Propeller Ground and Ceiling Effect in Forward Flight

The study of the fixed-pitch small-scale propeller in ground/ceiling effect is extended to forward flight conditions. Force-based experiment and smoke flow visualization is conducted at the University of Dayton Low Speed Wind Tunnel. The propeller is mounted at different incidence angles to simulate the transition to forward flight from hover and forward flight conditions. The effect of propeller incidence angle seems to be negligible at J=0. The power required at constant thrust shows an increasing trend after a threshold advance ratio for each h/D and then decreases steeply upon further increase in advance ratio. Smoke flow visualization revealed the presence of three distinct zones separated by the onset of the fountain vortex and the onset of the ground vortex at each ground distance. At advance ratios below the onset of the fountain vortex lies the optimal ground effect zone. An increase in advance ratio beyond this threshold will result in power increment due to the fountain vortex. Further increase in advance ratio initiates the onset of the ground vortex where the ground effect is significantly reduced. The onset of the fountain vortex and the ground vortex occurs at lower advance ratios for a propeller at an incident angle to the ground.