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Old 12-05-2020, 03:50 PM   #11 (permalink)
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It's possible that those dark smudges are from rubbing up against something and the phasing matches because the surface flexed. Or the rivet heads protected the surface. I lean toward the latter.*

That Sylph has a really clean front axle. And the 'elevator' has upswept tips.

*Like JulianEdgar speculated.

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Old 12-05-2020, 04:35 PM   #12 (permalink)
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Yes, yes - nevermind the smudges.
I was concentrating on the clean area behind the rivets that showed the airflow.
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Old 12-05-2020, 05:47 PM   #13 (permalink)
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Each hemispherical rivet head will generate a vortex street. Immediately behind each rivet the surface will experience a [buffeting] downdraft. IMHO, of course.

The scale being small to the surrounding surface, reattachment happens.
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Old 12-07-2020, 05:49 AM   #14 (permalink)
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Quote:
Originally Posted by aerohead View Post
Finally!,some images.At 1/4-scale in the Cal Tech GALCIT wind tunnel,Cd 0.103

I like that...except for the wings at the back. Presumably, they're necessary for downforce or other stability. Whatever, they have to go!
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Old 12-07-2020, 11:43 AM   #15 (permalink)
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Not saying it's the case here, but the VW Nils had protruding tail lights.



Spreading them out helps with depth perception of following drivers.
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Old 12-07-2020, 12:02 PM   #16 (permalink)
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Stick 'em on the rear fenders, plus the usual third/high brake light in the back window.
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Old 12-07-2020, 01:39 PM   #17 (permalink)
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I understand, but the Sylph has only one fender. Not sure about tail lights on a [moving] cycle fender.

One counterexample does not mean that I care.
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Old 12-08-2020, 09:51 AM   #18 (permalink)
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Hog riders put tail lights anywhere they want, including rear fenders on rigid frames. Other than vibration burning out the light, they seem to exist fine.
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Old 12-09-2020, 12:15 PM   #19 (permalink)
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clean area

Quote:
Originally Posted by Cd View Post
Yes, yes - nevermind the smudges.
I was concentrating on the clean area behind the rivets that showed the airflow.
That's the separation bubble. There's a captured volume of turbulence traveling behind the rivets. Air is of such a low mass, that is can enter and leave this region, however the mass of the water and entrained road debris particulates prevents their following. The inertia of the water and entrained solids are just too great to allow them to follow a trajectory like that. They 'overshoot.'
If the rivet heads were a perfect hemisphere, you'd see the separation at around 115-degrees from the forward stagnation point, like a PGA, Regulation golf ball. If a 'clock face', and air hit at 3:00 o'clock, separation would be at 5-seconds after 12- Noon. At 22-degrees of downslope.

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Last edited by aerohead; 12-09-2020 at 12:17 PM.. Reason: add data
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