Source Characterization

As part of an FAA led team, BRRC conducted noise measurements to characterize the noise emissions from Unmanned Aircraft Systems (UAS) during ground and airborne operations for the purposes of UAS noise analysis in support of 14 CRF Part 135. The team accomplished these measurements at Causey Airport in Liberty, North Carolina. The team performed measurement on three UAS vehicles: Flytrex FTX-M600P, Volansi VOLY C10, and DJI m210. The acoustic array included 20 microphones arraigned for flyovers, vertical take and landings, and hover test conditions. Five of the microphones were elevated above the ground up to 30m. The measurements included 172 flyover passes, 95 vertical operations, and 40 hover events. The measurement team included personnel from the FAA, Volpe, and BRRC. FAA coordinated the UAS and flight operations, Volpe led the vehicle tracking data collection, and BRRC led the acoustic data collection.

BRRC conducted a measurement campaign under ACRP Project 02-81 between November 2017 and April 2019 to collect acoustic, operational, and meteorological data during the launches of the Antares 230, Falcon 9, Delta IV Heavy, and Falcon Heavy vehicles. These events represented a range of mission and operation types, including cargo resupply missions to the International Space Station (OA-8E and CRS-15), a research mission (Parker Solar Probe), a communications satellite launch (Arabsat-6A), and first stage return-to-landing operations (Arabsat-6A). Additionally, the measured launch vehicles possess mass-to-orbit capabilities ranging from medium to super-heavy lift designations. In total, over the four measured events, more than 250 acoustic recordings were collected from 70 sites at distances between 0.2 km and 27 km from the launch and landing pads at two distinct spaceports. The acoustic recordings include propulsion noise measurements from all four launch events as well as sonic boom measurements from the return-to-landing operations. The combined acoustic, operational, and meteorological data were analyzed and compiled into a publicly accessible database with thorough supporting documentation. This well-documented, high-fidelity database will equip future researchers with the information necessary to validate current noise models, identify shortcomings, and improve model accuracy by way of better propulsion noise and sonic boom source characterizations.

BRRC was selected by the Agility Prime Program to inspect, process, and analyze the noise data collected from the April 2022 measurements of LIFT’s HEXA aircraft. Four microphones perpendicular to the flight path recorded continuously to capture the noise from three HEXA flyovers for two different payloads. BRRC identified and extracted the ascent, level fly-by, and descent portions of each flyover from each microphone recording using the vehicle’s tracking data. These events were then reviewed for quality and saved using a standard format (ANSI S12.75) which includes pertinent test and equipment information within an ASCII header. For each test condition, event, and microphone, BRRC computed the spectral time history as well as the average sound exposure level (SEL) and average A-weighted maximum sound level (LA,max). These data were delivered in a readable text file format that included the relevant test information. The results of BRRC’s review and analysis were summarized in a slide deck which was presented and delivered to the client. Photo Credit: Samuel King Jr, U.S. Air Force.