NOISE OF JET AIRCRAFT

Press, Volume XCIX, Issue 29264, 23 July 1960, Page 4

NOISE OF JET AIRCRAFT

“Houses Too Near Airport" The development of Christchurch Airport depended' on the measures taken to reduce the noise of aircraft, whether jets or otherwise, said Mr D. C. Stevenson, senior lecturer in mechanical engineering at the University of Canterbury, in an address on aerodynamic noise and its effect on structures, given to the Canterbury branch of the Royal Society of N.Z. Houses were already too. near the airport and when the new jet aircraft began to use Harewood, people would be certain to complain, he said. In London, restrictions had already been placed on jet airliners. The Boeing 707 was restricted in the hours which it could take off and the pilots had to climb direct to a height of 1000 feet before passing over the nearby houses. Mr Stevenson, who was at the Royal Aeronautical Establishment, Farnborough, on a year’s refresher leave to study aerodynamic noises, said that on one: occasion, a Boeing 707 had passed over the houses at a level of only 300 feet. The noise had been recorded at 117 decibels. This was getting near the pain level as 100 decibels interfered with speech. Research Intensified

Research into aerodynamic noise had only begun in earnest after 1930 but it had now intensified because of the greater number of aircraft and the beginning of the jet age. Until recently, most research into the noise of jets had been aimed at producing modifications of the exhaust. It had been found however, that an efficient muffler reduced the thrust of the engine and when this was reduced by 5 per cent., a muffler was not practical. Now engineers, were investigating the possibilities bf reducing noise by modifying an aircraft’s engine and from the results so far, this seemed the best answer to the problem. The suppression of noise was important but just as vital to the aircraft industry were the structural problems posed by noise from jets. It had been found that a high level of noise caused metal fatigue, said Mr Stevenson. This was caused by the noise starting structural vibrations which caused stresses in the fabric and metal of the plane. In spite of all the research into noise no real solution to the problem had been found and at present the only advice he could give was that persons should not build houses near airports that might accommodate jets, Mr Stevenson said.