4. LESSON 2 - USE OF THE FLIGHT CONTROLS
Key points of attention:
A deflection of the elevator causes a rotation around the lateral axis -> Pitch
Aileron deflection causes a rotation around the longitudinal axis -> Roll
The rudder makes the glider rotate around its vertical axis -> Yaw
After reading the section below, you will understand the rather technical key points ahead. In the section ‘Basic aerodynamics’ we explained how a plane can fly by generating an upwards force on the wings, called lift. In addition to the wings, the fuselage and horizontal stabiliser (or tailplane) at the back, a glider pilot has four rotatable surfaces that can be used to control the plane. We call these flight control surfaces and they are operated by the flight controls in the cockpit. By operating the control surfaces, we cause a deflection in airflow, which in turn will change the direction of the plane. The four different control surfaces are the elevator (located on the tailplane), two ailerons (one on each wing) and the rudder (connected to the fin). These allow you to rotate the plane around three lines or axes: two horizontal lines (the lateral axis and the logitudinal axis) and a vertical line (the vertical axis). We will discuss all three movements below and your instructor will demonstrate them during the flight.
THE ELEVATOR - PITCH
The elevator is located on the glider's tail and it is connected to the horizontal stabilizer. If we push the control stick forward in the cockpit, the tail will go up, the nose will move down, and the airspeed will increase. Pulling the stick towards you will make the nose go up and decrease the airspeed. This up- and downwards movement of the nose is called pitching. If you imagine a line going more or less from one wingtip to the other (the lateral axis), then moving the tail up and the nose down is a rotation around the lateral axis. (The official definition is an axis perpendicular to the symmetry plane, directly through the centre of gravity.)
THE AILERONS - ROLL
If we move the control stick to the right, the right aileron swings up and the left aileron moves down. As a result, lift reduces on the right wing and increases on the left wing, making the glider roll to the right. Imagine a line running from the nose towards the tail, through the centre of gravity. This is called the longitudinal axis. The ailerons enable you to rotate the plane along the longitudinal axis. We call these rotary movements rolling the glider.
THE RUDDER - YAW
With our feet we control the rudder pedals in the cockpit. By pressing the right pedal, the rudder is deflected to the right. The rudder makes the glider rotate around its vertical axis, a movement that is called yawing. The vertical axis is the third imaginary line on a glider and runs vertically through the center of gravity (remember the spoon balancing on the edge of a plate?). If you press the left rudder pedal, the nose of the glider moves to the left.
PRACTISE DURING THE FLIGHT
First we will practise flying straight ahead. Then, you will be asked to push the stick forward gently, and to pull it back after you notice a result. This is pitching, and we can pitch by deflecting the elevator. The next exercise, after getting back to straight flight again, is moving the stick to the right. Look at your left wing, it is moving up. This is called rolling and we can let the glider roll by using the ailerons. The last exercise is to step on the rudder pedals, first left then right. The nose will move left and right, called yawing.
DO NOT SQUEEZE THE STICK
It is not necessary, yet most new students tend to squeeze the control stick. Get used to holding the stick loosely between your thumb and fingers. This makes your input much more relaxed and enables you to notice more clearly what the aircraft is doing. Place your right forearm on your leg to calm the deflections. In most circumstances, steering from your wrist is enough to control the glider. Only during take-off and landing is it sensible to hold the stick a little more firmly – the ground surface is usually a bit bumpy. However, there is still no need to squeeze the stick excessively.
WHO CONTROLS THE AIRPLANE?It is important to know who is flying the glider. If your instructor tells you (in exactly these words) "you have control," it means that he or she is letting go of the flight controls and gives you full control of the glider. You need to confirm you understand by (literally) saying: "I have control." Your instructor can take over control of the glider at any time by saying "I have control". If this happens, immediately hand over the controls and confirm: "you have control." Unless your instructor has told you differently, accustom yourself to taking your hands and feet off the flight controls when you know that your instructor has control. If he or she takes control, it doesn't necessarily mean you're doing something wrong. By transferring control, you have more mental capacity available to receive new instructions for the next exercise. You can then keep your full attention to the instructions of your instructor without being busy flying the plane. There are a number of different levels of instructor intervention. In addition to taking over the control, it can also be a question or comment such as: "tell me what's wrong," "tell me what to do now," "do this afterward," and so on. The further you are in your training, the less your instructor will interfere with your decisions.
THE GLIDER FLIES BY ITSELF
A glider plan has been designed to fly itself. If you would let go of all flight controls during flight, the glider would just keep flying and it wouldn’t do anything unexpected. If a glider is brought out of its stable flight position by small disturbances or turbulence in the air, it will eventually come back to its previous position without you intervening. Really, you only need the control stick to restore the balance after major disturbances or to steer the aircraft in the direction you want it to go. After a while you will become the manager of the glider and the glider will respond to your commands. Even though the gilder can fly by itself, it needs you to pitch, roll and yaw.