ANCORA

ANotec-COmoti Rotorcraft Acoustics initiative for preliminary acoustic flight tests for the tuning of simplified rotorcraft noise models

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 Obiettivo del progetto (Objective)

'One of the objectives of GRC5 is to implement a tool for the minimisation of noise impact on the ground, capable of being executed on-board “on-the-fly”, providing flight directives to the FMS of the helicopter. To this end reliable and fast noise predictions will have to be made, based on actual flight conditions. The envisaged semi-emperical model to be used for this purpose requires information to be derived from experimental data.

The main objective of ANCORA is to determine the transfer function between the noise measured on-board the helicopter, close to the noise sources, and the noise received on the ground by a grid of microphones, during a flight test campaign.

ANCORA will investigate the application of surface microphones on the helicopter fuselage and will subsequently use this knowledge for the flight test campaign. ANCORA will deliver a robust and reliable mobile noise measurement system, easily scalable and optimised for minimum deployment time and cost. During the test campaign a large number of steady-state conditions and manoeuvres will be flown over a grid consisting of 31 microphones. ANCORA will develop an advanced method for the determination of the transfer functions between on-board and ground microphones All results from the flight tests and data analysis (raw data, 1/3 octave spectra, transfer functions) will be made available through a data repository.'

Introduzione (Teaser)

Minimising the noise produced by aircraft is an important concern of the EU aerospace industry. A new EU-funded project has demonstrated the feasibility of inferring ground noise from in-flight sensors to enable a fast response to muffle it.

Descrizione progetto (Article)

The Clean Sky initiative is a European aeronautical research programme working on technologies to produce less noisy and more fuel-efficient aircraft. One of its objectives is to develop a tool to minimise the noise impact of helicopters on the ground. The goal is a system that can be activated 'on-the-fly' from fast on-board predictions of ground noise levels based on noise from sensors on the helicopter itself.

This requires reliable noise predictions based on actual flight conditions. The accuracy of such a model depends on the quantity and quality of experimental data that go into it. The EU-funded ANCORA project met the challenge in a series of experimental flights using on-board and ground-based microphones.

Data collected from flights over a grid of 30 microphones were used to determine the transfer function between the helicopter noise measured on the aircraft and that received on the ground. All results from the flight tests and data analysis are available in a database.

Tests were carried out on a small propeller aircraft because the test helicopter was unavailable for a long period of time. However, maximum commonality with originally planned measurement systems, flight procedures and data analysis was maintained.

ANCORA demonstrated the feasibility of placing surface microphones on a helicopter fuselage and on a small turboprop plane, and developed a robust noise measurement system that can easily be deployed quickly and cost effectively. The advanced methodology for determining the transfer function can now be adapted following the flight test campaign on the original helicopter at a later date.