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F-20 Tigershark Integrated Digital Avionics

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The F-20A integrated avionics system provided air to air and air to ground target detection and weapons delivery for supersonic intercept, air superiority, combat air patrol, close air support, and interdiction missions----day or night and under adverse weather conditions.

The avionics design simplified pilot operations, reduced pilot workload, and rapidly provided data for successful combat missions. The design incorporated the newest USAF avionics standards. Primary avionics elements were integrated through a redundant MIL STD 1553B multiplex data bus and controlled by a MIL STD 1750A mission computer using MILSTD 1589 Jovial J 73 language. The computer contained 256,000 words of programmable memory and had a throughput of 1 million operations per second. The computer had a specified MTBF of 2400 hours. The F-20A was able to accept new MIL STD avionics and weapons with a minimum of modification and without additional wiring to the avionics.


TIGERSHARK CONTROLS AND DISPLAYS

The Tigershark display system consisted of two digital display indicators (DDIs), a head up display (HUD), a data entry panel, and a display processor. Integrated controls included a data entry panel, software controlled push buttons surrounding each DDI, and hands on stick and throttle (HOSAT) switches.

The two DDIs, located in the uppermost part of the main instrument panel, were easily visible to the pilot. The left DDI usually displayed mission data; the right DDI was normally assigned to the radar.

When a combat mode was selected by the stick or throttle switches, the HUD and DDIs changed immediately to the appropriate displays; the right DDI displayed the radar format while the left DDI displayed stores management data. The figure below illustrates a typical air to ground stores display with bombs selected.


HEAD UP DISPLAY

The HUD provided head up capability in all modes of flight: weapons aiming and delivery information for air and ground targets, and navigational and flight data. The HUD presented data and sufficient references (aim point, allowable steering error, launch boundaries, attitude, and weapon selection and status) to enable navigation and target acquisition and designation. Air to ground weapons could be released manually using the stick switch or automatically by the mission computer. The figure below shows a typical HUD display for an air to air engagement using AIM 9 missiles.


TIGERSHARK RADAR

The Tigershark avionics system included the General Electric AN/APG-67(V) radar. This radar was an X -band, pulse doppler, digital multimode radar using low pulse repetition frequency (PRF) in the look up mode, medium PRF in the look down mode, and high PRF for velocity search. It had an MTBF of 200 hours and included the following functions:

  • AIR TO AIR --Look up, look down, range while search --Velocity search --Single target track --Air combat modes with automatic acquisition --Track while scan*

  • AIR TO SURFACE --Ground map/Doppler beam sharpened map --Display freeze mode --Ranging --Moving target indication* --Moving target track* --Beacon track (option)*

  • AIR TO SEA --Sea surface search (SEA 1) --Sea moving target indication (SEA 2)* --Sea moving target track*

INERTIAL NAVIGATION SET (INS)

The F-20A AN/ASN-144 ring laser gyro INS was the primary navigation, attitude, and heading reference. It provided an all attitude self contained navigation capability anywhere in the world. Precision data were continuously available without degradation during all types of maneuvering and speed ranges. INS accuracy was better than 1.0 nmi/hour CEP.

The ring laser gyro used no moving parts. It operated by measuring the frequency difference between two counter rotating laser beams. The simplicity of the ring laser gyro resulted in a specified MTBF of 2000 hours and significantly improved navigation performance and rapid alignment.

The INS alignment time was 22 seconds, using position data stored prior to aircraft shutdown to facilitate fast scramble time.


BUILT-IN MAINTENANCE DIAGNOSTICS

The Tigershark featured built in (on board) system maintenance diagnostics for detection of failures at the line replaceable unit (LRU) level. Thus, no avionics flight line support equipment was required and scheduled inspections were reduced. Built in test (BIT) capability was included in the LRUs of the avionics system and the electronic flight control system. BIT failure data was processed by the mission computer and displayed on the digital display indicator.

When BIT indications resulted in LRU removal and replacement, the failed LRU was repaired at the intermediate level shop LRU test station using already available test equipment and off the shelf computers. Intermediate level testing identified the fault to the shop replaceable unit (SRU), which was then replaced; the failed card was then forwarded to the depot or supplier for repair.


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© Mark Wade, 1997 - 2006 except where otherwise noted.
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