the glider

In its simplest form, a glider is an unpowered aircraft, an airplane without a motor. While many of the same design, aerodynamic and piloting factors that apply to powered airplanes also apply to gliders, that lack of a motor changes a lot about how gliders work. Gliders are amazing and graceful machines, and are about as close as humans can get to soaring like birds.

From paper airplanes to the space shuttle during re-entry, there are many types of gliders. In this article, we will focus on the most common type of glider, often referred to as a sailplane.

Parts of a Glider
A glider has many of the same parts as an airplane:
  • fuselage
  • wings
  • control surfaces
  • landing gear
But, there are significant differences in these parts on a glider, so let's take a look at each.

Fuselage
Gliders are as small and light as possible. Since there is no large engine taking up space, gliders are basically sized around the cargo they carry, usually one or two people. The cockpit of a single-seat glider is small, but it is large enough for most people to squeeze into. Instead of sitting upright, pilots recline with their legs stretched out in front of them. The frontal exposure of the pilot is reduced and the cross-sectional area of the cockpit can be substantially smaller.


The glider's fibreglass construction enables a sleek, smooth design

Gliders, along with most other aircraft, are designed to have skins that are as smooth as possible to allow the plane to slip more easily through the air. Early gliders were constructed from wood covered with canvas. Later versions were constructed from aluminium with structural aluminium skins that were much smoother. However, the rivets and seams required by aluminium skins produce additional drag, which tends to decrease performance. In many modern gliders, composite construction using materials such as fibreglass and carbon fibre are quickly replacing aluminium. Composite materials allow aircraft designers to create seamless and rivet-less structures with shapes that produce less drag.

Wings
If you look at a glider next to a conventional powered plane, you'll notice a significant difference in the wings. While the wings of both are similar in general shape and function, those on gliders are longer and narrower than those on conventional aircraft. The slenderness of a wing is expressed as the aspect ratio, which is calculated by dividing the square of the span of the wing by the area of the wing.

Glider wings have very high aspect ratios -- their span is very long compared to their width. This is because drag created during the production of lift (known as induced drag) can account for a significant portion of the total drag on a glider. One way to increase the efficiency of a wing is to increase its aspect ratio. Glider wings are very long and thin, which makes them efficient. They produce less drag for the amount of lift they generate.


The aspect ratio of a wing is the wingspan squared divided by the area of the wing. The glider has a much larger aspect ratio than a conventional plane

Why don't all planes have wings with high aspect ratios? There are two reasons for this. The first is that not all aircraft are designed for efficient flight. Military fighters, for example, are designed with speed and manoeuvrability well ahead of efficiency on the designer's list of priorities. Another reason is that there are limits to how long and skinny a wing can get before it is no longer able to carry the required loads.

Control Surfaces
Gliders use the same control surfaces (movable sections of the wing and tail) that are found on conventional planes to control the direction of flight. The ailerons and elevator are controlled using a single control stick between the pilot's legs. The rudder, as in conventional aircraft, is controlled using foot pedals.


Mouse-over the control names to see where they're located on the glider

  • Ailerons
    Ailerons are the movable sections cut into the trailing edges of the wing. These are used as the primary directional control and they accomplish this by controlling the roll of the plane (tilting the wing tips up and down). Ailerons operate in opposite directions on each side of the plane. If the pilot wants to roll the plane to the right, he moves the control stick to the right. This causes the left aileron to deflect down (creating more lift on this side) and the right aileron to deflect up (creating less lift on this side). The difference in lift between the two sides causes the plane to rotate about its long axis.
     

  • Elevator (horizontal stabilizer)
    The elevator is the movable horizontal wing-like structure on the tail. It is used to control the pitch of the plane, allowing the pilot to point the nose of the plane up or down as required.
     

  • Rudder (vertical stabilizer)
    The rudder is the vertical wing-like structure on the tail. It is used to control the yaw of the aircraft by allowing the pilot to point the nose of the plane left or right.

Landing Gear
Another way to reduce the size of an airplane is to reduce the size of the landing gear. The landing gear on a glider typically consists of a single wheel mounted just below the cockpit.

 





 

3-view drawings of a modern sailplane. Although somewhat simplified, the drawings show the basic structure of a typical sailplane for the 15 metre class. There are many different racing classes of gliders, Standard Class (15m span, no flaps), 15 Metre Class (15m span with flaps), Open Class (Large metre spans, ranging from 15m to 25m and over), and the new World Class which uses the PW-5 sailplane exclusively.

Glider Cockpit

Inside a typical glider cockpit, you'll find the following:
  • Altimeter (to indicate your altitude)
     
  • Air-speed indicator (to tell how fast you are going)
     
  • Variometer (to tell what the air around you is doing)
     
  • Radio (to contact other planes or someone on the ground)
     
  • Control stick (located between pilots legs)
     
  • Tow rope release knob (to disengage the tow rope)

    Instrumentation on each sailplane varies according to pilot preference, but each carries a minimum of altimeter, airspeed indicator, a magnetic compass, a variometer (a sensitive vertical speed indicator), and the "yaw string".

    Most pilots immediately upgrade their factory "vario" for a total energy system. Simply put, the total energy system allows the pilot to get a more accurate reading on the lift or sink surrounding the sailplane, but does not take into account "stick lift" or a vertical acceleration by the pilot like an uncompensated vario would.

    The most useful instrument by far is the yaw string. Attached to the outside of the canopy at one end, this 3 inch piece of  red yarn shows the pilot the relative airflow of the glider. It works opposite to the more common "ball" found in powered aircraft. Glider pilots try to keep the plane co-ordinated at all times, but with large wings and ailerons on the planes, adverse yaw is a factor to be reckoned with. Glider pilots are forced to use the rudder pedals all the time to get the most from their plane.

    Of course, the most important instrument for all pilots remains on our body, the eyeball.

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