What are these for?

[Gand]

Does anybody know what those large pod shaped things on the rear bottom of the wings do? (as seen in this picture http://www.airliners.net/open.file/176214/L/). I always assumed they had aerodynamic functions that are too advanced for my piston brain to comprehend, but maybe there's more to them. Adding to my confusion are the times i've seen them involved with dumping fuel, as below. Thanks in advance.

Gand :D

http://www.airliners.net/open.file/144591/L/
http://www.airliners.net/open.file/189790/L/

[TR4A]

Flap track fairing or Canoe. The flaps have a worm gear drive.

[PaperTiger]

Occasionally found in back yards in Chicago.

[Volume]

TR4A, in this special case you´re wrong.
Airbus is no longer using worm gears as flap actuators on the newer models like the A330 in this picture. But you´re generally right, these are flap track fairings.

But they are not just an aerodynamic smooth fairing of a flap track structure, they also reduce transsonic drag by improving the ´area ruling´. Therefor wings with los of these fairings going far behind the trailing edge like on the photo, perform much better (at high mach number) as wings with only a few flap links under the wing ending in front of the trailing edge like on the DC10 or MD 11.
http://www.airliners.net/open.file/232182/M/

When Convair has designed the CV-990 with a very ´clean´ wing (all flap tracks were inside the wing structure so no fairings were needed) they had to add special bulbs at the trailing edge to reduce transsonic drag. Hard to understand, but these monsters really reduce the wing drag much stronger than their own drag is.

http://www.airliners.net/open.file/124558/M/

http://www.airliners.net/open.file/072343/M/