CEAS Aeronautical Journal

, Volume 6, Issue 4, pp 497–514 | Cite as

Flap efficiency analysis for the SAGITTA diamond wing demonstrator configuration

  • A. HövelmannEmail author
  • S. Pfnür
  • C. Breitsamter
Original Paper


The efficiency of deflected midboard flaps is investigated on a diamond wing-shaped unmanned aerial vehicle, the SAGITTA demonstrator configuration. The Reynolds-Averaged Navier-Stokes equations are applied to compute numerical results for a variety of flight conditions with varying angle of attack, sideslip angle, and midboard flap deflection. Low-speed wind tunnel conditions are regarded to compare the results to existing experimental data. The focus is particularly laid on the analysis of the aerodynamic coefficients and derivatives in both the longitudinal and the lateral motion. The occurring flow phenomena are motivated and discussed by flow field illustrations that are available from the numerical computations. The results show at small to moderate angles of attack linear flap characteristics, since the overall flow field is dominated by attached flow. With increasing angle of attack and additional sideslip angle, however, the leading-edge vortex originating from the inboard sharp leading edge and the wing tip separation region affect the midboard flap efficiency. Non-linear coupling effects become obvious, which particularly affect the roll and pitch control effectiveness.


Applied aerodynamics CFD Wind tunnel experiments  Vortex flow Trailing-edge controls Diamond wing UAV 

List of symbols


Wing span, [m]


Drag coefficient, \(C_{D} = \frac{D}{q_{\infty } \cdot S_{Ref}}\)


Lift coefficient, \(C_{L} = \frac{L}{q_{\infty } \cdot S_{Ref}}\)


Side force coefficient, \(C_{Y} = \frac{Y}{q_{\infty } \cdot S_{Ref}}\)


Rolling moment coefficient, \(C_{mx} = \frac{M_{x}}{q_{\infty } \cdot S_{Ref} \cdot s }\)


Pitching moment coefficient, \(C_{my} = \frac{M_{y}}{q_{\infty } \cdot S_{Ref} \cdot l_{\mu } }\)


Yawing moment coefficient, \(C_{mz} = \frac{M_{z}}{q_{\infty } \cdot S_{Ref} \cdot s }\)


Wing chord, [m]


Pressure coefficient, \(c_{p} = \frac{p-p_{\infty }}{q_{\infty }}\)


Drag (wind-axis COS), [N]


Prism layer stretching factor


Initial prism layer thickness, [m]


Lift (wind-axis COS), [N]

\(l_{\mu }\)

Mean aerodynamic chord, [m]


Rolling moment (body-fixed COS), [Nm]


Pitching moment (body-fixed COS), [Nm]


Yawing moment (body-fixed COS), [Nm]


Mach number


Static pressure, [N/m2]

\(p_{\infty }\)

Free stream static pressure, [N/m2]

\(q_{\infty }\)

Free stream dynamic pressure, [N/m2], \(q_{\infty } = \frac{\rho _{\infty }\cdot U_{\infty }^2}{2}\)


Reynolds number


Leading-edge radius, [m]


Wing reference area, [m2]


Semi wing span, [m]

\(U_{\infty }\)

Free stream velocity, [m/s]


Axial velocity, [m/s]


Cartesian coordinates, [m]


Side force (wind-axis COS), [N]


Dimensionless wall distance


Angle of attack, [deg]


Angle of sideslip, [deg]


Wing aspect ratio


Wing taper ratio


Midboard flap deflection angle, [deg], \(\xi = \frac{\xi _{R}-\xi _{L}}{2}\)

\(\rho _{\infty }\)

Free stream density, [kg/m\(^{3}\)]


Wing sweep angle, [deg]





Leading edge


Moment reference point




Root chord


Trailing edge


Tip chord



The support of this investigation by Airbus Defence and Space within the SAGITTA demonstrator program is gratefully acknowledged. Furthermore, the authors thank the German Aerospace Center (DLR) for providing the DLR TAU-Code used for the numerical investigations. The support of CENTAURSoft for its guidance during the grid generation process is also highly appreciated. Moreover, the authors gratefully acknowledge the Gauss Centre for Supercomputing e.V. ( for funding this project by providing computing time on the GCS Supercomputer SuperMUC at the Leibniz Supercomputing Centre (LRZ,


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Copyright information

© Deutsches Zentrum für Luft- und Raumfahrt e.V. 2015

Authors and Affiliations

  1. 1.Institute of Aerodynamics and Fluid MechanicsTechnische Universität MünchenGarching bei MünchenGermany

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