Editing Hang gliding (section)

== Stability and equilibrium ==
[[Image:Hyener PA2006.jpg|thumb|High performance flexible wing hang glider (2006)]]
Because hang gliders are most often used for recreational flying, a premium is placed on gentle behaviour, especially at the [[Stall (flight)|stall]] and natural [[Flight dynamics (aircraft)|pitch]] stability. The wing loading must be very low in order to allow the pilot to run fast enough to get above [[Stall (flight)#"Stall speed"|stall speed]]. Unlike a traditional aircraft with an extended [[fuselage]] and [[empennage]] for maintaining stability, hang gliders rely on the natural stability of their flexible wings to return to [[Mechanical equilibrium|equilibrium]] in [[Flight dynamics (aircraft)|yaw]] and pitch. [[Flight dynamics (aircraft)|Roll]] stability is generally set to be near neutral. In calm air, a properly designed wing will maintain balanced trimmed flight with little pilot input. The flex wing pilot is suspended beneath the wing by a strap attached to their harness. The pilot lies [[Prone position|prone]] (sometimes [[Supine position|supine]]) within a large, triangular, metal control frame. Controlled flight is achieved by the pilot pushing and pulling on this control frame, thus shifting their weight fore or aft, and right or left in coordinated maneuvers.

; Roll
: Most flexible wings are set up with near neutral roll due to [[sideslip]] ([[Dihedral (aircraft)#Anhedral|anhedral]] effect). In the roll axis, the pilot shifts their body mass using the wing control bar, applying a rolling moment directly to the wing. The flexible wing is built to flex differentially across the span in response to the pilot applied roll moment. For example, if the pilot shifts their weight to the right, the right wing trailing edge flexes up more than the left, creating dissimilar lift that rolls the glider to the right.

; Yaw
: The [[Yaw angle|yaw]] axis is stabilized through the backward-sweep of the wings. The swept platform, when yawed out of the [[relative wind]], creates more [[Lift (force)|lift]] on the advancing wing and also more drag, stabilizing the wing in yaw. If one wing advances ahead of the other, it presents more area to the wind and causes more drag on that side. This causes the advancing wing to go slower and to retreat back. The wing is at equilibrium when the aircraft is travelling straight and both wings present the same amount of area to the wind.

; Pitch
: The pitch control response is direct and very efficient. It is partially stabilized by the [[Washout (aeronautics)|washout]] combined with the [[Swept wing|sweep]] of the wings, which results in a different angle of attack of the rear most lifting surfaces of the glider. The wing centre of gravity is close to the hang point and, at the trim speed, the wing will fly "hands off" and return to trim after being disturbed. The weight-shift control system only works when the wing is positively loaded (right side up). Positive pitching devices such as reflex lines or washout rods are employed to maintain a minimum safe amount of washout when the wing is unloaded or even negatively loaded (upside down). Flying faster than trim speed is accomplished by moving the pilot's weight forward in the control frame; flying slower by shifting the pilot's weight aft (pushing out).

Furthermore, the fact that the wing is designed to bend and flex, provides favourable dynamics analogous to a spring suspension. This provides a gentler flying experience than a similarly sized rigid-winged hang glider.