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. 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. Common errors during maneuvers at minimum controllable  airspeed include: 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. 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. Signs of an impending stall include the following: •  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. 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. 3.  Feeling 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. •  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. 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  7-32 Stall Recognition and Recovery