Fig. 6-B. The Mann Two-Propeller Pusher Biplane. The Propellers Are Mounted on Either Side of the Body, and Are Driven by a Single Motor Through a Chain Transmission. This Drive Is Similar to the Early Wright Machines.
Fig. 7 is a sketch of a Sopwith Triplane Scout and shows clearly the three superposed wings. The small amount of interplane bracing, and the great aspect ratio, makes this type very suitable for high speed. The body, tail and chassis arrangements are practically the same as those of a biplane. The Curtiss Triplane Scout is the pioneer of this type of machine, although experimental work on the triplane had been performed in England by A. V. Roe many years ago. The Roe triplane was lightly powered and for its time was successful in a way, but the Curtiss is the first to enter into active competition against the biplane scout. Owing to the small span required for a given area, and the possibilities of very light and simple bracing, the triplane is an ideal type for heavy duty machines of the "bombing" species. Enormous triplanes have been made that are capable of a useful load running up into the tons, the large Curtiss and Caproni’s being notable examples. As the triplane is much higher than the biplane of equal area, the interplane bracing is deeper and more effective without causing proportionately higher resistance.
Fig. 7. Sopwith Triplane Speed Scout.
Quadraplane. The use of four superposed surfaces has not been extended, there probably being only one or two of these machines that can be said to be successful. The small "quad" built by Matthew B. Sellers is probably the best known. The power required to maintain this machine in flight was surprisingly small, the machine getting off the ground with a 4 horsepower motor, although an 8 horsepower was afterwards installed to maintain continuous flight. The empty weight was 110 pounds with the 8 horsepower motor. The span of the wings was 18' 0" and the width or "chord" 3’ 0", giving a total area of about 200 square feet.
Fig. 7-A. Curtiss Triplane Speed Scout. Courtesy "Aerial Age."
Tandem Aeroplanes. A tandem aeroplane may be described as being one in which the surfaces are arranged "fore and aft." The Langley "Aerodrome" was of the tandem monoplane type and consisted of two sets of monoplane wings arranged in tandem. This pioneer machine is shown in Fig. 8, and is the first power driven model to achieve a continuous flight of any length. Instead of two monoplane surfaces, two biplane units or triplane units can be arranged fore and aft in the same manner.
While there have been a number of tandem machines built, they have not come into extensive use. Successful flight was obtained with a full size Langley Aerodrome, and this machine flew with a fair degree of stability. The failure of other tandem machines to make good was due, in the writer's opinion, to poor construction and design rather than to a failure of the tandem principle. The Montgomery glider, famed for its stability, was a tandem type but the machine was never successfully built as a powered machine.