Couple of comments...
747FOCAL,
50's? Try this NACA report from the 20's:
NACA Report of Wingtip design
The argument has raged for almost a century!
teghjeet - You can see the exact effect on the pressure distributions of comparative aerofoils in the same report.
Prandtl found in the 20's that an elliptic planform was what was reuiqred on a finite wing for minimum
induced drag. Hence the reason for the Spitfire's elliptic planform. The only aircraft I know of with that planform.
If you do the maths, you find
induced drag is proportional to the inverse of the
aspect ratio, AR, for an elliptic planform. For non-elliptic planforms, you can correct the previous expression with a correction factor
Hence, the higher the AR, the less the induced drag, or conversely, the better the L/D ratio of the wing.
Winglets
effectively increase the AR because they reduce the downwash.
The problem with other solutions such as raked wingtips is that whilst AR is increased, its at a weight penalty that is linked to an increasing taper-ratio with the associated torsional rigidity problems.
Boeings Aero 17 Site includes some interesting information.
And just for reference
zerozero,
hypersonic flight is M > 5.
