Why no flap fences?

[BigHitDH]

All the time I see vortex's produced at the outboad ends of trailing edge flaps, I wonder to myself - why not put a "wing fence" on there?

More and more airliners now have "winglets" fitted to the wingtips to cure the exact same problem, so why not have it on the flaps also?

Am I missing something blindingly obvious?

[Bealzebub]

Flaps are only used for the take off and landing phases of flight, the rest of the time they are retracted so any gain would be negligable. For landing, drag is a required product of the later flap settings so reducing it would be pointless.

winglets on the other hand reduce drag (induced by the vortices), throughout the flight and therefore make a noticeable contribution to reducing overall fuel consumption.

[BigHitDH]

Hmm, interesting.

Surely however, by using "flap fences" greater lift would be produced allowing smaller/more simple flaps and thus a weight saving?

The drag issue is an interesting one. I always thought that at large flap deflections, a reasonably high thrust setting had to be set to maintain correct approach speed for most jet transports?

[AhDee]

hmm, IMO, its something about the weight and the design as well.
having a flap fence will add more weight to the wings and the results might just had not much differences on the drag that produced by the vortices.
And that might be a aerodynamic design problem as having a flap fence should have a bigger parasite drag while the flaps are retracted.

:D

[CosmosSchwartz]

The drag issue is an interesting one. I always thought that at large flap deflections, a reasonably high thrust setting had to be set to maintain correct approach speed for most jet transports?

That's the case, but conveniently it all works out quite well!;)
You want to land with a fairly high thrust setting in case you have to go around. The time for the engines to spool up to TOGA can be critical so you'd rather have circa 70% N1 on the approach than 30%.:ok: