Imitate the Bat: Membrane Wings and Balance in the Air
Why the flying machine should copy the bat, and how a bird rises against the wind without flapping
Leonardo argues that the artificial bird should imitate the bat rather than the feathered bird, because the bat's continuous membrane binds the whole wing while feathers are perforated and let air pass. He then turns to balance in flight: the heaviest part of a body guides its motion, so the driving mass stays behind and below. A final note explains how a bird can lift itself without beating its wings by setting itself obliquely against the wind. The margin carries small pen sketches of a bat and of birds in flight and diving.
On this page
Imitate the bat, not the feathered bird
The artificial bird should copy only the bat, because its membranes form the framework that binds the main ribs of the wings. This gives an unbroken lifting surface rather than one made of separate parts.
Membrane versus perforated feathers
Feathered wings rest on more powerful bone and sinew, but they are perforated: the separated feathers let the air pass through them. The bat instead is helped by the membrane that ties the whole surface together and is not perforated.
The heavier part guides the motion (a, b)
The heaviest part of a body always becomes the guide of its motion. With the bird in the arrangement a b, where a is lighter than b and b holds the driving power, a will always stay above b and can only get ahead of it by a passing accident.
Rising against the wind without beating the wings
To rise without flapping, the bird sets itself obliquely against the wind, presenting the wings with their elbows facing it and keeping its center of gravity toward the wind. If its tendency to descend has a force of 2 and the wind strikes with a force of 3, the motion obeys the 3.