Measurement Resolution of Noise Directivity Patterns from Acoustic Flight Tests
Abstract
A study was conducted to investigate the measurement resolution of noise directivity patterns from acoustic flights test. Directivity-angle resolution is affected by the data reduction parameters, the aircraft velocity and flyover altitude, and deviations of the aircraft from the desired flight path. Equations are developed that determine bounds for the lateral- and longitudinal-directivity-angle resolution as a function of the nominal directivity angle. The equations are applied to a flight test data base, and the effects of several flight conditions and data reduction parameters on the directivity-angle resolution are presented. The maximum directivity-angle resolution typically occurs when the aircraft is at or near the overhead position. In general, directivity-angle resolution improves with decreasing velocity, increasing altitude, increasing sampling rate, decreasing block size, and decreasing block averages. Deviations from the desired ideal flight path will increase the resolution. For the flight experiment considered in this study, an average of two flyovers were required at each test condition to obtain an acceptable flight path. The ability of the pilot to maintain the flight path improved with decreasing altitude, decreasing velocity, and practice. Because of the prevailing wind conditions, yaw angles of as much as 20 deg were required to maintain the desired flight path. Keywords: Acoustics; Flight testing; Acoustic directivity resolution; Aircraft flyover noise.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1989
- Accession Number
- ADA216014
Entities
People
- David A. Connor
Organizations
- Langley Research Center