Note however that the Center of Pressure is not fixed. We are not asking what will happen to the glider after a disturbance.ī) This answer will address the question in terms of Center of Pressure, not Aerodynamic Center, which simplifies things because we don't have to worry about a pitching moment coefficient. What is the relation between Center of Pressure (C.P.), Aerodynamic Center (A.C.), "hang point" (the point where the flexible "hang strap" connects to the glider, or the point where the "trike" unit is connected to the wing), and the control bar position relative to pilot's body, if the glider is to fly well, meaning that when I lift hands from bar, the glider will not pitch.Ī) It is important to note that this is a question about trim, not stability.An alternative method is to add a trimming surface behind the wing, and you will often see little adjustable mini-tails to both improve the wing's stability and allow a variation in trim speed by changing the trimming surface's incidence. Trikes will address this often by using a hang point that can be moved fore and aft over a range of a couple of inches, by some mechanism like a worm screw, allowing trim to a range of hands-off speeds.
If the flexible attachment of the hang point is fixed to one location on the glider's keel boom, that allows the glider to only seek one AOA with no pressure on the bar, which means only one speed that the machine will fly at hands off. When you see hang glider pilots yanking on a cord after launch, they are pulling in the trailing edge adjustment to reduce washout to improve glider performance - it's let out again before landing, because you don't want to be maneuvering at low speed like that close to the ground. Adjustable tension for the trailing edge on some hang gliders allows the reduction of washout by increasing tension on the trailing edge, to improve the wing's efficiency by loading the outboard end more, at the cost of some pitch stability and spin resistance. Pitch stability/trim of the wing is achieved by the extreme trailing edge washout hang gliders use toward the tips.
At that AOA, you can let go of the bar and the wing flies along merrily on its own (more or less).
The trimmed AOA that the wing will seek is that which places the hang point on the wing's CP (as Quiet Flyer says).
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