THAT OLD BLACK MAGIC
As military aircraft systems become more complex, aircrew workload has increased by an order of magnitude. Today, when the emphasis on allowing the aircrew to concentrate on the job whether it involves dealing with an enemy or search and rescue mission, airborne housekeeping tasks can intrude on the job in hand.
The solution came with new generations of computers, simultaneously shrinking in size and weight and increasing in memory and computing capacity. To reduce the burden of aircrew tasks, today’s computers have to be integrated into all the systems on an aircraft. The basis for this is the databus: an electronic ringmain which allows a tow-way dataflow between embedded processors in the various sensors and systems.
The Cockpit
However complex the ways and means of distributing data, the crux of the system is the man-machine interface—the cockpit, its instrumentation and displays. The single or twin-cockpit combat aircraft presents perhaps the most demanding avionics environment.
The traditional “basic six” instrument configuration (altimeter, air speed indicator (ASI), artificial horizon, direction indicator (i.e. compass display), rate of climb-and-descent indicator and the turn-and-slip indicator) have now all but disappeared. Information displayed on four of these different “clock faces” has been merged into one instrument. The flight situation indicator now combines the functions of the artificial horizon, altimeter, ASI and compass.
For air combat aircraft, the pilot’s need to maintain his eyes out of the cockpit (rather than at the instrument panel) led to the development of the Head-Up Display (HUD). This displays basic flight information, plus navigation and weapons aiming, on a transparent screen in front of the pilot at his eye level.
Since the development of the HUD, the instrument panel is now called a Head-Down Display or HDD. The wealth of information available on the HDD is vast, whatever the aircraft’s role. Besides flight information, there are the engine instrumentation, fuel gauges, oil pressure and temperature indicators. And the more engines an aircraft has, the more dials the HDD needs.
The improved by liquid crystal displays (LCDs), have led to the innovative “glass cockpit”. When related specifically to flying information, the expression EFIS (electronic flight information system) is used.
By placing two, three or four CRT or LCD panels before the pilot with a set of push button controls around the edge, we can call up the information he needs via a formatted menu.
Gone is the need for a periodic survey of the various major system displays in the cockpit to ensure all is well. The computer driving the main multi-function displays (MDFs) now does this. If there is a problem in a specific system, a series of small but highly visible hazard warning lights are located on either side of the HUD control panel.
If an aircraft is engaged in a weapons delivery run or air combat, the last thing a pilot should be doing is looking into his cockpit. He cannot afford the time to look-down and, for example, changed radio frequencies or armament details on the stores management system; the chances are the enemy will have shot him down.
As the pilot looks ahead of the cockpit, his flight information is all there on his HUD, while his hands are grasping the engine throttles and the control column. By adding two or three extra switches to both these controls, the pilot can now action the most vital systems needed for air combat. This technique is known as Hands-On-Throttle-And-Stick (HOTAS).
Helmet-mounted sights (HMS) now allow faster aiming of weapons. As the pilot looks at his target, he press a button on his HOTAS controls and the location of the target is passed to the weapons computer and the gun or missile is fired. Now, mini-HUDs are being attached to the pilot’s helmet, which continue to feed him information via helmet-mounted displays (HMDs) while he is moving his head within the cockpit, searching the sky for the enemy.
Cockpit layout itself is changing. In the past, the combat pilot’s control column was located between his legs in a central position. Now with the advent of fly-by-wire (FBW) controls and the removal of the mechanical linkages, it is no longer necessary to located it there. Moved to the starboard side console, this is referred to as a side-stick controller, as used on the F-16.
Also on the F-16, the pilot’s ejection seat has been angled backwards slightly to increase the pilot’s G tolerance. Being “laid back”, the blood finds it harder to move towards the body’s lower extremities.
Navigation & Attack
For navigation, the traditional map and stopwatch still work (with FLIR helping at night). More recently, navigation has been supplied by an inertial system, using three gyros in a stabilized platform. Today’s laser gyros are put together in a ring of three systems, hence the term Ring Laser Gyro (RLG).
Usually connected with an INS is a moving map display which pinpoints the aircraft position over a map display. As the aircraft moves along its track, so the map moves as well, always showing the pilot his position. Originally, moving maps were dependent on the map data being held on film and projected onto the display but other, smaller, means, including optical disks, are now being introduced, also increasing the map area available.
Satellite navigation is the latest aid to military air navigation. The US plans to use NAVSTAR global positioning satellites (GPS). Their signals can be picked up by GPS receivers on aircraft (ships or land vehicles, as well) and by using the coordinates obtained, the position of the aircraft is fixed.
The most recent innovation, yet to become operational but now in the final stages of development, is called Terrain-Reference Navigation (TRN). Terrain-following/terrain avoidance radar can show the pilot what is ahead and allows him (or the autopilot) to fly above the high ground as it is approached. Alternatively it can allow him to fly around the high ground, effectively masking the aircraft from ground radar detection. What it can not provide is information on the terrain over the other side of the hill. This is where TRN and several other parallel developments enter the scene.
Using digitized terrain elevation data (DTED) stored on board the aircraft, and comparing it with returns from a radar altimeter, an accurate fix of the aircraft’s exact position can be made. Once established (using INS or GPS) and the “fix” is obtained, then the area over which it is flying can be presented to the pilot on a map display. This shows him not only his position over the ground but can also be fed into the autopilot to allow an avoidance flight path to be flown.
System Control
Because modern combat aircraft are now designed to be unstable, they are only able to fly because the on-board flight control processors monitor the aircraft’s status, on average some 40 times per second, adjusting thing control surfaces to prevent the aircraft from deviating uncontrollably from the pilot’s intended flight path.
This is known as “relaxed stability” and control commands are transmitted via a fly-by-wire (FBW) system. Instead of taking the pilot’s input from the control column and rudder pedals by direct mechanical linkages, input is converted to an electrical signal transmitted by cable, via the flight control computer, to an actuator at the appropriate control surface, where it is converted back to a mechanical movement.
FBW technology is, even now, being superseded by the use of fibre-optic cables to transmit the signals between the pilot’s controls and flight control system. Instead of using an electrical signal down a wire, a light signal is used through the fibre-optic cable. This is known as fly-by-light (FBL). The advantages of FBL are that fibre-optic cables are lighter, have a greater data capacity, make no detectable emissions and are immune to the effects of the electromagnetic pulse (EMP) generated by nuclear explosions.
In the realm of propulsion, the advent of the full-authority digital engine control (FADEC) unit has done much to ease the pilot’s workload on the throttle. Throughout the aircraft’s variation in speed, altitude, maneuvering and fuel consumption limits, the FADEC monitors and adjusts the fuel flow rate to the aircraft’s engine to be operated closer to its temperature and shaft speed limits, allowing faster climbing, greater forward speed and higher altitudes to be attained.
Engine health monitoring is another task assigned to the new generations of airborne computers, along with fuel states, airframe stress, undercarriage cycles and fire detection.
Weapon stores management system have become very important on combat aircraft carrying the multiplicity of weapons, missile, ECM pods, designator pods and drop tanks available today. The cockpit display of such combat aircraft maintains an inventory of stores types, locations, quantities, status and special conditions, providing an operational assessment of each store and weapon stations. It is also involved in the futzing and release of the stores and can de-activate them required.
The Future
In some respects we are seeing science fiction becoming science fact. Rapid developments in computer science provide the key to virtually every new system and, most importantly, its integration into a while.
However, whatever the level of sophistication, there is still a need to keep a man in the loop. It will be a long time before the human brain can be totally replaced by a computer, however clever its software and however fast its processing speed.
