Technologies to IMProve Airframe Noise
TIMPAN (Technology to IMprove Airframe Noise) is a 3-year project of the European Community 6th Framework Programme, Priority “Aeronautics and Space”, launched in 2006, addressing the community noise reduction objectives for commercial aircraft by focusing on the airframe noise issue, caused by turbulent flow around the landing gear and the high-lift wing and responsible for about half of the total noise in approach situation for aircraft of recent design.
TIMPAN addresses both sources (landing-gear and high-lift) through investigation of innovative technologies and improvement of advanced low-noise designs. Mid-term objective is a 5 dB airframe noise reduction with respect to 2000 state-of-the-art.
TIMPAN brings together 14 actors from the European aeronautics industry including aircraft manufacturers, landing gear manufacturers, key research institutes, universities and SMEs .
Achievements on landing-gear:
Plasma actuators and air curtain technologies, providing each a broadband noise reduction of 3 to 5 dB on component, have proved to be relevant breakthrough technologies for long-term implementation. However, these innovative technologies will not be available to meet the mid-term challenge of 5 dB on airframe noise as further developments are needed for assessing their potential on representative aircraft components and for solving related integration issues.
Main outcomes result therefore from the improvement of advanced low noise design on the main-landing gear. In the EU-Project SILENCER advanced low noise gears had been investigated . In the EU-Project TIMPAN more advanced concepts were developed and noise tested on a ¼ scaled main landing gear model in the 6 m by 6 m open test section of DNW-LLF (German-Dutch Wind Tunnel – Large Low Speed Facility). The model test results were transposed to full scale and compared against the full-scale SILENCER A340 style main landing gear test results. In TIMPAN different modifications of the major gear components in combination with flow transparent fairings and variations of both bogie inclination and wheel spacing were tested. An optimal combination of all tested gear modifications led to a noise reduction of up to 8 dB(A) in terms of overall A-weighted noise levels, relative to the SILENCER reference gear configuration (Fig. 1) – which corresponds to more than 6 EPNdB landing-gear noise reduction in approach. The main contributions to this noise reduction originates from an increase in toe down bogie inclination angle, both a flow transparent bogie and torque link fairing, a low noise side-stay, brake and leg-door design in combination with a ramp.
 Dobrzynski, W., Schöning, B., Chow, L. C., Wood, Ch., Smith, M., Seror, Ch.: “Design and Testing of Low Noise Landing Gears“, AIAA/CEAS 2005-3008, 11th AIAA/CEAS Aeroacoustics Conference, Monterey / USA, 23-25 May, 2005.
Achievements on high-lift devices:
Slotted slats constitute the major noise sources of today’s high-lift systems of large commercial aircraft. In TIMPAN, three approaches are considered. The first one consists of developing a slat-less concept supported by a wing-flap arrangement utilising flow control on the flap (Coanda effect) to deliver the required high-lift performance. The second approach is linked to the implementation of add-on acoustic treatments (wing leading edge liner, slat wire meshes, slat trailing edge treatments) and the third one to the slat setting (slat gap and overlap) optimization.
The slat-less concept is surely the most aggressive technology. While allowing to maintain the required aircraft performance and strongly reducing airfoil noise, it leads to severe integration issues as the air-flow required for the Coanda flow control technology on the flap needs to be made available.
Add-on acoustic treatments may provide good source noise reduction but generally lead to performance degradation and poor results.
The most relevant outcome is therefore the slat setting optimization, which proved that a compromise in term of low-speed performance might be found for optimizing airframe noise in approach. With respect to the reference setting a noise reduction of up to 3.5 dB on airfoil noise has been demonstrated.