Modeling Full-Envelope Aerodynamics of Small UAVs in Realtime

Abstract

This paper focuses on full six degree-of-freedom (6-DOF) aerodynamic modeling of small UAVs at high angles of attack and high sideslip in maneuvers performed using large control surfaces at large deflections for aircraft with high thrust-to-weight ratios. Configurations such as this include many of the currently available propellerdriven RC-model airplanes that have control surfaces as large as 50% chord, deflections as high as 50 deg, and thrust-to-weight ratios near 2:1. Airplanes with these capabilities are extremely maneuverable and aerobatic, and modeling their aerodynamic behavior requires new thinking because using traditional stability derivative methods is not practical with highly nonlinear aerodynamic behavior and coupling in the presence of high propwash effects. The method described in this paper outlines a component-based approach capable of modeling these extremely maneuverable small UAVs in a full 6-DOF realtime environment over the full envelope that is defined in this paper to be the full ±180 deg range in angle of attack and sideslip. This method is the foundation of the aerodynamics model used in the RC flight simulator FS One. Piloted flight simulation results for four small RC/UAV configurations having wingspans in the range 826 mm (32.5 in) to 2540 mm (100 in) are presented to highlight results of the high-angle aerodynamics modeling approach. Maneuvers simulated include tailslides, knife edge flight, high-angle upright and inverted flight ("harriers"), rolling maneuvers at high angle ("rolling harriers") and an inverted spin of a biplane ("blender"). For each case, the flight trajectory is presented together with time histories of aircraft state data during the maneuvers, which are discussed. Nomenclature,c/4 = moment coefficient about quarter chord D = drag; propeller diameter J = propeller advance ratio based on V N L = lift M = pitching moment about y-axis (positive nose up) n = propeller rotational speed (revs/sec) * Associate Professor, Department of Aerospace Engineering, 104 S. Wright St. Senior Member AIAA.= propeller yawing moment due to angle of attack p, q, r = roll, pitch and yaw rate P N = propeller normal force due to angle of attack Q = propeller axial torque q = dynamic pressure (ρV 2 /2) R = propeller radius S = reference area T = propeller axial thrust u, v, w = components of the local relative flow velocity along x, y, z, respectively V = flow velocity x, y, z = body-axis coordinates, +x out nose, +y out right wing, +z down y c = airfoil camber TED = trailing edge down TEL = trailing edge left TEU = trailing edge up Subscripts N = normal component R = relative component Symbols α = angle of attack (arctan(w/u)) β = sideslip angle (arcsin(v/V )) β ′ = angle of attack for vertical surface (arctan(v/u)) δ a = aileron deflection [(δ a,r − δ a,l )/2], right +TEU, left +TEU δ e = elevator deflection, +TED δ r = rudder deflection, +TEL ǫ = wing induced angle of attack η s = dynamic pressure ratio for flow shadow (shielding) effect φ, θ, ψ = bank angle, pitch angle, heading angl...

Modeling Propeller Aerodynamics and Slipstream Effects on Small UAVs in Realtime

“…2,12 The simulation solves the full 6-DOF equations of motion using quaternions, and integration is carried out using a Runge-Kutta 4-th order scheme running at 300 Hz on a desktop PC. An efficient interpolation method is incorporated into the code to the extent that upward of 250 tables can be interpolated in realtime while running the simulation at 300 Hz and rendering the graphics through a typical PC gaming graphics card at ≈100 Hz or better.…”

“…The propeller methodology described here is included as one element of a larger full-envelope simulation framework that is discussed in a companion paper. 2 As such, some overlap between the two papers exists. …”

Journey to the Typhoon

“…Also, recent years have witnessed the advancement of radio controlled model airplanes across various classes, from sailplanes to the highly agile aerobatic airplanes. The socalled "3D aerobatic" model airplanes are well-known to be capable of performing an impressive array of post wing-stall maneuvers such as harrier (high-alpha horizontal flight), blender and torque rolls [15]. F5D is an international class ratified by the FAI (Fédération Aéronautique Internationale) which involves racing electricpowered model airplanes around a triangular course for 10 laps at speeds of approximately 322 km·h −1 [16].…”

A low-power architecture for high frequency sensor acquisition in many-DOF UAVs

“…Similarly, the problem of controlling variable scaled-size helicopters has been investigated in [8], while in [9] the problem of accounting for servo actuation delay is studied. Moreover, the problem of modeling [10,11] and controlling [12] fixed-wing UAVs (airplanes) with different configurations have been investigated.…”