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Aviation History
1926
1926 - 0624.PDF
SEPTEMBER 2, 1926 THE CRANWELL LIGHT AEROPLANE IV. An Interesting Training Machine Built by Amateurs IN view of the fact that this year's Cranwell light aeroplane, designed by Flight-Lieut. N. Comper and built by members of the Cranwell Light Aeroplane Club, was based mainly on the Pobjoy engine, a few words concerning this engine may serve to explain in manj^ respects the reasons underlying the fundamental design of the C.L.A. IV. Designed by Capt. Pobjoy, the " P " engine, as it is called in the entries list, is a seven-cylinder radial air-cooled engine of extra- ordinarily low power-weight ratio. Without going into details we may say that Capt. Pobjoy has been guided in the design of this engine by the principle that all parts subject to heavy loads of one sort or another should be very substantially built, while so far as possible there should be no parts which were not contributing to the work of the engine, all helping to " pay their way." The result has been an engine differing in many respects from orthodox practice, but achieving a maximum horse-power of 65 b.h.p. for the astonishingly low weight of 100 lbs., this figure I" FLIGHT " Copyright Sketches THE CRANWELL C.L.A. IV : Some constructional details : 1, The lower plane wing roots built into the fuselage. The bottom longeron is shown broken away behind the rear spar so as to show better the metal fitting, and between the spars this longeron passes just inside the inner rib. The rear undercarriage strut is attached to the front spar attachment. The hinges for folding the wings are also shown. In 2 is illustrated the inner end of the starboard lower plane, with hinge fittings, etc. The solid rib is partly broken away to show the form of the drag bracing clip. 3 illustrates the special rib and sheet steel fittings for the inter-plane I-strut on the lower plane. This strut slopes inwards, the sketch being viewed from outside the strut attachment. The spar is broken away to show the details of the special metal fitting for the attachment of the strut. The form of construction employed in the rear portion of the fuselage is illustrated in 4, while 5 shows details of this construction, the actual joint shown being on the lower longeron and viewed from inside. 548
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