Noise evaluation of battery powered small aircraft

Preliminary assessments of battery powered aircraft designs show potential for noise reduction. However, profound analyses estimating this noise reduction potential using white-sheet preliminary aircraft designs are missing so far. Additionally, an investigation on the sensitivity of crucial aircraft design parameters impacting both aircraft performance and noise emissions could be utilized to derive design recommendations for quieter battery powered aircraft without a considerable performance decrease. Feasible preliminary aircraft designs are derived using the multidisciplinary preliminary aircraft design and optimization tool MICADO. The derived preliminary aircraft designs are subsequently evaluated towards their noise emission. Because the propeller represents the dominant noise source, the noise evaluation is focused on the propeller as only source. The noise is evaluated at an observation point situated beneath the flight path on the ground 2500 m away from the brake-release point. Three different aircraft configurations are assessed employing one, two and four electric engines. Besides electric engines, a piston engine aircraft with one engine is assessed for proper baseline values. The design maximum propeller tip Mach number is varied for each configuration resulting in 22 different preliminary aircraft designs. Results substantiate that single electric engine aircraft compared to an analogous single engine piston aircraft, within the actual technology and in terms of propeller noise, produces a higher noise annoyance. Despite this result, important noise reduction potential for electric aircraft can be achieved. When increasing the number of electric engines from one to four, while reducing the design maximum propeller tip Mach number, a max OASPL reduction of 23.8 dBA can be observed for the given TLARs. © 2019, Deutsches Zentrum für Luft- und Raumfahrt e.V.