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Aviation History
1942
1942 - 0557.PDF
MARCH 12TH, 1942 FLIGHT 220 tubular shaft oi the larger air screw. Details of the gear are shown in the sectional view. From the general arrangement drawings of the machine it will be seen that the supports for the airscrew shafts were not shown in our drawings published at the time. The reason probably was that the details had not been worked out fully when the article was written. Obviously, the intention was to brace the shaft bearings to the tubes of the tail outrigger in some -Jffeshion, and deflections were certainly expected, for provision had been made to incorporate a flexible coupling, a section of which is given in another view. There is nothing very remark able in the coupling itself, but an ingenious dodge is the single ball between the ends of the two portions of the shaft. This ball was intended to transmit the air screw thrust from one portion of the shaft to the other, and would do so even if there should be a considerable '' bend '' in the shaft. It was not considered advisable to subject the large- diameter hollow airscrew blades to the sudden shocks of starting, and as a protection for them a multiple-disc clutch was incorporated between the crankshaft of the engine and the chain sprocket of the airscrew drive. Thus the engine could be started and run-up with the clutch out, and by careful manipulation the airscrew blades could be accelerated quite gently. That was a refinement not even found in modern airscrew drives. Perhaps the reason, or one reason, for the failure of this machine to '' make good '' may be found in the weight figures. The engine developed 70-80 b.h.p. at 1,400-1,600 r.p.m.; the clutch weighed 56 lb. and the differential gear 55 lb., so that the transmission must have amounted, all told, to nearly 2 lb./h.p., not counting the weight of the two airscrews. But the details are interesting from an engineering standpoint. The Piggott firm broke new grqund in quite a different direction in the following year. The First Enclosed Monoplane At the Olympia aero show, " 1911," they exhibited what must have been the first British all-enclosed monoplane. A year or so later the Avro company came along with a biplane and a monoplane which had that feature, and «!&oth these machines flew, but the 191 r Piggott did not, I believe, leave the ground. Our photograph, taken at Olympia, shows the perfect streamline form of the fuselage, the large spinner which completed the form, and the very TOOTHED ANNUIUS PLANET PINIONS ARMED SPIDER LARGE AIRSCREW SHAFT 3fL SMALL AIRSCREW SHAFT The section above shows the differential gears used in converting the chain transmission into contra- rotation. The lower section shows the flexible coupling which took care of deflec tions and misalignment of the shaft. Note the single ball which took the airscrew thrust. LEATHER CISC The first British all-enclosed monoplane. The Piggott was exhibited at Olympia in 1911. Perspex had not been invented then, else the windows might have been larger I Note the surface radiator on top of the fuselage. inadequate win dows through which the pilot was to get his view. In addition to the all-enclosed feature, the Pig gott monoplane of 1911 was in teresting in having what must have been the first '' shaped '' sur face radiator. In the picture it is the little patch on the '' forehead " of the fuselage. The engine was of 80 h.p., so that may explain the small area. In the Supermarine Schneider monoplanes the radiators occupied nearly all available area on wings, fuselage, and even floats. One thing the enclosed Piggott monoplane shared with its contemporaries: it had an undercarriage in which abso lutely no attempt had been made at streamlining. The old pusher biplanes usually had two skids, sometimes long and sometimes short, each carrying a pair of wheels side-by- side, the short axle crossing the skid and being connected to it by a lashing of rubber cord. Two radius rods from skid to axle kept the wheels tracking fairly well. The same arrangement was found on the Piggott, and at the time this appeared reason able, although nowadays it looks somewhat in congruous when married to a fuselage of perfect streamline form. Wing bracing was of the external type (the cantilever being regarded as far too heavy), and lateral control was by warping the whole wing. That was common practice in those days, especially on monoplanes. The biplanes were the first to adopt ailerons. I do not know why the Piggott enclosed monoplane came to naught, but I remember that the rudder was diminutive, and I do not think there was any fin, so the machine must have been very unstable directionally. CM. P.
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