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Research Papers: Flows in Complex Systems

Analytic and Experimental Investigation of Dihedral Configurations of Three-Winglet Planforms

[+] Author and Article Information
David S. Miklosovic

Aerospace Engineering Department, United States Naval Academy, 590 Holloway Road, MS 11-B, Annapolis, MD 21402-5042

J. Fluids Eng 130(7), 071103 (Jul 02, 2008) (10 pages) doi:10.1115/1.2948372 History: Received September 12, 2007; Revised March 16, 2008; Published July 02, 2008

An analytic and experimental effort was undertaken to assess the effectiveness and efficiency of three winglets mounted chordwise to the tip of a rectangular wing. The winglets, with an aspect ratio of 4.6, were mounted on a half-span wing having an effective aspect ratio of 6.29. 13 configurations of varying dihedral arrangements were analyzed with a vortex lattice method and tested in a low-speed wind tunnel at a Reynolds number of 600,000. While the analytic method provided fair agreement with the experimental results, the predicted trends in lift, drag, and (to a lesser degree) pitching moment were in good agreement. The analytic distributions of wake velocity, circulation, and downwash angle verified that highly nonplanar configurations tended to reduce and diffuse the regions of highest circulation and to create more moderate downwash angles in the wake. This was manifest as an overall drag reduction. More specifically, the results showed that the winglets could be placed in various optimum orientations to increase the lift coefficient as much as 65% at the same angle of attack, decrease the drag coefficient as much as 54% at the same lift coefficient, or improve the maximum LD by up to 57%. The most dramatic findings from this study show that positioning the winglet dihedral angles had the result of adjusting the magnitude and slope of the pitching moment coefficient. These observations suggest that multiple winglet dihedral variations may be feasible for use as actively controlled surfaces to improve the performance of aircraft at various flight conditions and to “tune” the longitudinal stability characteristics of the configuration.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Multiple winglet geometry

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Figure 2

XFOIL analysis of 2D airfoil sections used

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Figure 3

Reynolds number sensitivity of baseline wing results

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Figure 4

Louvered-wing experimental and analytic results

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Figure 5

Louvered-wing span load distributions for a lift coefficient of 0.8

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Figure 6

High-lift winglet configurations

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Figure 7

High-L∕D winglet configurations

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Figure 8

Effects of inverse winglet deflections

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Figure 9

A summary of aerodynamic improvements

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Figure 10

Wake velocity magnitude distributions for a lift coefficient of 0.8

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Figure 11

Wake downwash angle distributions for a lift coefficient of 0.8

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