Re: [RCSE] Ideal wing surface texture

[Walter Lynch]

Back when I used to race Hobie 16s, one of the many racing tricks was to
sand off the gloss finish on the hulls with very fine grit sandpaper- this
resulted in a slightly faster boat- something along the lines of the guy
sanding his Pik-20 wings I guess.  Walter
-Original Message-
From: Andrew Dignan [EMAIL PROTECTED]
To: [EMAIL PROTECTED] [EMAIL PROTECTED]
Date: Wednesday, January 05, 2000 8:04 AM
Subject: Re: [RCSE] Ideal wing surface texture


I have been made aware that sometimes a rough wing texture can indeed
increase performance in full scale gliders.

A few years ago, some tests were run on a PIK-20.  The tester then re
did the wing and had sanded it down with 600 to true the surface.  He flew
the glider and tested it just for grins.  He was surprised to find that the
glider had a few more points of L/D.  When he finished the wing off with a
gloss smooth finish, the points disappeared.  Hummm.


  Maybe it would not be a big deal with the Lower R's in the model world.


Andrew
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Re: [RCSE] Ideal wing surface texture

[John Roe]

Message text written by "Derek Boyer"

The moral of the story is that I’m being led to believe that smoother
is better even in our low-Re environment.  Pretty well unsupported
reasoning,  but beliefs aren’t always reasonable or wrong.

For what it's worth, as this is purely second-hand...

I have heard from God on this topic, in a discussion about very, very
low Reynolds numbers, specifically micro-hand launch.

Smoother is better. Period.

John Roe
Laguna Hills, Ca
www.martialartsacademy.org

"Wise men STILL seek Him."
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Re: [RCSE] Ideal wing surface texture

[Moved by the wind.]

Scobie

Back when Michael Selig was doing wind tunnel test at Princeton he told me he had run 
test on this very thing.  As I remember it
smooth was best, but you might want to ask him.

I did my own test by spraying hair spray on one wing and leaving the other smooth, I 
couldn't find any difference.

I did find that trip strips work on a E205 smooth wing though.  I put a strip on the 
right wing @ 15%, and one on the left @ 25%.  I
found the plane pulled to the left on launch, then to the right while soaring.  My 
conclusion was the 15% strip helped at high
angles of attack, the 25% worked at a lower angle of attack.  When I put a 15% strip 
on the wing with the 25% strip, the plane
launched straight but still went to the right while soaring.  I then put a 25% strip 
on the right wing and the plane launched
straight and flew straight.  I had no way to tell if the plane with the strips out 
performed the when it didn't have them.  I should
have done early morning dead air launches to test that but I didn't.  BTW a Saggitta 
was good for 3m 30s as opposed to a Windsong
that 5m 20s in dead air.  These were the averages of 5 launches each alternating 
between flying the Sag and the Windsong, the way I
remember it there wasn't 10s difference in each planes flight times.

Scobie Putter or Sarah Felstiner wrote:

 Any aero-heads out there have any comments about wing surface texture? I
 know that careful vacuum bagging can produce a 'mirror-smooth' finish, but
 is this in fact the ideal surface? At low reynolds numbers generally
 encountered in the rc glider realm, is there any texture that would be
 preferable in any way?

 Would you notice distinct flight changes if your favorite 'high-gloss' wing
 were suddenly switched to random orbit 400 grit for finish, all other things
 being equal?

 Thanks for insight.

 Lift,
 Scobie in Seattle

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Marguerite Prunyi
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