There are several ways of classifying a glider - number of seats, construction material, wingspan, competition Class - apart form the well known "cheap or expensive" classification. For the competition pilot, the Class system is more important.
Single seat gliders have one seat, are flown solo, and you usually get a briefing from an instructor before your first flight to familiarise you with the aircraft.
Two seaters are usually used only for training purposes, although some of the latest ones are also very good competition machines. Student pilots always start in a two seater with an instructor, and these are dual control machines - did you really think that the instructor would trust you with the only set of controls!!!
There is one three-seat model of glider, which is strangely popular in the States, where an instructor can take a couple up to 5280 feet.
Gliders can be made from several materials - wood, wood and fabric, aluminium, steel, glass fibre or carbon fibre. Glass fibre reinforced resin offers the highest performance due to the fine control over the exact shape that can be acheived. Almost every new glider in the world is a glass glider, often called plastic. The modern airline industry talks about composite construction as the modern way to make aircraft, but gliders have used composite construcion for over 30 years new. The newest designs often have glass fibre and carbon fibre mixtures reinforcing the resin, with some parts of the aircraft a mixture, and others made from one or the other. The wing spar may even have a wooden shape former inside the glass or carbon structure. The skin of glass gliders is covered in gel coat. this is a polmer which can be rubbed down with fine sand paper to control the shape after a repair and to produce a beautiful shiney finish.
Many wood and fabric gliders actually have a framework of steel tubes to form the fuselage, covered with thin plywood and farbic
In competitions, gliders are divided up into classes, either by their physical size and features, or their handicap. National Championships use the Class system, except that Club class is defined in terms of handicaps. Regional competitions use the handicap system to split the field into convenient sized groups of similar ability (the gliders, not the pilots).
Standard Class gliders have a maximum wingspan of 15 metres, and no flaps are allowed.
15 m Class gliders (sometimes called racing class) have a maximum wing span of 15 metres, and are allowed to have flaps.
Open Class gliders have no limit on wingspan (currently the largest wingspan is 31.5 m !!) and can have flaps.
The 18 m Class have a maximum span of 18 metres and can have flaps. This was created because Open Class gliders were getting very expensive, but the increase in performance wasn't in step with the increase in cost, and they were simply becoming too big and expensive fro most pilots. 18 m was seen as a good compromise between the increase in cost and increase in performance.
World Class was a futile attempt to introduce a new class, where only one type is allowed to be used. It is supposed to provide a cheaper route into competition gliding, but unfortunately they chose a new model with low performance when second hand gliders with much higher performance were already available at a lower price and in large numbers. The concept was driven by the Americans who like to own a glider outright. The final model chosen, the PW-5 or Pregnant Guppy, has a span of 13.5 m, because this will enable it to fit into the standard Amarican garage when de-rigged! It has a glide angle of 33:1, the same as many wooden gliders from the 60's and 70's.
The Club Class started in Europe as a competition for slightly older gliders that were no longer at the leading edge in competitions, but were still very good. Entry to the class is decided on the glider's handicap, and some countries use a different handicap to others. In America, the Sports Class is a close equivalent. Club Class has the major advantage over World Class in that there are thousands of Club Class gliders already in existance, and any country in the world could hold a Club Class competition and expect a full entry. But many countries only have one or two World class gliders (apart from America and New Zealand). To emphasise how wide spread Club Class is, the LS4 with a glide angle of 41:1 is a Club class glider in current production, and over 1000 have been made so far! Over 600 Libelles, glide angle 39:1, were made. Do you get the impression that World Class made a mistake?
Apart from the World Class, a glider can compete in any class were it does not exceed the maximum specification. I.E. you can fly a Standard Class glider in 18 m class or even Open class if you want to, but you can't fly an 18 m glider in Standard Class.
The Club Class and the World Class are the only two where water ballast can't be carried in a competition. Many Club Class gliders have the capability to carry water ballast of course, but the World Class glider does not. Club Class is the only National and International competition class where handicapping is involved in the scoring.