staff is held in an approximately vertical position with the lower end about shoulder high, and the launching is effected by giving a swaying motion to the body.
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By experimenting with a model constructed as above described the following facts may be demonstrated:—
(1) There is a critical velocity and angle at which if the aeroplane be launched it will continue to glide indefinitely. These may be termed the natural velocity and natural gliding angle.
(2) If the aeroplane be launched at other than its natural velocity and gliding angle, it will perform a wave-like trajectory, oscillating about the gliding path of natural velocity, the oscillations gradually diminishing in amplitude, and the path of the aero- plane approximating more and more closely to a uniform glide (Fig. 3).
(3) The natural velocity of a ballasted aeroplane of given dimensions will depend upon its weight and upon the position of its centre of gravity, being greater when the weight is greater and when the centre of gravity is nearer the front edge.
(4) That there is a particular position of the centre of gravity that results in a least value of natural gliding angle, and for planes of the form stated the least value of the gliding angle is about 8 or 9 degrees.
§ 4. The Ballasted Aeroplane. Longitudinal Stability.—The subject of the longitudinal stability of the ballasted aeroplane is dealt with briefly in the author's "Aerodynamics," § 162, from which the following passage is quoted:—
"Let us suppose that the position of the centre of gravity be such as will coincide with the centre of pressure when the plane makes an angle = β1 with its direction of motion. Now we
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