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Aviation History
1913
1913 - 0166.PDF
JOGHT] The Tractor-screw is 12 ins. in diameter and iS ins. pitch—it is laminated, being built up of cotton wood. The one shown in the drawings is two bladed—but Mr. Rippon proposes to fit on a four- bladed one at an early date. The Landing-chassis is of the simplest, but is found quite adequate in practice. The large central skid is composed of cotton wood reinforced on the underside with a strip of *fc in. clock-spring. The semi-circular connecting place between the lower longitudinal and the central skid is also made of clock-spring. The bamboo axle is rigidly bound to the skid and has two radius wires on either side, one is clearly shown in the drawings, but the other is attached to the skid immediately beneath the propeller and joins the axle near to each wheel. These wheels (of aluminium), are 25 ins. in diameter, they were supplied by Messrs. J. Bonn and Co., where a suitable tractor- screw can also be purchased. The Motive-power is 14 strands of J in. strip rubber (best quality) weighing 7.\ ozs. The number of turns given varies between 250 and 280, and the model is capable of making average nights of 90 to 100 yards. The best duration to date is 22 sees., i.e., 20 sees, power flight and 2 sees, glide—this refers to a hand-launched flight, the model so far not having been thoroughly tested for rising off the ground—on the few occasions when the model has been Geared Rubber Motors. so tried ; the average duration of run before rising was about 5 sees. No doubt with further tuning up both duration and distance will be improved. The following weights may be useful: Fuselage (complete with chassis), 6'5 ozs. ; main plane with cabane, 2 ozs. ; tractor screw and shaft, 0"5 ozs. ; tail plane and fin, 075 ozs. ; rubber, 2'25 ozs. Geared Rubber Motors. By F. MAYER. As some exceedingly interesting and useful articles on rubber motive power for models have appeared in these columns, a few •words en gearings for use with these motors may not be out of place. Having during the last five years made about 1,000 of these gearings of all sizes and forms for use with every form of aero model from the flying stick, with its 8 in. propeller, to the large model helicopter, with its 8-ft. screw, I can claim some knowledge of them. To be of any use they must be well made and designed. Some of those offered for sale have ratios as high as 8 to 1, and the wheels are merely screwed on cycle spoke hooks. Needless to say, when jany attempt is made to wind up the motor the wheels spin off the hooks. Geared motors get a bad name in consequence, yet I could mention many instances whereby the use of a gearing, an otherwise unsuccessful model has been made to fly, or its flights have been improved, and lengthened. FEBRUARY 8, 1913. The following short descriptions and sketches of some different types of gearing, with their respective good and bad points should be of use to those who are not already familar with them. I. Parallel Gearings, This type, Fig. I, is perhaps the most useful, as it possesses many advantages over a single strand motor. It can be made with any number of strands ; as a rule two strands are enough for models up to 4 ft. span, and three strands for models up to 6 ft. By its use more than twice the number of turns can be put into the motor, it also does away with the twisting of the motor-rod or fuselage, with its evil effect on the stability of the model; this is particularly noticeable in the single-tractor model. In the case of large bundles of rubber the outer strands get stressed much more than the inner ones. By using two smaller bundles this excessive stressing is partly avoided. Since this type of gearing practically does away with rubber torque, a lighter fuselage can be employed. II. Series Gearing. In this type, Fig. 2, the gearing is placed at the opposite end to the propeller and the fixed hook is placed by the side of propeller hook. This system can be used with advantage on scale models of Bleriot, Farman, &c, as it allows a large number of turns to be got into a short length of rubber. In the case of tractor monoplanes or biplanes, the rubber can terminate half-way along the/uselage, thus keeping the weight forward and allowing the planes to be fixed in a more forward position with a better resemblance to their prototypes. III. Geared-up Type. There are very few models on which this system can be used with any advantage (Fig. 3). Many model makers are under the impre- sion that by gearing up the propeller it will run faster. This i s not so, in fact it will run slower. Its speed in relation to the rubber will increase, but its revolutions per minute will decrease, owing to the power, or rather torque, having been divided in the process of gearing up. Those who wish to use this system should not try a gear ratio higher than 2 to I. IV. Concentric Spindles Gearing. In this type, Figs. 4 and 5, two propellers are used, one being placed close behind the other, and usually running in the opposite direction. As will be seen from the rough sketches the back propeller fits on a sleeve which is a running fit on the spindle that carries the front propeller. The sleeve is rotated in the opposite direction to the spindle by means of the gearing. Fig. 4 is for use with one bundle of rubber and Fig. 5 for two bundles. V. Vertical Spindle Gear. This type, Fig. 6, is chiefly used by experimenters with helicopters, as it allows the vertical height of the model to be reduced. Both gearings shown in Fig. 4 and 5, are particularly adaptable to heli copters, by their use two large propellers can be run one beneath the other in opposite directions. General Remarks. In the rough sketches no attempt is made to show any method of mounting as this depends on the construction of the model. In mounting the wheels care must be taken that the teeth do not crowd or bind on each other. The best form of teeth is the involute. Clock cogwheels as a rule are unsatisfactory for this purpose. Model makers who do not possess the necessary tools or skill should consult a firm who understand the requirements. I should be pleased to advise any model makers who wish to use any form of gearing on their models. A letter to J. Benn and Co., Ltd., 97, New Oxford Street, will receive attention. There is no doubt that the subject of gearings is a very important one and in the main we agree with Mr. Mayer's remarks, it is a subject, too, in which we have made many experiments and hope to make some more. Referring to " parallel gearings" we have not personally found it any advantage to split the rubber up into more than two strands, rather the reverse. How this might work out in the case of heavier models, i.e., models weighing between two and three pounds remains to be seen, the models we experimented with were about 10 ozs. Any geared-up type is absolutely useless. Concentric spindles are of especial interest, and we know of two or three very successful models that have been built in this manner, it is well worthy of experiment. As Mr. Mayer says, the gearing must be of the correct kind and properly mounted, unless this is done, failure is certain. We have seen many geared motors which would just " not" fly their machines. Vaseline should be used as a lubricant for the cogs, not of course for the bearings. Replies'in Brief.^i H. HUCKLE.—You do not state in your query for what type (hand-launched, r.o.g., &c.) of model you require the information asked for—it is impossible to supply it unless you do this. There is, however, considerable information re your second and third queries in recent back numbers of FLIGHT. 166
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