Even the experts in aeronautics differ so widely, however, that it is impossible to lay down any definite rules. One of the greatest authorities on the science of aviation, Mr. Horatio Philips, of England, believes that aeroplanes gain more support from the entering edges of their planes than from the rest of their surface. He argues that it is this edge, meeting the air currents, which serves to hold the aeroplane suspended.
This theory is founded on the experiments made with a machine of original design flown by Mr. Philips as far back as 1890. It consisted of a series of planes mounted one above the other at regular intervals, much the same as the strips of a Venetian blind. The lifting power of this model in proportion to its surface and the power exerted was enormous. This theory is borne out in part by the success of the model aeroplanes with very narrow wings which have been flown with great success during the year. The beautiful model built by Stewart Easter, for instance, which is illustrated on another page, depends for its support on planes which are no wider than ordinary window blinds.
There is an immense difference of opinion again as regards skin friction. Some writers believe the air has a tendency to stick to certain materials more than to others, and that this difference is so great as to materially retard some machines in their passage through the air. A complicate series of tables has been worked out in great detail to show the exact amount of this friction on various bodies. Some aviators go to great pains to make every part of their aeroplanes as slippery as possible. This is done by polishing the surfaces exposed to the air and in some cases enclosing the foreward part of the aeroplane, like a ship’s prow, to diminish friction.
On the other hand we find some of the greatest authorities on aviation disregarding this question almost entirely. In the Wright machines, for instance, the surface of the wings is usually left comparatively rough, and the sticks and wires are placed without any attention to diminishing friction. This is true as well of the Delegrange, Voison and Farman machines. Still other aviators design every detail of their machines to cut down this so-called skin friction. The uprights, for instance, are made elliptical in shape, with the sharp edges turned forward so that they will cut their way the more smoothly through the air.