"Thank you so much," said Efficiency. "I think I have now at any rate an idea of the Elementary Principles of Flight, and I don't know that I care to delve much deeper, for sums always give me a headache; but isn't there something about Stability and Control? Don't you think I ought to have a glimmering of them too?"
"Well, I should smile," said a spruce Spar, who had come all the way from America. "And that, as the Lecturer says, 'will be the subject of our next lecture,' so be here again to-morrow, and you will be glad to hear that it will be distinctly more lively than the subject we have covered to-day."
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Propeller Slip: As the propeller screws through the air, the latter to a certain extent gives back to the thrust of the propeller blades, just as the shingle on the beach slips back as you ascend it. Such "give-back" is known as "slip," and anyone behind the propeller will feel the slip as a strong draught of air.
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Helicopter: An air-screw revolving upon a vertical axis. If driven with sufficient power, it will lift vertically, but, having regard to the mechanical difficulties of such construction, it is a most inefficient way of securing lift compared with the arrangement of an inclined surface driven by a propeller revolving about a horizontal axis.
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Pancakes: Pilot's slang for stalling an aeroplane and dropping like a pancake.