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Since the glider is in a skidding turn during the crossed- control condition, the wing on the outside of the turn increases speed and produces more lift than the inside wing, and the glider starts to increase its bank. The down aileron on the inside of the turn helps drag that wing back, slowing it and decreasing its lift. This further causes the glider to roll. The roll may be so fast that it is possible the bank will be vertical or past vertical before it can be stopped. 

For the demonstration of the maneuver, it is important that it be entered at a safe altitude because of the possible extreme nose-down attitude and loss of altitude that may result. Before demonstrating this stall, the pilot should clear the area for other air traffic. While the gliding attitude and airspeed are being established, the glider should be retrimmed. When the glide is stabilized, the glider should be rolled into a medium banked turn to simulate a final approach turn that would overshoot the centerline of the runway. During the turn, excessive rudder pressure should be applied in the direction of the turn but the bank held constant by applying opposite aileron pressure. At the same time, increased back-elevator pressure is required to keep the nose from lowering. 

All of these control pressures should be increased until the glider stalls. When the stall occurs, releasing the control pressures and simultaneously decreasing the AOA initiates the recovery. In a crossed-control stall, the glider often stalls with little warning. The nose may pitch down, the inside wing may suddenly drop, and the glider may continue to roll to an inverted position. This is usually the beginning of a spin. It is obvious that close to the ground is no place to allow this to happen. 

Recovery must be made before the glider enters an abnormal attitude (vertical spiral or spin); it is a simple matter to return to wings-level, straight flight by coordinated use of the controls. The pilot must be able to recognize when this stall is imminent and must take immediate action to prevent a completely stalled condition. It is imperative that this type of stall not occur during an actual approach to a landing, since recovery may be impossible prior to ground contact due to the low altitude. 

Common errors during advanced stalls include: 

• Improper pitch and bank control during straight-ahead and turning stalls. 

• Rough or uncoordinated control procedures. 

• Failure to recognize the first indications of a stall. 

• Failure to achieve a stall. 

• Poor recognition and recovery procedures. 

• Excessive altitude loss or airspeed or encountering a secondary stall during recovery. 

## Operating Airspeeds 

## Minimum Sink Airspeed 

Minimum sink airspeed is defined as the airspeed at which the glider loses the least altitude in a given period of time. Minimum sink airspeed varies with the weight of the glider. Glider manufacturers publish altitude loss in feet per minute or meters per second (e.g., 122 ft/min or 0.62 m/sec) at a specified weight. Flying at minimum sink airspeed results in maximum duration in the absence of convection in the atmosphere. 

The minimum sink airspeed given in the GFM/POH is based on the following conditions. 

• The glider is wings level and flying a straight flightpath; load factor is 1.0 G. 

• The glider flight controls are perfectly coordinated. 

• Wing flaps are set to zero degrees and air brakes are closed and locked. 

• The wings are free of bugs or other contaminants. 

• The glider is at a manufacturer-specified weight. 

While flying in a thermaling turn, the proper airspeed is the minimum sink airspeed appropriate to the load factor, or G-load, that the glider is undergoing. The glider’s stall speed increases with load factor. The minimum sink speed needs to be increased with an increase in load factor. Another factor that always needs to be considered is that the gross weight and stall speed of the glider can vary if equipped with water ballast, which affects the minimum sink airspeed. For most gliders, the following weights will be of greatest interest: 

1. Maximum gross weight with full water and both seats occupied 

2. Maximum gross weight with both seats occupied and no water ballast 

3. One pilot on board 

The effect of only weight on stall speed can be expressed by using the basic lift formula that is manipulated and simplified to derive the necessary information. The modified lift formula is: 

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