"N:dlzc D:aol T:com (dlzc)" wrote in message
...
Dear Gregor Hall:

"Gregory Hall" wrote in message
...
Depending upon the size of the aircraft paint can add
a considerable weight burden.

The external tank of the space shuttle used to be painted. They stopped
for exaclty this reason.

However, when the paint is really smooth it can

... [increase] ...

drag along with it an increasingly thicker layer of turbulent
air building toward the aft end of the aircraft.

... better to say that it allows for earlier boundary layer separation,
essentially increasing the cross sectional area of the shape.

Dragging this thick turbulent boundary layer causes increased drag which
seems counter-intuitive to
smoothness.

It sure does.

This is why various small surface patterns (seems to
me somebody should try fractals) often decrease
drag - they decrease the extent of the turbulent boundary layer thus the
drag caused by it.

NASA had an aircraft where they sucked air into the upper surface of the
wing, to try and create a "laminar" boundary layer. I think it took more
power than they got extra-lift / reduced-drag.

David A. Smith


Probably reduced lift as well. Seems to me sucking air into the upper
surface of the wing would degrade the low pressure caused by the Bernoulli
effect because it would tend to slow down the sped-up air traveling across
the top surface of the wing.

http://www.av8n.com/how/htm/airfoils.html

--
Gregory Hall