Wing Tip Details.
The actual shape of the wing tip varies with the make of machine, and forms one of the distinctive features of the complete assembly. There is a general tendency to rake the ends, making the back spar longer than the front, on the score that increased efficiency due to reduction of end losses is attained. While this is somewhat problematic, seeing that several notable machines have square tips, and some actually constructed with the longest edge leading, it undoubtedly imparts a pleasing and distinctive appearance.
The actual construction is largely a matter for individual preference, as there are several ways of forming it. For instance, a single piece of ash may be bent to shape, or it may be cut out in sections from spruce boards and glued together with a long splice, while in another instance oval steel tube is the material. This small section steel tubing seems admirably suited for such items as wing tips, trailing edges, and the various components of the empennage, such as the fixed stabilizer, elevators, fin, and rudder.
Another method of construction used for the wing tips of some machines consists of a number of strips, about six for a wing tip 1 in. wide by ΒΌ in. thick, the joints between which are disposed vertically, forming a laminated wing tip. In manufacture, each piece is bent round bending jigs or blocks of the required shape, the edges of the strips having previously been glued. It is apparent that the smaller the section of strip used, the easier it can be bent, and with this arrangement quite sharp bends can be successfully formed in spruce. The alternative method of steaming a solid piece is often wasteful, apart from the fact that it enforces the use of ash.
CHAPTER V.
DETAILS OF PLANE CONSTRUCTION.
The tendency to lose lift, pronounced in some machines, hardly noticeable in others, may be directly traced and attributed to the manner in which the wings are built, which is largely dependent upon the design. In the preliminary stages of design it is usual to take as a basis the figures for lift and drift of a known tested section, that is if facilities are not available for testing an exact scale model of the section it is intended to use. Anyway, the whole design is dependent upon these figures, in respect of both the maximum and minimum speeds, and also the rate of climb, and the extent to which the actual performance of the machine complies with these calculations is determined solely by the exactitude and precision with which the full-size wing conforms to the scale model. By this means only is it possible to design with any degree of accuracy.