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Aviation History
1937
1937 - 0575.PDF
MARCH 4< I937- FLIGHT. 221 Another Interest ing Machine Described A Successful "Semi-scale" yx is an unfortunate fact that 1 the living performance of a rubber-driven model aeroplane tends to deteriorate as "true- scale" appearance and propor tions are approached. This is due to the effect on design of the absence ol a pilot, the varying power output of the rubber, and the weight of the rubber motor being distributed along the fuselage. Mr. C. Rupert Moore has succeeded in combining appearance and performance in a trulv remarkable manner in his Viper II Intercepter fighter. A speed of lH m.p.li., and a duration of 70 seconds have been achieved without any sacrifice of stability or structural strength, both of which have been severely tested by continuous bad weather. Built largely of balsa, the model weighs 20 oz., of which 5.8 oz. is accounted for by the rubber. With a mug area of 310 sq. in., the loading is 9.09 oz./sq. ft. The span is 48Jin., the chord 7Jin., and the overall length 33m. There are 5 degrees of dihedral, 4.5 of sweepback, and 3 of incidence. Four skeins, each of five strands of Jin. x 1/20111. rubber, drive the satin-walnut airscrew, the diameter and pitch of which are 15m. The thrust-line is offset to the right 2 degrees, and there are also 2 degrees of dow 11-lhrust. The wing is built in two parts, connected by bamboo pegs to a frame, which passes beneath a removable section of decking, and is held by rubber strip to anchorages within the fuselage. The method employed allows for a small variation in longitudinal trim, and imparts a certain degree of flexibility. The main spar consists of two lengths of Jin. x i'm. hard balsa, spaced f,in. apart, and reinforced with -33-in. balsa sheet be tween the ribs in such a manner as to constitute a box-spar for a third of the span, and U-section for a further third. A T-spar is used for the leading edge, and a triangular length for the trailing edge, both balsa, while the curved tip is formed from Jsin. x ^in. birch, reinforced with balsa. There is diagonal bracing of thin wood between the spars. Medium balsa is used for the ribs. Dihedral and sweepback are built into the centre-section frame. The fuselage varies from orthodox practice in having two shaped "spines" of hard balsa running the entire length, top and bottom. Between these are fitted bulkheads of 1 mm. buch three-ply, carrying numerous stringers to secure the ex ternal shape. The radiator and exhaust ports are formed from thin balsa sheet, and the nosepiece from fin. plywood, faced with whitewood and balsa. The final touch of realism is imparted by the presence of "Fit. Lt. Balsa," a most realistic-looking pilot, who, unlike most carved effigies, reallv does add to the ap pearance of the model. The compression Competition News By M. R. KNIGHT Each year's winner of the Fl ight Challenge Trophy for scale models at the Northern Heights Club's gala day re ceives a plaque, as shown here, to keep as a "replica." This year's event occurs on June 20. A sketch of Mr. C. R. Moore's 48! in. span mid- wing monoplane, partly laid bare. On the right is a diagram of the mechanism which stops the airscrew in a horizontal position to avoid risk of damage on landing. As the rubber tension relaxes, a small spring pushes one gear shaft forward to act as a stop against the spinner legs of the undercarriage are brown paper tubes, front and rear legs and axle are of bamboo, and the wheels are laminated newspaper! A two-ply balsa tail-wheel is fitted. The tail- plane consists of a single reinforced spar of fin. balsa, rs'n. balsa ribs, and rW'n. X rWm- birch edging. Rudder and fin are built similarly, with a s^in. balsa sheet over the leading edge, and a trimmer tab of fin. balsa, hinged with aluminium sheet, jap silk is used for covering the fuselage, and bamboo tissue for wings and tail unit. First 7937 Competition "ipHE 1937 outdoor season opens on April 9 witli the contest J- for the Carnage Cup, which will be held simultaneously on the grounds of clubs affiliated to the S.M.A.E. It is the only event where any type of rubber-driven model may be entered, and until comparatively recently was responsible for an annual muster of venerable twin-pusher "spars," one of which in variably won. Eventually the lightness of balsa brought victory to the fuselage type. Nowadaj's the best average of three rise-off-ground flights wins the Cup. An Indoor Record O N January 22 at the Albert Hall. London, Mr. R. Copland, of the Northern Heights M.F.C., who secured third place in the 1936 Wakefield Contest, raised the British Indoor Spar Duration Record to 18 vnin. 52 sec. Visitors who have previously encountered only outdoor models are amazed at the delicacy and lightness of these indoor craft which, with a wing- span of about 22in., weigh one-sixth of an ounce! The pear- drop-section motor spar is made by rolling a strip of 3'jin. balsa sheet around a knitting-needle, while the tail outrigger, which projects from the rear of the motor spar, is similarly con structed from 1/64in, sheet. Wing, tail, and sometimes even the airscrew, are covered with "microfilm," which is formed by pouring collodion, amyl-acetate and castor oil, or some alternative solution, on the surface of warm water, from which it is removed with a wire hoop. 1937 Wakefield Designs Hatching IT is alread3' apparent that opinions are somewhat diversified as to the best application of the new Wakefield Cup rules. The minimum weight, it will be recalled, is now 8 oz. instead of 4, while the wing area must still be.200 sq. in., but with a plus as well as a minus tolerance of 10 sq. in. (not 10 per cent..
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