§ Mr. Selwyn Lloyd
Important work is being done in this field, in conjunction with the Ministry of Transport and Civil Aviation and the aircraft and aero-engine firms 1690 concerned. We were considerably encouraged by the demonstration of one form of silencer at the South Bank on 24th January. The problems to be surmounted are, however, great. I propose, with permission, to circulate in the Official Report a more detailed statement of the work in hand.
Following is the statement:The causes of the noise generated by helicopters are various, but the two most important are the rotor system and the power generating system. The extent to which we can expect to reduce the noise caused by the rotor system is marginal and our main aim is to find ways of reducing engine noise to the same level as the rotor noise. Care is necessary, however, in designing methods for silencing engines not so to add to the weight of the aircraft and reduce the engine power as to make the helicopter uneconomical to operate.The demonstration of a silencer on an S.55 helicopter on 24th January showed that the noise of its particular piston engine can be reduced considerably so that, for instance, at 250 feet the residual noise level is about the same as the background noise level in a busy street. The noise is naturally greater during take-off and touch-down but does not seem objectionable at a reasonable distance. Further development is required to evolve a lighter installation.Similar work is being done by the Bristol Aeroplane Company directed to reducing the noise of the Bristol 173 twin rotor helicopter. Preliminary results suggest that a comparable reduction in noise will be obtained and a lighter installation will be possible.Propulsion by ducting compressed air through rotor blades and out of the blade tips may offer a considerable reduction of noise. Gas turbine engines with direct drive to the rotor will call for new methods of noise reduction when the aircraft concerned have flown and the level of noise can be assessed. Work done on the silencing of jet turbine engine exhausts by modifying their shapes will, it is hoped, be useful in helicopters which incorporate jet units at the rotor tips.All possibilities will be explored as the helicopters are developed. Research into the reduction of jet engine noise generally by aero-engine manufacturers, by the College of Aeronautics and by Southampton University, details of which were given to the House in a statement by my predecessor on 28th June, 1954, will also contribute.