NCR helps reduce airframe and landing gear noise
Oct. 26, 2011, Ottawa - The National Research Council of Canada (NRC) has commissioned a wind tunnel to help aircraft manufacturers measure the noise levels generated by aircraft landing gear.
Unique in Canada, this facility will help airline manufacturers meet internationally accepted and ever more stringent noise standards.
In Ottawa, one of the eight wind tunnels operated by NRC Aerospace has been outfitted with an acoustic liner and precision noise measurement technology. This tunnel can house landing gear and simulate the wind conditions during deployment and on approach, generating wind speeds up to 150 knots. NRC aerodynamics experts take landing gear apart and reassemble it part by part, measuring the noise generated by wind flowing around each component as well as that caused by components interacting. The idea is to guide manufacturers in the design of specific components to reduce their sound impact.
The body behind the research is the Green Aviation R&D Network (GARDN), a federally established business-led network of Centres of Excellence. Bombardier Aerospace, Bell Helicopter, Pratt & Whitney Canada and CMC Electronics are among the industry partners collaborating with NRC and nine universities to help manufacturers produce greener aircraft.
Regulations, targets and limits are set by the International Civil Aviation Organization (ICAO) and NASA’s Environmental Responsibility Aviation (ERA) program. In the next ten years, regulations will aim to reduce noise generated by commercial aircraft by 32 dB relative to the current standard.
Until recently, the industry had focused on measuring and reducing the noise generated by engines alone. Turbofan-powered airliners and business jets are becoming progressively quieter through higher bypass ratios, acoustic materials and nacelle design techniques, in order to meet increasingly stringent noise reduction targets.
Yet little known is the fact that the airframe also generates significant noise because of air flow turbulence around the landing gear, wheel wells, flaps and slats.
Turbulent flow around landing gear generates a significant proportion of the total noise output of an aircraft in close proximity to the ground,” said NRC’s Stuart McIlwain, group leader of fixed-wing aerodynamics.
“We adapted one of our wind tunnels to measure the noise from undercarriages because it’s the total footprint – not just engine noise – that is measured for ‘Stage 4’ compliance.”
NRC Aerospace has tested a full-scale Bombardier Learjet 60 landing gear, combining many permutations.
“We looked at the gear struts and axles individually, but also the interaction between such components,” said NRC aeroacoustics researcher Jerry Syms. “The drag strut/main strut combination, gear doors, brake lines, wheel wells and other components generate enough noise on their own to merit attention.”
“Our job is to search for where the noise comes from and suggest ways to reduce it,” added McIlwain. “The OEMs then can apply and certify their individual programs to ICAO standards.’’
Aircraft equipment manufacturers can now call on NRC Aerospace for this type of acoustic assessment.