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A fundamental principle of aeronautical engineering has been overturned

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Re: A fundamental principle of aeronautical engineering has been overturned

#31

Post by Groxx »

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 speeds with less energy.

And then just comments and links to other articles. No indication at all that there's more to the article beyond (apparently) an audio recording.

This might explain some of the "didn't read the article" comments? Not that it doesn't happen anyway tho.

Re: A fundamental principle of aeronautical engineering has been overturned

#32

Post by toss1 »

nullhole wrote: post #28
toss1 wrote: post #4

Earlier quoted context omitted.

Yes, but this is not that. Golf ball dimples are about 4 mm across and 0.2mm or 200μm (micrometers). These features are several orders of magnitude smaller at 38 to 53μm diameter. >>the first in the world to demonstrate that aerodynamic drag can be reduced by up to 43.6 percent simply by applying distributed micro-roughness (DMR), a surface roughness so fine and irregular that it cannot be distinguished by the naked…

Not to be that guy, but 38-53um is 1 order of magnitude smaller than 200um

Not to be that guy ;-) , but the diameter of the golf ball dimples is ~4 mm or about 4,000 μm, whilst the diameter of the spheres is 38-53 μm, or about 0.04 mm.

Diameter-to-diameter seems like about 100x or two orders of magnitude?

Similarly, 200 μm is the golf ball dimple depth (oops, just noticed I dropped that key word), and they didn't give us a measurement of the depth of the dents caused by the spheres or sandblasting, but it would likely be significantly less than half the radius of the spheres?

Sorry about misleading with dropping the "depth" word.

Re: A fundamental principle of aeronautical engineering has been overturned

#33

Post by smallerize »

sgc wrote: post #8

If the application method is as rudimentary as sandblasting, it sounds rather simple to retrofit to existing aircraft. If it works as they state it does, it's a virtually free same-day fuel efficiency boost. However, I did not see what the actual net improvement was. When they talk percentages, they are talking only about "in the transition zone". They say the coefficient improves throughout, but in theory, it could…

What I've seen is a more structured texture applied with plastic films. https://www.lufthansa-technik.com/en/aeroshark One company claims up to 4% less fuel use. https://mako.aero/insights/delta-partners-with-mako-to-test-...

Re: A fundamental principle of aeronautical engineering has been overturned

#34

Post by Maarten88 »

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 surprising question to me is how is it possible that something so simple was not known in this very well-researched and well-funded field. It probably was known, just not by the paper-publishing researchers.

Re: A fundamental principle of aeronautical engineering has been overturned

#35

Post by spacedoutman »

6stringmerc wrote: post #11

I wrote about this ages ago, in that shark skin is an evolutionary adaptation worth study because water is thicker than air, but when air compounds, blah blah blah. Basically think of making a composite mold with directional tiny tiny dorsal fin looking surface. If you rub your hand on it the wrong way it cuts you open. Could even be scaled for large cargo ship hulls. Next up: my personal wing invention which uses le…

>humpback whale fins

you might find this video interesting then, the fastest rc drone in the world and it uses humpback inspired props.

https://www.youtube.com/watch?v=k9n1h0rn9No

Re: A fundamental principle of aeronautical engineering has been overturned

#36

Post by drpixie »

adverbly wrote: post #27

I'll await the experimental measurements of fuel efficiency using real aircraft.

Me too. The number of "revolutionary" designs that are announced but disappear makes me cynical. Looking wings on real aircraft, unless freshly painted, they're pretty close to finely sanded :) If the airlines and engineers saw a significant performance degradation with wear, they'd be out there polishing and repainting wings.

On a similar note - How many times have you seen announcements about someones blended wing that is going to save 50% fuel? But there are very few blended wings in nature (eg. rays), and those are in a very slow-speed regime.

Re: A fundamental principle of aeronautical engineering has been overturned

#38

Post by dnautics »

drpixie wrote: post #36
adverbly wrote: post #27

I'll await the experimental measurements of fuel efficiency using real aircraft.

Me too. The number of "revolutionary" designs that are announced but disappear makes me cynical. Looking wings on real aircraft, unless freshly painted, they're pretty close to finely sanded :) If the airlines and engineers saw a significant performance degradation with wear, they'd be out there polishing and repainting wings. On a similar note - How many times have you seen announcements about someones blended wing…

The real obstacle to blended wing designs, I imagine, is more boring: airports are likely to be difficult to retrofit to support those, well for cargo anyways, and for passengers there's probably less appetite to board such a plane

Re: A fundamental principle of aeronautical engineering has been overturned

#39

Post by TomatoCo »

russellbeattie wrote: post #23
zonkerdonker wrote: post #19

Earlier quoted context omitted.

Based on the mechanism of flow attachment in the transition zone it seems like the overall airfoil profile would likely have to change to take full advantage of the reduced friction. I think its much more likely to see this technique played with somewhere like Formula 1, if it hasnt been already.

> "...like Formula 1" Or projectiles like bullets and missiles. A sniper bullet with nanoscale textured surface that's able to go x% farther due to reduced drag seems plausible.

On a metal as soft as copper I imagine that texture'll last about 30 minutes after it's issued to the soldier.

Re: A fundamental principle of aeronautical engineering has been overturned

#40

Post by [deleted] »

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…

[deleted]
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