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Aviation History
1946
1946 - 0611.PDF
MARCH 28TH, 1946 FLIGHT 313 NICHT BY DAY dayligbt is available for interior illu- mination, to see all the instruments and controls but has no appreciable vision beyond the blue windows. In the Two-Stage Amber scheme the positions of the colours are merely re- versed, though the spectroscopic pro- perties of the colours actually used differ considerably, for very good reasons, from those used in the Two- Stage Blue scheme. The amber screen scheme is now being standardized, since the use of this type of filter for the screens gives the instructor improved visibility in typical English weather conditions, and is not quite so prospectively de- pressing during long periods of flying. The blue screen is more suitable for semi-tropical conditions in which the natural visibility is good and in which amber might produce an unbearably "hot" psychological effect. One slight advantage of the blue scheme is that the pupil is better able to read maps during '' night'' navigation exercises through his amber niters than through his blue filters. In each case the screen colours have been carefully adjusted so that the green and red Aldis or Very signal lights can be seen correctly by the instructor. These two schemes have been dealt with first because the theory of their application is more easily explained and understood, but the original "day-night" system for flarepath landing practice has been that most used and useful for night-flying training. In this Single-Stage scheme use was made of particular properties of sodium-vapour iamps which emit an almost entirely monochromatic light between the orange and yellow bands. By using a special filter—which may be approximately described as being a compound of greenish and reddish browns—all the colours in the spectrum except that emitted by a sodium lamp can be held up, yet this particular light can be seen through the filter in almost its natural bril- liancy. If the pupil wears goggles in which this special One of the two types of goggles wornby the pupil for Single-Stage Flarepath training. The latest version hasimproved ventilation and a weight- reducing headband. A hinged supple-mentary filter and a sun shield are incorporated. Signal-flashing sodium lamps at the end of the runway are used to giveapproach guidance since the pupil is unable to see normal colour lighting during his flarepath training. Operator's aircraft sighting table on right. filter is used, and if the instrument board and controls can be lit by a sodium-vapour lamp, he will see only these instruments and controls and the sodium flarepath. Consequently he v^ill, in effect; be flying in pitch-black outside conditions relieved only by the lights of the flarepath. The instruc- tor, meanwhile, is able to see quite normally and can carry on with in- struction in weather which might be quite impossible during genuine night- flying operations. The normal arrangement of the sodium flarepath consists of eight lamp units, six of them facing the direction of approach, with duplicates at each end turned at right angles to the others to give the pupil an indica- tion of the position of the flarepath while making a circuit. Since coloured approach-indicator lights can- not be seen through the pupil's filter, special arrangements have to be ma4e to give him the necessary approach- angle guidance. A sodium lamp at the approach end of the runway is fitted with a series of shutters which can be mechanically set in motion to give signals which can best be described as quick-dot or slow-dash at the wish of the opera- tor. This operator watches the approaching aircraft through a grid-wire sighting device which tells him whether it is below or above the correct approach line. If it is below the line he signals quick-dots and if above he signals slow- dashes. Practical Limitations The Two-Stage (Flarepath), or Two-Stage Brown scheme, might have had a wider application had it not been for the fact that the filters must necessarily be of too dark a shade to be used separately for normal flying. Conse- quently, it is applicable only to tandem-seater aircraft— and it is just these aircraft for which the Single-Stage scheme cannot be applied because of the weight of the equipment necessary for instrument lighting. This system —in which the dark green screen (in a light-proof canopy) is seen through red-filtered goggles to produce the all-but-sodium black-out—was, in fact, the first to be demonstrated in the early days, but its limitations caused its development to be put on one side. With the normal amount of natural light directed through louvres in the canopy, the pupil can see the instruments through his red goggles, but is, through the screen, unable to see clearly anything other than the flare- path. For peacetime training the one outstanding advantage of the scheme—and apart from any cost or risk considerations—is that, by using different combinations of filters, the effective outside darkness can be modified to suit condi- tions of training. These combinations must also, of course, be varied to suit different weather and seasonal light conditions. Since it would obviously have been unsatisfactory to allow all the different. training units to carry on without supervision and help—and while possibly failing to make the best use oi the system—all development and supervision work was handed over, at the end of 1942, to the Empire Central Flying School. Here, in structional methods and suggestions are checked and special explanatory courses ar*> given bv the Day-Night Section
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