[aerohead]

Originally Posted by Otto

Regarding surface texture, about 20 years ago Dan Somers at NASA Langley did wind tunnel tests of factory painted, optically smooth and shiny, and sanded (in direction of flow) wing panels.

Guess what?

Draggiest was the shiny surface, next most draggy was factory painted surface, and least draggy was sanded-in-direction-of-flow surface. This is also essentially the reason 3M skins were used on America's Cup sailboats, to good effect if aligned with flow or no more than ~15 degrees off. Has about the same texture as a phonograph record.

For our purposed, probably best to forego attempts at laminar flow, but try for turbulent but attached flow, which is much less draggy than turbulent and detached flow.

Abbott and Von Doenhoff report of an investigation conducted by NACA in which aircraft surfaces,sanded in the direction of airflow with # 320 sandpaper exhibited no more drag than highly polished surfaces,and that this became their 'standard' for the high speed tunnel work.