Yaw-control efficiency analysis for a diamond wing configuration with outboard split flaps

  • Stefan PfnürEmail author
  • Sven Oppelt
  • Christian Breitsamter
Original Paper


The yaw-control device of a low-aspect ratio flying wing with diamond-shaped wing planform is investigated. Extensive low-speed wind tunnel experiments have been carried out to obtain surface pressure data and the aerodynamic forces and moments of the configuration for six different flap deflection angles at varying angles of attack and sideslip. Complementary unsteady Reynolds-averaged Navier–Stokes simulations are performed for selected configurations. The experimental data is used to examine the validity of the numerical results. The analysis is focused on the aerodynamic coefficients and derivatives. Yaw-control effectiveness, yaw-control efficiency, crosswind landing capabilities and coupling effects are discussed. The results show sufficient yaw-control effectiveness and efficiency for a wide range of considered freestream conditions. The outboard flap exhibits a non-linear characteristic with respect to the flap deflection angle and freestream conditions. The efficiency is considerably reduced at high angles of attack due to large-scale flow separation in the wing outboard section. Non-linear coupling effects with the rolling moment become obvious for moderate to large flap deflections over the whole angle of attack polar. The numerical results show good agreement with the experimental data in the surface pressure distributions and longitudinal aerodynamic coefficients. The yawing moment is overpredicted by numerical simulations for large flap deflection angles.


Aerodynamics Diamond wing Flying wing Stability and control Directional Stability Directional control Vortex aerodynamics Wind tunnel 

List of symbols


Wing span (m)

\(C_{D},C_{Y},C_{\text {L}}\)

Drag, side force and lift coefficient, \(C_{i} = \frac{i}{q_{\infty } \cdot S_{\text {ref}}}\)


Aerodynamic derivative (1/rad), \({\text {d}}Ci/{\text {d}}j\)


Rolling and yawing moment coefficient, \(C_{mi} = \frac{Mi}{q_{\infty } \cdot b/2 \cdot S_{\text {ref}}}\)


Pitching moment coefficient, \(C_{my} = \frac{My}{q_{\infty } \cdot l_\mu \cdot S_{\text {ref}}}\)

\(c_{\text {p}}\)

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

\(c_{\text {r}}\)

Root chord (m)

\(c_{\text {t}}\)

Tip chord (m)


Drag, side force and lift (N)


Sampling rate (Hz)


Axial and lateral force in body-fixed axis system (N)


Lever arm of force at outboard flap creating the yawing moment (m)

\(l_{\mu }\)

Mean aerodynamic chord (m)


Mach number


Rolling, pitching and yawing moment (Nm)


Static pressure (N/m\(^{2}\))


Dynamic pressure (N/m\(^{2}\))


Reynolds number

\(S_{\text {pr}}\)

Projected area (m\(^{2}\))

\(S_{\text {ref}}\)

Wing reference area (m\(^{2}\))


Temperature (K)


Time (s)


Velocity (m/s)

\(x_{\text {mrp}}\)

Moment reference point (m)


Cartesian coordinates (m)


Dimensionless wall distance


Angle of attack (\(^{\circ }\))


Angle of sideslip (\(^{\circ }\))

\(\gamma _1\)

Angle between body-fixed x-axis and optimal lever arm (\(^{\circ }\))

\(\gamma _2\)

Angle between body-fixed x-axis and outboard flap force vector in body-fixed xy-plane (\(^{\circ }\))


Outboard flap deflection angle (\(^{\circ }\))


Non-dimensional lateral coordinate, \(\eta =\frac{y}{b/2}\)


Wing aspect ratio


Wing taper ratio


Midboard flap deflection angle (\(^{\circ }\))


Density (kg/m\(^{3}\))


Wing sweep (\(^{\circ }\))





Hinge line






Leading edge




Outboard flap










Trailing edge




Freestram value



The support of this investigation by Airbus Defence and Space within the VitAM/VitAMInABC (Virtual Aircraft Model for the Industrial Assessment of Blended Wing Body Controllability, FKZ: 20A1504C) project is gratefully acknowledged. Furthermore, the authors thank the German Aerospace Center (DLR) for providing the DLR TAU code used for the numerical investigations. 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 Leibniz Supercomputing Centre (LRZ,


