Properties of the Various Types.
The necessity for increased size, with its inevitable sequence, increased weight, must be realized without a very great addition to the landing speed, the figure for the latter standing at approximately 45–50 m.p.h. This factor greatly influences the maximum wing loading possible, without detrimentally affecting this, so that in the design of the large machine a considerable increase in wing area is unavoidable. This fact practically rules out the monoplane system for the large aeroplane, as, although this arrangement possesses a superior ratio of lift to drag to that of the biplane or multiplane, the great span necessary to obtain the wing area is impracticable. It is quite obvious that to brace adequately a monoplane structure of 100 ft. span or so, a very complex system would be required, in addition to which the spars would essentially be of larger and heavier section. The biplane arrangement can be used successfully for spans up to 100 ft., and, assuming that the future commercial machine will necessitate still greater wing area, it is a feasible supposition that the triplane, or even quadruplane systems will be used. Certain modern triplanes have a reputed excellent performance, the carrying capacity and engine power being colossal. Against this we have the fact that the advantage of the triplane system is purely structural, as aerodynamically it is not nearly so efficient as the biplane, and it is at this stage that the question of the limiting size of aeroplanes is encountered. Various tests, both in model form and full size, have shown that the lift of the middle plane of the triplane system is greatly inferior to that of the top or bottom planes, this being due to the interference of the free air flow by the upper and lower planes. This circumstance is an indication that the biplane arrangement, viewed from the standpoints of modern design, is the most economical form for future commercial use.
CHAPTER VIII.
FUSELAGE CONSTRUCTION.
The body, or fuselage as it is generally described, constitutes the nucleus of the completed machine, and at the same time offers the most interesting examples of constructional detail. It may be as well to point out that the term “fuselage” is ordinarily applicable to a body of a machine of the tractor type; the short body of the average “pusher” or propeller aeroplane is termed the “nacelle.”
The material chiefly used in the construction of this component is wood, and there are but very few instances where metal is used.