The demand for high-resolution, in situ atmospheric data at high altitudes has driven the development of specialized unmanned aerial system (UAS). Multirotor platforms are increasingly favored for their vertical takeoff capabilities and maneuverability in confined or remote environments. As a multirotor ascends, the decrease in air density necessitates higher motor rotational speeds and larger propellers to maintain adequate lift. This requirement entails the use of high-KV (constant voltage) motors paired with large-diameter propellers. However, this configuration is suboptimal at low altitudes, where high motor revolutions per minute (RPM) can lead to excessive current draw and thermal runaway. To mitigate this issue, the multirotor initially generates slightly more lift than its weight, enabling a slow and steady climb. As altitude increases and air density drops, propeller efficiency declines, requiring higher RPM to maintain thrust. However, reduced aerodynamic drag and increased relative wind at high altitudes help offset the current demand, improving thermal performance. Therefore, this paper presents four technical contributions: 1) dynamic, guidance, and control system modeling for a multirotor for altitudes up to 7,500 m MSL; 2) an ordinary-differential-equation-constrained optimization framework for joint design of controller and propulsion components; 3) analysis of off-design parameters using commercial-off-the-shelf parts; and 4) validation through simulation and flight experiments.
Supsukbaworn et al. (Mon,) studied this question.