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Aviation History
1913
1913 - 0104.PDF
IfiiQgTl JANUARY 25, 1913. Edited by V, A Device for Overcoming: Motor Torque on Models with One Propeller. ME. ARTHUR P. PKTRIE (Rochdale) sends the following account (.accompanied with scale drawings) of a self-rising tractor monoplane, Constructed by him last November, the particular feature of which was the device employed for overcoming the undesirable deforma tion of the tail caused by the torque of the single skein rubber motor. The device is specially intended for use with monoplanes, because in the case of biplanes it is a fairly easy matter to sever all connections between the rear half of the motor and the elevator of the machine, but with monoplanes constructional difficulties present themselves, and weight is prohibitive of a large amount of framework. In this model the motor rod is rigidly connected to the body carrying the JOHNSON, M.A. 12 sq. ins. ; loading, 2\ oz. per sq. ft. approx. ; the two main longitudinals forming the body are pine, \ in. sq. section ; the motor rod is \ in. x ^ in. pine; the main plane is double sur faced save the tips; it is covered with silk chiffon made air-proof with Bragg-Smith varnish ; the tractor screw is birch, carved from the solid, it is 8 ins. in diam. and has a pitch of 12 37 ins. ; the wheels, 2J ins. in diameter, are turned from baywood and weigh \ oz. the pair. The idea of severing, as far as possible, all connections between the one end of the motor rod and the tail or elevator part of the machine, i.e., connecting these two by separate longitudinal members apart altogether from the rod carrying the motor, is an excellent one, but it is by no means new. It was used for instance, if we MOTOR ROD CONNECTION • J^^MAIN LONfrTITUDINALS MOTOR ROD \ /^^ ^___^ \ L-^ PIANO WIK.E ^ROUND) WHEEL SUSPENSION ' m H| \ ., RUBBER WM2tf 5HOCr;-AB50RBERS ^VWEtrCWlJE Mr. A. P. Petrie's model. wings, tail, &c, at three places. One of these is right in the prow of the machine, one by means of strut at a point level with the leading edge of the wings, and the other by means of struts at a point level with the trailing edge of the wings. The rear end of the motor rod is fastened to the body, as shown in one of the sketches. The end of the rod is made round, and fits loosely in a brass ring soldered to two piano wire struts. When the rear end of the rod becomes twisted by the torque of the rubber, it is thereby allowed to slip round in the ring without having any twisting effect whatever on the tail. As a result the model tends to fly much straighter, and ex periments can therefore be more satisfactorily carried out. The method does not present any great constructional difficulties, and is neither heavy nor clumsy in appearance. Another small advantage is that it offers a good opportunity for making the body streamline in form. Some other special points about the machine are (1) the •wheel mounting, (2) the large wing surface, (3) the upturned wing tips which, to all appearances, greatly increase the stability, especially in a slow-flying model. The chief particulars of the machine are: Total weight in flying order, 3! ozs. ; weight of rubber, 12 strands, -fa in. sq. section, $ oz. ; approx. area of main plane, ^178 sq. ins. ; of the tail 55 sq. in. ; area of elevator remember correctly, in the Bragg-Smith model, in the machine first entered for public competition. The introduction of machines with twin-propellers, of course, did away with the difficulty and the necessity of employing any such device, and the advantages of twin propellers in open competitions was so obvious, that the model with the single propeller became almost a rarity. Nevertheless it is by far the most interesting, and (as models with twin propellers are usually built) sometimes the more scientific of the two. Mr. Petrie says in his communication that the best flight he has had is 215 ft., and best duration 12 sees. Not a good performance, as he himself says, but the model owing to unfavourable weather conditions, and lack of time, has not undergone any very thorough tests as to its capabilities. As we have previously pointed out, the torque of the rubber motor in causing deformation in the framework can be entirely overcome by employing two rubber motors of equal weight, symmetrically arranged, and geared together by two small and light cogwheels of the same number of teeth, the axle of one of the cogs being also the axle of the propeller. The rubber motor can in such a case be run the whole length of the fuselage, and many more turns be given to the rubber. More than two years ago we obtained 52 sees, with 104
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