Why the Tail Turns the Bird More Than the Wing
A lettered diagram proving the tail, farther from the center, meets a stronger wind
A pen diagram at the upper right, lettered m a, o b, n c, sets a bird's wing and tail against the wind. Because the tail lies farther from the bird's center, the note argues, it meets a more powerful wind. It then proves that when the wind on the wing (a b, at m o) equals that on the tail (b c, at o n) the bird holds a straight course; but if the tail's wind is stronger, the tail gives way, the wing swings into the wind, is driven up like a wedge, and the bird turns.
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Diagram of wind on wing and tail (m a, o b, n c)
At the upper right a rectangular framework with a small bird at one end is lettered along its length, the transcription giving the points m a, o b, n c. It sets the wing (m o) and the tail (o n) at their differing distances from the bird's center, against the line of the wind.
The tail, farther from the center, feels a stronger wind
The wind striking the tail is always more powerful than that striking the wing, because the tail is farther removed from the bird's center. Being carried against the wind, the wing's own motion further increases its speed and power, so the wind wedges under it and lifts it.
When the two winds balance, the bird flies straight
If the wind a b that strikes the wing m o equals the wind b c that strikes the tail above at o n, the bird does not turn but is carried along the line of the wind's course. If instead the tail's wind is the stronger, the tail is overcome and the wing turns into the wind.