Copyright © A. Filippone (1996-2001). All Rights Reserved.

Wings for All Speeds

Wing Tip Devices


Tip devices have become a popular technique to increase the aerodynamic performances of lifting wings, short and slender alike.

Tip Vortices

The idea behind all the devices described below is to diffuse the strong vortices released at the tip and optimize the spanwise lift distribution, while maintaining the additional moments on the wing within certain limits. A visualization of tip vortices is shown in the photo below, that is a manoeuvering canard-wing Eurofighter EF-2000 on a demo flight over Le Bourget (France).

Eurofighter EF-2000

Figure 1: Eurofighter EF-2000

Similar vortices are visible on commercial aiplanes when landing and taking off in high humidity weather conditions.

The Winglet

Several theoretical investigations (for ex. Weber, 1954), and later experiments, indicated that the use of vertical lifting surfaces placed at the wing tips produce a beneficial effect on both lift and drag characteristics. This is found at the cost of increased bending moment.

The increase in root bending moment is found to be lower than for an equivalent tip extension. Fig. 2 shows a complicated, yet common, winglet design, with one large tapered upper winglet, and a smaller lower winglet (Whitcomb, 1977). The winglet sections can be airfoils with their own design.


Figure 2: side view of a winglet

Winglets can be used to produce extra lift, besides lower drag. The winglets must be mounted on the rear part of the wing (region of lowest pressure), to minimize interference effects. Drag reduction rates are of the order of 5 %.

Winglets are applied in the latest generation of Boeing 747, MD 11, Airbus, and most executive jets, besides sail planes. Data available for the Boeing 747-400 indicate that without winglets the aircraft suffers about 2.5 % drag losses, which corresponds to +9.5 tons at take-off.

Wing Endplates

The endplates are vertical surfaces (generally rectangular) added to a wing to redistribute the lift along the span. The effect is an strongly increased lift coefficients, against a drag coefficient that decreases by a tiny amount.

The resulting efficiency L/D is generally greatly improved. The effect of the endplates is generally described as an increased wing aspect-ratio, that is proved to be effective. Endplates are generally considered a more simple engineering solution than the winglets.


Typical applications of endplates are in racing cars, where the aspect-ratios are necessary small, and enormous efforts are made by the engineers to produce a few percent of extra lift, while not penalizing the drag. A typical example of lift distribution for a short wing (AR=2) is shown in Fig. 3. The computations were performed with the panel method VSAERO.


Figure 3: Spanwise Cl distribution w/ and w/o endplates

Hoerner Tips

Hoerner tips are crescent-shaped geometries with a slight upward feathering. They are proved to be slighly better than conventional round tips, since they promote a better diffusion of the tip vortex.

In the figure below two geometries (Hoerner and round tip) are being tested in the low speed wind tunnel of the University of Illinois. The two geometries are designed as to not change the effective aspect-ratio of the wing.

Hoerner Tip Round Tip

Figure: 4 Hoerner tips (at left) and round tips (at left) before wind tunnel testing

Tip Tanks

Tip tanks are devices that extend beyond the physical range of the wings and protrude from both the leading-edge and the trailing-edge. They are generally cylindrical bodies that modify the tip vortex structure and work as endplates, although they are not as effective. On fighter aircraft they can be disposable bodies.

Tip Sails

Tip sails are more complicated devices, as shown in the figure below, consisting of several tapered fins (or smaller winglets), placed radially with an axial gap between two elements (Spillman, 1978). They also have the leading edge protuberance similar to the tip tanks.

Tip Sail

Figure 5: tip sail

For best performance is it suggested that the number of vanes be no more than 4, at angles 15-20 deg between 2 vanes; each vane should have a chord no larger than 30 % of the tip tank chord.

Selected References

  • Green, Sheldon I (editor). Fluid Vortices, Kluwer Academic Press, 1995.

  • Milne-Thompson LM. Theoretical Aerodynamics, MacMillan Co., London, 1966.

  • Clancy JC. Aerodynamics, John Wiley, New York, 1975.

  • Jones RT. Wing Theory, Princeton Univ. Press, Princeton, NJ. 1990.

  • Hoerner SF. Fluid Dynamic Drag, Hoerner Fluid Dynamics, 1965.

  • Larson, G. “How Things Work: Winglets”, Air and Space Magazine, Aug/Sept 2001. Smithsonian Inst., Washington DC.

  • Whitcomb RT. A Design Approach and Selected Wind-Tunnel Results at High Subsonic Speeds for Wing-Tip Mounted Winglets. NASA TN D-8260, July 1976.

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Copyright © A. Filippone (1996-2001). All Rights Reserved.