Aviation & Defence

Aviation & Defence

From fly-neighbourly profiles for civil helicopters to verification of noise data for the Joint Strike Fighter, The Acoustic Group has shaped how aircraft noise is measured and assessed in Australia.

Helicopter noise assessments

The introduction of noise criteria for helicopter landing sites in the early 1980s required investigation of flight profiles and operating characteristics so helicopters could operate near residential premises. To achieve compliance with criteria issued by the NSW State Pollution Control Commission, testing was carried out at a remote site using a Bell JetRanger to determine profiles and procedures that satisfied the noise limits. The JetRanger fly-neighbourly profiles were then extended to other helicopter types, since different main-rotor configurations, rotation directions and tail rotors call for different techniques.

At the request of the SPCC, Steven Cooper joined the Australian aircraft standards sub-committee AV/52 in 1985 (later the full committee AV11/EV11) and was a major contributor to both versions of AS 2363. He has served on the Acoustics and Fly Neighborly Committees of Helicopter Association International, was a co-reviewer of the US Helicopter Fly Neighborly Guide, and is the author of the Australian Helicopter Fly Neighbourly Guide. Applying these techniques, several projects that regulators and other consultants considered unable to comply were shown to meet the noise limits.

After evaluating some 60 helipads across Australia, Steven was engaged by the Department of Defence to assess helicopter operations and incorporate them into noise contours around defence bases. As no recognised test procedure existed, Noise Power Distance (NPD) curves were derived using the Effective Perceived Noise Level descriptor, differential GPS tracking and multiple time-coded microphone positions.

Comparing measured results with the Integrated Noise Model (INM) revealed an anomaly for circuit operations, traced to the program’s lateral attenuation algorithms. A correction was presented to the US aircraft noise standards committee (SAE A-21) in 2003 and the INM was subsequently modified for helicopter operations. A further anomaly in the INM’s atmospheric attenuation has since been presented to the acoustics community in Australia, New Zealand and the United States. NPD testing for new military helicopters confirms significant differences between certification-type and operational NPD results.

Aircraft noise assessments

The Australian aircraft standards committee is also responsible for AS 2021. With the opening of Sydney Airport’s third runway, a research project part-funded by the NSW Environmental Trust measured jet aircraft on the northern flight paths. It found that several aircraft noise tables in the Standard needed revision, including splitting Boeing 747 departures into Stage 1 and long-haul classifications.

Later work on the Sydney Aircraft Noise Insulation Project identified issues with the attenuation of aircraft noise set out in the Standard, leading to significant amendments between the 1994 and 2000 editions of AS 2021. Steven was convener for the new compliance-testing appendix, Appendix C of AS 2021-2000.

Military aircraft and the Joint Strike Fighter

Following the helicopter NPD work, compliance testing determined NPD curves for military jets as part of the assessment of the Joint Strike Fighter for Australian operations, exposing problems with INM default take-off locations and atmospheric attenuation. Verification of preliminary JSF NPD curves led to testing in late 2008 at Edwards AFB, California, with an international team of acoustic experts. That program has been identified as the most comprehensive noise testing of any military aircraft, and included Australian-specific measurements with microphones up to 10 nautical miles along the extended centreline. The results led to a significant refinement of the ANEF contours for RAAF Base Williamtown.

Aircraft noise verification has also been undertaken for the Hawk Lead-In Fighter, FA-18 Hornet, F-111 and FA-18E/F Super Hornet.

Noise and flight path monitoring

The firm was involved in developing Noise and Flight Path Monitoring Systems (NFPMS) for defence facilities, which are more complex than civil aerodrome systems, and carried out certification of the NFPMS at RAAF Base Williamtown, RAAF Base Townsville, RAAF Base Amberley and HMAS Albatross.

Relevant papers

• “The INM Program is a much better program than HNM for helicopter modelling, but…” HeliExpo, Las Vegas, March 2004
• “Problems with the INM: Part 1 – Lateral Attenuation” Noise of Progress Acoustics Conference, New Zealand, 2006
• “INM – Getting it to work acoustically” 20th International Congress on Acoustics, Sydney, 2010
• “Military Aircraft Noise in the Community” 20th International Congress on Acoustics, Sydney, 2010
• “Alternative Aircraft Metrics – Useful or like moving the deck chairs on the Titanic” 20th International Congress on Acoustics, Sydney, 2010
• “Aircraft Noise Measurements can be fun” Australian Acoustical Society NSW Division, August 2011

Several of these papers are available in our free whitepaper library.