Aircraft Avionics
Total Page：16
File Type：pdf, Size：1020Kb
P1: FHK Qu: 00, 00, 00, 00 Encyclopedia of Physical Science and Technology EN001H-913 May 25, 2001 21:11 Aircraft Avionics Robert G. Loewy Georgia Institute of Technology I. Definitions of Avionics Components (Glossary) II. Aircraft Avionics Systems, General III. Traditional Avionics, MEP IV. Avionics Applications Influencing Aircraft Design; VMS V. Impact Of “Smart Materials” VI. Summary I. DEFINITIONS OF AVIONICS Power Source Most avionics system components require COMPONENTS (GLOSSARY) power sources independent of pilot/crew; i.e., avionics systems are “active” systems. Power sources may be Actuator An element of a control system that will move electrical (e.g., batteries, generators, fuel-cells) or me- another element, by providing a force, pressure or mo- chanical (e.g., hydraulic pumps and reservoirs, pneu- ment (force acting through a lever arm) in response to matics, etc.) a command signal. Processor A system component which may analyze (i.e., Effector A control system element that will provide the extract useful information from), combine or store sig- desired change in an aircrafts’ behavior; e.g., aerody- nals or may model aircraft behavior for comparative namic control surface such as a “rudder,” to change purposes. Such operations may be analog or digital; heading, or a “speed brake” to reduce flight speed. when the latter, processors have much in common with Linkage A control system component that carries use- computers, but usually having special, i.e., more lim- ful signals, forces or moments from one location to ited functions, rather than being general-purpose. another location. These useful signals can be analog Sensors A device that responds to some physical quan- electromagnetic or optical or digital, i.e., quantitative, tity such as pressure or temperature (or conceivably a and such transport can be within the aircraft or from chemical quantity such as acidity) by converting it to a and to points external to the aircraft. Only when forces useful signal. and moments are transmitted are linkages mechanical. Software The capability of digital processors and the When digital signals are transmitted the linkages are complexity of their functions, defined above, are such often called “data buses.” Data buses are the conduits that the (usually) specialized codes that command their through which outputs are sent or inputs are received operations are considered a separate avionics “com- by a digital system or subsystem in order to perform ponent.” In written form such computer or processor its function. codes may require tens of thousands or millions of 319 P1: FHK Encyclopedia of Physical Science and Technology EN001H-913 May 8, 2001 14:54 320 Aircraft Avionics lines of instructions and their development may in- ages (fly-by-optics, FBO) are used less often than elec- volve equal or greater expense than the “hardware” trical linkages (fly by wire, FBW) and in FBW systems elements of avionics systems whose components are there is no need for electro optical transducers. Where defined elsewhere in this glossary. fiber optics linkages are used it is usually because of their Transducer A device that takes a useful signal in one superior capabilities for carrying large quantities of infor- form, say electrical, and converts it to another useful mation (high bandwidth) and insensitivity to ElectroMag- form, perhaps optical. (Note that “sensors” and “actu- netic Interference (EMI), including that associated with ators” are, in a more general sense “transducers,” but lightning. common usage restricts the meaning of the term as de- Once aircraft were recognized as vehicles with realiz- fined here.) able potential for transportation, the need for a number of Transponder A component which, on receiving an Elec- kinds of electronics-based equipment became apparent, troMagnetic (EM) signal, often coded, will respond by based on the importance of increasing aircraft utility and sending a similar signal, usually after a known, con- safety. These functions, roughly in the chronological or- trolled delay time. der in which the related avionics equipments were first adapted for use on aircraft in service use, are as follows: II. AIRCRAFT AVIONICS 1. Communication SYSTEMS, GENERAL a. Ground to air b. Air to ground The term “avionics” results from combining “aviation” c. Air to air with “electronics,” in recognition of the growing use and 2. All weather, blind flying importance of the application of devices making use of 3. Navigation electronics in aircraft design, development and operation. 