Wings, Wheels & Sails [antikvár]

II kiAn "¦L ¦ < t i .-.ii.t t. !1 '¦.I il How fast can aeroplanes fly? Faster and faster planes have been built since the first powered flights took place early this century. Today, the record for the world's fastest jet plane is still held by the USA's Lockheed SR-71A. In 1976, it flew at 3530 km/h. The fastest planes in the world are those powered by rocket engines - only Space rockets can fly faster. In 1967, the USA's X-15 rocket plane flew at 7297 km/h! The USA's X-15 (above) remains the fastest plane ever made. Its rocket engine propelled It to nearly seven times the speed of sound. DO YOU KNOW The speed of sound slowly drops with height above sea level, but above about 11,000 metres it stays the same. It's around 1225 km/h at sea level, and about 1060 km/h above 11,000 metres. A plane flying at the speed of sound is at Mach 1. Twice the speed of sound is Mach 2, and so on. The first plane to fly faster than the speed of sound in level flight was the USA's rocket plane, the Bell X-1 (above),-in 1947.