Red Bull Flugtag (German: flight day, airshow) is an event organized by Red Bull in which competitors attempt to fly home-made, human-powered flying machines, size-limited to around 10 metres (33 ft), weight-limited to approximately 150 kilograms (330 lb). The flying machines are usually launched off a pier about 9 metres (30 ft) high into the sea or body of water. Most competitors enter for the entertainment value, and the flying machines rarely fly at all. The format was originally invented in Selsey, a small seaside town in the south of England under the name “Birdman Rally” in 1971. The first Red Bull Flugtag competition was held in 1991 in Vienna, Austria. It was such a success that it has been held every year since and in over 35 cities all over the world. Anyone is eligible to compete in the Flugtag event. To participate, each team must submit an application and their contraption must meet the criteria set forth by Red Bull. The criteria vary with location. In the United States each flying machine must have a maximum wingspan of 30 feet (9.1 m) and a maximum weight (including pilot) of 450 pounds (200 kg). In Australian Flugtags the wingspan is limited to 8 metres (26 ft) and the weight (not including pilot) to 180 kilograms (400 lb). The craft must be powered by muscle, gravity, and imagination. Because the aircraft will ultimately end up in the water, it must be unsinkable and constructed entirely of environmentally friendly materials. The aircraft may not have any loose parts and advertising space is limited to 1-square-foot (930 cm2).