Problem.-To the engineer, airplane design presents questions differing in many ways from those he has to deal with in other branches of his work. Essentially an engineering problem, its satisfactory solution must on that account demand consideration of questions which are common to all structural work. At the same time other important factors which are peculiar to it, enter into and complicate it.
The American definition of an engineer as " A man who can do for one dollar what any fool can do for two " may well be amended in the case of the aeronautical engineer. The latter must build for one pound avoirdupois what anyone could build for two, and in this importance of the weight question lies the primary difference between airplane and other structural design.
Not only is the saving of weight of primary importance in the structural members of the airplane, but also in the power unit. The greatest difficulty confronting the pioneers of flying was to obtain an engine which would give the necessary power for flight for a reasonable weight, and it is safe to say that the lack of this held back the science for many years.
With the advent of the petrol engine, however, the problem was solved, and flight became a practical proposition, purely on this question of pounds per horse-power