A fundamental principle of aeronautical engineering has been overturned • Hacker News Board

Re: A fundamental principle of aeronautical engineering has been overturned

#111

Post by warumdarum » Mon, May 25, 2026, 2:20 PM UTC

naasking wrote: post #106

Arodex wrote: post #89

Earlier quoted context omitted.

Water is fairly viscous, and when you try to pull through too fast you completely change regime due to cavitation. In comparison, from my days studying aerodynamics for RC soaring, air has a wider range of "viscosities" (represented by the Reynolds number) depending on the scale of your aeroplane and the speeds you intend to go through the atmosphere. The aerodynamic ideal or what count as useful tricks (winglets, di…

Water is also largely incompressible. The fluid dynamics are just too dissimilar to air to carry over simplistic assumptions.

Wasnt there something about building abblative vortexes that convert the friction into rotation and are then discarded at the edge of the surface?

Re: A fundamental principle of aeronautical engineering has been overturned

#112

Post by matt-attack » Mon, May 25, 2026, 2:38 PM UTC

I’d be curious to know if this sort of thing could’ve been predicted through computer modeling. And if not, does that mean, we have a gap in our fundamental fluid equations?

And if so, couldn’t we just have a model iterate on different surface patterns and optimize?

Re: A fundamental principle of aeronautical engineering has been overturned

#113

Post by larusso » Mon, May 25, 2026, 2:52 PM UTC

plorg wrote: post #81

larusso wrote: post #80

Earlier quoted context omitted.

I thought that shark skin foil was a thing for years. Where they tried to emulate the micro roughness of shark skin.

The article says the investigators identify this as something fundamentally different than the shark skin effect.

Sorry the article is paywalled and I reacted to the comment about sanded surfaces. I remember seeing documentation or other nature documentation’s about the shark skin effect. I had the chance to touch a shark and a ray in an aquarium but never felt the shark skin foil. I assume the properties would be the same though.

Re: A fundamental principle of aeronautical engineering has been overturned

#114

Post by zobzu » Mon, May 25, 2026, 3:43 PM UTC

Maarten88 wrote: post #34

Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…

as usual these things are presented as new and revolutionary but aren't actually.

the specific process and implemention however are usually newer or slightly different from before.

this is our sensationalistic based society - any iterative progress, or sometimes even copy, is explained as a revolution.

now show me a 737 using 40% less fuel - guess what - that wont happen - however, perhaps we'll get a slightly better process to create aircraft skins. keep in mind you cant re-sand a fuselage every week, it needs to work reliably with no maintenance.

Re: A fundamental principle of aeronautical engineering has been overturned

#115

Post by zobzu » Mon, May 25, 2026, 3:46 PM UTC

dilawar wrote: post #58

Maarten88 wrote: post #34

Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…

> and airfoils also benefit from micro-roughness for lowest friction. I thought this was known to some extent that smooth surfaces are not always the best e.g. golf balls have dimples on them? No?

dimples are used for stability and lift, not for friction reduction / low cx

Re: A fundamental principle of aeronautical engineering has been overturned

#116

Post by stasomatic » Mon, May 25, 2026, 4:17 PM UTC

Arodex wrote: post #89

Maarten88 wrote: post #34

Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…

Water is fairly viscous, and when you try to pull through too fast you completely change regime due to cavitation. In comparison, from my days studying aerodynamics for RC soaring, air has a wider range of "viscosities" (represented by the Reynolds number) depending on the scale of your aeroplane and the speeds you intend to go through the atmosphere. The aerodynamic ideal or what count as useful tricks (winglets, di…

Asking as a complete neophyte - how does this reconcile with modern war planes being inherently unstable as far they flight dynamics go, without their enormous thrust capabilities? I’m just curious, I know nothing about the subject, but it seems that the solution we came up with is thrust, baby.

Re: A fundamental principle of aeronautical engineering has been overturned

#117

Post by stasomatic » Mon, May 25, 2026, 4:34 PM UTC

mlmonkey wrote: post #9

> It's long been accepted that the smoother the surface, the lower the aerodynamic drag. That turns out not always to be the case. Huh... I'd always heard that a golf ball's dimples help reduce drag?

Me too. Is it known by how much though in relatives percentage terms? Sometime things are just worth the effort. If larger than 20%… okay, but then if everyone uses dimpled balls (I understand they do), it’s just a thought experiment, then what’s the point. Why aren’t ping pong balls dimpled?

Re: A fundamental principle of aeronautical engineering has been overturned

#118

Post by kjkjadksj » Mon, May 25, 2026, 4:44 PM UTC

degamad wrote: post #71

djeastm wrote: post #26

Earlier quoted context omitted.

From the article: >This principle is fundamentally different from the effect of dimples on golf balls. Dimples reduce pressure resistance by intentionally turbulizing the airflow and suppressing backward separation. DMR, on the other hand, delays the transition, thereby suppressing not pressure resistance but the wall friction itself. They are opposite mechanisms.

mlmonkey did not say that this new observation was the same phenomenon as golf ball dimples, just golf ball dimples already disproved the "long accepted" belief that "smoother the surface, the lower the aerodynamic drag".

They don’t though. Hit your golf ball into the cart path and see what happens after. Pro or competitive golfer will toss it and use a new ball.

Re: A fundamental principle of aeronautical engineering has been overturned

#119

Post by littlexsparkee » Mon, May 25, 2026, 4:45 PM UTC

Groxx wrote: post #31

It's almost certainly my adblocker playing poorly with their "subscribe to read" stuff, but I had to lol at the failure mode. When I load the page, I get the splash image/headline, and below it: > Subscribe to listen [9 minutes] > Aerodynamic drag is a major “barrier” in high-speed airplanes, automobiles, and bullet trains. This is because a design with less aerodynamic drag allows the aircraft to move at higher spee…

If you're quick to hit the play button (it briefly says 'Listen' on page load) with page inspect open, you can get the audio link in the network tab.

Re: A fundamental principle of aeronautical engineering has been overturned

#120

Post by delecti » Mon, May 25, 2026, 4:53 PM UTC

rogerrogerr wrote: post #49

aeternum wrote: post #43

Earlier quoted context omitted.

I wonder how quickly airlines will adopt sanded/rough wings. It's also interesting that the efficiency of winglets were known for quite awhile but only somewhat recently have nearly all airliners adopted them.

It’s probably operationally easier to keep surfaces smooth than to keep them a specific amount of roughness.

Also matters a bit what happens to a surface that they don't do anything to. Does a precisely rough surface get too rough or too smooth? Does a precisely smooth surface get rougher in a way that's beneficial?

Could be the case that in-practice this means they just worry less as their perfectly smooth planes get a bit rough.