This paper discusses the systematic experimental and vehicle design/development studies conducted
at the University of Maryland which culminated in the development of the first flying Cyclocopter in the
history. Cyclocopter is a novel Vertical Take-Off and Landing (VTOL) aircraft, which utilizes cycloidalrotors
(cyclorotors), a revolutionary horizontal axis propulsion concept, that has many advantages such as
higher aerodynamic efficiency, maneuverability and high-speed forward flight capability when compared
to a conventional helicopter rotor. The experimental studies included a detailed parametric study to
understand the effect of rotor geometry and blade kinematics on cyclorotor hover performance. Based on
the experimental results, higher blade pitch angles were found to improve thrust and increase the power
loading (thrust per unit power) of the cyclorotor. Asymmetric pitching with higher pitch angle at the top
than at the bottom produced better power loading. The chordwise optimum pitching axis location was
observed to be around 25-35% of the blade chord. Because of the flow curvature effects, the cycloidal
rotor performance was a strong function of the chord/radius ratio. The optimum chord/radius ratios were
extremely high, around 0.5-0.8, depending on the blade pitching amplitude. A flow field investigation was
also conducted using Particle Image Velocimetry (PIV) to unravel the physics behind thrust production
of a cyclorotor. PIV studies indicated evidence of a stall delay as well as possible increases in lift on
the blades from the presence of a leading edge vortex. The goal of all these studies was to understand
and optimize the performance of a micro-scale cyclorotor so that it could be used in a flying vehicle. An
optimized cyclorotor was used to develop a 200 gram cyclocopter capable of autonomous stable hover using
an onboard feedback controller.
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