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Aviation History
1910
1910 - 0482.PDF
" Flight" Copyright. Another view of the propellers on the Dunne aeroplane. levers are simultaneously pulled backwards, which raises the trailing edges of both flaps.* The pilot's seat is situated in the bows of the machine, the seat being formed inside the principal longitudinal girder, which is a lattice-work construction of timber and strip steel, shaped somewhat on the lines of a flat- bottomed boat. The bows and the stern come to a sharp edge, but in the centre there is sufficient beam to accommodate the 50-h.p. Green engine that drives the twin screws. The pilot sits a little in front of the engine, and there is just room for a passenger behind the pilot. The sides as well as the bottom of the girder are covered in, so that the pilot's head is alone exposed, lieut. so much on account of the advantage of stream line form in respect to minimising head resistance, as because of the locality of those masses in respect to the sup^ porting surfaces. A large mass situated above the supporting surface gives rise to disturbances in the air currents similar to those that would be created by a verti cal plane set at right angles to the sup porting surface, which in turn might be represented by an equivalent cambered aerofoil of inverted position, for the air current would, in effect, disregard the right angle by conforming to an upwardly curved path. Arguing on these lines, it seems that the relative position of the principal masses has considerable im portance from an aerodynamic point of view, and might possibly affect the re sultant centre of pressure in a way that would be serious on a machine like the Dunne aeroplane, which is designed for a high degree of natural stability. It is in order to avoid any tendency to reverse " Flight" Copyright. Detail view of the mounting of one of the propellers on the Dunne biplane. " Flight " Copyright. View of one of the propellers on the Dunne biplane showing its general shape. Dunne is of opinion that this surfacing of the girder and the almost complete enclosing of such principal masses as the engine and pilot is of very great importance, not * For an explanation of the aerodynamic reactions accompanying these actions, see Lieut. J. W. Dunne's letter in Correspondence. the direction of the air stream that the girder of the Dunne machine is so carefully surfaced. The twin propellers that drive the machine are carried on the extremity of a light transverse lattice-work beam, and are driven by chains from the crank-shaft. 480
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