Bill Daniels wrote:
"Discus 44" wrote in message
ups.com...


Anyway I was just curious if there was a secret competition reason for
roughing the surface to keep the airflow attached longer than a shiny
smooth surface would give.


There is research to suggest that a slightly rough surface will keep airflow
attached a bit longer than a mirror smooth surface. I've flown wings sanded
with various grits from 400 to 2000 and find no difference in performance.
Stopping at 400 grit is a LOT less work than continuing to 2000. The REAL
reason for a mirror surface is that it's a lot easier to keep clean.

That said, I've always suspect that the "sand your wings" suggestion came
from a well known competitor trying to mess with another competitors head.
80 grit anyone?

Bill Daniels

IIRC, one reason that was given for not waxing wings was to avoid
beading of raindrops if you flew through a shower. I've also heard
the other suggestion that a slightly rough surface reduces drag. I
imagine one of the problems is that measuring the delta between these
two conditions would be outweighed by the measurement errors
themselves. I'm sure someone lurking here has thought more about
this?

P3

ps. I always encourage my competition to use a coarse file on the
leading edge; removes bugs very effectively :-))