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sanding and flying in the rain

A5555

Well Known Member
sanding dust streamlines, light rain, 120 kts, 3K altitude. shows the air bending downwards at a significant height above the wing along the fuselage.

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Neat!

Interesting how the NACA vent changes the flow pattern--you must have had the air vent open. How'd the dust taste?:D
 
Intersection

Is the pattern affected by the fuselage to wing intersection? Could that be the cause of the lines going highe over the wing area?
 
Neat!

Interesting how the NACA vent changes the flow pattern--you must have had the air vent open. How'd the dust taste?:D

vent was open, it tasted sweet! amazing how the lines converge to the NACA vent.
 
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I can get the same effect without sanding Steve. Atlantic salt :)


all the aero data is right there in this picture! shows the boundary layer building as it moves from the leading edge. if only all the air molecules that have been slapped around by this propeller could talk!
 
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Is the pattern affected by the fuselage to wing intersection? Could that be the cause of the lines going highe over the wing area?

It is really the flow over the wing that pushes the streamlines up (basically) parallel to the wing. Look up, or look at, the T-28's the oil in the exhaust acts the same on that plane. If you see one at OSH, look at the streamlines, they spit a lot of oil to help the visualization.

edit: The line of interest, surprise, to me is the one off the corner of the canopy/top forward skin. I would not have thought it would have dropped so low as it reaches the HS. I wonder about the effect of gravity (centrifugal force) on the droplets.
 
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edit: The line of interest, surprise, to me is the one off the corner of the canopy/top forward skin. I would not have thought it would have dropped so low as it reaches the HS. I wonder about the effect of gravity (centrifugal force) on the droplets.

I once read that the air will have this same downward slope approx 1/2 the wing span above the wing. maximum in the center and tapering out towards the wing tips. it could be true.
 
Thank you for the interesting photos, Steve.

Please note that whenever you do flow visualization on the surface of an aerodynamic body, you are seeing what the boundary layer is doing.

The air 1" away from the surface may be doing something quite different.

The boundary layer is moving slower than freestream, has less total pressure, and consequently can be turned at steeper angles by pressure gradients than the air away from the boundary layer.

This is a known issue with oil streak testing of wind tunnel models, for example. If there is a small local flow separation, the oil drops may move backwards, sideways, or in lazy circles.

I was once involved in oil drop testing inside a large commercial turbofan engine fan duct. The oil drops were placed in a rectangular array on the ID of the fan duct, downstream of the fan. It was remarkable where some of the oil drops ended up - some of them crawled radially outward along the trailing edges of the fan outlet guide vanes, and streaked back along the fan duct OD. I"m quite certain that on average the fan duct air doesn't turn over from the ID to the OD of the duct, but the boundary layer flow can in fact migrate around quite a bit...


Best Regards,
-Paragon
Cincinnati, OH
 
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