With the advent of low noise high bypass ratio turbofan engines airframe noise gained significant importance with respect to the overall aircraft noise impact around airports. Already around 1970 airframe noise, originating from flow around the landing gears and high-lift devices, was recognized as a potential “lower aircraft noise barrier” at approach and landing. Since then, the outcome of extensive acoustic flight tests and aeroacoustic wind tunnel experiments enabled a detailed description and ranking of the major airframe noise sources and the development of noise reduction means. In the last decade advances in numerical and experimental tools led to a better understanding of complex noise source mechanisms. Efficient noise reduction technologies were developed for landing gears while the benefits of high-lift noise reduction means were often compensated by a simultaneous degradation in aerodynamic performance. The focus of this paper is not on the historical sequence of airframe noise research but rather aims to provide a concise survey of the achievements in airframe noise source description and reduction over the last 40 years worldwide. Due to the vast amount of work focused on a variety of airframe noise problems, this review can only provide examples but does not claim to be complete.

Almost 40 Years of Airframe Noise Research: What Did We Achieve?

https://cyberleninka.org/article/n/1284788.pdf

Control strategies for aircraft airframe noise reduction

Landing gear related airframe noise is one of the dominant aircraft noise components at approach, so continued research efforts to reduce landing gear noise are essential. This paper describes further development of an advanced low noise main landing gear that was previously designed and tested in the European SILENCER project. The work was carried out under the current European co-financed TIMPAN project (Technologies to IMProve Airframe Noise) using a 1/4 scaled landing gear model that was tested in the German-Dutch Wind Tunnel. A variety of gear configurations were tested including a new side-stay design and various modifications to the bogie inclination, wheel spacing, bogie fairings with different flow transparency, leg-door configurations and brake fairings. The farfield noise data from the tests are compared with results from a landing gear noise prediction model, transposed to full scale flight conditions and compared with the full scale test data obtained for the original SILENCER advanced A340 s...

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Experimental assessment of low noise landing gear component design

Noise reduction technologies for aircraft landing gear-A bibliographic review

In support of the QTD II (Quiet Technology Demonstrator) program, aeroacoustic measurements of a 26%-scale, Boeing 777 main landing gear model were conducted in the Virginia Tech Stability Tunnel. The objective of these measurements was to perform risk mitigation studies on noise control devices for a flight test performed at Glasgow, Montana in 2005. The noise control devices were designed to target the primary main gear noise sources as observed in several previous tests. To accomplish this task, devices to reduce noise were built using stereo lithography for landing gear components such as the brakes, the forward cable harness, the shock strut, the door/strut gap and the lower truck. The most promising device was down selected from test results. In subsequent stages, the initial design of the selected lower truck fairing was improved to account for all the implementation constraints encountered in the full-scale airplane. The redesigned truck fairing was then retested to assess the impact of the modifications on the noise reduction potential. From extensive acoustic measurements obtained using a 63-element microphone phased array, acoustic source maps and integrated spectra were generated in order to estimate the noise reduction achievable with each device.

Screening of Potential Noise Control Devices at Virginia Tech for QTD II Flight Test

The advances in aircraft engine noise reduction and the increasing demand for quieter aircraft has led noise research to focus more attention on airframe noise. Landing gears and high lift systems have been known to significantly contribute to the total aircraft noise at approach idle conditions, especially in cases where high by-pass ratio engines are used, when noise from the engines is low enough that it could be considered comparable or lower than the noise from the airframe. Landing gears in service on today’s aircraft were not designed with noise impact in mind and contain a myriad of possible noise generating features. Today’s landing gear designer is challenged to consider noise among many other factors when designing efficient aircraft landing gear systems. It is a challenge further complicated if noise reduction solutions are required for retro-fit applications. Much of the experimental noise research conducted on landing system noise has centered around the understanding of noise generating mechanisms and evaluation of noise reduction concepts in model-scale environments such as wind tunnel tests. These experiments have provided valuable insight into landing gear noise sources. However, little effort has been made to integrate noise reduction research with full-scale landing gear design and evaluate noise reduction potential in a full-scale flight environment. The work conducted under the Quiet Technology Demonstrator 2 (QTD2) program marks a first step in the successful integration of noise research with landing gear design with the focus being to design, implement and evaluate noise reduction solutions in a full-scale flight environment. This paper discusses the design and analysis of a ‘toboggan’ shaped main landing gear noise reduction fairing for full-scale flight evaluation on a B777-300ER aircraft in the QTD 2 program. The fairing was selected for flight evaluation after a series of model-scale wind tunnel acoustic experiments were conducted in conjunction with full-scale feasibility studies. The fairing design addressed issues such as gear kinematics and stowing, brake cooling, ground operations and noise reduction potential. The design was supported by static stress analysis and flutter analysis to ensure that the fairing was flight worthy.

Gene Stuczynski

Papers

QTD 2 (Quiet Technology Demonstrator 2) Main Landing Gear Noise Reduction Fairing Design and Analysis