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

Wings for All Speeds

The Oblique Flying Wing


The oblique flying wing (OFW) is a wing of elliptic planform having mininum wave drag at transonic and supersonic speeds up to M=1.4. For minimum wave drag due to lift the equivalent body of revolution must be a Karman Ogive; whereas for minimum wave drag due to volume of the equivalent body of revolution must be a Sears-Haack body.

The first to prove that such a wing has minimum wave drag was R.T. Jones (1951). More recently, inviscid CFD calculations proved that the best performances are obtained with a wing of aspect-ratio 10:1 with a cruise CL=0.068. The best yaw angle would be 68 degrees, and the wing would have the flying operation shown in Fig. 1 below.

Oblique Flying Wing
Figure 1: Oblique flying wing, AR = 10:1, yaw = 68 deg

The use of the OFW would be limited to transonic and low supersonic speeds, since the increasing sweep reduces the effective wing span, which on turns increases the induced drag. Fig. 2 below shows a qualitative behavior of the CD of the OFW as compared with the swept-back wing (SBW).

CD of Oblique Flying Wing
Figure 2: Oblique flying wing vs Swept-back wing

There has been recent research devoted to the computational aerodynamics, to the optimization of the wing, and to preliminary sizing/design. The data reported below are those relative to a McDonnell- Douglas study for a commercial transport oblique wing:

Table 1: MD Oblique flying wing
Aspect-ratio 10:1
Wing span 165 m
Wing chord, max 16.5 m
Surface 2270 m²
Volume 3600 m³
Cruise level 41,300 ft
Thickness t/c 0.19

From the above data we find that the optimal oblique flying wing is a huge body, with a span more than twice as big as the Boeing 747-400 ! Such an aircraft is unlikely to be able to land on any airport, although the wing is the best theoretical compromise for weight, flutter, flexibility, and other aeroelastic problems.

Related material

Selected References

  • Seebass R. Supersonic Aerodynamics: Lift and Drag, in Fluid Dynamic Research on Supersonic Aircraft, Notes from the Special Course at the Von Karman Institute, AGARD-RTO EN-4, Nov. 1998

  • Jones RT, The Minimum Drag of Thin Wings in Friction- less Flow, J. Aero. Sci., Vol 18, No. 2, pages 75-81 (1951).

  • Sears JHB, On Projectiles of Minimum Wave Drag, Quart. Appl. Math. Vol. 4, No. 4, pages, 361-366 (1947).
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Copyright © A. Filippone (1996-2001). All Rights Reserved.