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Aviation History
1920
1920 - 0655.PDF
JUNE 17, 1920 MODEL AEROPL^NfeS NOTE.—All communications should be addressed to the Model Editor The Groves C.A. Plant in a Tractor MonoplaneSINCE writing the brief resume of the compressed-air plant designed by Mr. H. H. Groves, which appeared in FLIGHT,April 1 issue, I have had an opportunity of building a machine to suit the plant. It is shown by the appended photograph.At the outset I should like to endorse the remarks I pre- viously made regarding the plant, which I consider to be agreat improvement on most of those at present on the market. The rotary valve throughout my experimentsworked extremely sweetly, and there is only an infinitesimal amount of leakage in the engine—this, too, only at highpressure. I have had no trouble with the engine but a broken crankshaft, but this was in no way due to faulty design.The flimsiness apparent in so many C.A. motors is quite absent, and the whole motor is rigid, light, and free fromvibration. Mr. Groves has promised, as a favour, to supply one to each reader desirous of possessing one, and I shalltherefore be glad to forward any enquiries to the right quarter. The total weight of the plant is 14 oz. without thescrew, and the thrust at full pressure nearly 6f oz., quite sufficient to fly a machine weighing two pounds or more.With a 1 in. bore foot pump the pressure averages about 1 lb. per stroke. I found that a pressure of 40 lbs. wassufficient to just fly the model without climb, thus proving that a pressure of 40 lbs. is sufficient to fly a machine, althoughit has been stated by others that a pressure of 50 lbs. was necessary for flight. As has been previously mentioned, the machine has beendesigned on the double-acting principle. The cylinder heads are attached by means of buttress threads (to resist pressure),and altogether the plant is an engineering job, combining great power with lightness, compactness and strength. Thedrawings show the machine presented by the photograph, and I do not think simpler or lighter construction, commen-surate with rigidity and strength, could have been used. The machine at the first flight collided with a roof, hence thebroken crankshaft previously alluded to. The duration was in the neighbourhood of 45 sees., and since then 63 sees, has been obtained. I have no doubt that with further tuningeven better results will be obtained. I used a rather novel form of construction in the planes,but this will be dealt with in a later issue. The wing section Tractor monoplane by Camm, driven by GrovesC. A. plait. (something akin to a well-known full-size section) is here given ; twelve such ribs will be required, each -jV-in. thick and 1 in. wide, of birch. The slots are to admit the leading and trailing spars, which are of spruce. (To be Continued) Replies to Correspondents W. T. NEWTON (Hither Green).—Sorry, but the preparationof the drawings would entail too much time, and is hardly of general interest. I shall, however, bo pleased to assistyou in any way within my power, and I wish you success in the undertaking.
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