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Fig. 7. Sopwith Triplane Speed Scout.

Quadraplane

Fig. 7-A. Curtiss Triplane Speed Scout. Courtesy "Aerial Age."

Tandem Aeroplanes

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.

The wings must be separated by a sufficient distance so that the rear set will not be greatly influenced by the downward trend of the air caused by the leading wings. As the rear surfaces always work on disturbed air they should be changed in angle, increased in area, or be equipped with a different wing curvature if they are to carry an equal proportion of the load. Usually, however, the areas of the front and rear wings are equal, and the difference in lift is made by changes in the wing form or angle at which they are set. In some cases the wings are approximately the same, the difference in lift being compensated for by moving the load further forward, thus throwing more of the weight on the front wings.