Re: [ATM] Wind resistance & golf balls

[Stan Truitt <s.truitt@verizon.net>]

>At a recent viewing session the wind got up a 
>bit and started shaking my 8.75 inch sonotube 
>scope.  A friend who was observing with me 
>commented adversely. He is a keen golfer and 
>suggested that I think laterally and take the 
>example of a golf ball.

Aloha Roger,

Perhaps thinking even more laterally might help 
here.  Splendid reductions in wind effects were 
noticed when the upper part of my 12.5 inch OTA 
was replaced by a truss tube arrangement.  It was 
a surprise, when a light baffle, opposite the 
focuser, was improved by using a thin dark gray 
open cell foam sheet.  It let the wind blow 
through, instead of generating pressure 
differences and the concomitant aerodynamic 
effects.

Later the truss tubes were increased in diameter 
and coated with pipe insulation, without 
noticeably deleterious effects.  Subsequent 
replacement of the cylindrical tube at the mirror 
end, gave no noticeable improvement, perhaps due 
to the wind shear effects near the ground.

Chapters IV and V of:  Fluid-dynamic Drag. 
(Hoerner, S. F. , (1965) Midland Park, NJ: 
Published by the author), have useful 
information.  At these Reynolds numbers surface 
dimples have a very small effect, even though fun 
to speculate about.  <g> 
http://www.darcorp.com/Textbooks/fluid-dynamic_drag.htm

My thoughts go to the reduction in trunk stress 
after a tree is significantly trimmed.


Let the breeze blow through,

Stan Truitt     20° 51'  N,  156° 22'  W
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