Quietening a Quiet Engine-The RB211 Demonstrator Programme

Against the background of the RB211/Lockheed L1011 development programme, which led to the certification of the quietest modern jet aircraft then entering service, Rolls-Royce determined to establish the realistic potential for further noise reductions on a high bypass ratio engine. Following a two year feasibility study the programme was launched in mid 1972 based around a standard production RB 211 engine. It is now essentially complete and the lessons learned from tests on almost 100 powerplant configurations bear witness to the problems of making inroads into further quietening similar modern engines. This paper summarises the important findings, highlights areas in which Research and Development should be concentrated and presents a judgment of future trends and implications.