Document created: 2 September 03
Air University Review, May-June 1975

F-111 The Wave of The Future

The F-111 has certainly had its share of publicity since joining the Air Force inventory. Unfortunately, not all of this publicity has been favorable. Nevertheless, despite the controversy surrounding the aircraft (some of it justified, most of it not), there is one aspect of the F-111 that is deserving of considerably more than just passing attention: its avionics system.

The F-111D--only one of the many F-111 models--is the one that I wish to single out as a truly unique aircraft and indeed as the test bed for much of the B-1 avionics system, which may well be the "wave of the future."

What does the future portend? Well, if the F-111D’s Mark II avionics system is an example, the crew members of tomorrow will be in an entirely new environment. The low-level profiles flown, using the new automatic terrain-following radar systems often set to fly at a terrain clearance of only one hundred to two hundred feet, will he commonplace. Crews of the future can anticipate notable innovations. They will no longer be required to carry local area maps and charts on each mission, because a set of maps and charts covering the flying areas will be on color film and displayed on a screen in the cockpit. The display will be tied in with the computer system, inertial navigation system, airspeed and compass system to insure that the chart is always centered on the screen, with the aircraft position in the center and with the aircraft heading and projected ground track displayed on the screen. With the adoption of microfilm, maps and charts for the entire world will be stored in each aircraft.

Fumbling for the right page in the checklists will be a thing of the past, because at the flick of a switch the checklist that has been put on film will be projected on a cockpit display. In the F111D the horizontal situation display (HSD) serves a double purpose: showing the maps and charts in one mode and the pages of the aircraft checklists in another.

Navigating from TACAN to TACAN may be a thing of the past. With the F-111D’s computerized Mark II avionics system, a tape can be made of a planned route, including such items as enroute check points, turning points, targets, offset aiming points for targets, fuel requirements, and even an alternate route. This tape is then stored in the aircraft computer's memory bank prior to takeoff. Once airborne, the route is called up by the computer, and the auto pilot and inertial navigation system are tied in with the computerized flight program so that the aircraft automatically flies the route as programmed without any additional instruction or action by the crew.

Additional refinements include a data display panel for such items as the distance and time to the next turning point, ground speed and ground track, true airspeed and true heading, wind speed and direction. Also, symbols for each turning point, target, and check point for a given route are displayed on the chart and map display (HSD) as the route is being flown. Of course, if for some reason (bad weather, etc.) the crew wishes to change the route or destination, a computer terminal in the cockpit is available for feeding new or corrected information to the system. The computer will then calculate the new heading and turn the aircraft, and the display panel can show distance and time to go as well as fuel required if desired. The system even provides for a backup computer if the primary computer fails.

The radarscope found on other aircraft has been replaced by television, providing many advantages without detracting from the system. Radar imagery can be displayed on the TV screen just as easily as on the former radarscopes. Additional features include an expand mode that allows for a radarscope presentation of the immediate area around the radar cross hairs regardless of the range. The advantages of being able to concentrate on and expand a particular target while still forty or even two hundred miles away are obvious.

Other modes of operation allow for the aircraft attitude to be displayed on the TV along with airspeed, heading, altitude; the E-scan presentation use when flying low-level terrain-following radar routes; a situation display that depicts only obstacles above the aircraft for flying low level; and numerous air-to-air modes for air intercept work as well as a moving-target indicator mode picking out moving vehicles and trains. Other modes that have been incorporated but at present are not activated in the F-111Ds allow for the addition low-light TV system and infrared displays. Using the radar mode at long range to acquire the target complex, we can switch to the IR or TV modes, which tied in with the computer to be the cross-hair aiming point. At short range, by using a zoom feature, we can refine the cross-hair placement to a small area.

The bombing tables, ballistic curves and bombing calculations for the F-111D are all things of the past. The ballistic of the various weapon systems are put on computer tapes and selected when desired. The stored ballistic information, coupled with airspeed, altitude, and heading information supplied to the computer, allows for instantaneous computation of the proper release point The crew needs only to arm the weapon system, and it will then fly automatically to the target and compute the correct release point for the bombs. This allows the crew to take evasive actions until one second prior to release, with the computers continuously recomputing the release point. If for some reason the crew does not fly over the target or within "X" number of feet, the bombs will not release in the automatic mode. They can, of course, always be dropped manually or jettisoned.

I have covered only a few of the revolutionary concepts that are employed today p the F-111D’s avionics package and that will be commonplace in the Air Force of the future. The backup computer system has been only briefly mentioned, and the primary and two alternate radar systems, along with the heads-up display (HUD), we have not been mentioned at all. The HUD is an optical sighting glass, one for each crew position, on which target cross hairs, target information, and flight data are projected. The symbology, cross hairs, etc., are focused at infinity so as not to interfere with the crew members' view when making a visual target run. A multitude of data is also displayed on the HUD. Typical data displays might be low fuel warning, a breakaway signal, a roll up signal, or a fire or caution signal.

In all fairness it must be admitted that some of the technical problems still have to be ironed out. Expected life of some components has not been as long as originally planned for, and often funding for spare parts has not been enough. Yet, a great deal has been learned. The feasibility of using advanced state-of-the-art avionics equipment has been proven. It is also evident that the crew members of the future not only will have to possess all the attributes of the past but also will have to be highly knowledgeable in the use of the advanced electronic equipment as well as skilled in the arts of computer-operated components. While not all the facts are in yet, it is clear that today's F-111l may well be the wave of the future. Indeed, it is here today.

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