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Aviation History
1958
1958 - 0659.PDF
PLIGHT* 16 May 1958 675 Three tense moments in the fully automatic, 200 m.p.h. touch-down of one of the North American X-10 unmanned research rehicles. Its auto- matic round out system was designed by Autonetics and reduces a descent at 65H/sec at 500/t to about 4H/sec at touchdown. PRECISION APPROACH Next Step: Automatic Touch-down THERE is no doubt that the development of a reliable andsuitably simple automatic-landing system for civil aircraftis one of the major missing links in the road to true all- weather operation by civil airlines. Automatic approaches are now routine, but a break-off height of about 200ft is still mandatory. This is not to say that a successful touch-down and ground run have not or cannot be achieved with the present combinations of I.L.S., autopilot and approach coupler, but it is a "hands-oil and blind faith" technique of which the engineers do not wholly approve. To make automatic landings routine, some way must be found of guaranteeing accurate azimuth guidance at the final stage and of accomplishing a satisfactory round-out. Azimuth guidance less critical than that of the final stages of the I.L.S. localizer is needed; and the whole system must be tied-in with autopilot characteristics suited to the required precision of manoeuvre. Since automatic landing postulates occasional touch-downs in zero visibility, the automatic phase should be continued through the landing run and at least up to the point of clearing the runway. Automatic throttle, braking system and ground steering control are therefore also required. Throughout this time the pilot must be able to ascertain beyond all reasonable doubt and be confident that he will in fact touch down at the right point and be moving in the right direction. If, as at present, the touch-down must be completed under manual control a certain finite time must be allowed for the pilot to make the transition from instrument to visual flight. He must positively recognize the visual references (usually patterns of approach lights up to 1,000 yd from the threshold), correct any errors in attitude and lateral position and then make the actual touch-down. Recent researches into this process have shown that the time allowances, translated into terms of critical or break-off height, cannot well be reduced below 150ft and that there must be 500 yd slant visibility. Even this leaves little or no room for mistakes. With D.M.E.-type aids such as BABS/Rebecca, these limits have to be doubled. The accuracy of an instrument approach can, of course, be very greatly increased by the use of a Zero Reader flight director or one of the integrated instrument groups, either under manual control or coupled to the autopilot, but this tends to improve the position at the present break-off height rather than reduce the break-off height itself. It seems that the only way of bridging the gap between present break-off height and touch-down is to make this whole phase fully automatic. Several methods have been tested both in Britain and the U.S.A. For some years the Blind Landing Experimental Unit at Martlesham Heath, and at R.A.E. Bedford, have been working with magnetic leader cables buried in the ground either side of the runway and extending some 1,500 yd beyond the threshold. These give a signal proportional to lateral displacement from the centre-line to an accuracy of five feet and provide directional information between the break-off point of an automatic I.L.S. approach and the beginning of the ground run. The reduction in rate of descent from about 12ft/sec on a three-degree I.L.S. The Pye, Ltd., I.LS. system as adopted as standard by the HAJ. and installed at many civil airfields. The localizer beam is transmitted in one direction only from a parabolic aerial system. GLIDE-PATH TRANSMITTER SITE FOR OFFSET LOCAUZER TRANSMITTER LOCAUZER TRANSMITTER
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