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The dihedral would be very effective in still air, but in turbulent air, and with the body swinging back and forth, the dihedral would act in the nature of a circular guiding path, and thus tend to allow the swinging to persist or increase rather than to damp it down, as would be the case with level straight wings. Again, with the wing bent up at a considerable angle, a side gust as at (S) would tend to throw the machine still further over, and thus increase rather than diminish the difficulty. In practical machines, the dihedral is usually made very small (d = 176 degrees), the angle of each wing with the horizontal being about 2 degrees, or even less. I think the advantage of such a small angle is rather more imaginary than actual, and at present the greater number of war machines have no dihedral at all. In the older monoplanes the angle was very pronounced.

Fig. 15 shows the dihedral applied both to the upper wing (U) and the lower wing (L), the usual method of applying dihedral to large biplanes. Fig. 16 shows the method of applying the dihedral to small, fast machines, such as speed scouts, the dihedral in this case being used only on the lower wing. The dihedral on the bottom wing is usually for the purpose of clearing the wing tips when turning on the ground rather than for stability. A lower wing with a dihedral is less likely to strike the ground or to become fouled when it encounters a side gust in landing or "getting off." The use of straight upper wings makes the construction much simpler, especially on the small machines where it is possible to make the wing in one continuous length.