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Aviation History
1912
1912 - 1206.PDF
DECEMBER 21, 1912. Edited by V. E. *' Flat" Plane Models. SEVERAL corresponding have written to me relative to what they term flat plane models, i.e., models in which the main plane or planes is constructed without any camber, i.e., with flat ribs or no ribs at all. Some have written asking for information as to how such models can possibly fly. I should have stated that the main plane is fixed flat OB ihe motor rod without any angle of incidence, Otlurs again have asked which is the more efficient, or to speak more correctly which is the better to use, a cambered or nun- Fig. 1.—A "flat" plane model. cambered plane, taking into account possible extra weight, resist ance, stability, its. Let us first of all try and get a clear idea of what our correspondents mean when they speak of a flat main plane ; they undoubtedly mean a model with planes like that shown in Fig. 1, in which the main plane is set flat on the motor rod without any angle of incidence, and has no ribs, i.e., the main plane is just a rectangular framework, on which the fabric (<-ilk) is stretched. The elevator is similarly constructed. The model is one constructed by the writer, some nineteen months ago, and in the Wakefield Cup Competition of loii, it scored 84 marks out of a po-sible 100. In calm air, this model would rise off linoleum after a run of 4 ft., and sometimes less (less, of course, when facing a breeze), and when fully wound up, 900 turn?, would remain in the air three-quarters of a minute. Out of 17 flights, its least duration was 28 sees., and its best 57 sees. It would rise to a considerable altitude, sweeping upwards in a left- handed spiral. Dimensions, &c. : length, 4 ft. 4 ins. ; width of main plane, 29± ins. Total weight, 6A ozs., i.e., weight of model, 4 ozs., rubber, 2 ozs. (f^ square). Length of rubber strands, 47 ins. Number of strands to each propeller, 14. Backbone T sectioned pitch pine, 4 ft. long, weight I oz., greatest thickness TV in. Wheels made of hollow brass curtain rings with cross pieces of thin tinned-iron. Propellers, centrale type—diam., 11 i ins. Main plane and elevator constructed of satin-walnut, that of the main plane being |-in. wide by ,',;-">• thick. Dimensions, 29 ins. by 5$ ins. Dimensions of elevator, J\ ins. by 3 ins. The bearings for the propellers weighed half a gramme each. Jap silk gut was used to "stay" the model. As already stated, neither plane nor elevator were given any intentional camber, and the fabric (Hart's) was stretched as tight us was practical—it was fairly taut— no more. The main plane was placed flat on the backbone or motor rod, the elevator, of course, inclined ; this inclination was such that the front or leading edge was about |-in. higher than its back. In the year 1911, a r.o.g. model which could give such results JOHNSON, M.A. as the above was not common, and the design or, to speak more correctly, the chief points in the design were fairly widely copied. To return, however, to the question of camber when such a model is in actual' flight, under the consequent positive wind pressure on the under and negative pressure on the upper side of the fabric, a natural camber is formed, the extent of which depends partly on the wind pressure and partly on the tautness of the fabric. That such is the case can easily be seen by flying such a model (in which the fabric is not very taut) oyer a fiat ground on a rather gusty day—chooiing a spot where the wind " rolls " over the ground—such a model, when it encounters a down current, is straightaway put flat on the ground, the camber in this case being reversed. Tfle advantage of using a properly cambered plane is that more lift is obtained at a fine angle, and at the expense of less resistance ; in fine, it is a more " efficient" form. If the camber be large, some small loss in natural automatic longitudinal stability probably occurs owing to the well-known tendency of a cambered surface to " follow its own curve." But it is a mistake to use too great a camber. Suppose, however, that the planes shown in Fig. 1 were so constructed as to remain really flat when in actual flight, i.e., supposing them con structed of very light wood, say, as in Clarke's flyers but without their camber, would such a model fly? The answer, founded on the personal practical experience of the writer is yes ! Such a machine can be got to fly very well, although not, of course, so well as when a small camber is present. We will try to explain in untechnical language why this should be so. We have, it will be noticed, two flat surfaces rigidly connected, one of which (the elevator), has a positive angle of incidence, i.e., the two planes therefore form a vee opening skywards, and such a system forms a proper system for longitudinal stability, the dihedral angle or vee given to both the elevator and main plane do the same thing so far as lateral stability is concerned. Imagine the motors and propellers wound up and the machine launched horizontally into the air. Leaving out the resistance of >he air we have the push or thrust of the propellers tending to drive it straight forward, and its weight, i.e., the pull of gravity tending to make it fall. But it does not fall, in spite of the supposed non-lift of the main plane, supposed flat and quite horizontal ; not only does it not fall but it m ty rise to some 20 or 30 ft. into the air, and make what appears to be a perfectly horizontal flight of, say, 100 yards before gliding to earth. In the first place, it must be remembered that the elevator is set at a positive angle, and is therefore capable of carrying a load ; also, the load which it carries per unit area is greater than that carried by the main plane. The elevator then prevents the nose of the machine from falling— the main plane (in fact, any body travelling through the air) always takes the path of least resistance—it is alwaysadvancing on to fresh air, i.e., before it has any, time to have dropped vertically it has advanced on to fresh air, and so on. It is very similar to a skater skating over thin ice ; provided he skates fast enough, he passes on to fresh ice so quickly that before any particular section has had time to give the pressure is removed. Of course, it is not perfectly correct to suppose that either the ice or the air do not yield somewhat, no matter however rapid the pace may be ; but it must be remembered that so soon as our flat plane drops slightly it becomes virtually inclined, and therefore ex periences more lift while dropping. The reader should compare the above remarks with Prof. Langley's THE GAMAGE 4-H.P. SINGLE-SCREW PETROL-DRIVEN HYDROPLANE.-Speed 14 m n h 3,000 r.p.m.; speed of propeller, 1,500 revs.; length, 4 ft. 1206 speed of engine,
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