thoughts on this research?

[Matt Herron]

Microscale roughness breakthrough defies 80 years of fluid dynamics

https://phys.org/news/2026-07-microscale-roughness-breakthrough-defies-years.html?utm_source=flipboard&utm_content=topic/science#google_vignette

[Kevin S.]

Interesting.

George Moffatt use to sand his wings with 400 (or 600?) grit sandpaper, believing that surface had lower drag than a glossy surface.  i’m not sure if thats the same thing as what this article is referencing, but it reminds me of it.  Sanding wings is not a practice I see much of recently,  Not sanding,  may be more about what is the best surface long term to prevent crazing and moisture damage?    Any thoughts before I break out the sand paper???  (joking!)

Kevin

On Jul 22, 2026, at 10:55 PM, 'Matt Herron' via RAS_Prime <rasp...@googlegroups.com> wrote:

Microscale roughness breakthrough defies 80 years of fluid dynamics

https://phys.org/news/2026-07-microscale-roughness-breakthrough-defies-years.html?utm_source=flipboard&utm_content=topic/science#google_vignette

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[Tango Eight]

“something’s missing here…”

Oh, right.  Where’s the ad for the $4995 BD-5 kit?  

-Evan

[SCOLLd01]

Isn't this why golf balls have dimples? I've always assumed the roughness would be advantageous but only at certain speed regimes....

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[Michael Opitz]

People sanded wings because the technology at the time was at the point that a new glider would get spar waves (maybe 1.5 years after manufacture) where the surface would

shrink down as the thick epoxy resin in the spar cap rovings would (long term) cure.  These spar waves would sometimes be more than .005" which was far more than the consensus 

.002" allowable to keep the flow laminar.  Some people ordered their new gliders with an extra coat of Gel-coat sprayed into the wing molds just  to have the extra thickness available

to sand off without going through to the green glass underneath when the time came to address the inevitable spar waves.  Newer manufacturing techniques have reduced this issue 

to the point where it's not as big a factor anymore.  Dick Johnson made performance measurements when he tuned his gliders and decided that once one gets to ~320 grit smoothness,

"the air doesn't care anymore".  He determined that anything smoother/shinier was just for easier cleaning / maintenance and visual appeal.

Mike Opitz

RO

On Thursday, July 23, 2026 at 2:18:19 AM UTC-4 Kevin S. wrote:

[Cliff Hilty]

30 years ago A couple of partners on a PIK 20 (known for its horrible performance when wet) sanded their wings with 120 grit. They swore it canceled the bad performance when wet issue. 

CH

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[Mark Mocho]

My first Pegase 101A had an absolutely horrible, crazed surface on the wings. I flew the heck out of it, and I am still convinced it performed better than the second Pegase 101A I purchased. Of course, my memory has been influenced by beer and age.

[Kirk Stant]

I'm convinced that shape is a lot more important than surface finish (within reason). My old LS6 has original gel coat - never the best on LSs! - but I haven't observed much performance drop off as it has gradually crazed over the years. I had it lightly sanded 10 years ago to knock off the edges of the crazing, but otherwise just keep it clean and waxed. OTOH, a friends Ventus B that had it's wings completely refinished and painted (they looked beautiful!) had a noticeable drop off in performance when we flew together before/after. My feeling is that the shape changed enough to affect performance.

Then again, this is a good way to convince myself that I don't need a new glider!

Kirk

66

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[Charles Mampe]

The PIK-20 and SGS-1-35 (same basic airfoil) were not tolerant of bugs or water. They were best sanded (45* bias) to give turbulent flow full chord. Also wiping the "D tube" with liquid soap helped if you thought you might hit rain as the soap sheeted the water, not beaded.

The linked article is along the lines of "shark skin" which was also used in racing swim suits. Not really sure how well it worked.

[Michael Opitz]

The shark skin idea was patented by 3M quite a while ago.  One of my cousins worked for 3M in the thin films division, and told

me that they were sitting on the patent awaiting adhesives that were strong enough to bond and not come off at high speeds and

very cold high altitude temperatures.  Evidently, it has enough merit so that 3M spent the time and money to secure the patents.

Mike Opitz

RO

[Chip Bearden]

Yes, RO is correct: wings used to "cure" a lot more than they do now and that sometimes resulted in significant waviness. My LS3 needed to be sanded three times about 2 to 4 years apart and the area over the spar built up with gelcoat before it stopped moving around. By comparison, my ASW 24 has moved hardly at all in 34 years and other 24s I checked were similarly solid. I understand a lot has to do with how the spar caps are designed and the materials used. 

I left my LS3 at about 320 or 400 grit and didn't use wax because it seemed to make the airfoil (in the same family as that of the PIK-20, Nimbus, Mosquito, et al.) much less sensitive to rain. The water sheeted rather than beaded up on the leading edge. Newer airfoils seem much more tolerant of bugs and rain.

Given the uncertainty of whether a sanded finish really improves performance (I also think it's the profile rather than the roughness that matters, based on my LS3 and other older sailplanes) and the impact of moisture, if I had a gelcoat glider, I'd be waxing it or otherwise protecting the finish. 

Chip Bearden

JB