Flow Sensing for Height Estimation and Control of a Rotor in Ground Effect: Modeling and Experimental Results

This paper describes a dynamic controller for rotorcraft landing and hovering in ground effect using feedback control based on flowfield estimation. The rotor downwash in ground effect is represented using a ring-source potential flow model selected for real-time use. Experimental verification of the flow model is also presented. A nonlinear dynamic model of the rotorcraft in ground effect is presented with open-loop analysis and closed-loop control simulation. Experimental results of the open-loop dynamics are presented and the effect of motor dynamics on the overall dynamics are investigated. Flowfield velocity measurements are assimilated into a grid-based recursive Bayesian filter to estimate height above ground in both simulation and experiment. Height tracking in ground effect and landing are implemented with a dynamic linear controller. Experimental validation of the closed-loop controller is ongoing.