Investigation on same-track multirotor separation using CFD simulated flow field and software in the loop stability analysis

Abstract

An important factor of maintaining modern air traffic safety is the determination and enforcement of separation minima. Two major factors affect the determination of separation minima in civil aviation: the radar separation to manage uncertainties due to communication, navigation, and surveillance performance, and the wake separation due to aircraft instability when encountering aircraft generated wake turbulence. Similar implementation would be needed in urban airspace for unmanned aerial system traffic management (UTM) given the elevated risk to third-parties population that could result from a mid-air collision. With the widespread use of satellite-based navigation and transponder-based surveillance in UAS, the uncertainties contributing to CNS separation would greatly reduce. However, the physical forces driving the need for wake separation remains, and could be the dominating factors in UTM separation requirements. Comparing to their fixed-wing counterpart, few studies have been conducted on wake turbulence profile of the multirotor UAS, and even fewer on the stability of multirotor following a wake encounter. This paper investigates the consequence of multirotor encountering wake produced by another multirotor using a combination of CFD and software in the loop simulation with Pixhawk4 flight controller. The results suggest that while larger multirotor has greater wake turbulence strength hence greater hazard upon encounter, the larger initial separation gap between the vortex structures could also create a safe passage for multirotor with sufficiently small arm-span.