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Aviation History
1917
1917 - 0281.PDF
MARCH 22, 19x7. gives another example, where the observations were verygood ; the air speeds and revolutions per minute lie very closely on a smooth curve except at one point (about10,000 ft.), where they were probably affected .by a downward current of air. In a brief paper it is impossible to do more than explain themore important of the " performance " tests of aeroplanes, considered solely as flying machines. For military purposesa number of tests are necessary, some of which cannot easily be reduced to figures. Nor can it be supposed for an instantthat the methods outlined here are final. Aeroplane testing, like all other work connected with aeroplanes, is only in itsinfancy; and as time goes on, and knowledge accumulates, better methods and instruments will be evolved. There aresome who lay considerable emphasis on the necessity of every test instrument being self-recording, and although thisscheme appears at first sight Utopian and would relieve the pilot of a single-seater of considerable trouble, there aremany objections to it when considered in detail, not the least of which is the difficulty of getting new and elaborate instru-ments made at a time when all manufacturers are fully engaged on other important work. When an observer canbe taken I would personally place much more reliance on direct observations at the present time, and one great advan-tage of direct observations is that the results are there, and no time is lost through the failure of a recording instrument torecord, a circumstance which is not unknown in practice. So far as we use recording instruments, vte use them only as acheck on direct observations, although we shall probably soon adopt recording air speed indicators for the calibrationtests. But whether recording or direct reading instruments are used, it is, as I said before, the flyer on whom the accuracyof the tests depends. I feel that too great stress cannot be laid on this ; he is the man who does most of the experi-ments, and like all experimenters in every branch of science, he requires training and a great deal of practice. Althoughthe methods themselves may be greatly changed, this much may perhaps be claimed, that the general principles on whichthey are founded are sound, and will only be altered in detail. The importance of the work can hardly be exaggerated ;model experiments are notoriously subject to scale and other corrections, which, if not carefully scrutinised, may be verymisleading, and it is only by accurate full scale work that we can hope to maintain a steady improvement in theefficiency of aeroplanes. DISCUSSION. During the discussion that followed several interesting pointswere raised, and the opinions expressed could, generally speaking, be divided into two groups—those in favour ofemploying recording instruments and those who preferred to rely on the observations of skilled test pilots. Capt. Farren expressed himself in the main in agreementwith the lecturer, but said that he thought it possible to maintain a horizontal flight path with the aid of the aneroid,as he knew pilots who could fly for 10 minutes without the aneroid showing any deviation. He expressed regret thatthe lecturer should have referred to the instrument indicating the rate of climb as the climb-meter, as it was known amongpilots as the " Coffeeometer." He agreed with the lecturer that reliable testing should preferably be done by men whohad some experience in other kinds of scientific tests, and thought that care was really of more value than great skill inflying. His experience had been that it was difficult to make pilots see that it was necessary during altitude tests to go anodd thousand feet higher than shown by the aneroid, and that the only way to get the pilots to go to 18,000 ft. correctedheight was to tell them that they were required to go to 20,000 ft. by the aneroid. Capt. Grinstead was of the opinion that further progresswould largely depend on improvement in instruments. At present, he said, if appeared that the only two phases ofa machine's performance that were measured were speed and climb, and he expressed the belief that before long instru-ments would be needed which would indicate how long a machine took to turn through a given angle—in other words,some measure of a machine's manoeuvring power. Major Fowler pointed out the importance of standardisa-tion on a basis of density, and expressed the hope that the data relating to these tests might be communicated to designersand manufacturers. Although thermometers were old friends of his, he had never yet met one without lag, and asked whatthe experience of the lecturer had been in this respect. He admitted that recording instruments still required greatimprovements, but thought progress would lie along lines of improved instruments, as it was really asking too much ofa pilot to expect him to handle the machine and, at the same time, read a thermometer, aneroid, speed indicator, revolu-tions indicator and statoscope. Squadron-Commander Busteed thought that very oftenmuch valuable time might be saved by not relying too much on instruments. He said that his experience had been thatif you were waiting for instruments the weather was generally fine, and by the time the instruments arrived the weatherhad changed, necessitating further delay. When suitable weather came it was often found that something was adriftwith the delicate instruments, and personally he believed in getting the job done quickly, if necessary by observation ratherthan trusting to instruments. Lieut. A. R. Low was in favour of recording instruments,and advanced the interesting theory, based on personal experience as an observer, that every machine had its periodof oscillation, and that if this period coincided with the time taken in " making the round " of all the various instrumentsmisleading results might be obtained. Mr. B. Cooper asked whether it had not been found thatthere was a lag in the climb-meter, due to accummulated pressure in flask, v, Lieut. Miller tffiugM that the standard atmosphere,instead of being empirical, should be on a mathematical basis, which gave sufficiently accurate results. He did not like theexpression " true air speed," as no one ever used the term " true water speed " regarding a ship. He suggested " aero-speed " for corrected speed. Mr. Bairstow expressed surprise at the lecturer's statementthat model experiments might, under certain conditions, be very misleading. He said that in no instance had the errorbetween model and full-size experiments been found to exceed 10 per cent. Capt. Tizard, in reply, said that he had found that lag inaneroids was less than expected, due probably to the fact that the instrument was subject to vibration. The lag in thermo-meters had not been found to be appreciable, but the lag in the climb-meter was rather more serious. By descending instages of 2,000 ft. and then flying level for some time, this drawback could, however, be largely remedied. Gyroscopiccontrol had, he said, not been tried for test purposes. la regard to model experiments he did not in any way under-estimate the value of these, but, as so much depended on engines and propellers, errors were bound to occur, and otherfactors affected the performance of a machine, as, for instance, the consumption of fuel during a climb. AEROPLANES IN THE ADVANCE. WRITING from the British Headquarters, Mr. Philip Gibbs,im his pen-picture of the big advance round Bapaume, gives the following glimpses of the work of the R.F.C. :— " An aeroplane had crashed to earth in the shell-blastedfields, and it was one of ours. A car came along, and I saw a young pilot lying back wounded, with another officersmoking a cigarette, but grave-eyed and white. A little farther on I saw the fallen aeroplane. Pools of red mudwere on each side of the road and in the middle of it. ... " Flights of British aeroplanes were up and singing witha loud, deep humming music, as of monstrous bees. Our Archies •were strafing a German plane, venturesome over ourcountry. High up in the blue was the rattle of machine-gun fire. " Our cavalry patrols are over the hills and far away. Ourinfantry patrols are pushing forward into new territory, so that only aeroplanes know the exact whereabouts. As one aviator has just reported : ' Our men are lighting fires andtaking their dinners at places off the map.' They are going into pubs which have been burnt out to find beer which isnot there. North and east of Bapaume our patrols have gone beyond the villages of Rocquenes, Bancourt, Favreuiland Sapignies. " Much farther south, in the neighbourhood of Nesle,French and British cavalry patrols came into touch to-day, and one of our aviators reports that he saw French civilianswaving flags and cheering them. " The Germans have a cavalry screen behind their rear-guards. They were seen yesterday north of Bapaume and southwards beyond Roye. And some of them were chasedby a British airman at a place called Ennemain. He swooped low like an albatross, and brought a man off his horse by amachine-gun bullet. Others stampeded from this terrible bird." . • 281
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