"Very good," said Mr. Giddings; "but I understand that has been tried before, with the result that the airplane at once tipped forward and stuck its nose into the ground, or rather tried to, smashing its propeller to smithereens."
"They will do that every time unless something has been devised to counteract this tendency to pitch over," explained John. "We have devised the thing to prevent it, Mr. Giddings."
"See here, dad," put in Bob at this point. "Stoop down a bit and look under the forward end of the body here."
His father did as requested, and Bob pointed out a circular opening about the size of a saucer, from which protruded the end of an aluminum-encased shaft bearing a small rubber-tired wheel of very sturdy proportions.
"That is our preventer, dad," smiled his son.
"In a few minutes we'll show you how it works," added John Ross. "I see you are wearing a cap, sir, as I suggested. That is all the special dress you will need, as our enclosed cabin makes helmets and close bundling unnecessary. We fellows will wear our regular working togs."
Everything being in readiness, the four young men easily pushed the big airplane out of the building and to a place where it would have a smooth runway for a hundred yards ahead. The weather was ideal for the trip. There was little wind, and the few strato-cumulus clouds which were visible showed great stretches of azure-blue sky between them.
"Everybody climb in," ordered Tom, with a wave of his hand. "I'll crank her up. You take the joy-stick, John."
All hands complied. Then Tom began to turn the big burnished propeller, just as John threw a lever from the inside which caused the auxiliary ground wheel to shoot down and engage the sod. At the same time the movement of another lever by Paul set the airplane's brakes.
Several times Tom turned the propeller around. Then, with a pop, the engine cylinders began to fire, Tom jumped swiftly back, and the propeller whirred like a mad thing. At the same time the Sky-Bird gave a start, as though to dash forward; but beyond a steady, slight vibration of her whole body, as Tom slowed down the motor to four hundred revolutions per minute, there was no indication to her inmates that she was straining to get away. Tom now quietly mounted the step, and came into the cabin, pulling the step up after him and closing the self-locking door.