Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/365

Rh '''§ 227. Dines' Experiments (continued). Aeroplane Investigations (Apparatus).'—The description and results of these experiments are given in Mr. Dines paper on “Wind Pressure upon an Inclined Surface,” (Proc. Royal Soc.'', Vol. XLVIII.). The apparatus employed is a form of the centrifugal balance described in § 223, and the “planes” employed are of the triangular section already illustrated in Fig. 100 (a).

Two diagrammatic views of the centrifugal balance employed are given in Fig. 142, which is reproduced from Mr. Dines' paper. In this, like letters refer to like parts in the two views; and we have the pressure plane $$P$$ mounted on the arm $$E\ F$$ pivoted to turn about the axis $$M\ N ,$$ which is arranged radial to the axis of the whirling table. We have the bar $$A\ B ,$$ which is the mass whose centrifugal force is employed to measure the reaction, mounted slidably in a pivot piece free to turn about the vertical axis $$C\ D ,$$ and the pivot piece and the pressure plane arm are geared together by a stud projecting from the former and engaging with the latter. This may be looked upon as equivalent to a single tooth of an imaginary pair of bevel gears. A counterpoise weight $$K$$ performs the double function of statically balancing the pressure plane, and of rendering the arm $$E\ F$$ symmetrical in respect of wind pressure.

The adjustment of the bar $$A\ B$$ by an ingenious device was arranged to take place automatically. This automatic arrangement consists of a windmill carried on the arm of a whirling table, arranged to drive whenever possible a crown wheel, by means of a long pinion engaging with the crown wheel on both sides. The crown wheel is carried on the pivot piece, and by means of a rack and pinion moves the bar $$A\ B$$ in the one direction or the other. When the pivot piece reaches either of its extreme positions (the total range being a few degrees), the crown wheel becomes disengaged from its pinion on the one side or the other, the windmill immediately begins to operate, and the bar undergoes displacement in the direction required to restore equilibrium. So long as the balance is perfect and