glider and the maneuvering load imposed by turns and pull- ups. Flight at minimum controllable airspeed requires positive use of rudder and ailerons. The diminished effectiveness of the flight controls during flight at minimum controllable airspeed helps pilots develop the ability to estimate the margin of safety above the stalling speed. 

Common errors during maneuvers at minimum controllable airspeed include: 

• Failure to establish or to maintain minimum controllable airspeed. 

• Improper use of trim. 

• Rough or uncoordinated use of controls. 

• Failure to recognize indications of a stall. 

## Stall Recognition and Recovery 

All pilots must be proficient in stall recognition and recovery. A stall can occur at any airspeed and at any attitude. In the case of the self-launching glider under power, a stall can also occur with any power setting. A stall occurs when the smooth airflow over the glider’s wing is disrupted and the wings stop producing enough lift. This occurs when the wing exceeds its critical AOA. 

The practice of stall recovery and the development of stall awareness are of primary importance in pilot training. The objectives in performing intentional stalls are to familiarize the pilot with the conditions that produce stalls, to assist in recognizing an approaching stall, and to develop the habit of taking prompt preventive or corrective action. 

Intentional stalls should be performed so the maneuver is completed by 1,500 feet above the ground with a landing area within gliding distance, in the event lift cannot be found. Although it depends on the degree to which a stall has progressed, most stalls require some loss of altitude during recovery. The longer it takes to recognize the approaching stall, the more complete the stall is likely to become, and the greater the loss of altitude to be expected. 

Pilots must recognize the flight conditions that are conducive to stalls and know how to apply the necessary corrective action since most gliders do not have an electrical or mechanical stall warning device. Pilots should learn to recognize an approaching stall by sight, sound, and feel. The following cues may be useful in recognizing the approaching stall. 

1. Vision—useful in detecting a stall condition by noting the attitude of the glider versus the horizon. 

2. Hearing—also helpful in sensing a stall condition. In the case of a glider, a change in sound due to loss of airspeed is particularly noticeable. The lessening 

of the noise made by the air flowing along the glider structure as airspeed decreases is quite noticeable, and when the stall is almost complete, the pilot starts to feel airframe buffeting or aerodynamic vibration as the stall occurs. 

3. Feeling 

a. Kinesthesia, or the sensing of changes in direction or speed of motion, is an important intuitive indicator to the trained and experienced pilot. If this sensitivity is properly developed, it warns of a decrease in speed or the beginning of a settling, or mushing, of the glider. 

b. The feel of control pressures is also very important. As speed is reduced, the resistance to pressure on the controls becomes progressively less. Pressures exerted on the controls tend to become movements of the control surfaces. As the airflow slows and stalls, the aerodynamic controls (ailerons, elevator, and rudder) have significantly less authority and require much more movement to create the same amount of directional change as compared to the normal flight regime responses. As the wing airflow stalls and the stalling strongly affects the controls, the controllability of the glider can become questionable. Properly designed and certificated gliders should retain marginal control authority when the wing is stalled. The lag between these movements and the response of the glider becomes greater until in a complete stall. 

Signs of an impending stall include the following: 

• Nose-high attitude for higher wing loading with possible increasing trend. 

• Low airspeed indication with a decreasing trend. 

• Low airflow noise and decreasing. 

• Back pressure increasing, requiring more elevator trimming and/or not having anymore aft trim. 

• Poor control responses from the glider and decreasing feedback pressures from control movements. 

• Wing (airframe) buffeting as stalling begins. 

• Yaw string (if equipped) movement from normal flight position. 

Always make clearing turns before performing stalls. During the practice of intentional stalls, the real objective is not to learn how to stall a glider, but to learn how to recognize an approaching stall and take prompt corrective action. The recovery actions must be taken in a coordinated manner. 

