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Aviation History
1954
1954 - 0075.PDF
FLIGHT, 8 January 1954 35 INSTRUMENTATION by REFLECTION A New Approach to the Design of Aircraft Instrument Panels DURING the past forty years the number of instruments facing an aircraft pilot has increased alarmingly yet inevitably. The fact that this trend has been accompanied by increases in landing speeds and decreases in weather minima has emphasized the problem of the time factor in pilots' vision. The time taken to re-focus the eyes from instrument to visual flying, and to read and act on instrument indica tions—previously a comparatively short period —is now of extreme importance. There have been many attempts to reduce "eye acrobatics" and eye travel while scanning instru ments, by combination or re-rpositioning, and by the separation of essential flying instruments from others such as engine-monitoring instruments. One notable achievement was, of course, the R.A.F. wartime standard blind-flying panel, while recent trends have been towards the combination of several indications on one dial. We have recently received details of a novel approach to instrument presentation put forward by Mr. O. W. Neumark, who has for some time been interested in the design of aircraft instrument panels. The basis of his suggested scheme is the principle that while the pilot is flying on instruments his eyes should be in long-range focus. Briefly, this would be achieved by the use of collimating lenses and reflec tors—an extension of the reflector gun-sight principle. Although existing instruments could be viewed with advantage by this method, a marked improvement would be obtained, it is suggested, by basically re-designing the main flight and engine instruments. Details of Mr. Neumark's thesis are given below. General Principles.—The basic aims of the system are: (1) The area of instrument indications to be scanned by the pilot's eyes should be greatly reduced, eliminating the eye acrobatics necessary to scan present-day instrument layouts. (2) All instru ments should be viewed with the eyes of the pilot accommodated and focused at infinity. (3) All instrument indicator movement should be capable of being seen and interpreted by wide-angle (parafoveal) vision when the image of the central instrument is in direct focus (on the fovea centralis). This requires that indi cated movement should be rationalized, that indications and lubber lines should have a definite thickness, that interpretation should in most cases be based on indicator position (as opposed to reading an exact value), and that light-intensity coding should be used to define operating limits. The proposed method of achieving these aims is to view the instrument through collimating lenses and reflectors, the images becoming visible to the pilot as red or orange reflections on a black panel which is effectively a continuation of the windscreen into the cockpit. Thus, the "background glare" which sometimes interferes with reflector gun-sight indications should not prove troublesome. The principle is shown diagrammatically in Fig. 1. As the image of the instrument face after passing through the collimating lens is effectively "at infinity" (the emergent light rays from the lens being parallel) no re-focusing of the pilot's eyes is necessary when viewing the panel. As mentioned, it would be possible to view existing dial-type instruments by this method. The ideal arrangement under Mr. Neumark's scheme, however, would involve a re-designing of the main instruments. By replacing the movement of mechani cal levers inside an instrument by that of optical-mirror levers (as has already been done in the miniature flight-recorders made by the French firms S.F.I.M. and Beaudouin) it is probable that instruments can be made more efficient and less delicate. To take full advantage of the optical-lever principle, the standard clock- type instrument dial would be replaced by a vertical scale along which would move a narrow beam of light. This presentation would help considerably in reducing the total area of the instrument display. By using the proposed system, it is claimed, the psychological conflict inherent in instrument-flying training would be elimi nated, for the pilot never stops looking outside the cockpit, and the subjugation of the sense of balance is made easier. "Outside" is meant only figuratively, since no binocular eye-convergence or accommodation for near vision is required when viewing the instruments. The greatest advantage claimed for the system is that there would be no time-delay at all for refocusing one's eyes during the REFLECTORS Fig. 1. A diagrammatic view of the proposed installation. The indications of the main instruments are reflected through collimating lenses on to a black reflector panel. The main advantage is that the pilot views the panel with his eyes in long-range focus; what he sees is shown in Fig. 2 overleaf. transition from instrument to visual flight during bad-weather approaches and landings. This delay, referred to recently by Mr. E. S. Calvert, B.Sc, the approach-lighting expert, as the final "time barrier," can be overcome only by a system such as this, or by approaching at speeds of 30-50 m.p.h. The reflector gun-sight was adopted years ago because the time required for refocusing on target, fore-sight, back-sight and target again was too long during the brief seconds available during an attack. Exactly the same principle—"indications at infinity"—will, it is claimed, eliminate almost entirely the time delay of the transition period from instrument to visual flight, and also remove many causes of present-day mid-air collisions. Another advantage of the "instruments at infinity" concept is seen in the case of stratospheric flying, where pilots have found great difficulty in seeing and focusing their eyes on other aircraft. The images on the instrument panel will help to force the pilot's eyes to remain in long-range focus, while a further means of ensuring this would be to project in the same manner small crosses of light at intervals on to either side of the actual cockpit canopy, again to force the eyes back into focus should they become unfocused during sky searching. It is appreciated that human eyesight by itself is insufficient for stratospheric combat and must be extended by radar; nevertheless, full use of the eyes must be made, even if only to monitor automatic radar systems. Unless all indications are at infinity, exactly the same time penalty occurs in the stratosplfere as is encountered during the final approach change-over from instrument to visual flying in bad weather. A Suggested Layout.—For a hypothetical single-seat twin- jet aircraft, the instrument presentation shown in Fig. 2 is suggested as a possible layout. The central image is that of a combined artificial horizon, turn-and-slip indicator and directional gyro. The first two of these three have already been combined in the wartime Horn instrument, generally found preferable to separate dials by many pilots. To this combination is here added the indication of the directional gyro either by optical combination from a separate instrument or by mechanical combination in one instrument. The instrument shown is based on the HL 5 or HL 6 artificial horizon, indication being "natural" as opposed to inverse sense movement. A completely "untoppleable" artificial horizon would be preferred if available. The angle-of-bank indicator of the HL 5 or 6 has been omitted here, but could be included. The logical position for directional indications would be along a 90 deg arc at the top of the circumference of the horizon indicator or, if relative radio bearings were required, on a complete annulus around the horizon (as shown in the diagram). Radio bearing markers are reflected on to the central image and move around the annulus, there being no needle visible from the centre. The rate of turn indicator is at 12 o'clock, as in the Horn horizon. It is immediately below the heading lubber-mark of the directional indicator, which is also the central lubber-mark for the rate of turn. This is believed to be an original combination and would greatly facilitate accurate course keeping. The slip/skid indicator is at six o'clock as on the Horn horizon. It is of ball type but could, of course, be a pendulum. The remaining instruments on the main line oh either side of
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