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Aviation History
1945
1945 - 1461.PDF
IOO FLIGHT JULY 26TH, 1945 TEST PILOTS AND DESIGNERS the pilot's language and the designer's language. Let us both speak English and let the pilot realise that if he wishes to understand the more difficult technical problems, let him go to college, after passing matriculation, and then spend many years in the industry learning, learning. But were the test pilot to do that, surely '' Indicator'' must appre- ciate that most of them would fall by the wayside, and those who did manage to get on the long, arduous and difficult path to the job of chief designer might not have sufficient time to be the efficient test pilots they otherwise would have been. But time will be wasted if one proceeded to question every sentence of the article, for they are nearly all double- edged swords and the way in which "Indicator" assumes that only one edge, and always the same edge, is sharp, is really astounding. Incidentally, it appears that test pilots must have a very easy time at present, if, as "Indicator" suggests, they can acquire all this extra knowledge and still do their present work. Let me conclude by trying to place the two jobs, both important, in their true relationship to each other. All designers will not make good test pilots, and all test pilots will not make good designers. The qualifications required for the two jobs are so vastly different that it is difficult to realise that one can seriously suggest that the test pilot f must in future be as knowledgeable as the chief designer. The chief designer must, and particularly so in the future, have had intensive technical training, practical experience and many years in the industry. To this end not only is hard work and much time required, but also the would-be designer must possess the necessary brain-power to absorb the knowledge, and the ability to apply it. Such gifts are not necessarily given to those whoJi5ecome test pilots. Surely the characteristics of the test jatflot are more physical than mental. And whereas there is no doubt that the par- ticular characteristics, similar to but considerably more developed than those required for driving a car, necessary for the would-be test pilot are not granted to everybody, these characteristics are not those required for a chief designer. The solution appears to be that the designer should, if possible, be a pilot, and the better pilot he is the better for his firm. The test flying must still remain in the handsA of the test pilot, wTho will now have no difficulty in speaking® to the designer, since they both fly, and the primary job of the test pilot must continue to be the assessing of the flying qualities and the conveyance to the design staff of what happens. Dangers in/1/urning Author of Qjagrfmt^Afticlp Replies to His Critics . vi » B# A. SIPOWICZ, Si A LTHOUGH readers have beenfkind enough to con/"A ment me on the lucidity of ikjr article "jDaagdls m ""• "*• Turning," published tn' Flight "oTTtpfiT foth^^945,their criticism shows that I was not lucid enoug»-K)i com- plete undeistanding of the subject. The following explana-tions may supplement the article and make it more under- standable. One objection concerns the statement "All accidentsfollowing badly performed turns are caused by an inadver- tent stalling of the aircraft with a subsequent spin." Mystatement is based on my experience as a former member of the Investigatiojj^Board for Accidents in the Polish Air Ldr., Polish Air Force (A.P. 129, Ch. 1, Para. 80-84), or T. G. Whitlock's"Elementary Applied Aerodynamics," p. 175. I am, how- ever, aware that this reply may not satisfy the critics whoare pilots and know from experience that it is possible to make steeply-banked turns without a corresponding in-crease in load (according to the equation). But this possibility does not mean that the turn so per--."formed is a correct horizontal turn, as considered in the article. It is possible to make a 90 deg. banked turn withonly a small increase in load, though the equation implies that in such a turn the load becomes infinite. Of course,this denotes only that a correct horizontal turn is impos- consequence of stalling the aircraft. The view that such keep altitude during the turn be may bank steeply and amHBnfc,™tK»r»c,,H,;—i,, ~t; ,,_4~ *„! pull back Qnly gijghtly, letting the aircraft turn with-**side-slip but without an excessive overload. The exact*' realisation of these facts would help many to avoid mis-takes which may be fatal. Such realisation is not shown by the critics. Tightness of Turn Force. I remember about a dozen accidents following steep sible at 90 deg. bank, but it does not exclude the possi-turns at low altitude. All of them were recognised as a bility of a non-horizontal turn. If a pilot does not care to . ' "'" ' ' ' ' -accidents are the result simply of inaccurate control, covers, of course, all the possibilities but explains nothing aboutthe nature of the inaccuracy. In my experience, so long as an inaccuracy does not impair the controllability it nevercauses an accident. Only the loss of controllability 'is dan- gerous, and this is produced by stalling. Critics are wrong in assuming that my understanding offlying is more academic than practical. Actually, I dis-^ A further statement that "In steep turns the governingcovered the cause of difference in turns in a wind after «T factor is the acceleration in the pitching plane or tightness had badly side-slipped several times, with only a small of the turn" shows that one critic is not sufficiently'margin of safety left My discussion of the causes with acquainted with the mechanics of flight. The acceleration Professors of Aeronautics in Warsaw Engineering College, in the pitching plane (a) may be expressed as theand repeated flying tests, led me to the discovery that .the quotient of the lift (L) and the mass of the aircraft apparent track of the aircraft was a cause of faulty steering. /Q\ I fail to understand a second objection: In steady flight ( - j, minus the gravity component in the same plane,"The greater the angle of incidence the lower the air g speed "conveys to me the same fact as vice versa "The i.e., a = = - gcs d, while the tightness of a turn may belower the air speed the greater the angle of incidence " " ' ' ' " expressed as its radius. This radius may be easily found by equalling the centrifugal force to the horizontal com- Both statements are frue and express the mutual interde-pendence of air speed and angle of incidence. B^Tt, it is necessary to pull the stick back and thus increase /he angleof incidence before the air speed is lowered. This shows that the original sequence of the statement is more natural.A third objection concerns equation (2) and is a flat denial of a known mechanical principle. This equation isnot mine, it is to be found in many manuals on the mechanics of flight, e.g., in "Flying Training Manual" ponent of the lift. G V2 This gives : where p — density of air. g.p — weight of the air per unit volume. S — area of the wing.
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