front edge is insufficient, then the up-current will no longer strike the edge conformably, and, in the case of a real fluid, a discontinuity will result, as illustrated in Fig. 117; such a discontinuity may be a trivial matter involving only a small pocket of "dead water" (a), or it may be more serious so that the form of flow resembles that generated by an aeroplane (b); in either case we
Fig. 117a.
know, from the great efficiency obtainable from the aeroplane, that the effects are not disastrous.
If, secondly, we suppose that the leading edge has too much
Fig. 117b.
"dip," the want of conformity is in the opposite direction, and the surface of discontinuity springs from beneath the leading edge as depicted in Fig. 118; the result of this is destructive to the whole peripteral system of flow, for the moment the pressure region commences to occupy the upper surface of the aerofoil a condition of instability arises and a new system of flow is inaugurated which produces a downward instead of an upward reaction. This is a fact easily demonstrated experimentally: a model in which
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