Polyhedral
Polyhedral refers to the multiple angle wing panels make with the horizontal. A wing with polyhedral has more than two wing panels and the angle of the wing changes at each joint.

Wing Loading
Wing loading is defined as the weight of the aircraft divided by the wing area. It is usually described in ounces per square foot.

Glide Ratio
The glide ratio is the distance travelled in a horizontal direction compared with the vertical distance dropped on a normal glide. A 20 to 1 glide ratio means that the aircraft would loose one foot of altitude for every twenty feet of distance travelled.

Conventional Tail
A conventional tail is one with the stabiliser mounted directly on the fuselage and is the usual configuration of an aircraft. These are the simplest to construct and are the most popular.

T-Tail
The T-Tail refers to a stabiliser that is mounted on top of the fin. This moves the stabiliser away from the turbulent airflow of the wing and makes pitch control more responsive. It also gets the stabiliser out of the way when landing on rough ground. The T-Tail construction is usually more fragile than the conventional tail, and can be more difficult to build.

V-Tail
The V-Tail is where both the fin and stabiliser are replaced with two surfaces mounted in a V-shape approximately 45 degrees from the horizontal. The control surfaces mounted on a V-Tail control the aircraft in both pitch and yaw.

Ballast
Ballast is extra weight added to a glider to help it penetrate better in windy weather or to increase its speed. Ballast is usually added in tubes in the inner portion of the wings or in the fuselage at the centre of gravity.

Tow-hook
The tow-hook is a small metal hook mounted on the bottom of the glider fuselage around the centre of gravity and to which the hi-start or winch can be connected.