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Aviation History
1944
1944 - 1120.PDF
584 FLIGHT J UNE IST- J944 Indicator Discusses Topics of the Day Approach Attitudes \n — and the Effects of the Modern Technique on Landing Characteristics: The Need for Qreater Clarification During Advanced Training : "Mushing" Manners and Methods : Unqualified Variations DESPITE all that was said in these columns a few weeks ago about "learning to walk before we can run" where really big aircraft are concerned, it is an interesting. fact that pilots very quickly fall into the way of things when new and faster types are produced, each with special characteristics of its own. And for that we.have, in large measure, to thank the designers. If any one of these present-day aircraft—with landing speeds well over the hundred mark, and approach speeds of the orderpf airline block-to block averages of the year 1938— suffered bad and difficult habits near the stall it would indeed be a very different story. There is nothing intrinsically more difficult about judging an approach at 150 m.p.h. and a landing at 115 m.p.h., than there is in approach and landing judgment at half these speeds. Always provided there is enough_,je©m te, allow for the slight variations in technique^—variations which only made a difference of 50 yards,.-m the old daysi but alter the run by anything up to 300-yards now. Give» adequate space and good characteristics, a 115 m,njn landing presents no particular difficulties—it isS.inirMy' that any accident is mdre than jfroportionately s^rrcBs. The mildest swing removes tee upderparts if iy is not checked in good time;/ any uncorrected ^er-j shoot generally means a write/off; Jind the ^iWf^pthjf of the flap operating gear or tfe batkes u^u^UfTnyc^ar a belly landing if no two-mile rtmw/ys\ara a\lmablejjr the vicinity. Pilots must be mora carefulVrSdJpore ofrefuily trained, so that the now greatlV exaggerate*?! enjrfs are the exception rather than the rule.X r There is, however, one characteristic common to mauy modern types which is not, I feel, sufficiently well explained or understood by instructors and experienced pilots respec tively. This is the vital importance of attitude during the last part oi the approach and, Jo a less important degree, during the take-off and initial climb. Old-time Attitudes In the old days any aircraft would take up a fore-and-aft attitude in almost direct relation to the speed of approach or climb. One was given a " best" climbing speed and a . " safe " approach speed, and everything went according to plan if one stuck, within reasonable limits, to these figures. Later on, as the pilot got to know his aircraft, he could invent his own variations—but these variations always involved a change of speed as well as of attitude. Now, with certain wing sections, high loadings, and the customary rumble approach, there is a rather different story to tell. Anywhere within 30 m.p.h. or even more, of the actual stall during a motoring approach, there seems to be little connection between speed and fore-and aft atti tude, whether the flaps are up or down. This " sinking " or '' mushing'' peculiarity is more~pronounced on aircraft fitted with camber-changing rather than with split-type flaps, but I noticed it first in two highly loaded types which were each fitted with split flaps. In each case I found that from exactly the same approach speeds and in the same weather conditions the landing could be either normally " floaty" or straight off the approach and some what heavy. The air-speed indicators were checked and found to be correct, so I put the trouble down partly to poor handling on my part, and partly to the probability that the aircraft had, unknown to me, greater all-up weights. One aircraft was a fairly unconventional fighter of which I expected to see no more, and the other was a really big affair with which I made a mental note to use more power during the last stages of the approach and otherwise forgot all about it. Although I have only realised it since (while flying two types of aircraft having this "mushing" characteristic to a pronounced degree) the fact was that in each of the land ings I had allowed the aircraft to sink into the ground— the fina! checking motion on the control column merely aggravating the effect and producing a " G" stall at a speedy still higher than that at which the type normally lost its capacity for flying. Incidentally, the "mushed" land- lngJmust not be confused with the heavy landing—some times on three points—caused by checking too violently a# the last moment. Any modern aircraft with a reason ably high wing-loading and good slow-speed elevator con trol can be given a momentarily higher stalling speed by over-zealous checking and a consequent temporary increase in wing-loading. The effect is merely a minor example of .the sort of results obtained by any ham-fisted aerobatic pilot who, even with a fairly good aircraft, will flick off the top of a loop or spin off a tight turn at quite astonishingly Siigh indicated airspeeds. Engine On and Off Since the aerodynamic experts will tell me that, what ever the loading and wing section, there must be a con nection between speed and attitude, I will forestall them by giving the probable explanation. Every high-efficiency aircraft must, to some degree, be brought in under power, and the use of engine upsets all the calculations, because in any aircraft which has a pronounced natural sink at low speeds a very wide choice of attitudes is possible while holding the same speed and the same approach line, .but while, perhaps quite innocently, using different boosts. , Let us say that one's recommended approach speed with a particular type is 130 m.p.h. and that the stalling speed is 115 m.p.h.: the aircraft can be brought in with a whiff of throttle and with the tail up, or, at the other extreme, with the tail well down and enough power to deal with the necessarily increased drag at this attitude and to coun teract the incipient sink. We will now imagine that two pilots cut their throttles as they cross the boundary. Pro vided that the pilot doesn't check too violently, the air craft in the first case will take some time to float off the excess 15 m.p.h. because it is in a level low-resistance atti tude. In the second case, however, the aircraft is being dragged along by the engines tail-down, and when the motor assistance is no longer there it will lose that 15 m.p.h. very rapidly indeed and will, in the words of the pilot, " fall out of his hands " straight off the approach. So we have two pilots, perhaps, arguing about approach speeds and results, but each innocently using a different degree of throttle opening during the vital part of the approach. One of them will say that he comes in at 120 m.p.h. and yet floats half down the runway ; and the other will say that he comes in at 140 m.p.h. yet touches down beside the chequered box every time. Each makes his final turn at the same height and in the same position rela tive to the boundary and each is telling the truth about the aircraft, which may be as alike as two peas. But, while one may be using zero boost during the first part of his straight approach, the other is using a figure off the clock, and the two aircraft cross the boundary in totally different attitudes—one ready to land"«Lnd the other with the tail still well up Except in the case of engine failure with a twin, initial climb attitudes are not so often discussed, but the., story
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