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Old 04-24-2022, 09:34 PM   #191 (permalink)
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thanks. those are the shape i need. i was going to weld and fuse them into the actual skirt so i wont need to have screws sticking out for people to see. only issue will be it may be tough to unscrew and screw back in the skirt since ill have to get up and underneath it any time i do that. unless i find some flat low profile style screws and paint them black too...

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Old 04-24-2022, 11:11 PM   #192 (permalink)
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en.wikipedia.org/wiki/Dzus_fastener

The street rodder's choice is Dzus fasteners. There exist similar captive plastic turn-lock fasteners.



You can use a coin to turn them.
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Old 04-25-2022, 12:06 AM   #193 (permalink)
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Mock up rear diffuser with tape and poster board. Obviously wouldn’t make a real one till I get the rear smooth under tray

Real one would be set at about 10 degree angle, give or take depending on how well it can have airflow stay attached from the undertray. Also real version would have strakes/fins too
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Old 04-25-2022, 11:05 AM   #194 (permalink)
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cheapest rear section

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whats the cheapest way about going about the rear section? im doing this to save money in the long run

kind of bummed that wheel skirts have a smaller impact than simple side mirrors
1) A welded framework is virtually a given for the speeds you're talking about.
2) Purchasing an entry-level flux-core wire welder from HARBOR FREIGHT TOOLS would probably pay for itself, compared to hiring out welding services.
3) You'd need to be doing spot-welds under the car, to guarantee fit and clearance.
4) 1/2-inch EMT, or light square tubing.( Angle, square, rectangular aluminum extrusion, drilled, bolted, pop-riveted , epoxied, attached to 'hangers' suspended from wherever you can.
5) Curves can be produced with a pipe-bender.
6) Attachment tabs can be welded on wherever you need. Dzus fastener females as well.
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Old 04-25-2022, 11:19 AM   #195 (permalink)
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diffuser angle

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Originally Posted by Phase View Post
Mock up rear diffuser with tape and poster board. Obviously wouldn’t make a real one till I get the rear smooth under tray

Real one would be set at about 10 degree angle, give or take depending on how well it can have airflow stay attached from the undertray. Also real version would have strakes/fins too
Historically, 'low-drag' diffusers are never at more than 4-degrees upsweep angle.
'(C)hange in a pressure distribution is highly significant for the origin of drag.' Wolf H. Hucho
'With a long diffuser, a notable reduction in drag can be achieved with a very small angle... however, this effect is only assured with a smooth underside..' Wolf H. Hucho.
'L)ow energy flow cannot withstand a pressure increase and therefore separates from the contour.' Wolf H. Hucho.
'Steep tapering...is limited as the resulting flow separation increases air drag.' Wolf H. Hucho.
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Old 04-25-2022, 12:54 PM   #196 (permalink)
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Originally Posted by aerohead View Post
Historically, 'low-drag' diffusers are never at more than 4-degrees upsweep angle.
'(C)hange in a pressure distribution is highly significant for the origin of drag.' Wolf H. Hucho
'With a long diffuser, a notable reduction in drag can be achieved with a very small angle... however, this effect is only assured with a smooth underside..' Wolf H. Hucho.
'L)ow energy flow cannot withstand a pressure increase and therefore separates from the contour.' Wolf H. Hucho.
'Steep tapering...is limited as the resulting flow separation increases air drag.' Wolf H. Hucho.
Well I was just going off Julian Edgar saying 10 percent in his videos. I’ve seen a few cars with much steeper rear diffusers like the polestar 2 EV. Obviously the mock up diffuser I made is less than 10 percent. Pretty much was just trying to continue and elongate the existing panel and angle by another foot
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Old 04-25-2022, 12:55 PM   #197 (permalink)
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1) A welded framework is virtually a given for the speeds you're talking about.
2) Purchasing an entry-level flux-core wire welder from HARBOR FREIGHT TOOLS would probably pay for itself, compared to hiring out welding services.
3) You'd need to be doing spot-welds under the car, to guarantee fit and clearance.
4) 1/2-inch EMT, or light square tubing.( Angle, square, rectangular aluminum extrusion, drilled, bolted, pop-riveted , epoxied, attached to 'hangers' suspended from wherever you can.
5) Curves can be produced with a pipe-bender.
6) Attachment tabs can be welded on wherever you need. Dzus fastener females as well.
My girlfriends family is full of welders. They have all the tools and they agreed to help. All I need is the material and measurements pretty much
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Old 04-25-2022, 01:26 PM   #198 (permalink)
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Quote:
Pretty much was just trying to continue and elongate the existing panel and angle by another foot
I've never understood why people think a break angle and flat plate are superior to a curved panel with no leading angle.

Colani at Bonneville:

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Old 04-25-2022, 02:02 PM   #199 (permalink)
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steeper

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Well I was just going off Julian Edgar saying 10 percent in his videos. I’ve seen a few cars with much steeper rear diffusers like the polestar 2 EV. Obviously the mock up diffuser I made is less than 10 percent. Pretty much was just trying to continue and elongate the existing panel and angle by another foot
I can't address the videos. Unless the rules have changed.
I tried to give you insights into the mind of someone who witnessed low drag firsthand. Hucho's Cd 0.15 'template' of 1978 didn't have a diffuser.
Volkswagen's lowest drag, Cd 0.14 'Flow-body' of 1981 had a 'slow' diffuser.
I have tuft-testing images of a 'steep' Lamborghini diffuser experiencing 100% counter-flow. There IS an angle at which air behind the car begins to flow forwards down under the car, not visa-versa.
There may be caveats attached to specific designs that you'd want/need to know about.
Volvo and Polestar aren't necessary known for low drag.
'High-performance' cars will pay a drag penalty for high speed stability.
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Old 04-25-2022, 02:24 PM   #200 (permalink)
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Quote:
I can't address the videos. Unless the rules have changed.
Phase -- FYI, there is drama that predates your join date.

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