§ 246
AERODYNAMICS.
is formed by the face in presentation, being the normal plane the pressure on which constitutes a measure of the reaction on
Fig. 158.
the friction plane. The area of the normal plane can be extended at will by cementing a mica plate to its face, the edges of which are clipped until exact balance is obtained.
Fig. 159.
The opposite arm of the beam carries the friction plane E (Fig. 159); this is carefully formed of cedar of 6 mm. maximum thickness, the grain being well filled and served with a thin coat of varnish, or otherwise finished as may be required. The friction plane is carried on a holder formed by two pen steel
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