on or below the horizon to establish a specified airspeed. Any  change in pitch attitude results in a change in airspeed. There  is a pitch attitude reference for best glide speed, another for  the minimum sink speed, and another for slow flight. The  pitch attitude is adjusted with the elevator to hold the specific  airspeed. The glider elevator trim control allows the pilot to  trim the glider to hold a constant pitch attitude and, therefore,  a constant airspeed. Straight glides should be coordinated as  indicated by a centered yaw string or slip-skid ball. The glider pilot should also stay alert to airflow noise changes.  At a constant airspeed in coordinated flight, wind noise should  be constant. Any changes in airspeed or coordination cause  a change in the wind noise. Gusts that cause the airspeed to  change momentarily can be ignored. Holding the glider at  a constant pitch attitude results in maintaining the desired  airspeed control. The glider pilot should learn to fly throughout a wide range of  airspeeds, from minimum controllable airspeed to maximum  allowable airspeed. This enables the pilot to learn the feel of  the controls of the glider throughout its speed range. If the  glider is equipped with spoilers/dive brakes and/or flaps, the  glider pilot should become familiar with the changes that occur  in pitch attitude and airspeed when these controls are used. Common errors during straight glides include: The performance of turns involves coordination of all three  flight controls: ailerons, rudder, and elevator. For purposes  of this discussion, turns are divided into the following three  classes as shown in  Figure 7-29 . Before starting any turn, the pilot must clear the airspace  in the direction of the turn. A glider is turned by banking  (lowering the wing in the direction of the desired turn, thus  raising the other). When the glider is flying straight, the total  lift is acting perpendicular to the wings and to the earth. As  the glider is banked into a turn, total lift becomes the resultant  of two components: 1) the vertical lift component continues  to act perpendicularly to the earth and opposes gravity and 2)  •  Steep turns are those resulting from a degree of bank  (45° or more) at which the overbanking tendency of  a glider overcomes stability, and the bank increases  unless aileron is applied to prevent it. •  Shallow turns are those in which the bank (less than  approximately 20°) is so shallow that the inherent  lateral stability of the glider levels the wings unless  some aileron is applied to maintain the bank. •  Medium turns are those resulting from a degree of  bank (approximately 20° to 45°) at which lateral  stability is overcome by the overbanking tendency,  resulting in no control inputs (other than elevator)  being required to maintain the angle. •  Rough or erratic pitch attitude and airspeed control. •  Rough, uncoordinated, or inappropriate control  applications. •  Failure to use trim or improper use of trim. •  Improper use of controls when using spoilers, dive  brakes, and/or flaps. • Prolonged uncoordinated flight—yaw or ball not  centered. Figure 7-29.  Shallow, medium, and steep turns. 20° 45° 60° Shallow turn Medium turn Steep turn Turns 7-28