In World War II when Spitfires and Mustangs and Messerschmitt 109s and other aeroplanes of that category were quite common, we were all aware of the troubles that these particular aeroplanes got into when starting to dive. When getting up to around 80 per cent of the speed of sound, the aeroplane starts shaking, buffeting we call it; some of them lost ailerons and tails and it proved to be fatal to some of the pilots. It was quite obvious to all people who have an engineering mind that something just was not quite right, especially in the speed range they were flying in those days.