Riblets

Riblets

Post by Larr » Sat, 21 Dec 1996 04:00:00



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.

Regards,
-Larry Curcio

 
 
 

Riblets

Post by Bob Kapl » Sun, 22 Dec 1996 04:00:00


Quote:

> 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.
...
> 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.

Sounds like turbulators. The idea is to trip laminar airflow to turbulent
airflow. Turbulent flow hugs a surface better, and can reduce overall drag.
Look at most commercial airliner wings, and you will see all sorts of little
protrusions. Turbulators!

        Bob Kaplow      NAR # 18L       TRA # "Abort, Retry, Fail?"

 
 
 

Riblets

Post by Wol » Sun, 22 Dec 1996 04:00:00


Quote:

> Sounds like turbulators. The idea is to trip laminar airflow to turbulent
> airflow. Turbulent flow hugs a surface better, and can reduce overall drag.

More like - By inducing turbulent flow at the wings surface, the laminar
flow over the upper surface of the wing won't separate.  There is an
informative
little article about turbulators in the latest issue of RC Modeler (the big RC
plane mag.).

Wolf

 
 
 

Riblets

Post by Larr » Sun, 22 Dec 1996 04:00:00


Quote:

> Sounds like turbulators. The idea is to trip laminar airflow to turbulent
> airflow. Turbulent flow hugs a surface better, and can reduce overall drag.
> Look at most commercial airliner wings, and you will see all sorts of little
> protrusions. Turbulators!

Hi, Bob.

Actually, it's just the opposite of a turbulator. It *prevents* turbulence a
tad. It's friction drag, not base drag that's being reduced.

Curious, ain't it?

-Larry

 
 
 

Riblets

Post by Bill Nels » Mon, 23 Dec 1996 04:00:00


: Sounds like turbulators. The idea is to trip laminar airflow to turbulent
: airflow. Turbulent flow hugs a surface better, and can reduce overall drag.
: Look at most commercial airliner wings, and you will see all sorts of little
: protrusions. Turbulators!

Interestingly enough, the Turbulent flow does NOT hug the surface. That is
why controlled turbulent flow has less drag than laminar flow. The laminar
flow means that the air is flowing along the surface - producing friction.

Bill

 
 
 

Riblets

Post by The Silent Observe » Mon, 23 Dec 1996 04:00:00


Quote:


> > Sounds like turbulators. The idea is to trip laminar airflow to turbulent
> > airflow. Turbulent flow hugs a surface better, and can reduce overall drag.
> > Look at most commercial airliner wings, and you will see all sorts of little
> > protrusions. Turbulators!

> Hi, Bob.

> Actually, it's just the opposite of a turbulator. It *prevents* turbulence a
> tad. It's friction drag, not base drag that's being reduced.

> Curious, ain't it?

It's also at right angles to a turbulator -- turbulators are
perpendicular to the airflow; the riblets described are parallel to the
flow, it seems...

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