illuminate the target or continue to track it after launch. If the target tries to protect itself by jamming, the AMRAAM can switch over to a medium-PRF home-on-jam mode. Although the AIM-120 handles its own terminal homing onto the target, it usually still requires radar illumination from the fighter for a portion of its initial run-in to the target.

  The AMRAAM is 11.97 feet long, has a wingspan of 20.7 inches, and a diameter of 7 inches. The AMRAAM is considerably lighter than the Sparrow, weighing about 350 pounds at launch. It carries a 48-pound high-explosive directed-fragmentation warhead. Maximum speed is about Mach 4, and the maximum range is of the order of 35-45 miles.

  Test firings of the AMRAAM began in 1981, with initial deployment being scheduled for the mid-1980s. However, the development of the AMRAAM turned out to be much more difficult than expected, and numerous problems turned up which required time-consuming and expensive fixes. The schedules began to slip and costs began to rise. Congress became so dissatisfied with AMRAAM that in 1986 they seriously threatened to cancel the whole program unless the original specification could be met at a unit cost of no more than $440,000. Deployment slipped into the early 1990s. A few AMRAAMs were rushed into service in the final stages of the Gulf War, but none were fired in actual combat. However, the AMRAAM has been fired in combat incidents following the Gulf War with highly successful results, although one of these involved a “friendly-fire” incident in which a pair of Blackhawk helicopters were shot down by mistake.
  
  

• Sidewinder:

  Four AIM-9 Sidewinders (today AIM-9M) can be carried on the underwing pylons of the F-15, two on each side. Attachment points for Sidewinder missiles are provided on each side of the underwing pylons, enabling a drop tank or a bomb ejector rack to be carried underneath the pylons at the same time as the Sidewinders.

  The Sidewinder infrared homing missile dates back to 1956, but the missile has been continuously upgraded over the years. Early F-15As carried the AIM-9J, which was the first major post-Vietnam improvement of the Sidewinder missile. The J model had an expanded target-engagement cone which enabled it to be launched at any spot in the rear half of a target aircraft rather than merely at its exhaust. Compared with the Vietnam-era AIM-9G, it had a more powerful motor and an improved warhead. The AIM-9J introduced the Sidewinder Expanded Acquisition Mode (SEAM), which slaved the seeker head of the missile to the radar when in “dogfight” mode, which enabled the AIM-9J seeker head to be uncaged, slewed toward a specific target by the aircraft radar, and made to track that particular target only. The AIM-9H introduced some minor improvements. The AIM-9L introduced in 1979 was “all-aspect”, and was no longer limited to engaging an enemy aircraft from the rear. The seeker head was more sensitive and was able to pick up heat from the friction off the leading edges of an aircraft’s wing and was able to distinguish between aircraft and decoy flares. The AIM-9L also uses a higher-impulse rocket motor, a more powerful warhead, and a proximity fuse rigged to blow outward toward the target in order to ensure better probability of a kill. The AIM-9M introduced in 1982 had better capability to distinguish between aircraft and decoy flares, and has a low-smoke rocket motor so that it is less likely to be seen by its prey. The number of vacuum tubes was reduced to two.

  The AIM-9 Sidewinder is 9.4 feet long, has a wingspan of 25 inches and a diameter of 5 inches. The missile has four tail fins on the rear, with a “rolleron” at the tip of each fin. These “rollerons” are spun at high speed by the slipstream in order to provide roll stability. The missile is steered by four canard fins mounted in the forward part of the missile just behind the infrared seeker head. The Sidewinder missile has a launch weight of about 180 pounds, and a maximum effective range of about 10 miles. The blast-fragmentation warhead weighs 21 pounds. Despite the advanced age of the basic design, the all-aspect Sidewinder remains a potent threat, exceeded in effectiveness perhaps only by the Russian-built Molniya/Vympel R-73 (known in the West as the AA-11 *Archer*) which combines aerodynamic and thrust-vectoring control systems.
  
  

• Cannon:

  For the very closest air-to-air encounters, the F-15 carries a 20-mm M61A1 cannon installed in the starboard wing leading edge lip, just outboard of the upper air intake. The gun is fed by ammunition drum containing 940 rounds located inside the central fuselage just below the hinge of the large dorsal air brake. The lip on the port side of the aircraft is taken up by a receptacle for midair refuelling by the boom/receptacle method.

  The Eagle was originally intended to have been armed with a 25-mm Ford-Philco GAU-7 cannon that fired caseless ammunition. Caseless ammunition offers the advantage of a higher round velocity with a flatter trajectory. In addition, it has the advantage that there are no spent casings that need to be handled. However, the feed system of the GAU-7 never did work properly, which meant that the gun could not be fired at high rates lest it jam. In addition, caseless ammunition is much more difficult to handle than conventional ammunition, and there is always the danger of it “cooking off” inside the gun, so every part of the gun system (including the ammunition drum) had to be lined with armor, adding to the weight. Consequently, it was decided to opt instead for the 20-mm M61A1 Vulcan cannon, since it was by that time a fully-proven weapon
  
  

• Bombs:

  Although primarily an air superiority fighter, the F-15 Eagle has a secondary air-to-ground capability. Up to 16,000 pounds of bombs, fuel tanks, and missiles can be carried, although the F-15A/B/C/D very rarely functions in a ground-attack role.

  The underwing pylons can each accommodate a multiple ejector rack which can carry six 500-pound bombs. The bomb racks can be installed on the underwing pylons without disrupting the normal carriage of Sidewinder missiles.

  Air-to-ground stores can also be carried on the underfuselage centerline.

  A typical load consists of 18 500-pound bombs, carried 6 each on underwing and centerline ejector racks.

  The F-15A/B/C/D can carry and deliver laser-guided bombs such as the GBU-10E/B Paveway II or the GBU-12D/B Paveway II. However, it does not have the capability of guiding these weapons by itself, and must rely on laser designators carried by other aircraft or by personnel on the ground.

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.