4. Limited visibility landing Aircraft avionics systems, however, make use of compo- 5. Bad weather avoidance nents which may not all be electronic, and an understand- 6. Flight path stability augmentation ing of their functions usually requires consideration of 7. Improved flight handling qualities the whole system. Figure 1 illustrates a hypothetical sys- 8. Flight data recording tem for control of an aircraft about its pitch axis (i.e., 9. Collision avoidance pointing the “nose” of the aircraft up or down), which 10. Formation flying (military) would “boost” the pilot’s force output in moving an aero- 11. Target acquisition (military) dynamic control surface by a variable and appropriate 12. Secure identification (military) amount, depending on the aircraft’s flight speed. In this 13. Crew/passengers comfort improvement case “the pilot’s longitudinal sidearm controller motion 14. Structural load alleviation is converted into an electrical signal by a motion1 sensor 15. Terrain avoidance (Loewy, 2000). That electrical signal is converted to an 16. Noise reduction optical signal by an electro-optical transducer. Fiber optic a. Internal linkages carry the optical signal to a processor. After be- b. External ing transduced back into an electric signal, it is amplified 17. Suppressing servo-aeroelastic instabilities or attenuated there according to a second signal originat- 18. Performance improvement ing from an airspeed sensor ( this may be simple gain changes), so that the aircraft’s pitch response will be the It will be noted that this list is long, some items involve same at all airspeeds (assuming this is a desirable char- further breakdown (Items 1 and 16), and since such adapta- acteristic). The signal from the processor then regulates a tions continue apace, any attempt at completeness is likely valve on a hydraulic actuator, which drives the aircraft’s to soon be thwarted by new developments. For example, elevator, i.e., pitch attitude control surface. Several com- in-flight entertainment systems for commercial airliners ments may be pertinent for this illustrative example. The are not listed, but they could be considered avionics sys- electromechanical input valve on the hydraulic actuator tems. Their use is already commonplace and the services might be considered a transducer, but for our purposes they provide are growing by leaps and bounds. it is viewed as part of the actuator. Such an assembly is As implied by the order of functions in the list, often called an integrated servoactuator. Fiber optic link- the application of electronic devices to aircraft can be thought of as beginning with radios for communications 1 For illustrative purposes: side-arm controllers usually have force, (Items 1(a) and (b)), between aircraft crew members— rather than motion sensors. pilots, copilots,navigators, flight engineers, etc.—and P1: FHK Encyclopedia of Physical Science and Technology EN001H-913 May 8, 2001 14:54 Aircraft Avionics 321 FIGURE 1 Schematic of avionics components in a Fly-By-Optics (FBO) flight control system for the pitch axis. (From Loewy, R. G. (2000). “Avionics: A ‘New’ senior partner in aeronautics.” AIAA J. 37(11), 1337–1354.) ground crew members; among dispersed crew members With the advent of devices (so-called “control actua- of large aircraft—although this is more likely to use tele- tors”) capable of moving aircraft control effectors (e.g., phone rather than wireless technology—e.g., from the aerodynamic surfaces) reliably and as quickly or more cockpit of military aircraft such as bombers, on the one quickly than a human pilot, avionics systems could be hand, to the tail gunner via an “intercom,” for example, on used, not only to help the pilot and crew perform their the other; and (Item 1(c)) between flight crews of different missions but also to fly the aircraft safely. These automatic aircraft. systems are often referred to as Vehicle Management Sys- Later, what can be considered radio technology, i.e., tems (VMS). To emphasize the highly integrated nature transmitters and receivers of wireless EM signals, was ap- of VMS into the aircraft for which they are part of the plied to navigation (i.e., helping the pilot know where to control system—on an equal, flight-safety footing along go) and landing aides (i.e., helping the pilot to land safely, with airframe structure, aerodynamic shape and propul- particularly under reduced visibility conditions). In mili- sion systems—it is useful to think of VMS avionics as tary applications of aircraft, such “assistance” by avionics part of the host vehicle. As might be expected, then, for the pilot and/or other crew members was extended VMS avionics are not “added on” but are usually con- to acquiring and identifying targets; pointing, firing or sidered during the design or developmental stages of the launching weapons; countering—i.e., thwarting through introduction into service of a new or substantially modi- so-called “electronic countermeasures”—similar systems fied flight vehicle. used by