In the old days of crudely
designed and under-powered aeroplanes this gyroscopic action
was very marked, and led the majority of pilots to dislike
turning an aeroplane to the right, since, in doing so, there
was some danger of ``stalling.''
LATERAL STABILITY is far more difficult for the designer
to secure than is longitudinal or directional stability. Some
degree of lateral stability may be secured by means of the
``lateral dihedral,'' i.e., the upward inclination of the surface
towards its wing-tips thus:
Imagine the top V, illustrated opposite, to be the front
view of a surface flying towards you. The horizontal equivalent
(H.E.) of the left wing is the same as that of the right
wing. Therefore, the lift of one wing is equal to the lift
of the other, and the weight, being situated always in the
centre, is balanced.
If some movement of the air causes the surface to tilt
sideways, as in the lower illustration, then you will note that
the H.E. of the left wing increases, and the H.E. of the right
wing decreases. The left wing then, having the greatest
lift, rises; and the surface assumes its first and normal
position.
Unfortunately however, the righting effect is not proportional
to the difference between the right and left H.E.'s.
In the case of A, the resultant direction of the reaction
of both wings is opposed to the direction of gravity or weight.
The two forces R R and gravity are then evenly balanced,
and the surface is in a state of equilibrium.
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