“What is the machine made of?” asked Sam.
“The frame is of hard wood; the covering of varnished fabric, while the various parts are connected by wire stays. You will observe that the planes are slightly curved; that is to prevent the air from escaping too freely from beneath, and gives more lifting power.”
“How is the aeroplane operated?” asked Bob.
“Its movements are controlled by levers; this one, for instance, operates the elevating planes in front; and this moves the main planes, for the frame is jointed, you see, allowing the surfaces to be warped to a certain extent. These pedals control the rudder and tail.”
“But what in the world makes it go up?” asked Willie.
“Well, William actually seems to be waking up a bit at last,” grunted Tommy.
“When the engine is started, the aeroplane is propelled swiftly over the ground. Naturally, the air is at once forced beneath the planes, exerting a powerful pressure upon their surfaces. Now, it follows that unless the aeroplane has sufficient weight to push this air downward or aside the machine is bound to overcome the force of gravity and rise.”
“Like a kite, I s’pose,” said Willie.
“Yes; and the faster the pair of powerful propellers revolve the stronger, of course, becomes this air pressure,” added Rob. “By reducing the speed of the engine, the aeroplane can be made to descend; and, I tell you, boys, volplaning, with the power shut off, is great sport.”
“Volplaning! What’s that?” cried Tom.