The current (It may not be on the stands yet) Scientific American has a lead
article on aerodynamics. The article is so-so, but there is at least one item
of interest. It seems that friction drag can be decreased 3%-6% by a surface
feature called riblets. These are apparenly similar to the grooves on a
record (yall remember records dontcha?), and they are directed longitudinally.
I bring this up cuz this is exactly the kind of texture one obtains with
acrylic paint that has not been well thinned. The texture results even when
a foam brush is used, and can be avoided by adding enough Future(tm) and
water. I can remember many a night before launch when I stayed up sanding and
coating rockets to get rid of exactly this kind of texture.
Fact is, my Initiator has this kind of texture on its nose cone. I completed
it in a motel room in Front Royal, VA, on the night before a Culpeper launch.
I made the paint thick so I wouldn't mess up the place with drips, and also
so the paint would stick better to the polypropylene plastic.
Maybe I haven't really lucked out. Maybe the grooves have to be more carefully
constructed than this (though sharks likely don't construct their so-textured
skins that carefully), but at least I now have an excuse.
Just thought it was worth a remark. In superrocs, for example, friction drag
is important - though weight is as well. What the heack, it's a direction.