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Aviation History
1911
1911 - 0081.PDF
JANUARY 28, 1911. 1st. If the length was 3 ft., would it be correct if the front plane was 2 ft. 8 ins. and 10 ft. in width ? 2nd. What width and length should the back plane have ? 3rd. Would it be advisable to camber both planes ? 4th. Would a rudder be of disadvantage ? Highbury. M. MILNE. [It is impossible to advise definitely on questions of detail such as whether one length or another length is correct for a model. The only way to get successful results is to bear prominently in mind the fundamental principles at stake. If the problem is to design a model that is to fly the greatest distance, that problem must be re- expressed in terms that apply to the practical difficulties of the case, thus, for example, we may assume that the model is going to be driven by an elastic motor and that the elastic motor is going to have a certain limited amount of energy in proportion to its weight. A few preliminary experiments should be made to ascertain approximately what size of elastic motor could be made and mounted in a suitable frame to give the greatest amount of energy for the least amount of weight. There is generally some mean range of values that gives the best results, because it is more difficult to make something that is exceedingly small or exceedingly large than to make it of ordinary proportions. A recent article in FLIGHT, by Mr. Langdon-Davies, should be of assistance in obtain ing an appreciation of the operation of elastic motors. Having decided on the weight of the motor, and having estimated an allowance for the weight of the planes and propellers—which should be done, in the light of previous experience with other models, in which it has been found, for example, that the planes weigh as much as the framework carrying the motor, or in which it has been found that there is some other helpful relationship between the weights of different members—it becomes possible to have a fair idea of the probable weight of the model complete. The problem now is to design the planes so that they shall use the power available in the motor with the greatest possible efficiency, and, as an aid to this, some study might advantageously be given to those articles that we have published entitled " Can we fly faster for less power?" They were written in reference to full-sized machines, but, in prin ciple, they are applicable to models, and those who would learn from model construction should study principles. The gist of the articles in question may be summed up in saying that the plane of least resistance has a camber of about 5 , in other words, it is almost flat, but, and this is the important point, a plane of such little camber will carry very little load unless the speed is very high, and if the speed is very high the body of the machine must be very small and very well designed, otherwise its resistance, which must always be considered as an independent quantity supplementary to the resistance of the planes, will be very high also, and muoh of the advantage of using a plane of least resistance will be lost. In any case, however, the best practical result is likely to be attained by reducing the loading to the least possible value, in other words the planes should be made as large as possible in proportion to the weight of the machine. In making them large, however, it is very necessary to bear in mind the value of aspect ratio and not seek to make them unduly large merely by increasing the chord.—ED.] L/UGHT] M^del Twin-Screw Monoplane. [1047] Enclosed you will find phcto and scale drawings of my model aeroplane. The problem I set myself to solve was not so much a question of speed or distance flown as of natural stability. I set myself experimenting with gliders in an atmosphere of tobacco smoke in sunlight, and the result is a model which will fly straight, level, and horizontal. I can launch it blindfolded, and it will fly as far as its motors will make it, at a height of five or six feet from the ground the whole of the journey. It alights flat, and its lateral stability in flight is perfect, and if disturbed by a wind-gust the model recovers itself instantly. Much of the difficulty which model builders meet with is due to the fact that their model frames are not rigid enough. Unless the Paper Gliders. [•1046I I enclose a rough sketch of a small biplane glider, partly my own design, which I hope will be of interest to some of your readers, and that you will consider worthy of pubhcation. frame is rigid longitudinally, the tension of the elastic alters the relative angle of the main plane and elevator, and so causes the model to either rise unduly or dip disastrously. In my model the frame is built girder fashion out of \ in. by \ in. satin walnut. The elastic is inside the frame, and no bending of the frame is perceptible with 250 turns on the propellers. At 250 turns the model flies 130 ft. The propellers are 75 ins. diameter, \\ ins. across the blades, and f in. pitch. Eight yards of elastic to each propeller. The great stability of this model is due to the fact that at either end of the main aerofoil is built at right angles an erect paneL This panel is the same width as the main plane, and one-fifth to one- sixth as high as the aerofoil is long. These panels, if plain, give some little increased stability, but their action is increased greatly, almost incredibly even, when their entering edges are inclined inwards and downwards, in a manner impossible to describe verbally, but which may be seen at a glance in the print. The dimensions of this triangular plane are very important. If too large it acts as a brake and elevating-plane com bined. This elevating action is so marked that the "elevator" in front has no angle, but is practically flat. The angle, however, can be found by adjusting the screw at B, and pressing the wedge either in or out as required. The main plane rests at E, on two jr-in. blocks giving that amount of front elevation, and the camber is i in. The weight of this model works out at 4^ ozs. I should be glad if you could tell me if the performances of this model are anything DETAIL VIEW OF B The bend in the main frame is obtained by painting with thin lue, bending, and then left to dry. Hull. C. MARR. BALANCING PANEL out ot the common, and how you consider the idea would work out in actual practice. I consider the problem cannot be solved without the utilisation of some counter resistance, as in the case of the inclined tips of my model or similar devices. I may say that I have applied for patent protection for this particular model and pattern of main aerofoil. 83
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