Fig. 7.—Air-flow Round Cambered Surface
Fig. 8.—Air-flow Round Streamline Strut
Fig. 9.—Air-flow Round Square Strut
The reason why a perfectly flat plane is never used on full-size aeroplanes will be followed from [Fig. 6], which shows the flow of air over an inclined plane, the term “plane” being used here in its technical sense.
It will be noticed that a region of “dead air” or partial vacuum is caused, which seriously affects the lift of the plane. [Fig. 7] shows the flow of air over a cambered aerofoil (or to use the popular colloquialism “plane”). Less disturbance occurs in this instance, the air following very approximately the contour of the surface. It has been proved by test in the Wind Tunnel at the National Physical Laboratory at Teddington that an efficiently-designed aerofoil section has a lift two-thirds greater than a true plane. For a similar reason all struts or aeroplanes are “streamlined,” as shown by [Fig. 8]. The air flow, it will be seen, is less disturbed than by a square strut [(Fig. 9)].
Fig. 10.—Flow of Air over Ends of Plane
[Fig. 10] shows the air flow round a square-ended and taper-ended plane respectively. It will be noticed that the air has a tendency to leak over the end of the square plane, which is obviated by the tapered wing.