Span wise flow

[south coast]

i asked a question about the prevention of span wise flow earlier and just wanted to confirm something.

i understand wing fences are used to reduce/prevent span wise flow, but someone told me they are located on the TOP surface of the wing.

is this correct? i would have thought that since the flow is from root to tip on the under side, then they would be on the under side surface.

are those elongated 'bubble' type things on the underside of a Boeing/Airbus wing- wing fences, they would seem to also cover the jack screws for the flaps (i am guesssing, but they end up anlging when the flaps are run).
there are normally about 3 or 4 on a large wing with about 2m spacing.

if they are not wing fences, can someone tell me what they are.

thanks

[Halfbaked_Boy]

Well you certainly find them on the top side of the wing - don't forget there is a certain amount of tip-root spanwise flow on the top surface.

Cheers, Jack. :ok:

p.s. with regards to the latter, sounds very much like you're describing the flap supports and engine trailers... main purpose to assist in running the flaps down smoothly and creating a more aerodynamic shape. Or at least that's what I've always understood. :cool:

[Erebus]

Wing fences have been around for decades, and are used to prevent the spanwise airflow causing wingtip stalling.
The structures under the wing are there to protect and streamline the trailing edge flap operating mechanism. On the 747 they were known as "flap canoes" because of their size and shape. As a matter of interest, the 747 has triple-slotted trailing edge flaps with four flap canoes, but the 747SP has only single slotted trailing edge flaps and no canoes, resulting in some 9% less drag.

[cwatters]

Are true wing fences actually used much these days? I think all the little vertical devices on the top surface of moden passenger jets are turbulators - or perhaps I haven't looked hard enough?