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Aviation History
1945
1945 - 0858.PDF
476 " Indicator " Discusses Topics of the Day FLIGHT MAY 3RD, 1943 Getting Over the * I lump* The Paramount Importance of the Experimental Test Pilot's Work : Advanced Technical and Theoretical Knowledge as a Necessity Rather than an Asset : The Scientific Pilot as the Key Man of the Immediate Future SINCE it is obviously impossible to make every designerinto a test pilot, then we must try our best to makeevery test pilot into a designer. The time has cer- tainly come when the amount of very real technical know- ledge required by the experimental test pilot is immense, and very soon this knowledge will have to be supplemented by an even greatei amount of modern aerodynamic theory. The design of aircraft intended to fly at super-sonic or near- sonic speeds is such that progress will be ultimately possible only through the exertions of the test pilots, and their work will tend to be partly wasted if they themselves cannot put their fingers on the causes of various phenomena encountered. There has been, and will in future be, the occasional prodigy who is equally at home in the air or behind water-cooled slide-rule, and the test pilot of to-day iswtffn- nitely more knowledgeable in matters of aerod^flamic theory than was his forerunner of a decade agoyt&t some- thing a great deal more than casually obtained knowledge and experience will be needed during the cpming decade if we are to mount the next step of flying p^ftgress. It would be too much to expect the man who has/thti kind qLims inative intelligence and training needed fW the design a modern aircraft to be necessarily citpabifeof ftfj/t thing as well. Apart from the fact ftiat it\> uii*uS**f5r the clever mathematician or '' inventor'' to\>a'tel3jpera- mentally suited to the job'of flying * prototyiX he might have poor eyesight or be incapable,! by agayji' for other reasons, of the co-ordinated dexterityvequired even for the casual driving of an ordinary machineX It would be more,, than stupid if the best designers were toSbe shelved sir because their reactions or nervous syst to the business of carrying out straightforward diving tests, or a general handling routine on a new type. Technical Test Pilots The whole thing must obviously be developed from the other end, and the existing test pilots, and those who are on the way towards becoming test pilots, must be given the opportunity of taking a much more considerable interest in present-day aerodynamic theory. The rule-of-thumb knowledge which is, at present, such an excellent foil to the sometimes self-satisfied prognostications of the design staff, will not be enough in the future. Not only must the test pilot be capable of speaking the designer's own lan- guage, but he must be capable of absolute and final decisions in consultation with the design staff—for he will be the only person to know what is happening to the air- flow, and to be really capable of translating the practical effects into necessary alterations. It will not be enough for hin\to offer an accurate second-by-second account of the aircraft's behaviour—and certainly not to bring back a mere cinematographic, or load-graph record of this behaviour. Such a record can so easily be, and is, in fact, so often, misconstrued by technicians with their own patent theories and their own fixed ideas of aerofoil behaviour. Such theories and ideas must be leavened before reissue in the form of modifications—and the leaven- ing agent will obviously be the highly-technical test pilot. Aerodynamic theory has always been a step behind the actual observed results. So much so that the cynically minded pilot can be forgiven for suggesting that aircraft design is still very much a rule-of-thumb affair. Just when, with the help of practicai results, a wing-section or aileron system has been perfected, the need arises for further development, to deal with greater speeds or loadings, and the same process of trial and error must be repeated. The test pilot brings back his figures and the designer cannot understand them. Only after the same figures have been brought back for a second or third time does the designer —who has only his theoretical knowledge and previous precedents on which to work—begin to wonder whether his initial assumptions were correct. He is doing his best with the experience and information available, and flight tests are so pften disproving of the previously obtained results Local Compressibility With v/ry modern aircraft the divergence of fact and expectati/n can be easily understood. Though the air- craft itfemf may not be flying at a speed within a century or so dj compressibility, there may be small areas where flOTp velocijy is nearing the speed of sound and so sntrtey upsetting the characteristics, for instance, of aL mtrcl surface./It is often very much simpler than that, long ag<f the immediate development of one of our otstanding nfototypes was held up simply because of an inSfcpIicableJuid apparently incurable bout of tail-buffeting! A similar lityout, with much less clean cowlings and centre- section jjfiad given no previous cause for complaint, and theNpbdTOtype had almost been given up when somebody— proliably the drawing-office blue-print boy—pointed out it, for one reason or another, the lip of an air intake ' shall we say) had had its shape changed in the course of development from the previous design. The shape of this intake, with no great faith in it as a likely cause, was altered. No further trouble was experienced. Again, one of the better-known pre-war American transports was designed with a high-lift type of flap so that the take-off run could be shortened. But the take-off flap setting could, in fact, never be used because the down-wash, bouncing back off the runway, upset the fore and aft trim. And even the full-down limit setting was reduced later because of violent trim-changing when full power was used after a baulked approach. ( The reasons for such comparatively simple effects can^, easily be worked out by the design staff when the facts" are given in the form of a pilot's report, but something a great deal more explicit and basic than a mere state- ment of successive facts will be necessary when every pro- totype is designed to fly at a speed which, at high altitudes and low temperatures, is dangerously near that of sound. Furthermore, the period during which strange phenomena in control and trim reactions can be allowed to continue must be very short, and all possible information must be garnered, if possible, in one flight and without the neces- sity of carrying a load of irreplaceable technicians. In any case, these technicians will not be in the best position to judge control forces, instabilities, and trim changes. Only the pilot himself can provide the essential informa- tion which, coupled with the various graphs drawn by sundry G-meters, accelerometers, stick-force meters, and altitude recorders, will offer the data necessary for sue- ; cessful modification. In the case of single-seat fighters, of course, it will not even be possible to carry either observers or a great deal of recording gear, and most of the story must be obtained from the pilot's own reasoning during the few seconds in which the Mach number is very
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