Testing the Lifting Force of a Great Flapping Wing
A 20-braccia paper-and-cane wing against a 200-pound bench, with the underwater-arm analogy for flight
Leonardo proposes a concrete experiment to see whether a wing can generate lift: build a wing at least 20 braccia in span from paper stiffened with netting on cane ribs, fix it to a 200-pound bench, and beat it with a quick force; if the bench rises before the wing descends, the test succeeds. He explains the physics with an underwater analogy, a swimmer whose arms, if made to fall in two beats instead of four, drive his body upward. He concludes that of the 200-pound load, 100 falls to the operator holding the lever and 100 is discharged onto the air through the wing. The page carries a large careful drawing of the wing-and-lever apparatus with an operator, plus smaller repeat sketches.
On this page
The true test of a wing: a quick beat that lifts a 200-pound bench
Make a wing of paper armed with netting, its ribs of cane, at least 20 braccia in breadth and length, and fasten it to a bench weighing 200 pounds. Apply a quick force as figured above; if the bench rises before the wing falls, the test is good. If the force is not quick, waste no more time on it.
The underwater-arm analogy and sharing the 200-pound load
A swimmer at the bottom of deep water whose open arms fall at their natural speed simply sinks them to his thighs and stays put; but arms that should fall in four beats, made to fall in two, drive the body upward. Likewise, of a 200-pound bench, 100 pounds is borne by the man at the lever and 100 is discharged onto the air by the wing.
The wing-testing apparatus
A large, careful drawing shows the wing mounted on a stand with a lever worked by an operator, drawn expressly to demonstrate the force required by the wing's movement. Smaller sketches repeat the same arrangement.