Ground Based Measurements and Acoustic Characterization of Small Multirotor Aircraft
Open Access
- Author:
- Konzel, Nicholas
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 28, 2022
- Committee Members:
- Amy Pritchett, Program Head/Chair
Eric Greenwood, Thesis Advisor/Co-Advisor
Eric Norman Johnson, Committee Member - Keywords:
- Acoustics
UAV
Data Collection
Noise Characterization
Multirotor - Abstract:
- Electric Vertical Takeoff and Landing (eVTOL) systems are growing in popularity across several industries due to their adaptability and usability. Different flight missions and configurations are being defined every day and with each new design comes new environmental concerns. The noise of these vehicles is characterized by the high frequency and variability of the noise generated by the rotors. The noise of these systems is not well understood due to a lack of high quality measured acoustic data. Furthermore, the wide range of possible operating conditions and their unique noise characteristics makes it difficult to quantify noise and collect repeatable acoustic data in the field. This thesis details the development of a measurement approach that gathers consistent and accurate noise data as a function of space and time. Using the measurement approach defined in this thesis, noise data was collected for one specific Unmanned Aerial System (UAS) in a variety of different flight conditions including, but not limited to, varied altitudes and speeds. Additionally, adequate weather and vehicle state data was recorded to supplement the noise data and used in a summary analysis to find any acoustic dependencies. Signal to noise ratios were investigated at several different microphone and vehicle locations. Using these comparisons, the proposed microphone array proved to be adequate for the size of the test vehicle and the conditions it flew. Two different microphone installations were used and found to have noticeable spectral differences. Furthering the investigation showed that integrating the noise metrics in the time domain produced a consistent and small (1 dB) offset between the two installations. The noise characteristics of the eVTOL aircraft are unique. Examination of the spectral data showed that, while broadband noise was significant directly below the aircraft, the rotor tones were more prominent at the beginning and end of the flyover, especially at higher speeds. The frequency of these tones varied in time as the rotor RPM varied to stabilize the vehicle during flight.