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Aviation History
1911
1911 - 0275.PDF
APRIL I, 191 I. JySBf] General view of the Roe triplane from behind. " Flight " Copyright. will be observed that in the latest machine the lowest of the three planes has less span than the others, and it is only the latter that are influenced by the warping movement. The body of the machine is an open triangular section girder made of ash and trussed with wires. It is situated just beneath the level of the middle plane, and its fore part is cased in from the engine to the pilot's seat. The engine itself, as may be observed from the illustrations, is mounted high up in the bows, and the direct driven propeller is some little distance in front of the leading edge of the planes. A simple undercarriage, supported on the Farman principle by four wheels mounted independently in pairs on the two skids, serves to support the entire weight of the front part of the machine, while the tail is kept clear of the ground by a rocking skid anchored to the frame by a piece of elastic. A minor detail of construction indicative of thoughtfulness in design can be seen in the sketch of the mounting of this tail skid, which shows how it has been provided with a special rocker-shaped surface where it takes abutment against the base of the rudder post. Some other interesting construc tional details are also illustrated in the sketches, which show the method of fitting the end struts of the main planes loosely into their sockets, and taking the tension by auxiliary tie- wires in order to facilitate the warping of the wings. Another detail illustrated by a sketch is the method of anchoring the diagonal tie-wires to thin steel plates that are clipped against the spars of the body by the principal aluminium brackets. A characteristic feature of the Roe machine, considered as a triplane, is, of course, the relatively high aspect ratio of its planes. Owing to the fact that it has three planes, the same equivalent surface is available from a given span with a considerably reduced chord, and consequently the ratio of span to chord in each plane, which is termed the aspect ratio, has a higher value than is ordinarily to be found in^biplane construction. In the machine illustrated a span of 32 ft. is accompanied by a chord of 3 ft. 6 ins., which corresponds to an aspect ratio of over nine. In most biplanes the same factor seldom exceeds six, and in monoplanes it is still less likely to be as high. The advantage of a high aspect ratio is fundamental in character, and has been sub stantiated in such laboratory experiments as have been " Flight '• Copyright. Sketch of the tail on the Roe triplane. conducted. It is concerned with the leakage of air over the extremities, which leakage bears a smaller percentage of the total volume of air dealt with as the aspect ratio increases for a given area of plane. Fundamentally, therefore, the triplane is potentially a more efficient combination than the biplane—provided always that other practical considera tions do not interfere with the realisation of this feature— and it is at least to Mr. Roe's credit that he has flown with less power than anyone. Sketches illustrating some constructional details on the ROJ triplane. 277 "Fl ght" Copyright.
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