In normal flight our wings are flying overhead, gliding through the air stable and pressurized. Assuming we are not doing any acro, etc., there are basically three things that can happen in flight, changing the glider’s normal flight configuration. They are:
1. Stall
2. Spin
3. Collapse
A stall is when the glider loses lift as a result of too high an angle of attack. The wing no longer glides through the air, but slips and falls through the air. A stall is usually pilot-induced as a result of too much brake.
A spin is when the glider rotates along its yaw axis (an imaginary line drawn from the pilot to the symmetrical center of the wing. It is basically when the glider spins like a helicopter prop. A spin is also generally pilot induced as a result of too much braking on one side. That side stops flying (enters a stall) and starts to drop back, while the other side continues to fly. The glider then flat-spins, kind of like a helicopter.
A collapse happens when all or part of the glider deflates, loses internal pressure, and tucks under or shrinks into a piece of loose cloth. This happens most often when the angle of attack is too low. If the angle is too low on a single side, the collapse will be asymmetric. If the angle is too low for the entire glider, a frontal collapse will result. Unlike a stall or a spin, a collapse can happen without pilot input and due to, for instance, a significant down-draft of an airmass encountered by the glider.
To avoid stalls and spins, we need to know the stall point of our glider, both in straight flight and during a turn (such as when thermaling). This should keep us from applying too much brake, whether on one or on both sides. Also, when the wing pitches back as a result of encountering a strong updraft or turbulence, we need to recognize it and apply less brake even if we are within the otherwise permissible range of braking relative to the normal stall point. (Sometimes, even some speed bar may be warranted to reduce the angle of attack.) Avoiding too much brake this way should keep the glider from both stalling and spinning.
To avoid collapses, we need to keep the pressure constant regardless of air movements. This is known as active piloting. This takes practice and involves constant adjustment of brake tension and hip “loading” (hip dropping), all to feel the same pressure in the glider. I think a more precise term would be “anticipation piloting.”
Recognizing the rough air takes flying experience in varied conditions and continuing interest in reading and discerning the weather. Similarly, reacting quickly and recovering from collapses takes both knowledge of what to do and trained reflexes of actually doing it, which can be learned and practiced both in SIVs and in regular flying.
Recovering from asymmetric collapses is generally governed by the principle “steer and clear”. That means that our immediate and spontaneous reaction to such a collapse is to lean away from the collapse and apply some brake on the good side – all to keep the glider from turning too fast as a result of the collapse. This is first priority, as allowing the glider to go into a deep turn and spiral is likely to put us in a dangerous position of being unable to stop the dynamics and unable to even throw a reserve. After steering, we can clear the collapse by banging the brake on the collapsed side if needed. Banging the brake in most cases means a deep and quick, momentary input, as opposed to a multitude of short/shallow tugs or prolonged inputs.
Recovering from a full frontal is dependent on the glider, but in most cases is done by going hands up and/or banging on both brakes until the glider re-inflates. We then need to check the surge to avoid another collapse or problematic configuration.
Sometimes, when a glider is not responding to corrective inputs or there is a cascade of troublesome events, a full stall can be used as a “reset button”, to reset the glider and resume normal flight. Obviously deliberate full stalls and exits from them should be practiced in an SIV if possible.