A Static Aeroelastic Analysis of a Flexible Wing Mini Unmanned Aerial Vehicle

Abstract : The static aeroelastic behavior of the Nighthawk mini unmanned aerial vehicle is examined using a combined experimental and computational approach. Three wings are examined. In order of increasing stiffness they are: a flexible wing, a stiff wing, and a fictitious rigid wing with zero deflection. Photogrammetry is used during wind tunnel testing to measure the average deflected shape of the flexible and stiff wings during flight. The independent variables during wind tunnel tests are angle of attack (ranging from -5.1 deg through 13.4 deg) and velocity, which is 20 mph, 30 mph, and 40 mph. Roll angle and yaw angle are control variables, held constant at 0 deg. The measured deflection of each wing is used to adjust the wing shape for computational fluid dynamics analysis. Solutions are obtained for the flexible, stiff, and undeflected (or rigid) wings using a steady-state viscous flow solver with a Spalart-Allmaras turbulence model. The flexible and stiff wings experience two forms of deformation during flight. They bend upward along the span increasing the dihedral, and the leading edge twists downward (wing washout). The amplitude of deflection is greatest for the flexible wing. As a result, the flexible wing is more stable, but also exhibits worse static aerodynamic performance. The rigid wing has the greatest lift (CL max=1.29) and the highest lift-to-drag ratio (L/Dmax =10.2). Stall occurs first near the root for all three wings. None of the wings stall at the tip in the range of angles of attack tested. A separation bubble forms under the wing at angles of attack less than 8o. This separation decreases the overall lift. It is most prominent on the flexible wing.

[1]  G. Parker,et al.  Dynamic Aeroelastic Analysis of Wing/Store Configurations , 2005 .

[2]  Robert C. Nelson,et al.  Flight Stability and Automatic Control 2nd Edition , 1998 .

[3]  Stuart Robson,et al.  Photogrammetry Methodology Development for Gossamer Spacecraft Structures , 2002 .

[4]  L. F. Crabtree,et al.  Effects of Leading-Edge Separation on Thin Wings in Two-Dimensional Incompressible Flow , 1957 .

[5]  Wei Shyy,et al.  Flapping and flexible wings for biological and micro air vehicles , 1999 .

[6]  J. F. Donovan,et al.  Low Reynolds Number Airfoil Design and Wind Tunnel Testing at Princeton University , 1989 .

[7]  Peter Ifju,et al.  Experimental Analysis of Deformation for Flexible-Wing Micro Air Vehicles , 2005 .

[8]  Marilyn J. Smith,et al.  An Evaluation of Computational Algorithms to Interface Between CFD and CSD Methodologies. , 1996 .

[9]  Arthur F Huber,et al.  Death by a Thousand Cuts: Micro-Air Vehicles in the Service of Air Force Missions , 2012 .

[10]  Jean Duchon,et al.  Splines minimizing rotation-invariant semi-norms in Sobolev spaces , 1976, Constructive Theory of Functions of Several Variables.

[11]  Yongsheng Lian,et al.  A COMPUTATIONAL MODEL FOR COUPLED MEMBRANE-FLUID DYNAMICS , 2002 .

[12]  Brian J. Gamble,et al.  Experimental Analysis of Propeller Interactions With a Flexible Wing Micro-Air-Vehicle , 2006 .

[13]  Thomas J. Mueller,et al.  Low Reynolds Number Vehicles , 1985 .

[14]  W. Shyy,et al.  Rigid and Flexible Low Reynolds Number Airfoils , 1999 .

[15]  Anthony M. DeLuca,et al.  Experimental Investigation into the Aerodynamic Performance of Both Rigid and Flexible Wing Structured Micro-Air-Vehicles , 2012 .

[16]  E. Mikhail,et al.  Introduction to modern photogrammetry , 2001 .

[17]  J. A. Freeman,et al.  Experimental Investigation into the Aerodynamic Properties of a Flexible and Rigid Wing Micro Air Vehicle , 2004 .

[18]  Andrew Simpson,et al.  Flight Control of a UAV with Inflatable Wings with Wing Warping , 2006 .

[19]  Daniel P. Raymer,et al.  Aircraft Design: A Conceptual Approach , 1989 .

[20]  Dragos Viieru,et al.  A Numerical and Experimental Investigation of Flexible Micro Air Vehicle Wing Deformation , 2006 .

[21]  Jonathan T. Black,et al.  Videogrammetry Using Projected Circular Targets: Proof-of-Concept Test , 2003 .

[22]  Ludwig Prandtl,et al.  Applications of Modern Hydrodynamics to Aeronautics , 1923 .

[23]  Yuan-Cheng Fung,et al.  An introduction to the theory of aeroelasticity , 1955 .

[24]  Mario A. Gomarasca,et al.  Elements of Photogrammetry , 2009 .

[25]  Robert C. Nelson,et al.  Flight Stability and Automatic Control , 1989 .

[26]  Wei Shyy,et al.  A Study of Flexible Airfoil Aerodynamics with Application to Micro Aerial Vehicles , 1997 .

[27]  Richard G. Cobb,et al.  Computational Aeroelastic Analysis of Micro Air Vehicle With Experimentally Determined Modes , 2005 .

[28]  Peter Ifju,et al.  Flexible-wing-based Micro Air Vehicles , 2002 .

[29]  William H. Rae,et al.  Low-Speed Wind Tunnel Testing , 1966 .