The Aeroplane Speaks. Fifth Edition

CHAPTER I FLIGHT Air has weight (about 13 cubic feet = 1 lb.), inertia, and momentum. It therefore obeys Newton's laws[14] and resists movement. It is that resistance or reaction which makes flight possible. Flight is secured by driving through the air a surface[15] inclined upwards and towards the direction of motion. S = Side view of surface. M = Direction of motion. CHORD.--The Chord is, for practical purposes, taken to be a straight line from the leading edge of the surface to its trailing edge. N = A line through the surface starting from its trailing edge. The position of this line, which I call the Neutral Lift Line, is found by means of wind-tunnel research, and it varies with differences in the camber (curvature) of surfaces. In order to secure flight, the inclination of the surface must be such that the neutral lift line makes an angle with and above the line of motion. If it is coincident with M, there is no lift. If it makes an angle with M and below it, then there is a pressure tending to force the surface down.