Overview
One of the objectives of GRC5 was 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 were made, based on actual flight conditions. The envisaged semi-empirical model to be used for this purpose required information to be derived from experimental data.
The main objective of ANCORA was 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 investigated the application of surface microphones on the helicopter fuselage and will subsequently use this knowledge for the flight test campaign. ANCORA delivered 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 were flown over a grid consisting of 31 microphones. ANCORA developed 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) were made available through a data repository.
Funding
Results
Executive Summary:
One of the objectives of GRC5 was 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 had to be made, based on actual flight conditions. The envisaged semi-empirical model to be used for this purpose required information to be derived from experimental data.
The main objective of ANCORA was therefore 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.
In the first phase of the project, a test campaign was performed with the on-board microphones to establish the optimum microphone positions for the final flight tests. However, due to the long-term unavailability of the helicopter in the configuration required for these final tests, it was decided to use an alternative test vehicle. Although the flight tests were performed on a small propeller aircraft, maximum commonality was pursued with the originally envisaged flight plan in terms of measurement systems, flight procedures and data analysis. The main objective of ANCORA was therefore adapted accordingly: validate the full measurement system (both on-board and ground-based) and the software needed for the data analysis and the determination of the transfer functions, developed in ANCORA. This allowed the originally envisaged flight tests with the helicopter at a later stage (beyond the ANCORA project) with low risk.
ANCORA demonstrated the feasibility of the application of surface microphones on the helicopter fuselage and on a small turboprop aircraft and subsequently use this knowledge for a flight test campaign with the same helicopter at a later stage. ANCORA delivered 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 were flown over a grid consisting of 30 microphones. ANCORA developed 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) are available through a data repository.
Based on the above it can in general be concluded that the hardware and software tools developed in ANCORA are valid and that thus the main objective of the ANCORA project had been achieved.