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
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/bf/Aerial_Flight_-_Volume_1_-_Aerodynamics_-_Fig_117a.png/350px-Aerial_Flight_-_Volume_1_-_Aerodynamics_-_Fig_117a.png)
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
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7b/Aerial_Flight_-_Volume_1_-_Aerodynamics_-_Fig_117b.png/400px-Aerial_Flight_-_Volume_1_-_Aerodynamics_-_Fig_117b.png)
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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