On Wed, 09 Jul 2008 08:13:04 -0600, Ralph Jones
wrote:

On Wed, 9 Jul 2008 04:26:33 -0700 (PDT), Dan G
wrote:

I'm crewing this season, and no doubt my pilot will be expecting me
out at 7am with Mer in hand.

My question is (and I'm sure it's been debated before, I did search,
but want fresh input) how worthwhile is polishing?

I can understand keeping the fuselage as slippery as possible to
reduce skin drag, but I've heard that glider wings would still work as
well as possible if their surface was 40 grit sandpaper! Also take a
look at a golfball -- it's dimpled specifically in order to reduce
drag, again implying that a smooth surface may not be perfect.


There's a major difference between blunt bodies like a golf ball and
slender ones like an airfoil. Drag on the former is mostly pressure
drag, while drag on the latter is dominated by skin friction.

[snip]

I forgot one other effect of the dimples: they make lift. A golf ball
is normally hit with backspin, and the curveball effect creates a
little bit of lift, making the ball a super low-performance
glider...;-)

The dimples magnify the effect somewhat, by generating a little extra
flow circulation around the ball in the proper direction.

If you've read up on the spinning mines that were used against the
Ruhr Dams, it's precisely the same effect: the backspin on the mine
kept it pressed against the surface of the dam as it sank.

rj