  1. 1.
    Airbus Defence and Space: Successful first flight for UAV demonstrator SAGITTA (Press Release) (2017). Accessed 26 July 2018
  2. 2.
    Allmaras, S.R., Johnson, F.T., Spalart, P.R.: Modifications and clarifications for the implementation of the Spalart–Allmaras turbulence model. In: 7th International Conference on Computational Fluid Dynamics, Big Island (HI), United States, ICCFD7-1902 (2012)Google Scholar
  3. 3.
    Begin, L.: The Northrop flying wing prototypes. In: Aircraft Prototype and Technology Demonstrator Symposium, Meeting Paper Archive, Dayton (OH), AIAA Paper 1983-1047 (1983).
  4. 4.
    Bourding, P., Gatto, A., Friswell, M.I.: Potential of articulated split wingtips for morphing-based control of a flying wing. In: 25th Applied Aerodynamics Conference, Miami (FL), AIAA Paper 2007-4443 (2007).
  5. 5.
    Burns, B.R.A.: Design considerations for the satisfactory stability and control of military combat aeroplanes. In: AGARD Specialists’ Meeting on “Stability and Control”, Braunschweig, Germany, April 10–13, 1972, no. 119 in AGARD Conference ProceedingsGoogle Scholar
  6. 6.
    Campbell, J.P., Seacord, C.L.: Determination of the stability and control characteristics of a tailless all-wing airplane model with sweepback in the langley free-flight tunnel. NACA-ACR-L5A13 (1945)Google Scholar
  7. 7.
    Crenshaw, K., Flanagan, B.: Testing the flying wing. In: 33rd Joint Propulsion Conference and Exhibit, Seattle (WA), AIAA Paper 1997-3262 (1997).
  8. 8.
    Donlan, C.J.: An interim report on the stability and control of tailless airplanes. NACA/TR-796 (1994)Google Scholar
  9. 9.
    Fears, S.P., Ross, H.M., Moul, T.M.: Low-speed wind-tunnel investigation of the stability and control characteristics of a series of flying wings with sweep angles of 50 deg. NASA-TM-4640 (1995)Google Scholar
  10. 10.
    Fulker, J.L., Alderman, J.E.: Three-dimensional compliant flows for lateral control applications. In: 43rd Aerospace Science Meeting and Exhibit, Reno (NV), AIAA Paper 2005–0240 (2005).
  11. 11.
    Gerhold, T.: Overview of the hybrid RANS code TAU. In: MEGAFLOW-Numerical Flow Simulation for Aircraft Design, Vol. 89 of Notes on Numerical Fluid Mechanics and Multidisciplinary Design. Springer (2005)Google Scholar
  12. 12.
    Gillard, W.J., Dorsett, K.M.: Directional control for tailless aircraft using all moving wing tips. In: 22nd Atmospheric Flight Mechanics Conference, New Orleans (LA), AIAA Paper 1997-3487 (1997).
  13. 13.
    Hövelmann, A.: Analysis and control of partly-developed leading-edge vortices. Dissertation, Technische Universität München. Dr. Hut Verlag, ISBN 978-3-8439-2807-6 (2016)Google Scholar
  14. 14.
    Hövelmann, A., Breitsamter, C.: Leading-edge geometry effects on the vortex formation of a diamond-wing configuration. J. Aircr. 52(2), 1596–1610 (2015). CrossRefGoogle Scholar
  15. 15.
    Hövelmann, A., Grawunder, M., Buzica, A., Breitsamter, C.: AVT-183 diamond wing flow field characteristics part 2: experimental analysis of leading-edge vortex formation and progression. Aerosp. Sci. Technol. 57(1), 31–42 (2016). CrossRefGoogle Scholar
  16. 16.
    Hövelmann, A., Knoth, F., Breitsamter, C.: AVT-183 diamond wing flow field characteristics part 1: varying leading-edge roughness and the effects on flow separation onset. Aerosp. Sci. Technol. 57(1), 18–30 (2016). CrossRefGoogle Scholar
  17. 17.
    Hövelmann, A., Pfnür, S., Breitsamter, C.: Flap efficiency analysis for the SAGITTA diamond wing demonstrator configuration. CEAS Aeronaut. J. 6(4), 498–514 (2015). CrossRefGoogle Scholar
  18. 18.
    Hummel, D., John, H., Staudacher, W.: Aerodynamic characteristics of wing-body-combinations at high angles of attack. In: 14th Congress of the International Council of the Aeronautical Sciences, Toulouse, France, September 10–14, ICAS Paper 2.7.1 (1984)Google Scholar
  19. 19.
    Jameson, A., Schmidt, W., Turkel, E.: Numerical solutions of the Euler equations by finite volume methods using Runge–Kutta time stepping schemes. In: 14th AIAA Fluid and Plasma Dynamics Conference, Palo Alto (CA), AIAA Paper 1981–1259 (1981).
  20. 20.
    Sears, W.: Flying-wing airplanes: the XB-35/YB-49 program. In: The Evolution of Aircraft Wing Design, Proceedings of the Symposium, Dayton (OH), AIAA Paper 1980-3036 (1980).
  21. 21.
    Spalart, P.R., Allmaras, S.R.: A one-equation turbulence model for aerodynamic flows. In: 30th Aerospace Sciences Meeting and Exhibit, Reno (NV), AIAA Paper 1992-0439 (1992).
  22. 22.
    Turkel, E.: Improving the accuracy of central difference schemes. NASA-CR-181712 (1988)Google Scholar
  23. 23.
    Weyl, A.R.: Tailless aircraft and flying wings: a study of evolution and their problems. Aircr. Eng. Aerosp. Technol. 17(2), 41–46 (1945)CrossRefGoogle Scholar
  24. 24.
    Wood, R.M., Bauer, S.X.S.: Flying wings/flying fuselages. In: 39th Aerospace Sciences Meeting and Exhibit, Reno (NV), AIAA Paper 2001-0311 (2001).

Copyright information

© Deutsches Zentrum für Luft- und Raumfahrt e.V. 2018

Authors and Affiliations

  1. 1.Chair of Aerodynamics and Fluid Mechanics, Department of Mechanical EngineeringTechnical University of MunichGarching bei MünchenGermany

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