Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/376

§ 333 '''§ 233. Langley's Experiments. “The Plane Dropper.”'—The plane dropper'', as its name implies, is an apparatus in which the aeroplane is allowed to fall under the influence of gravity against the aerodynamic resistance encountered in its flight. In this instrument the “plane” is clamped to a “falling piece” arranged with friction rollers to slide freely on a vertical guide bar; a detent is employed to hold the falling piece in its top position until released by an electro-magnet. The angle made by the plane to the line of flight has a range of adjustment from horizontal up to 45 degrees. The total fall permitted is four feet, and the time of fall is registered electrically, both at the top and bottom, and later in the experiments at each foot of fall, the observatory chronograph being employed.

The experiments made with the plane dropper are numerous, and the results are highly instructive from a qualitative point of view; it would not seem, however, that the method is one that should be imitated by future experimenters: the results are in general deficient in quantitative value, except in the special case when the plane is recorded as “just soaring.” The weak point in this kind of instrument is the uncertainty that must prevail as to the existence or otherwise of a steady state. During the first portion of the drop there is acceleration taking place, that is to say, part of the weight of the paraphernalia is spent in overcoming its own inertia, and only a portion is supported aerodynamically; so that a considerable calculation is necessary before the results recorded can be made quantitatively available.

Admitting its defects, the method is one that appeals strongly to the imagination, imitating as it does many of the conditions of free flight, and in the hands of Prof. Langley it was shown capable of giving some valuable information. The chief points demonstrated were as follows:—

(1) That the time of fall of a horizontal plane in horizontal motion is greater than when no horizontal motion exists, and is greater the greater the horizontal velocity.