Engineering Wonders of the World
Volume III

THEORY AND PRINCIPLES OF THE AEROPLANE. 7 varies, within certain limits, relatively to the lift with the angle of inclination : thus, an aeroplane set at an angle of 1 in 12 (that is, having the forward edge 1 inch higher than the rear edge for every foot of width) develops twelve times as much lift as drift. Also that (/) the lift increases as the square of the velocity of motion relatively to the air : therefore the Fig 3.—DIAGRAM TO EXPLAIN TERMS “ ANGLE OF INCIDENCE,” “ ANGLE OF ENTRY,” “ CAMBER,” ETC.' higher the speed, the smaller the angle of the plane needed to sustain a given weight, and the greater the lifting effect in proportion to the power employed. This fact is due to the inertia of the air, and has its analogy in the fact that a skater travelling fast will be sup- ported by ice that would not bear him at rest. The cause of the great lifting power of a curved aeroplane with a downward-pointing front edge is not yet clearly understood. .. . . Phillips advanced the theory that the upward push given to the air by the front edge creates a partial vacuum over the upper rear portion of the aeroplane. Maxim, on the other hand, has recorded his opinion that the air follows the upper curve and joins that passing along the underneath surface at the trailing edge, giving a resultant upward push. Whatever the cor- rect explanation may be, the curved section is used generally, the ribs in some cases being tapered and covered on both sides, so as to make the curvature more pronounced on the top than on the bottom ; in others, covered on the lower side only. There seems to be a lack of standardization in this respect at present. As the lifting power of a flying machine in- creases, other things being equal, with its bear- ing surfaces, and is augmented by increasing the length of forward edge of these surfaces, as wide a spread as ^^sPos^’on °f . ... , Planes, possible is, in this respect, a desideratum. The spread must, however, be limited to convenient dimensions. Hence one section of experimenters have adopted the biplane, with, two “ decks ” set one above the other at a distance apart at least equal to the width of the decks, and a few have tried the triplane and multiplane. Blériot, Latham, and others have chosen the alternative of the monoplane, having a single deck subdivided into two wings, one on each side of a central “ body.” From the constructional point of view the biplane has the advantage of admit- ting a girder-like form of cross bracing between the two decks, and enabling the propeller or propellers to be mounted conveniently behind the decks, where, by virtue of acting on air already disturbed, they prove more efficient than the monoplane’s tractor screw, which bites air previously undisturbed, and drives it back on to th© body it is moving. Yet the performances of the monoplane have been so satisfactory as regards speed that one is driven to the conclusion that as yet it is too early to dogmatize on the respective merits of the two types. We may digress here for a moment to intro- duce and explain the term “ aspect ratio,” now commonly used in describing the shape of a deck. An aspect ratio of p . c .... Aspect Ratio. 6 to 1, tor example, implies that the greatest length from end to end is six times the greatest depth from the front to the rear edge. From what has been said already, it will be deduced that the ability of a flying machine to keep in the air depends on (1) the design of the supporting surfaces ; (2) the area of the supporting surfaces ; (3) the inclination of the supporting surfaces ; (4) the speed of