Wind Tunnel Evaluation of Powered Static Aerodynamics of an Aerobatic UAV

Abstract

A wind tunnel test of an off-the-shelf scale model of the Edge 540 aerobatic aircraft shows substantial improvement of pitch and yaw authority upon application of propeller wash, without markedly changing the qualitative aerodynamic response. High thrust at low advance ratio linearizes the response of control surfaces (elevator, rudder; and to a lesser extent, ailerons) and delays stall. This offers potential for simplification of aerodynamic models for Unmanned Air Vehicles in maneuvering situations, in gust-response, and for unconventional vehicles transitioning from wingborne to rotor-borne flight. Calculation with the panel-method PMARC was surprisingly successful, at least at low angles of attack. On the other hand, a modern Reynolds Averaged Navier-Stokes computation (AVUS) was seen to underpredict both zero-lift drag and maximum lift coefficient, ironically suggesting that lower-order methods may be superior not only in implementation but in accuracy. Experimental uncertainty due to control surface hysteresis is a notable complication of using off-the-shelf hobby-airplanes as wind tunnel test articles. Nevertheless, systematic trends in control surface effectiveness with and without propwash were identified.

Real-Time Flight Simulation of Highly Maneuverable Unmanned Aerial Vehicles

“…Any tuning must result in prescribed data that remain within reasonable physical bounds, such as the approach used here to model the shielding effects at high angles. Where tuning of physical models is used, any of these methods are candidates for refinement by other means as new data become available, for example, when full aircraft wind-tunnel testing becomes routinely available [9] and/or when it is economical to simulate in CFD defined spin states that could be used to advance models for use in real-time simulations. Finally, in the development of the approach, field tests were performed, recorded on video, and used in tuning and refining the methods.…”

“…Physical wind-tunnel measurements also fall short of capturing the aerodynamics of the full static and dynamic envelope due to a number of factors; for example, the sheer time and expense of a full test campaign, as well as the most basic issue of wind-tunnel wall effects, such as propeller-wash recirculation within the test section, present many challenges [8]. However, recent measurements presented in [9] are a notable exception, wherein a full aerobatic vehicle configuration was tested in a vertical wind tunnel. One might envision using brute-force computational fluid dynamics (CFD) analyses to generate lookup-table data for a full vehicle, but the computational resources needed to cover a typical flight envelope in a reasonable period of time exceed current-day capabilities [10][11][12].…”

Experimental Validation of an Aerodynamic Sensing Scheme for Post-Stall Aerodynamic Moment Characterization

“…Landman et al investigated the longitudinal and lateral aerodynamic characteristics of a small UAS with and without power applied to the propeller [2222]. Recent work by Ol et al tested an aerobatic RC airframe in the presence of prop-wash using force and moment transducer instrumentation and found that high thrust settings at low advance ratios serve to linearize control-surface response [23]. Their results are also supported by this work, with the distinction of this work in the use of onboard instrumentation capable of providing real-time aerodynamic moment feedback in hover and mixed flow (free stream plus prop-wash) conditions.…”

Fixed-Wing Unmanned Aircraft In-Flight Pitch and Yaw Control Moment Sensing

“…Landman et al investigated the longitudinal and lateral aerodynamic characteristics of a small UAS with and without power applied to the propeller [35]. Recent work by Ol et al characterized the low-airspeed high-thrust aerodynamics of an aerobatic RC airframe in the presence of prop-wash using transducer-based instrumentation and found that high thrust settings at low advance ratios serve to linearize control-surface response [36]. This paper seeks a novel approach to fixed-wing UAS instrumentation that meets the challenges of high-alpha flight through expanded sensing and reformulation of the steady-flight equations to incorporate poststall aerodynamic force based on in-flight measurement.…”

“…(34)(35)(36):Slope AeroM;N Mom Aero;2 M;N − Mom Aero;1 M;N θ 2 M;N − θ 1 M;N(34)Slope FT M;N Mom FT;2 M;N − Mom FT;1 M;N θ 2 M;N − θ 1 M;N…”