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Aviation History
1960
1960 - 0652.PDF
FLIGHT, 13 May I960 f:52 SYSTEM SURVEY Smiths Para-Visual Director The new system as installed in a Dove IN a paper first read at the 13th I ATA technical conference atLucerne, Smiths Aviation Division have revealed a revolu-tionary development in fiight-director instrumentation. Known as the Para-Visual Director, it is primarily the work ofA. M. A. Majendie, the Division's director of operational require- ments, and K. Fearnside, director of research and engineering,and is being demonstrated to IATA delegates in a de Havilland Dove. PVD consists of a series of helically striped ("barber's pole")rods which are viewed through long slits in their housings. When the rods rotate in accordance with commands from a flight-directorcomputer they provide a moving pattern of white diamonds which gives the pilot an instruction which he can perceive and followwithout directly watching the indicator. Three PVD indicators are arranged above the instrument panel just below the pilot'sline of sight, one athwartships and the others almost longitudinally on each side. When the flight-path is correct the indicators arestationary, but if the aircraft deviates in heading, the central direc- tor moves to demand a bank in the appropriate direction. If apitch change is required the other two indicators move in the direc- tion in which fore or aft control-column movement is necessary.PVD, which may be operated from the same flight computer as the autopilot, has proved effective both for manually controlledblind landings and as a direct monitor for automatics. While following PVD a pilot may directly scan a wide area—for instance,he may watch other instruments or look ahead for contact with the ground. - ... ... :. Typical display unit of the Para-Visual system PVD, probably the most advanced innovation in director instru-mentation, is to be fitted in the Airco D.H. 121. It has also been tried in helicopters and may find many other applications. Itoriginated from an attempt to overcome shortcomings in the con- ventional dial arrangement when this had to be used in actualpoor-weather operation. Traditional instruments have consistently failed to solve threeparticular operational problems: first, the difficulty of transition from instrument to visual flight after a poor-weather approach;secondly, distraction from instrument control caused by factors such as fatigue or keeping a look-out for other aircraft; and,thirdly, the monotony and inefficiency of using instruments to monitor automatic controls. This particular problem reaches itspeak during high-altitude, high-speed cruising in a jet transport, and in the final stages of an automatic approach, automatic flare,or automatic landing, on any type of aircraft. These three problems all stem from the same basic difficulty.Using traditional instrument designs a pilot sees only what he chooses to look at. The exception to this in the contemporary cockpit is the flashing warning light, but such devices have to bereserved for genuine emergencies because, under critical condi- tions, they can seriously distract the pilot's attention from otherurgent tasks. The problem is to provide flight-control intelligence withoutdiverting attention from other tasks and without preventing the pilot from looking freely about, either through the windscreen orwithin the cockpit, so that he can take appropriate corrective action from the information provided without serious interruptionof his other tasks. The solution produced by Smiths is the Para- Visual Director. Systems designed to feed information to the pilot when hisattention is directed at some independent task can be broadly classified into those that depend on visual information and thosethat do not. Any of the latter kind must be capable of providing angular attitude intelligence about pitch and roll axes, and mustalso be able to signal a malfunction condition. Fascinating pos- sibilities arise for the non-visual requirement; theoretically it wouldbe possible to employ the senses of taste or smell; but, unfor- tunately, the inadequacy of these senses in the interpretation ofangular errors rules them out at the start. Tactile—i.e., touch —information demands more serious consideration, but there areformidable objections—effects of turbulence, the need for per- manent and uniform physical contact with the source of signalintelligence, the difficulty of indicating malfunction, attenuation through clothing and the difficulty of relating tactile with visualinformation. Such devices as stick-shakers are not useful for primary flight control. Smiths have had considerable experience in the developmentof audio-airspeed indication but, unfortunately, there are serious obstacles to their application to overall flight control. First, it isextremely difficult to provide effective intelligence about the two axes required; secondly, audio intelligence over prolonged periodsis extremely tiring; thirdly, passive indication of malfunction under power-failure conditions is only possible if continuous noiseis present in normal use. Finally, the aural senses are already fully occupied with radio and intercom. For visual systems there are only two ways of providing thepilot with intelligence when he is concentrating on any point at random within his field of view. Either the intelligence is super-imposed by optical means upon his field of fixated vision, or adequate intelligence is provided external to the direct line ofsight but still within his general field of view. For the first method any optical projection system must inter-pose a reflecting transparency in the pilot's line of sight, but serious disadvantages are that it is of little use during manoeuvringor turbulent flight; that it is unusable when the pilot's line of sight is more than about 8" from the centre-line of the projective display,e.g., during lateral displacement or wind drift; that it is unusable when the pilot's attention is within the cockpit; and that indica-tions of malfunction are not inherently available, except to an attentive pilot. In addition, although ground and projection dis-play are within the line of sight of the pilot there is no guarantee that he will perceive both. Smiths have carried out regular auto-matic landing trials with such a system even during fog conditions, and have confirmed the opinions here stated. The last remaining solution is to provide adequate visual intel-ligence external to the pilot's field of fixated vision, but still within his general field of view; and the Smiths PVD does this. Testssuggested by Capt Majendie, and carried out by E. S. Calvert of RAE Farnborough just over ten years ago, showed that significantvisual clues were received by a pilot when landing from the dynamic pattern of the runway environment. It was also shown (Continued on page 655)
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