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Aviation History
1942
1942 - 0294.PDF
/ Topics of the Day FLIGHT F\J BRUARY 5TW, I942 STALLABILITY^°e ) Do Landing Speeds Matter? : Strange Effects of High Wing-loadings Increasing Lift at Low Speeds I F there is one thing that the average stooge pilot of pre war days has learnt during his or her wartime excur sions, it is that high stalling speeds make little or no difference to the actual difficulty or otherwise of learning to fly. The idea that it is intrinsically more difficult to land an aircraft at 70 m.p.h. than at 35-40 m.p.h. was commonly held at one time ; in fact, once flying and the essentially more difficult business of approach judgment have been mastered, the faster the landing speed the easier ••everything is—because the machine is so much less affected by odd variations in atmospheric structure and, once down, tends to remain where it is—at least in the up and down plane. Floatability Needless to say, it is originally necessary to learn to fly on slow types because the novice—and the instructor— need so miich more time and space for their respective struggles. Floatability " is a very great asset in trainers because it gives both the teacher and the taught time to discuss things in comparative leisure and safety, while sheer slow ness allows a vast margin of error during the approach —-»nd so saves training time. If the pupil were put straight into something of the Master calibre, he would not on, have to cope with a lot of devices, but would als< allowed about one landing attempt in three, and th^*tim wasted would be tremendous, but he mighty onceyTie ha recovered from the shock of sheer power/and isize, fin the outfit very much more easy to put down thjan akTigi Moth. I have never been one of the "we maniacs. Even in light aircraft days affair which was still ballooning abo •-m.p.h. or, less. Even on calm days A thing of a menace, and on gusty dfyk almost uncontrollable near the dack;. machine which* stalled quite firmly Ian in the region of 50 m.p.h.—high enough craft a practical proposition on windy days it from trailing wing tips and things go entirely- according to plan. ust land slow! always 1»ated ti in the av at! e thin of po»e, Jfcj#as prerStfed the ,ly at %. speed akeithe air- **to prevent if everything didn't Tricycle Stalling Now I should prefer the figure to be 60 m.p?rr.-=witn a tricycle undercarriage and/or enough drag to bring the —*peed down rapidly after landing in comparatively small spaces. Unless and until somebody invents a fully variable wing—-so that a Jekyll and Hyde machine is a practical affair—the "aircraft for all," which can be flown from the backyard, is not very likely, though a good deal may still be done with the auto-rotating wing provided the blades can be so controlled that, at a critical second before touching, every atom of excess lift can be entirely removed. But that is where the tricycle comes in with more rational types; as soon as the main wheels —have hit the ground the whole thing tips on to the nose wheel and remains forcibly dowrn in an attitude at which the stalling speed is higher than anything likely to be encountered in gusty conditions. So a very slow-landing device might be a practical possibility if it were fitted with this type, of undercarriage and if it were otherwise so efficient that it would cruise at a useful speed and not sit about in the sky going nowhere whenever the wind was blowing at more than a mild breeze. I remember setting off in a Drone, or some similar machine, to go to an airfield •—which was only about 30 miles away. Unfortunately, the airfield in question was directly up-wind, and after remain ing pointed in the right direction, but with the place of departure still in view below the centre-section, I gave it up. After this war, in which most of us have been flying aircraft with a cruising speed of 200 m.p.h. or more, we shall be very impatient indeed if we have to loiter around making a ground speed of 50 m.p.h. or less. I think we shall prefer to take the minor risk of engine failure and forced-landing crack-ups to the pain and anguish of travel ling at the speed of a motor car. Engines very rarely pack- up completely and suddenly, and there will be a host of airfields at our disposal until the runways crack after successive years of frost and lack of attention. Some of these airfields are not in very useful places, but they will be good enough for forced landings due to weather or to any other cause. Of course, there is a reasonable limit to rational wing- loadings, especially where small aircraft are concerned, and this will be so until some bright person devises a new and ingenious series of wing sections to suit such loadings. Everything seems to be all right until figures higher tha»- 40 lb. /sq. ft. are reached; above that figure some \fc|y queer things begin to happen. So far, stalling characlB* isiics are not showing signs of becoming more dangerous, Sut most of the machines with very high wing-loadings ^appear to start an initial stall at speeds, some 50 m.p.h. higher than the actual stall as written in the book of words. Underpowered Hens ThlJt is possibly a characteristic of certain wing sections only, bmt I have noticed it on two entirely different types. The curiosity is so marked in one of the types that it is [possible to lose several hundred feet during a final circuit, aid while fiddling about inside with undercarriage controls and sunflry other little matters. If, due to poor visibility For other!causes, this circuit is being made at 500 feet, the newcomer, after reducing speed and lowering the under- carriagf, may look out to find trees going past the win dows./ Needless to say, it is possible to stop the sink »y h*sting the aircraft on its tailplane and flying around with/the outfit looking rather like an underpowered hen; 'the attitude feels all wrong and therefore, I think, is f wrong. The ideal cure is to lower the flaps by a«- lount sufficient to increase the lift and to supply enough irag to make the attitude more normal. In fact, I think r that the lowering of flaps, almost before the undercarriage, for the whole of the final circuit is a good thing. Control is greatly improved and the aircraft feels much more normal at comparatively low speeds. If we are to think in terms of phenomenal loadings will be necessary to develop still further the type of flarT' which really increases lift to a very marked extent. I have never felt that sufficient energy has been devoted to the-' development of such extra-lift devices. Most people will remember that on the first type to be fitted with the Fowler flap—the Lockheed 14, now the Hudson—most of the high-lift advantages were lost because the slipstream and/or the airflow bounced off the ground on to the tail- plane when the flaps were lowered and they could not, therefore, be successfully used to shorten the take-off run. Bounce Effect In fact, there was, at one time, a tendency to use com paratively little flap on this type, even for landing, because, I believe, the "bounce" effect of the air trapped under the large flap area made landing more difficult. Pilots would rather use more field than to use full flap and risk a '' short one '' which might not come off properly—and a bad landing with this type certainly resulted in the most extraordinary series of leaps and bounds. I have no knowledge of the technique employed by real Hudson pilots—I am merely talking from the small personal experiV/ ence gathered while ferrying the type, light, from place \o place. I repeat—with higher wing-loadings people will reallx have to get down to the development of useful lift-increas ing devices, war or no war and tricycles or no tricycles. INDICATOR.
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