The diagram above shows the main features of a glider. Click on the required feature to view a description of the part and it's function.
The fuselage serves a number of functions. The forward section is expanded as the cockpit which contains the seating for the pilot, the glider controls and instruments. The midsection is the attachment point for the wings and undercarriage. The rear section, or “tailboom” is narrower to minimise weight and drag. Its length provides the leverage for the empennage(the term for the fin and rudder, and the tailplane and elevator) to control the gliders direction of flight.
The fuselage is carefully streamlined to minimise the drag of moving through the air. It, like the other main parts of the glider, may be constructed of a number of alternative materials, fibre reinforced plastic (glass, kevlar or carbon fibre), metal, wood or steel tube and fabric. The material chosen depends on the required performance, ruggedness and cost.
The cockpit contains the seating and harnesses for the pilot, usually in a semi-reclining position. In front of the pilot will be the instrument console, and the various flight controls.
It is hinged to enable the pilot to enter and leave the aircraft. Provision is made for the canopy to be jettisoned in the event of catastrophic damage to the glider in flight (a parachute is usually worn by the pilot).
A towhook is placed near the front of the aircraft to connect the tow rope, from the tug, to launch the glider. It is often mounted in a recess on the nose incorporating a pitot. Another towhook is usually provided below the fuselage, near the undercarriage for winch launching.
The towhook can be controlled by the pilot to enable release of the tug or winch. The tug is also provided with a towhook for it's end of the tow rope so in the event of the glider's towhook failing the tow rope can be released.
The undercarriage or mainwheel enables the glider to be moved on the ground, and for launching and landing. It is also serves an important function in absorbing landing shocks. Most gliders only have a single central mainwheel, the glider wingtip, which may have a small wheel or skid under it, resting on the ground when the glider is at rest. On launching even at a very slow ground speed the wings provide sufficient lift to keep the wingtips clear of the ground.
The tailskid or wheel protects the tail of the fuselage from damage while on the ground. As it is situated at the end of the lever provided by the tailboom it is constructed to minimise weight.
Some training, and lower performance gliders provide an additional wheel or skid under the nose.
WING
The wings provide the lift that keeps a glider flying. Most of the lift is provided by the plane of the wing being inclined into the oncoming airflow (the “angle of attack”). Some additional lift is provided by the upper surface of the wing being more curved than the lower surface so the airflow is faster, and the air pressure above the wing is consequently lower. The cross-section of the wing (it's “aerofoil”) is very carefully designed and manufactured to maximise these effects. At the same time it is designed to be as smooth and slippery as possible to minimise the “drag” or resistance to the flow of air across it's surface.
These conflicting requirements of maximising lift, minimising lift yet maintaining the strength of the wings have led to the distinctive long narrow wings (a high “aspect ratio”) which characterise the shape of glider wings. Some gliders have been built with wing “spans” (the length from wing tip to wing tip) approaching 30 meters.
The wings may contain integral tanks or flexible plastic bags vented to the outside. These can be filled with water with the purpose of increasing the weight (1-200 kg.) of the glider. A heavier glider will sink faster, but also flies faster which is desirable in cross-country flying. This “water ballast” can be dumped by the pilot if the increased sink rate becomes a problem.
To enable a glider to be transported from site to site the wings can be dismounted from the fuselage. The glider and wings can then be transported in a long trailer.
WINGLET
In flight the air below the wing is at a higher pressure than that above the wing. Consequently the air is tending to leak around the wing tip. This movement of air combined with the forward movement of the glider produces a “wingtip vortex” which induces extra drag on the gliders forward movement.
Some gliders, usually more recent aircraft, have winglets fitted to minimise this air movement. This results in less drag at low speeds (when the pressure difference is greatest), and improved function of the aileron.
FLAP
The ideal aerofoil; the wing cross section, for slow flight is thicker than that for high speed flight. It will also result in a lower minimum flying speed which can be an advantage when thermalling or landing. The usual aerofoil is a compromise between these two considerations.
Some gliders are fitted with flaps which effectively changes the wing's aerofoil to meet these conflicting requirements. The flaps on the both wings move together, in the same direction, unlike ailerons.
A few gliders have flaps that can be lowered to almost 90° to increase drag as a form of airbrake.
AILERON
The ailerons on each wing moves in the opposite direction to each other hinging up or down into the airstream. This increases the lift on one wing, decreasing it on the other and rolling the glider around it's longitudinal axis. The lift provided by the wings is then directed to one side turning the glider. These controls are consequently the primary control for “steering” the glider.
If the glider is fitted with flaps the ailerons may also move together to augment the effect of the flaps, alternatively called “flaperons”.
AIRBRAKE
As gliders have been designed to keep flying with minimum loss of height (or sink) for a given forward movement, it would be very difficult to land them, even in a large field without some means of increasing this loss of height. So gliders are fitted with airbrakes (or divebrakes) to increase the rate of sink.
These project upwards from the wings (some have a paddle projecting downwards as well), under the control of the pilot, increasing the gliders drag and rate of sink. They do not alter the gliders minimum flying speed appreciably.
Some older gliders may be fitted with a hinged panel, which swings up from the top surface of the wings, known as “spoilers”. An alternative arrangement uses the glider's flaps to provide this function. A very few gliders provide a small drogue chute attached to the tail to augment this function.
FIN
The fin is like a small vertical wing fixed to the fuselage. It acts in the same way as a weathercock to keep the glider facing directly into the oncoming airstream. It contributes to the stability of the glider, the ability of the glider to keep flying normally without control input from the pilot.
RUDDER
The rudder is is hinged to the trailing edge of the fin. It is controlled by the pilot.
It is used to augment the function of the fin in keeping the glider facing directly into the oncoming airstream. For example, the ailerons in use will tend to swing the glider sideways (known as yaw) due to generating asymmetric drag. The rudder is used to overcome and balance that yaw.
The rudder can also be used to overcome the stability of the fin. This is used in generating a sideslip, a condition where yaw is generating to intentionally generate drag to mimic the effects of airbrakes.
PITOT, STATIC TOTAL ENERGY PROBES
The pitot is a tube facing into the oncoming airstream measures the pressure of that airsteam. It is a sensor for the airspeed indicator. It is often incorporated in a recess on the nose incorporating the towhook.
A static is a probe, or more often an orifice on the fuselage, and measures the outside air pressure which is inversly proportional to altitude. It is a sensor for the altimeter.
A total energy probe is a specially shaped and/or slotted tube which measures the combined pressure from outside air preasure & the oncoming airstream which is inversly proportional to both air speed and altitude. It is a sensor for the variometer.
These sensors can all be combined into the one probe.
TAILPLANE
Also known as the stabiliser. Its function is to keep the glider flying directly into the airstream, without pitching up or down under the effects of small gusts or air disturbances. It contributes to the stability of the glider, the ability of the glider to keep flying normally without control input from the pilot, despite small wind gusts and air disturbances.
ELEVATOR
The elevator is usually hinged to the rear of the tailplane, but sometimes is incorporated with it, and hinged to the fin or fuselage, an arrangement known as an “all flying tail”. In use it pitches the nose of the glider up or down. It is under the control of the pilot and is the primary means for controlling the speed of the glider.
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