To perform a straight glide, the glider pilot must hold a constant heading and airspeed. The heading reference should be some prominent point in front of the glider on the ground. The pilot also notes that, during a straight glide, each wingtip should be an equal distance above the ground. With the wings level, the pitch attitude is established with reference to a point 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:
- 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.
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.
- 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.
- 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.
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) the horizontal lift component (centripetal) acts parallel to the earth’s surface and opposes inertia (apparent centrifugal force). These two lift components act at right angles to each other, causing the resultant total lifting force to act perpendicular to the banked wing of the glider. It is the horizontal lift component that actually turns the glider, not the rudder.
When applying aileron to bank the glider, the aileron on the rising wing is lowered, producing a greater drag than the raised aileron on the lowering wing. This increased drag causes the glider to yaw toward the rising wing or opposite the direction of turn. To counteract this adverse yawing moment, rudder pressure must be applied in the desired direction of turn simultaneously with aileron pressure. This action is required to produce a coordinated turn.
After the bank has been established in a medium banked turn, all pressure applied to the aileron may be relaxed. The glider remains at the selected bank with no further tendency to yaw since there is no longer a deflection of the ailerons. As a result, pressure may also be relaxed on the rudder pedals, and the rudder is allowed to streamline itself with the direction of the slipstream. Rudder pressure maintained after establishing the turn causes the glider to skid to the outside of the turn. If a definite effort is made to center the rudder rather than let it streamline itself to the turn, it is probable that some opposite rudder pressure will be exerted inadvertently. This forces the glider to yaw opposite its turning path, causing the glider to slip to the inside of the turn. The yaw string or ball in the slip indicator is displaced off center whenever the glider is skidding or slipping sideways. In proper coordinated flight, there is no skidding or slipping.
In constant airspeed turns, it is necessary to increase the AOA of the wing as the bank progresses by adding nose-up elevator pressure. This is required because the total lift must be equal to the vertical component of lift plus the horizontal lift component. To stop the turn, coordinated use of the aileron and rudder pressure are added to bring the wings back to level flight as elevator pressure is relaxed.
There is a direct relationship between airspeed, bank angle, and rate and radius of turn. The rate of turn at any given true airspeed depends on the horizontal lift component. The horizontal lift component varies in proportion to the amount of bank. Therefore, the rate of turn at a given true airspeed increases as the angle of bank is increased. On the other hand, when a turn is made at a higher true airspeed at a given bank angle, the inertia is greater and the horizontal lift component required for the turn is greater, causing the turning rate to become slower. Therefore, at a given angle of bank, a higher true airspeed makes the radius of turn larger because the glider is turning at a slower rate.
As the angle of bank is increased from a shallow bank to a medium bank, the airspeed of the wing on the outside of the turn increases in relation to the inside wing. The additional lift developed by the bank balances the lateral stability of the glider. No aileron pressure is required to maintain the bank. At any given airspeed, aileron pressure is not required to maintain the bank. If the bank is increased from a medium bank to a steep bank, the radius of turn decreases even further. The greater lift of the outside wing then causes the bank to steepen, and opposite aileron is necessary to keep the bank constant.
As the radius of the turn becomes smaller, a significant difference develops between the speed of the inside wing and the speed of the outside wing. The wing on the outside of the turn travels a longer circuit than the inside wing, yet both complete their respective circuits in the same length of time. Therefore, the outside wing travels faster than the inside wing, and as a result, it develops more lift. This creates an overbanking tendency that must be controlled by the use of the ailerons. Because the outboard wing is developing more lift, it also has more induced drag. This causes a slip during steep turns that must be corrected by rudder usage.
To establish the desired angle of bank, the pilot should use visual reference points on the glider, the earth’s surface, and the natural horizon. The pilot’s posture while seated in the glider is very important, particularly during turns. It affects the interpretation of outside visual references. The beginning pilot may lean away from or into the turn rather than ride with the glider. This should be corrected immediately if the pilot is to properly learn to use visual references.
Applications of large aileron and rudder produces rapid roll rates and allow little time for corrections before the desired bank is reached. Slower (small control displacement) roll rates provide more time to make necessary pitch and bank corrections. As soon as the glider rolls from the wings-level attitude, the nose starts to move along the horizon, increasing its rate of travel proportionately as the bank is increased.
As the desired angle of bank is established, aileron and rudder pressures should be relaxed. This prevents increase in bank because the aileron and rudder control surfaces are neutral in their streamlined position. The up-elevator pressure should not be relaxed, but should be held constant to maintain the desired airspeed. Throughout the turn, the pilot should crosscheck the airspeed indicator to verify the proper pitch is being maintained. The cross-check and instrument scan should include outside visual references. If the glider is gaining or losing airspeed, the pitch attitude should be adjusted in relation to the horizon. During all turns, aileron, rudder, and elevator are used to correct minor variations in pitch and bank just as they are in straight glides.