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Aviation History
1942
1942 - 0556.PDF
228 Ahead of Their Time FLIGHT MARCH 12TH, 1942 INGENUITY IN 1910 Contra-rotating Airscrews with Metal Blades and Adjustable Pitch : Wings of High Aspect Ratio and Elliptical Plan Form : A Totally-enclosed Cabin By THE EDITOR LOOKING back on the early flying days, one is struck by the number of amazingly ingenious devices and •^ ideas which many of oar pioneer designers incorpor ated in their " flying machines." (Incidentally, why didn't we stick to that term? It is English and it is descriptive, which is more than can be said of the bastard r concoctions that have since gained currency.) It was usually the case that the greater the number of "advanced" ideas in a given type the less likelihood was there of the firm making a financial success. That was but natural; most firms or individuals had small capital, and customers were few and far between, so that, unless a design could be pretty well guaranteed not to require many modifications, it was either not built or it '' broke '' its constructors. One result of this was that many useful ideas either did not get beyond the drawing-board stage or they were seen in one example only, never to appear again. That was quite often due to features or circumstances unconnected with the special new feature. For example, many a useful machine was damned by a feeble and unreliable engine. I well remember that when the 50 h.p. Gnome rotary engine came along we thought we had almost un limited power for a very low- weight, and that engine re moved flying from the " tangent " stage and made possible a reasonable speed range. For the purpose of our younger readers I might explain that the word "tan gent " was used to denote an aircraft in which the power- required and ' power-avail able curves just touched one another, so that only at one particular speed would the machine fly ; it. had no speed range. In these days of 2,000 h.p. and 400 m.p.h. it will probably come as a surprise to many to learn that men did venture into the air in contraptions which were horribly under powered and only flew be cause of their very light wing-loading. A reader, Mr. W. A. Woodward, has reminded me that in 1910 Flight pub lished an illustrated de scription of a type of air craft which had a number of features which one would hardly expect to find at that stage of evolution. The firm of Piggott *Brothers and Co. built the machine, which was designed bv their engineer, Mr. S. C. Parr So far as I remember, the machine never flew. Verv probably it never really had a chance to fly, but. the designer was undoubtedly on the right track. ^ The Piggott-Parr was a biplane of 60ft. span, and the remarkable thing about its wings was that it had a chord of only 6ft. Remarking on this fact at the time, Flight said: "The aspect ratio is thus nominally 10, but the equivalent value of this ratio for an ellipse as compared with, a rectangle is unknown." Apparently at that time span2 the definition of aspect ratio as had not come into area use. Remembering that this was in 1910, it is remarkable to find that not only the high aspect ratio but the ellip tical plan form, both now known to be conducive to law drag, were a feature of the design. Mr. Parr, I remem ber, gave full credit to Dr. F. W. Lanchester, whose theoretical works on aerodynamics were as much ahead of their time as were the machines designed to his ideals. In other respects, too, the Piggott-Parr was remarkable. Not only did it have four-bladed, contra-rotating airscrews, but the blades were hollow DIFFERENTIAL 4 BLADED AIRSCREW 8FT. D* 4 BLADtD AIRSCREW 14 FT. DIA. The Piggott-Parr biplane of 1911 had contra-rotating airscrews driven by differen tial gear. Note also the large span, high aspect ratio, and elliptical plan form. The bracing of the airscrew shaft is not shown. and made of aluminium sheet, and the pitch was adjustable. In addition to the two airscrews being rotated in opposite direc tions, they were indirectly driven through a differential gear, so that they were self- balancing to the extent that if one absorbed less power than was intended, it would speed up and the other slow down until a balance was struck. Here, again, we see Lan chester influence. It may be recalled that in our issue of December nth, 1941, we published an article by Dr. Lanchester in which we gave a drawing of a dif- a»-, ferential airscrew drive patented by him in 1907! It may be assumed that Mr. Parr was indebted to Dr. Lanchester for the general idea, although the details of the Piggott- Farr gear were somewhat different. The two airscrews were chain - driven, the chain wheel being attached to the casing of the differential gear. The casing carried a toothed annulus which en-. gaged with planet wheels carried on a three-armed spider. The sun wheel was carried on the end of the solid shaft of the smaller of the two airscrews. The spider was attached to the
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