David Coleman

Experiments on Rigid Wing Undergoing Hover-Capable Flapping Kinematics at Micro-Air-Vehicle-Scale Reynolds Numbers

The paper focuses on understanding the mechanism of force production on a hover-capable flapping-wing system by using a combination of direct force measurements and flowfield studies. The experiments were conducted in air at a Reynolds number of approximately 25,000 (based on mean chord and maximum tip speed), which is the typical operating regime of small flapping-wing micro air vehicles. The forces and moments were measured using a miniature six-component force transducer installed at the wing root. The wing was flapped in air and vacuum at the same frequency and wing kinematics, and the vacuum forces were subtracted from the total forces to obtain the pure aerodynamic forces. Flow visualization and particle image velocimetry were used to characterize the formation, strength, and structure of the leading-edge vortex on the flapping wing. A rapid increase in wing lift coefficient was associated with the growth of the leading-edge vortex and a progressive reduction in lift coefficient with the convection ...

Design and Development of a Meso-Scale Cyclocopter

This paper describes the design, development and flight testing of a meso-scale cyclocopter. Weighing only 29 grams, the present vehicle is the smallest cycloidal rotor based aircraft ever built. Unlike the previous cyclocopters, the current prototype utilizes a novel light weight (3 grams) cycloidal rotor design with cantilevered blades having semi-elliptical planform shape and no exposed rotor shaft. To minimize bending deflections the blades use a unique, lightweight (0.15 grams each) but high strength-to-weight ratio unidirectional carbon-fiber based structural design and are fabricated using a specialized manufacturing process. The blade kinematics was chosen through systematic performance measurements conducted using a custom-built miniature three-component force balance. Based on experimental parametric studies, symmetric blade kinematics with a pitch amplitude of 45° provided the highest thrust and power loading (thrust/power) and was used in the final rotor design. The airframe is fabricated using a combination of carbon-fiber and state-of-the-art 3D printing techniques. The attitude control strategy utilizes a combination of rpm-control of the two cycloidal-rotors/tail-rotor and thrust vectoring of the cycloidal rotors. The control strategy is implemented on a custom-built 1.3 gram autopilot, which uses a closedloop proportional-derivative controller for hover stability. The vehicle has been systematically flight tested by tuning the feedback gains and has demonstrated marginal stability in hover.

Aeromechanics Analysis of a Hummingbird-Like Flapping Wing in Hover

This paper presents an in-depth investigation into the instantaneous forces, flowfield, and wing deflections of a flapping wing used on a hover-capable robotic hummingbird. The goal was to understa...

On the Development of a Robotic Hummingbird

This paper describes the design, development and flight testing of a 62-gram hummingbird-inspired flapping wing micro air vehicle with hovering capability. There were several design challenges encountered and innovative techniques were implemented to overcome them. To achieve the required large flap-stroke amplitudes necessary to generate lift for hover at moderate flap frequencies (~25Hz), a novel “5-bar” mechanical linkage system was developed which amplifies the output of a standard 4-bar crank-rocker mechanism. Utilizing aeroelastic tailoring techniques, lightweight (~0.8 grams), flexible wings were designed which produce the required lift for hover and their performance was optimized for a specific operational frequency range. Insect-based wing kinematic modulation mechanisms were developed for control and stabilization by varying two parameters: the tilt of the flapping planes relative to the vehicle, and the flapping amplitude, both of which alter the magnitude and direction of the lift vector of each wing to achieve motion or trim in a particular direction. These mechanisms are controlled via a kinematic autopilot, which senses the vehicle attitude and, using an on-board closed-loop proportionalderivative controller, transmits corrective signals to the modulation mechanism actuators which stabilize the vehicle. A systematic approach to tuning the vehicle trim and controller gain values has been implemented, leading to several stable controlled flight experiments. One such flight test lasted ~5.0 seconds in which the vehicle ascended and sustained an altitude of ~1 meter with minimal drift. The final vehicle weighs 62 grams and flaps at about 22Hz during hover.