FAQ Answer

FAQ Answer

How is helicopter noise modelled?

Helicopter noise is inherently more complex to model than jet aircraft noise. Helicopter noise tends to have a pulsating quality caused by the blade passing frequencies of the rotors. Under certain conditions, this can become pronounced and is termed ‘blade slap’. The forward motion of a helicopter in normal flight results in variations of blade speed through the air during each rotation formed by a combination of the forward speed of the aircraft and the rotation of the blade. This variation of blade speed through the air results in complex noise propagation. This effect applies to both the main and tail rotor. There is also an interaction between noise produced by main and tail rotors. Below is a short list of references to research on helicopter noise:

•Civil Aviation Authority (1983), 'DR Report 8304 – 1982 Helicopter Disturbance Study', September 1983;

•Department of Transport (1994), 'London Heliport Study – Noise Sub Group Report', November 1994;

•Fields JM and Powell (1987), 'Community reactions to helicopter noise: Results from an experimental study', Journal of the Acoustical Society of America 82(2), August 1987;

•Lowson MV and Ollerhead JB (1969), 'Studies of Helicopter Rotor Noise', Wyle Labs Huntsville, January 1969;

•Molino JA (1982), 'Should Helicopter Noise be measured differently from other Aircraft Noise? – A Review of the Psychoacoustic Literature', National Aeronautics and Space Administration, NASA Contractor Report 3609, November 1982;

•Munch CL and King RJ (1974), 'Community Acceptance of Helicopter Noise: Criteria and Application', National Aeronautics and Space Administration, NASA-CR-132430;

•Newman JS et al (1986), 'Analysis of Helicopter Noise Data using Helicopter Noise Certification Procedures', Federal Aviation Administration, FAA-EE-86-01, March 1986;

•Smith MJT (1989), 'Aircraft Noise', Cambridge University Press, Paragraph 3.10