Design, Development, and Flight Testing of a 25-Kilogram Quad-Cyclocopter

This paper describes the design, development, and tethered flight testing of a quad-cyclocopter weighing 25 kilograms and 1.8 m x 1.4 m x 0.8 m in dimension. This cyclocopter features four cantilevered cyclorotors with a unique five-bar blade pitching mechanism. The cyclorotor design is chosen through systematic parametric studies using an in-house 2-D computational fluid dynamics (CFD) solver. Based on the parametric studies, the final design selected is a 6-bladed cyclorotor with 0.67 chord-to-radius ratio, symmetric NACA 0015 airfoil, and pitch amplitude of 45-degree because it provided high thrust and power loading (thrust/power) at a low operating rotational speed of 700 RPM. The cyclorotor blades are manufactured with a foam core and carbon fiber skin resulting in lightweight blades with large bending and torsional stiffness. The rotor supporting structure and transmission is designed to be lightweight and resilient to large centrifugal loads and dynamic torques, respectively. A minimum mass airframe is designed and constructed from carbon fiber tubes to handle the vibratory loads from cyclorotors, mount electronics and batteries, and provide attachment points for the carbon fiber cowling. The attitude control strategy utilizes a combination of RPM control and thrust vectoring of the four cyclorotors (eight independent control parameters), resulting in an overactuated system. A custom autopilot uses a closed-loop cascaded proportional-integral-derivative (PID) controller to stabilize the aircraft in hovering flight. The vehicle has been flight tested while tethered and achieved lift off.