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Aviation History
1946
1946 - 0608.PDF
FLIGHT MARCH 28TH, 1946 Night by Day Semi-synthetic Night Landing and Instrument Flying Training : The " Day'Night" Scheme : Sorting Out the Spectrum ORIGINALLY developed during the first two yearsof the war so that the necessary flare-path landingtraining could be speeded up and its hazards re- duced, the " day-night " instructional system is now part of the normal training curriculum of the Royal Air Force. Whereas it was then vitally necessary to devise means by which night-flying training could be continued through the longer and safer daylight hours, the system was found to be so satisfactory, at least for initial training, that it has found its place in peace conditions. A year or two ago a somewhat similar American syn- thetic night and instrument training system was described • in Flight. At that time our own system was still on the secret list, and it was impossible, even for those in the the pupil wears special goggles and is only able to see the sodium lamp flarepath and his sodium-lit instruments; (2) the Two-Stage (Flarepath) or Two-Stage Brown Scheme, in which all but the light from the flarepath and instruments are cut off in two stages for the pupil; (3) the Two-Stage Blue Scheme, in which the aircraft is fitted with pale blue screens and the pupil wears amber goggles; and (4) the Two-Stage Amber Scheme, in which the colour positions are reversed. Schemes 3 and 4 are used solely for instrument-flying and night-navigation training. Before enlarging on the features and objects of the four different schemes it will be as well to deal, first, and as simply as possible, with the basic principles. As everyone knows, normal daylight is made up of a combination of The inside and outside world as it might be seen by the pupil (left) and the instructor (right) in an Oxford, arranged with theTwo-Stage Blue or Amber equipment. With the latter arrangement, the interior would appear blue to the pupil and all outside vision would be removed, while, to the instructor, the interior would appear quite normal while the outside world would beamber-coloured. know, to explain that the whole idea had really been borrowed from this country, where it was the direct result of "backroom" work by Sqn. Ldrs. A. W. and C. H. Wood—the former an R.A.F. instructor, and the latter, then in civilian life, a technical photographer. Variable Conditions It should perhaps be explained immediately that the un-tidy compound word " semi-synthetic " is used in the sub- title for a reason. Unlike the methods of training whichhave variously appeared with the adjective "synthetic," " day-night " flying training, though only imitative, as thecase may be, of night or instrument flying conditions, is carried out in the air and is, therefore, only partially syn-thetic. In fact, and for all practical purposes, the condi- tions which can be provided during '' day-night'' instruc-tion are more useful from the training point of view than any which can be obtained naturally, and they can,furthermore, be modified to suit the particular capacities of and the training stage reached by any pupil. In theordinary way, it might be necessary to wait many weeks for these conditions. There is, in addition, the consider-able advantage of greater safety, since the instructor is not himself flying under night conditions and can prob-ably judge the pupil's aptitude and incipient errors more accurately. There are four different " day -night" ftying schemes inuse: (1) The Single-Stage (Flarepath) Scheme, for which colours which can severally and collectively be cut off bythe use of filters of different colours. For instance, the use of a green filter prevents any but very small propor-tions of the other colours from reaching the eye. In the same way, two separate filters may be superimposed sothat one will cut off certain colours, while the other will deal with some or all of the others. By suitable experi-mentation it is possible to develop two niters which, though giving adequate working vision when used separ-ately, will also entirely cut off all visible light when they are superimposed. *Complementary Filters Two such "complementary" filter colours are blue andamber. Whereas the particular type of blue used in the "day-night" scheme will cut off all but the red, green,blue and violet of the spectrum, the amber will cut off all but the orange and yellow. At the same time there isadequate visibility through each of the niters for all nor- mal purposes, yet the two together can cut off almost theentire spectrum. This fact forms the basis of schemes 3 and 4 designedfor instrument training. With the Tv/o-Stage Blue system the aircraft screens, side-windows arid roof are coveredwith blue filter material, while the pupil's goggles have amber filters. The instructor is able to see the outsideworld normally, though with a bluish tinge which soon becomes familiar, and the pupil is able, since unfiltered
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