> I was wondering why fences are hardly or never used in newer airliners
and
> fighters, whereas most of older sweep wing aircraft had fences to
redirect
> spanwise flow.
They're not really there to redirect the spanwise flow. They use the
spanwise flow to generate a vortex to help energize the boundary layer and
flow attached. They also help keep the separation points steady at very
high angles of attack so that you don't generate wierd rolling moments as
you approach stall.
Fences (and leading edge notches, which do the same thing) are easy and
relatively "free" fixes for aerodynamic problems elsewhere on the wing.
With modern CFD codes, lots of experience, and really good wind tunnel
testing you can design the wing so that it doesn't need them. That's why
you don't see them very often on newer designs.
Tom.
