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Aviation History
1938
1938 - 0304.PDF
io6 FLIGHT. FEBRUARY 3, 1938. FLYING SPECIALISED LUGGAGE : One wayof overcoming the luggage accommo- dation difficulty. Specially built andfitted suitcases are designed for the production model of the C.W. Cygnetsome flying impressions of which appear on pp. 112-114. Topics of the Day Air Brakes AgainN OW that the good (01 bad) old days of the conven- tional biplane, with its coarse approach angle and capacity for indefinite sideslipping, appears to be numbered save for training purposes, it becomes more and more certain that real thought will need to be extended on the development of new ideas in flap gear. So far as the variable air brake is concerned mine is no longer a voice crying in the wilderness—that is, if the interest in this kind of device may be gauged from the way in which the subject has cropped up time after time in recent Royal Aeronautical Society lectures and discussions. The two primary needs in both small and large aero- planes are nigh lift for the take-off and high drag for the approach and landing. There is nothing new about this demand, but the layout of flying machines does appear to be so much in the hands of very superb test pilots and extremely conservative designers that there can be no harm in saying it all again. More important still, this high drag must be variable—and both safely and quickly variable at that. Some of the most modern transport aeroplanes possess flaps of an efficiency which, coupled with the effect of an unfaired undercarriage, make the approach angle tremendously steep and yet, once the flaps are fully down, it is not safe to lift them up again. In the aforementioned lectures and discussions various possible methods of achieving this desirable variation in drag have Deen put forward. There are quite a number of ways in which the matter can be tackled?iDut in the present state of design perhaps the most natural is to arrange the flaps so that a certain useful degree of movement towards the full down position can become solely of drag-varying interest, whilst the first thirty or forty degrees are con- cerned only with lift increase. Needless to say, whatever specially controlled movement is allotted to the business of approach adjustment, this must not be such as to change the lift characteristics of the aeroplane. Most of us know the feeling experienced as flaps of normal design are retracted suddenly when flying near the ground; the effect is that of losing about a couple of hundred feet, though, in fact, the loss is really quite slight. Nevertheless, the effect can be extremely dangerous with little speed to spare. Action .... AS a means of personal education I recently attempted torecord all my actions and my reasons for such actions while bringing in any flapped low-wing monoplane of unfamiliar type. By so doing I hoped to obtain a better understanding of the difficulties which were still experi- enced, particularly by the pilot who had been brought up 0x1 training bi planes with their capacity for making what in air traffic rules is alluded to as '' acrobatic landings ''—in other words, sideslips, swishtails and the various tricks which one invents on the spur of the moment in order to lose height and/or speed. My first action is to fly parallel to the leeward boundary at a height which seems quite ample for a motor- __j less approach, however steep. The •-Flight" photograph. throttle is then closed, the nose pulled up till the speed has been brought down to that at which it is safe to apply the flaps—and a surprisingly long time this can take with a modern type. Attempts at judging the approach angle, particularly in a strong wind, leave me at one moment with a feeling that the machine is going to sit firmly on the aerodrome bound- ary fence, and at another that it just not going to get into the aerodrome at all, this change of opinion occurring regularly throughout the approach and usually according to the slight variations in speed. Partly to assuage fears that a piece of undershootment is in progress, and partly to ensure that the motor (which is so often necessary as an assistance during the first ap- proach and landing with a strange machine) is still func- tioning as it should, the throttle is opened from time to time—or even left a little open during the entire approach. Only when the boundary has been crossed and the church spires, telegraph wires, housetops and what-not are well behind, is this throttle finally ignored and attention con- centrated on keeping the air speed at a constant figure. Meanwhile, again, the far boundary appears to be astonish- ingly near, though the landing is almost invariably made with a good two-thirds of the aerodrome still available. .... And ReactionM Y reason for flying alongside the leeward boundary is the obvious '' right-angle approach '' method of keeping this boundary in view the whole time without getting too close to it. The first danger concerns the need for pulling the machine up so steeply in order to lose speed without unreasonable delay. The novice might very easily overdo this and then add a fatal chunk of extra drag by pulling the flap-lever up with the nose still miles above the horizon. Although the better kind of modern low-wing machine has a particularly easy- going straight stall, especially when the flaps are down, the danger is present, and my first suggestion is that the speed which is customarily fixed as a limit for safe flap operation should be very much higher; in other words, 1 should be usual for the flaps to be applied almost as soon as the throttle has been closed from level flight. What may be called the speed-sink ratio of the modern aeroplane is quite pronounced, whereas in the old days machine rarely started to sink much before the actual sta • This characteristic tends to make the judgment of heig and distance more difficult, in spite of the fact that the "»» of flaps has steepened the natural approach an&!e' y] The danger here is, of course, that the engine migMj^ to pick up after undershooting, and, in any case, a £®? ^ forced landing must be a very hit-or-miss affair. TWS nlwavs fnrmftH +h« nrimarv rfiasnn for fflV derflanalway formed the primary reaso my safely adjustable air brakes. INDICATOR.
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