Comprehensive Acoustics Characterization Framework for eVTOL/HSVTOL Aircraft

Emerging eVTOL and HSVTOL aircraft for the USAF future force structure currently are focusing on high-speed VTOL performance. However, the Air Force currently lacks a unified, commercially available and validated acoustic characterization framework for emerging aircraft designers in industry to use for optimizing their concepts for low acoustic signatures. The AF also currently lacks a generalized acoustic characterization framework for evaluating the emerging low-noise technologies from a holistic perspective. Research in Flight and Auburn University are proposing to develop a Comprehensive Acoustics Characterization Framework (CACF) for the USAF to allow for the holistic characterization of acoustic signals from emerging eVTOL and HSVTOL class aircraft. The proposed CACF will focus on key acoustics metrics that the USAF and vehicle designers must consider when evaluating vehicle acoustic signatures from the standpoint of acoustic stealth, safety and mitigation. CACF also serves to allow the USAF to analyze emerging acoustic mitigation technologies in early design stages, thereby increasing efficiencies and evaluating emerging concepts. The technical focus of this activity is on the physical and psychoacoustic (human perceived) effects of noise at the observer on the ground. Within physical effects, the CACF will look at the magnitude of the signal and the spectral analysis as well as directional dependence. The acoustic framework would include the ability to capture the directional dependence of propagated sound due vehicle design and layout of propulsion system. Psychoacoustic analysis metrics will focus on both spectral and temporal effects. The human auditory system is both highly-nonlinear and hard to model. The use of specially defined weighting-functions and metrics designed by the ICAO and others to account for this bias in perceived loudness is critical to the success of missions that rely heavily on discrete acoustic footprints of eVTOL and HSVTOL aircraft. Loudness as an element of psychoacoustic analysis plays an important role in the human-perception of a signal and will be characterized in the CACF. Loudness is dependent on frequency, physical intensity, and signal duration. Consequently, the CACF will characterize loudness in the form of A-weighting (frequency sensitivity dependence), sound exposure level (signal duration) and effective Perceived Noise Level (pure-tone sensitivity). In Phase I, the team will expand on the proposed CACF with AF customers to identify needs and confirm alignment with AF requirements for acoustics in eVTOL and HSVTOL aircraft. The team will also identify key USAF customers that would benefit from this capability; identify upstream and downstream integration issues; and develop a roadmap to a commercially-viable prototype development in Phase II.