The heart of the F-15A’s electronics suite is a Hughes AN/APG-63 X-band (8-12 GHz) coherent pulsed-Doppler radar set with look-down, shoot-down capability. It has a maximum detection range of greater than 100 miles.
This radar has several different air-to-air modes, employing different pulse repetition frequencies (PRF), depending on the type of search that is being carried out. The long-range search mode uses high and medium PRFs, which offer a compromise between the best air-to-air tracking of tail-on and nose-on targets, with the pilot selecting search ranges between 10 and 200 miles. A velocity search mode using high PRFs is intended exclusively for head-on, high-closure rate targets. For short-range search modes, medium PRF is used. This is generally chosen for engaging short-range maneuvering targets, in situtions where the Sidewinder missile or the gun is to be used. There is also a non pulse-Doppler mode using low PRF , which is useful only when “looking up”, since it offers no clutter rejection. There is a beacon mode for interrogating other warplanes’ IFF transponders. There is also a manual tracking mode used as a backup when the radar is not automatically tracking well, and a “sniff” mode which detects jamming and emits tiny bursts to minimize self-illumination. There is even a radar mapping mode that was made available in later versions of this radar.
Data from the APG-63 radar is processed digitally and is fed to an IBM CP-1075 central computer. Information is displayed to the pilot on either the Honeywell Vertical Situation Display or on the AVQ-20 Heads-Up Display (HUD). The Vertical Situation Display is a cathode ray tube mounted in the upper left dashboard of the control panel. It is mainly used in the long-range phase of an engagement, displaying a cleaned up radar picture and presenting target data such as altitude, IFF return, ground speed, etc. At shorter range and in actual combat, the HUD is generally used, which combines target information with vital aircraft performance figures.
The main control panel for the radar is on the console at the pilot’s left side, although key functions can be controlled from switches on the throttles and stick. One control on the stick activates the automatic acquisition system at close ranges in one of three modes. First, a “boresight” mode is used to lock the radar on to the first hostile aircraft to enter the F-15s boresight, as designated by the gun reticle on the HUD. Second, a “super-search” mode locks onto the first target to enter the HUD field of view. Last, a vertical scan mode locks onto the first target into an elevation scan button. Steering and weapon information is then supplied to the pilot on the HUD.
The F-15A is equipped with the Hazeltine APX-76 IFF interrogator with Litton reply evaluator. The F-15A also has a Teledyne APX-101 IFF transponder. The Litton ASN-109 inertial navigation system carried by the F-15A is a completely passive, on-board system which does not need any external references. It is backed up by various ground-based navigation aids such as an ARN-118 TACAN, ADF, and ARN-112 ILS receivers. These aids can be used to update the inertial system. It is backed up by Honeywell ASN-108 AHRS.
Other navigation and communication receivers included a Collins-built HSI which displays navigation information on a symbolic pictorial display, Magnavox ARC-164 transceivers, Dorne and Margolin glidescope localizer antennae, and a Teledyne angle-of-attack sensor.
The F-15 carries a classified electronics warfare package known as the Tactical Electronic Warfare System (TEWS). Defensive avionics include the Northrop ALQ-135(V) internal countermeasures system, which acts on information from the Loral ALR-56C and Magnavox ALQ-128 radar warning suites and provides active jamming against enemy radar threats. The Loral ALR-56 radar warning receiver (RWR) system has external antennae mounted on the each fin tip and on both wingtips. A fifth blade-shaped antenna is mounted underneath the forward fuselage. The all solid state ALR-56 is based on a digitally-controlled dual channel receiver that scans from 6-20 GHz, while changes in the perceived threat can be accommodated by changing the software. Tracor ALE-45 chaff/flare dispensers are provided.
Sources:
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McDonnell Douglas Aircraft Since 1920, Volume II, Rene J.
Francillon, Naval Institute Press, 1990.
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Observers Aircraft, William Green and Gordon Swanborough,
Frederick Warne, 1992.
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Combat Aircraft F-15, Michael J. Gething and Paul Crickmore,
Crescent Books, 1992.
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The American Fighter, Enzo Angelucci and Peter Bowers,
Orion, 1987.
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The World’s Great Interceptor Aircraft, Gallery Books, 1989.
- F-15 Eagle, Robert F. Dorr, World Airpower Journal, Volume 9, Summer 1992.
