The problem of designing a machine capable of taking off and landing vertically was perhaps the greatest challenge faced by the early aviation pioneers. When the Germans and then the Russian emigre,Igor Sikorsky finally solved the complicated physics involved, the world quickly benefited from an ultimately flexible aircraft - the helicopter. The military were quick to realise its potential, indeed the Americans fought a war with it - Vietnam. With the advent of the jet engine though, came a new breed of vertical take-off aircraft. One was to outlast, outperform and outmanoeuvre all its rivals - the Harrier jump jet. As airport congestion grows, vertical-flight aircraft will be a vital part of the future of aviation.