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Aviation History
1943
1943 - 1038.PDF
422 Topics of the Day FLIGHT APRIL 22ND, I943 Tricycles Then and Now How Ideas Have Changed with Added Experience of the Tricycle Type : Present-day Technique : The Advantages of the u Straight Running" Characteristic : Difficulties and Dangers AFEW days ago I came across an old reprint of anarticle which was penned—to use the Bramah man-ner—by this unworthy scribe in the days of " peace." There were only a few wars going then—markedly in China and Spain—and nobody was bothering very much about the ugly possibilities. The article was, in fact, about tricycles and their various advantages. It dealt with centres of gravity and direc- tional stability, and was, if I remember correctly, written soon after my first experiences with this type of undercar- riage on a quaint little machine known as theScheldemusch. At that time mine was the lesser of two voices crying in the wilderness on this distressing subject which, if then treated seriously, would have involved the most expensive drawing-board work before any new type of aircraft could be produced. The other voice has, unhappily, been stilled for ever—but not before its owner had had all the chance he wanted of trying out this type of undercarriage when fitted to the size of aircraft he had in mind when he wrote so vigorously and amusingly about this and many other aeronautical matters. It still seems curious to me that this country's designers haven't made more use of the tricycle system. With one exception in the medium and larger classes, the whole of the development work has been left to the Americans. Admittedly, it is difficult and even dangerous to start experi- ments on new lines when a country has its back to the wall and when all efforts must be directed to the job of producing more and more aircraft, even if these cannot have all the fads and fancies which might or might not be ultimately successful. When I wrote that article I named a number of advan- tages which have not turned out to be so veFy important, and I also overlooked a few disadvantages which may yet prevent this undercarriage layout from becoming universal. For instance, I stressed the ease of landing, particularly in the dark or in bad visibility, and suggested that shorter landing runs would be possible because the brakes could be applied firmly as soon as the machine was down. I believe I even mentioned that the take-c/ff could be short- ened by the simple expedient of getting up a certain amount of speed before turning into wind ! Aircraft in thoae days didn't require the same amount of concentrated thought before opening up ; imagine doing the "drill " while dash ing round the perimeter track at 50 m.p.h.! Two-point Landing's As it happens, the present technique, with both large and small machines, is to hold oiT as long as possible in the ordinary way and to keep the control column back while landing. The enforced tail down drag offers better " slow- ing-down '' forces than arty brakes can be expected to offer, and the whole process reduces both the load on the nose-wheel and the wear on the all-important tyres. Short- est runs are not made by placing the aircraft firmly on the deck and applying the brakes; good old-fashioned aerodynamic drag still leads the way. Of course, the tail cannot be held down after the main wheels have touched, but the idea is to lose as much way as possible before the aircraft lands, and then to apply brakes in little bursts as and when it is considered neces- sary. This applies particularly to fast-landing and heavy aircraft, in which the tyres and brakes are working very nearly at their maximum capacity. The important point is that, for instance, if the slowest landing speed (i.e., the ' slowest at which the aircraft can be held off the ground by use of the elevators) is 90 m.p.h., then the actual distance covered while reducing the speed from no m.p.h. is less when airborne than when dashing along in a " no-drag'' attitude with the tyres screaming. Needless to say, the bad-weather advantage is still there—a tricycle can be lobbed firmly on the ground at any reasonable speed when conditions necessitate such an action, but it is not the nor- mally recommended one or even the most efficient from the slowing-down point of view. The technicians may dispute the claim—and I must bow to their superior knowledge—but I.feel fairly certain, too, that a tricycle's take-off is better, wing-loading for wing- loading. From visual measurements, the actual load doesn't make a great deal of difference—a matter of a hundred yards or so between the length of "light" and "heavy" runs. The reason for this seems to be fairly obvious, and is the reverse of the landing picture. The very fact—lack of aerodynamic drag—which makes the tricycle's landing run somewhat long, makes its acceleration phenomenal. And load, except that it increases the necessary take-off speed by a few miles an hour, does not affect this accelera- tion to the marked extent that it affects a machine in which the tail must be forcibly lifted and held up. I've often wondered how much power is used in that antediluvian process. Tricycle Steering From the pilot's point of view the real joy of the tricycle is the way in which the aircraft runs straight on the take-off and after landing. In that article I talked a lot about the "natural" anti-swing properties of the tricycle, both in the ordinary way'and in cross-winds, and tried to explain it all with the aid of little diagrams. We won't go into all that now—even if I were capable nowadays of such an effort of reasoning—but I never realised then quite how important this straight-running characteristic could be in aircraft quite a little heavier and more complicated than those I used to fly in the years of peace. In the very best of multi-engined "conventional" air- craft, the process of getting the tail up and keeping the thing straight during the take-off run involves an enormous amount of juggling with rudder, brakes and throttles. With a cross wind tending to head the machine in the direction in which it is already, by reason of torque, trying to swing, it is not unusual for the outfit to be half-way down the runway and nearly airborne before it is possible to bring up the power of one or other of the outboard engines. And how often, even in well-behaved medium-sized twins, has it been necessary for us to pull one of the throttles sharply back for a second in order to check a swing which has been allowed to get out of hand? The tortuous movements of one's throttle hand must be a source of amazement to the uninitiated, who probably imagine that it is all a kind of " line," like the continuous jagging of the wheel by certain pseudo-racing motorists. With modern self-centring tail- wheels, the landing process isn't quite so hectic, and most machines run fairly straight unless and until they develop a really startling swing—and then nothing but Providence and a good strong undercarriage will save you. It is the pilot's job to prevent that swing from even starting—hence his itching brake-thumb immediately after touch-down. None of this worries the triryde driver. One has a few seconds of initial unfoappincss while, with bursts of engine and touches of brake, the pirouetting nosewheel is finally straightened out. Once the machine is running true, the two or four throttles can be opened to maximum boost
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