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Aviation History
1947
1947 - 0714.PDF
FLIGHT MAY 8TH, 1947 BUND-APPROACH PRESENTATION Stereoscopic Range Indication Combined with Essential Flight Information A RECENT article by " Indicator" (January 27th, 1947) in-cluded some apt and outspoken comments on the subject of blind- approach systems and their unnatural methods of presentation of informa- tion to the pilot. The author;*who is in full agreement with "Indicator's" views, has for some time past been working en the design problems asso- ciated with this question, as there is no doubt that there exists at present a definite need for a more natural and compact method of presenting to the pilot all of the information he requires during a blind approach. In evolving the system which this article describes, an attempt has been made to approach the problem from a new angle, by first endeavouring to determine the optimum method of presentation from the pilot's point of view, and then trying to adapt this method for satisfactory operation by the energy recovered from the appro- priate signals radiated by the trans- missions from existing B/A systems. In the following description the essen- tial items of information required during a blind approach are dealt with separately in the following order: — (a) Range from estimated touch-down point, (b) Position in the beam, (c) Airspeed. (d) Height above ground level. Clearly, a normal daylight landing carried out in good visibility is effort- less for the pilot because be obtains continuous and co-ordinated informa- tion relative to range, height and plan-position, through the medium of 'natural stereoscopic colour vision. For this reason, any system intended to provide similar information during a blind approach should endeavour, as nearly as possible, to present it in a similarly natural manner. Unfor- tunately, a radar television picture of the approaching runway, presented in colour with full stereoscopic effect, is not at present a practical proposition, owing to the weight of the necessary airborne VHF equipment and to the relatively poor definition of the picture. Continuous Rang-e Presentation If one considers an aircraft operat- ing on a clear, calm day, making a series of practice approaches down the B/A beam to an airport runway, it will be apparent that, provided the machine is always flown accurately down the centre of the beam, the actual physical details comprising the view of the approaching runway as seen from the pilot's seat will be iden- By MAJOR G. H. PARKES tical on each occasion ; the only quan- tity capable of variation is the apparent rate of approach. Let us suppose that a miniature cinemato- graph camera, designed for stereo- scopic photography in colour, is fitted in the nose of this hypothetical air- craft, and that a film record is made of a " perfect " beam approach. When this film is run through the projector of a stereograph viewing apparatus, an observer will receive a startlingly real impression of being seated in the nose of an aircraft during a daylight approach down the beam to the par- ticular runway of the airport in ques- tion. Furthermore, by varying the speed at which the film is being run through the projector, the observer will automatically vary the speed at which the runway appears to be approaching him. I AST week our contributor "Vertigo" •" stressed the importance of not over- looking the vital link between the dashboard and the controls—the pilot. He drew attention to that dangerous moment when, after a long flight, the pilot suddenly has to shift his attention to a totally different set of indications for the let-down and final approach in bad weather. The author of the present article suggests a scheme which, if proved practical, will provide the pilot with an artificial but highly realistic view of what he would see if he were making the approach in perfect visibility. Here, then, is a possible solution to the question of how best to present continuous range information in a natural manner, for it will be appre- ciated that, if means can be contrived whereby the speed of operation of the projector motor may be placed under the control of the range signals trans- mitted by the particular B/A system, it becomes possible .for the indicated range to be kept in step with the actual range throughout the period of approach. To make this point clearer, it is con- venient to consider the case of a pilot and co-pilot seated side-by-side in the cockpit during a practice beam ap- proach in daylight. Imagine that the pilot looks straight ahead, through the windscreen, at the runway, while the co-pilot looks through the eyepieces of a small and compact version of the stereograph viewing apparatus, through the miniature projector of which is passing the film of a previous daylight beam approach to the same runway. Under these conditions the details of the view,of the runway pre- sented to both the pilot and co-pilot will be the same. If we further assume that, at the moment the film started to move through the projector, the indicated range as seen by the co-pilot is syn--4L»- chronized with the actual range as seen by the pilot, and that thereafter the speed of operation of the projector is so controlled by the B/A transmis- sion signals that the indicated range remains always in step with the actual range, then under those conditions there will be nothing to choose between the indirect view seen by the co-pilot as distinct from the direct view seen by the pilot. When, therefore, visi- bility is such that no direct view of the runway is possible, the pilot may use the indirect but equally natural view of that same runway afforded him by the stereograph viewing apparatus. In practice, the realization of the conditions assumed in the preceding paragraph is not such a difficult prob- lem as may at first be supposed. It is not, however, intended at this stage to describe the method of control evolved, as the successful operation of the system depends upon the accuracy with which the aircraft is held in the centre of the beam during the period of approach, and this brings us to the next item on the list, namely, informa- tion relative to the position of the aircraft in .relation to the centre of the beam. Position in Beam An average person, visualizing in his mind a picture of the beam formed by, for example, the glide path and direc- tional transmissions of the SCS.51 sys- tem, sees it as a cone of small included angle, extending from the touch-down point out into space, over and beyond the end of the runway concerned. This is a useful picture to have in mind, the only unnatural point about it being that the cone is not in fact visible. But supposing it were visible and that, so long as an approaching aircraft remained within the cone, the pilot could see a clear picture of the airport and runway ahead, although the visibility everywhere outside the cone was ten-tenths. Would a pilot have any difficulty in effecting an approach under these conditions? No, because if his aircraft swung off-course to port or starboard, or if it climbed above or sank below the edge of this imaginary cone of vision, the fact would be made known immediately to the pilot by a progressive "blacking- out " of his field of vision, originating
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