Dancing Fingers wrote:
Last night the Mythbusters put about a 2 inch layer of clay a a sedan
and drove it at 65 mph and recorded their mileage. They put dimples
in the clay, like a golf ball, and repeated the same test and got 11%
better mileage. This again begs the question why don't wings have
dimples, especially for STOL type aircrat, where you still have
laminar flow? Heck, hexagonal dimples might reflect radar better for
all I know?

The Mythbusters tested an automobile that wasn't aerodynamically shaped at
the tail end. They showed wind tunnel flow lines that indicated the
reduction in drag was due to keeping the flow separating a tiny bit farther
downstream. A wing, unlike most autos, is already shaped so that the flow
separates as far down stream as reasonably possible.

Since dimpling causes extra friction, at some point the gain from delaying
flow separation equals and then exceeds the loss due to the extra dimpling
friction.

(There are vortex generators that do something similar to dimpling for STOL
wings. Basic idea is to help keep flow from separating as far down the wing
as possible at high angles of attack.)