Development and Flight Testing of a Turbulence Mitigation System for Micro Air Vehicles

Abstract

There are significant challenges associated with the flight control of fixed-wing micro air vehicles (MAVs) operating in complex environments. The scale of MAVs makes them particularly sensitive to atmospheric disturbances thus limiting their ability to sustain controlled flight. Bio-inspired, phase-advanced sensors have been identified as promising sensory solutions for complementing current inertial-only attitude sensors. This paper describes the development and flight testing of a bio-inspired, phase-advanced sensor and associated control system that mitigates the impact of turbulence on MAVs. Multihole pressure probes, inspired by the sensory function of bird feathers, are used to measure the flow pitch angle and velocity magnitude ahead of the MAV's wing. The sensors provide information on the disturbing phenomena before it causes an inertial response in the aircraft. The sensor output is input to a simple feed-forward control architecture, which enables the MAV to generate a mitigating response to the turbulence. The results from wind-tunnel and outdoor testing in high levels of turbulence are presented. The disturbance rejection performance of the phase-advanced sensory system is compared against that of a conventional inertial-based control system. The developed sensory system shows significant improvement in terms of disturbance rejection performance compared to that of standard inertialonly control system. It is concluded that a phase-advanced sensory systems can complement conventional inertial-based sensors to improve the attitude-tracking performance of MAVs. C 2015 Wiley Periodicals, Inc.

Distributed Pressure Sensing–Based Flight Control for Small Fixed-Wing Unmanned Aerial Systems

“…Suitable control can then be implemented to mitigate the developing effect of the gust. [17] • Faster response -The total moment, and therefore angular acceleration, of the aircraft can be estimated by integrating the airflow measurements over the surface of the aircraft. This in theory allows a faster response to disturbances in attitude which are normally measured as changes in angular rate using an IMU [18].…”

Cascaded incremental nonlinear dynamic inversion for MAV disturbance rejection

“…As disturbances may come from all directions, a minimum of six Pitot tubes would be necessary (two for each axis, as a Pitot tube can not measure negative airspeed). Alternatively, Mohamed et al [9] used multiple multi-probe sensors to obtain flow pitch angle and velocity.…”

Response of a Flat Plate Wing to a Transverse Gust at Low Reynolds Numbers

“…ψ(x/c) = 4(x/c) 2 + 2(x/c) 4(x/c) 2 + 5.64(x/c) + 0.80 (2) While equation (2) describes the lift for a gust of unit magnitude and infinite extent, the response to any other arbitrary gust profile can be calculated by means of Duhamel's integral. The response is found by decomposing the input function into a series of impulses, for each of which a change in lift coefficient is calculated in accordance to equation 1.…”

“…1 In this region the wind turbulence intensity can exceed 50%. 2,3 For a typical radio aircraft sized fixed wing UAV, rapid changes in incidence in excess of 25 • , as well as span-wise variation in incidence of up to 15 • causing roll instability have been measured. 1 Such extreme variations in incidence are compounded where reducing flight velocity leads to high gust ratios.…”

“…Consequently it has been shown that for both biological fliers and man-made machines, the safe operating wind speed is significantly reduced with decreasing flight platform size. 1,2,[4][5][6] Despite clear flight limitations of UAVs, existing research into the response of aerofoil lifting surfaces to wind gusts has historically been directed toward the application of manned flight, whether that be rotor or fixed wing aircraft. During forward flight of helicopter or tilt-rotor aircraft, tip vortices from the upstream blades is advected downstream and can interact with the following blades.…”