An Empirical Evaluation of Ceiling Effect for Small-Scale Rotorcraft*

Ceiling effect refers to the apparent increase in lift that a rotorcraft experiences when flying close to a ceiling or any similar surface that is present above the rotor(s). Ceiling effect is similar in principle to ground effect, in which an increase in lift is observed flying close to the ground. Ground effect has been well studied for conventional helicopters since the 1950's, and more recent research is exploring this phenomenon for multirotor aircraft. Ceiling effect, however, was never explored in detail for conventional helicopters because large manned aircraft do not operate in enclosed spaces. The recent widespread use of small-scale UAVs and the demand for increased autonomy when flying in enclosed environments has created a need for detailed studies of ceiling effect. This paper discusses the benefits of an improved understanding of ceiling effect, the current state-of-the-art, and a comprehensive experimental evaluation of ceiling effect for single and multirotor UAVs. The experimental results for multirotors presented are for multiple propeller configurations, speeds and spacings. In addition, a comparison is made with ground effect, and the fundamental differences that exist in these two cases. Ultimately, this work provides foundations for the development of an improved UAV flight controller that can accurately account for various aerodynamic disturbances that occur near surfaces and structures to improve flight stability.