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Old 05-04-2021, 03:30 PM   #1 (permalink)
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Sharkskin on aircraft.

Saw this announcement and am very interested in it's applications.

https://www.basf.com/global/en/media.../p-21-204.html

Could it be made and applied to road vehicles?

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Old 05-04-2021, 03:56 PM   #2 (permalink)
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No.

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The surface structure consisting of riblets measuring around 50 micrometers imitates the properties of sharkskin and therefore optimizes the aerodynamics on flow-related parts of the aircraft.
There's form drag and skin friction. Aircraft strive for laminar flow but don't reach 100% (witness swing fences, etc).

Cars are immersed in time-varying microclimate turbulence and crosswinds that can exceed their velocity.
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Old 05-04-2021, 06:44 PM   #3 (permalink)
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Quote:
Originally Posted by RustyLugNut View Post
Saw this announcement and am very interested in it's applications.

https://www.basf.com/global/en/media.../p-21-204.html

Could it be made and applied to road vehicles?
0.05mm high riblets. No good on a road car - deep within the boundary layer. Might be applicable to solar race cars though.
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Old 05-04-2021, 08:49 PM   #4 (permalink)
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I assume that is a net gain of 1% fuel reduction, with the added (?) weight of the coating process, plus whatever its in use longevity works out to be?

I'm just wondering if this is mainly a PR climate change "we are on board" press release.

Don't get me wrong, I'm a believer in the climate change pending calamity, just not sure if everyone else is operating with full transparency.

Note, we know from the article the thickness of the aero coating, but not for the entire process needed for its use.
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Old 05-05-2021, 08:23 PM   #5 (permalink)
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Makes me wonder how suitable it could be to replace painting in a fiberglass bodyshell, such as of a VW-based dune buggy or while restoring some Brazilian kit-car from the '80s.
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Old 05-07-2021, 10:17 AM   #6 (permalink)
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suitable

If you're going to drive it 590- miles per hour, at 35,000- feet, go for it!
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Old 05-07-2021, 10:26 AM   #7 (permalink)
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This reminds me of watching glasshole glider pilots preparing for a contest: one guy is sanding his wing, one is spreading talcum all over, another is waxing and polishing everything, and the last is speading goop on the leqding edge.

None of those guys won.
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Old 05-07-2021, 12:13 PM   #8 (permalink)
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aircraft......................laminar

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Originally Posted by freebeard View Post
No.



There's form drag and skin friction. Aircraft strive for laminar flow but don't reach 100% (witness swing fences, etc).

Cars are immersed in time-varying microclimate turbulence and crosswinds that can exceed their velocity.
I just wanted to make a comment about 'laminar' aircraft.
1) typically, 'laminar' would only be in reference to the wing
2) when referenced to wing and fuselage, the 'laminar' boundary layer flow is limited to the portion between the leading edge, and location of of 1st minimum pressure. Beyond this point, all boundary layer flow is turbulent boundary layer flow.
3) in the example of the Boeing 777 cargo aircraft, any laminar fuselage flow would be limited to between the forward stagnation point, and to just before where the nose forebody reaches maximum cross section width and height.
4) behind this point, all flow would be turbulent boundary layer flow.
5) unless the 777 is converted from tricycle to tail-dragger landing gear it's not a problem.
6) @ critical runway position/ airspeed- defined V2, the aircraft is required to perform elevator-induced 'rotation', which now configures the wing's angle of attack for takeoff lift.
7) with tricycle landing gear this would otherwise 'crash' the tail-boom into the runway.
8) as so, designers must 'mutilate' an otherwise streamlined boom, by scalloping it's bottom, to remove any material within this interference region.
9) a turbulent boundary layer on the bottom of the fuselage helps the air remain attached across this 'scalloped' upwards ramp, minimizing separation and drag.
10) there exists, some critical skin roughness which mimics what optimized vortex generators, in the vicinity of the tail boom would produce, to enhance this flow attachment.
11) absence of the VGs might have improved safety implications for ground crews working in the vicinity of the tail.
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Old 05-07-2021, 02:03 PM   #9 (permalink)
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Quote:
10) there exists, some critical skin roughness which mimics what optimized vortex generators, ... would produce, to enhance this flow attachment.
I've always wondered about the optimum for geodesic domes. A sphere has one Cd and an icosahedron [perhaps] another. Is there is a sweet spot (mayhap around 2v or 3v) where the angular edges promote reattachment as on the Cybertruck and the overall drag is at minimum?

I can't find a Cd for an icosahedron, but a cube's Cd varies quite a bit with it's orientation.
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Old 05-07-2021, 02:42 PM   #10 (permalink)
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icosahedron

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Originally Posted by freebeard View Post
I've always wondered about the optimum for geodesic domes. A sphere has one Cd and an icosahedron [perhaps] another. Is there is a sweet spot (mayhap around 2v or 3v) where the angular edges promote reattachment as on the Cybertruck and the overall drag is at minimum?

I can't find a Cd for an icosahedron, but a cube's Cd varies quite a bit with it's orientation.
There's probably a Cd out there. Doppler radar domes are of this shape, and someone had to do the load calculations for their towers.
If they just went from scale models, knowing the measured loads observed, plus the frontal area of the dome, the Cd would drop out.

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