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Aviation History
1911
1911 - 0936.PDF
(jpycHT] A number of models which were experimented with exhibited less lateral stability than the simple form of model No. I. Descrip tions of these have been omitted as superfluous. Several other gliders were discarded, although some seemed stable, as being impracticable owing to the constructional difficulties which would occur on a full-size machine. Of all the gliders experimented with, types 2, 3, and 4 proved themselves the most efficient. The dropping wing tip of No. 3, forming a sideways camber of the whole of one wing, certainly imparts a great degree of automatic lateral stability, and should be worthy of trial on a power-driven model, and then on a full-size OCTOBER 28, 1911. machine. No. 4 has a drawback in that at a certain angle the effect of the lower tip overcomes the drag of the upper owing to the down ward movement of the whole machine, and the model turns com pletely over. The angle at which this happens, however, is sufficiently steep to be practically unattainable in flight. Each of these models proved themselves far superior in lateral stability to the simple model, and one hopes that in this branch of aeronautics the great opponent of efficiency—constructional necessities—may not be too powerful. MESSRS. H. C. DAVIS and P. APPLEYARD, Nelson Villa, Sunnyside Road, Worcester. ® © ® ® HOW TO BUILD A MODEL. By W. IT is about eighteen months ago since I caught the fevers It was a stray copy of FLIGHT that did it, and FLIGHT has been my guide, philosopher and friend from that day to this, I well remember my first flyer. It was a rough scale model of a Farman machine. I took the idea from an illustration, and wonderful to relate the thing flew at the first try. It was a main-plane-first affair, with a o-in< tractor. It made circular flights and broke its main-plane spar with the most exasperating regularity. It was a case of 2 mins. fly, and then 2 hours in the repair shop ; which in time became monotonous. Want of stability, both lateral and longitudinal, was the great fault of No. 1, otherwise it was a nice-looking model. My second, third, fourth and fifth machines were Bleriots fitted with twin tractors. I made endless experiments and gained much experience, but I never got a flight of more than 20 ft. But at this stage it suddenly dawned upon me that toyshop models travelled "tail first" and that pro pellers were more in vogue than tractors. My sixth, seventh and present flyers were built to this new idea, and although I am not a long-distance man as yet, my forte being stability rather than the mere multiplication of yards, I can get my 36 in. by 29 in. model to do its 300 ft, without unduly straining its elastic muscles. No one can build nine model aeroplanes without learning something. Actually I have seen only one other model fly. Such knowledge as I possess is, therefore, first hand and very much based on practice. Often I am asked why so many model flyers are so unlike actual machines. My reply is that the "conditions are so different. In a model the weight of the motor is necessarily dis tributed over the whole length of the machine; in the real FIGI FIG.4. BOOTH. flyer this weight can be concentrated within a square yard or so. Also the fact that, in a model, control must be either natural or automatic, means that the design must be very different. ,.!»„" In successful model-building there are many things^to be considered : general design ; planes; area and proportion ; propellers; elastic, tension and amount; control; and constructional details. All these points are interdependent, and success depends on their careful correlation. Come with me to my workshop and we will rebuild my latest flyer. My tools, as you see, are few. A little tenon saw, a tiny iron plane, a 2-ft. rule, a drill, some screws, and a sharp penknife complete my outfit. I have already decided that it shall be a monoplane ; you have no voice in that. Secondly, I am determined that it shall fly tail-first. Thirdly, that it shall be pushed through the air by pro pellers, and not pulled along by tractors. Fourth, that it shall have twin screws, and lastly that its lateral balance, at any rate, shall be automatic. And now we will make a start on the design. How big shall it be ? What length ? What size planes ? How much elastic ? How can we be sure it will fly when com pleted ? These are fair questions. It has taken me twelve months to work out the answers. In the first place, I have evolved an axiom or two that have proved useful. (a) For every ounce of weight allow not less than 35 sq. ins. or more than 50 sq. ins. of plane area. Too much slows the flight. (b) For every 3 ozs. of weight allow not less than 1 oz. of elastic. (c) Allow two 10-in. propellers with f oz. each of elastic to a 4 oz. model; or two 12-in. propellers with i-J oz. each of elastic to an 8 oz. model. (d) Rigidity and strength are more important than mere lightness* Experience shows also that too small a model is a mistake, and one too big a blunder. We will, therefore, adopt the happy medium and make ours 36 ins. long, and as longi tudinal stability is increased when the length is greater than the width, we will make it 29 ins. wide. A model this size, if carefully made, is capable of a lengthy flight and will weigh, complete, from 7f to 8 ozs. This weight is made up as follows :—Frame, 2^ ozs. ; elastic, 2 j ozs. ; main-plane (silk covered), 1 oz. ; two 12-in. propellers, with bearings, 1 oz. ; elevating plane, Stability fins and skid, J oz. Applying axiom (a), i.e., 35 sq. ins. to the ounce, we get an advisable plane-area of 280 sq. ins. Having thus arrived at size of model, weight and necessary plane area, we can go on to the question of construction. First, I take a straight-grained flawless piece of spruce or pine, and plane it down until it measures £ in. by J in. Then I cut off one spar 36 ins. long, two 11 ins. in length, and another 13 ins. in length, and join these pieces together into a frame (Fig. 1). Six ins. from the end, R, a stout wire pierces the main stick. This is bent to hold the looped elastic. Next, take two strong thin wires, and, first seeing that the frame is quite true and square, stretch them tautly from A and B to the point, K, 9 ins. from R. Then bore holes in the cross 938
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