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Wilbur Wright, [Observations on Soaring], circa September 1900
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The dihedral angle is of advantage only in still air. It greatly increases
the disturbing effect of side gusts.
The buzzard which uses the dihedral angle finds greater difficulty to maintain
equilibrium in strong winds than eagles and hawks which hold their wings
The hen hawk can rise faster than the buzzard and its motion is steadier.
It displays less effort in maintaining its balance.
Hawks are better soarers than buzzards but more often resort to flapping
because thy wish greater speed.
A damp day is unfavorable for soaring unless there is a high wind.
No bird soars in a calm.
The object of the tail is to increase the spread of surface in the rear
when the wings are moved forward in light winds and thus preserve the
center of pressure at about the same spot. It seems to be used as a
rudder very little. In high winds it is folded up very narrow.
All soarers, but especially the buzzard, seem to keep their fore-and-aft
balance more by shifting the center of resistance than by shifting the
center of lift. Thus a buzzard soaring in the normal position will be turned upward by a sudden gust.
It immediately lowers its wings, much below it body . The momentum of its body now acting
above the center of resistance
turns the bird downward very quickly.
Viewed from directly beneath, the motion of the wings fore and aft seems
very small indeed. Neither do birds appear to draw in one wing more than
the other. The raising and lowering of the wings is very perceptible
whenever the observer is almost on a level with the bird.
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