Now if this rope is hooked to a spring balance, which in turn is made fast to the stationary object, the "thrust" of the propellers will be registered in pounds on the scale of the balance. Anywhere from five hundred to nine hundred pounds of thrust will take a monoplane or biplane up. But Tom wanted more than this.
Once more the motor coughed and spluttered, and the big blades whirled about so fast that they seemed like solid pieces of wood. Tom stood on the ground near the levers which controlled the speed, and Ned watched the scale.
"How much?" yelled the young inventor.
"Eight hundred."
Tom turned on a little more gasolene.
"How much?" he cried again.
"Ten hundred. That'll do!"
"No, I'm going to try for more."
Again he advanced the spark and gasolene levers, and the comparatively frail craft vibrated so that it seemed as if she would fly apart.
"Now?" yelled Tom.