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Old 05-04-2020, 10:03 PM   #41 (permalink)
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Originally Posted by JulianEdgar View Post
The strakes I trialed are 410mm apart. I've seen production cars with strakes as far apart as the full diffuser width, all the way to being only about 75mm apart. In my book, page 95 and pages 183 - 185 have some good views of strakes in diffusers of production cars.

The plywood (both strakes and base) is 3mm thick. I didn't bother describing the assembly because it's shown in the third post in this thread - https://ecomodder.com/forum/showthre...tml#post622797

When it was in position, it was taped around all edges. The sheet was sized to be the same as the rear diffuser, which in this part is flat (ie not curved). I would guess the boundary layer as being something like 10mm thick at this point, so I can't see small discontinuities making much difference to anything. At their maximum, the strakes are 90mm deep.
So 410mm is a little over 16", wider then "norm" by my definition IMO, I also suspect many strakes on today's road cars/SUV's are often more cosmetic , kinda like the wings mounted an inch above the "boot". I also believe strakes more then two, are mainly to enhance DF goals, rather then reduce drag (when used for a performance goal not cosmetics), I don't know precisely.

Would a curved piece of PW been a more proper fit? I get that almost all testing accepts some compromises.

I totally agree 3mm would be hard to image as great impediment on this application, but also remember in aircraft wing tests, bug splatter is even detectable. The tape was visible in posted pics, so it was apparent you were likely trying to minimize any "discontinuities".

Regardless, something caused the increase in measured air pressure, and I can't still conclude it was only caused by the three strakes.

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Old 05-05-2020, 01:00 AM   #42 (permalink)
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Off topic, but I really appreciate Structural technology at its finest. I've never seen an up-close examination of the truss work in the classic airships.

The 'flanged' holes are created by dimple dies.
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Old 05-05-2020, 02:38 AM   #43 (permalink)
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Off topic, but I really appreciate Structural technology at its finest. I've never seen an up-close examination of the truss work in the classic airships.

The 'flanged' holes are created by dimple dies.
Yes, the 1930s airships are just stupendous. If postage didn't cost me an arm and leg, I'd send you a gratis copy of my Discovering Engineering that Changed the World book. I think you'd love it. Lots of really cool stuff - the chapter on airships also covers hovercraft, another incredible technology.
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Modifying the Aerodynamics of Your Road Car

A really good book that should be added to the library of everyone working in automotive aerodynamics, as well as those making car aero modifications at home. - Rob Palin, former Tesla aerodynamicist
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Old 05-05-2020, 03:01 AM   #44 (permalink)
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I built the proper versions of the Edgarwits aerofoil air curtains today.

Cutting the GOE222 aluminum extrusion to length. If you were careful you could use just a hacksaw.


Note the proper aerofoil profile.


The drilled and tapped aluminum spuds that fit into the 25mm openings in the extrusion. Buying 25mm (1 inch) bar would make this easier.



The spuds glued into place. I used threadlock - ie an anaerobic adhesive.



Marking out and then cutting the 3mm ABS end plates (same material as my front undertray). This material is easy to 'work' with normal tools.



Folding a flange on the heated ABS. (Could have just used blocks of wood.)



The two finished Edgarwits. Each end plate is different so they all needed to be labelled.



Attaching the bottom end plate of the LH side. Note the rubber seal that fills the gap between the straight flange and the slightly curved bumper.



Inside view of bumper. Washers and Nyloc nuts. Don't want to lose a second pair!
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Old 05-05-2020, 03:06 AM   #45 (permalink)
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Now for some more throttle-stop testing, including in windy conditions. The aerofoil is easily removed for A/B testing (but not the sideplates).
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Old 05-05-2020, 03:57 AM   #46 (permalink)
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Thanks. I don't know that I have the ability to read a whole book anymore.


Ron Covell: Beading Machine Basics
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Old 05-05-2020, 05:04 AM   #47 (permalink)
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Thanks. I don't know that I have the ability to read a whole book anymore.


Ron Covell: Beading Machine Basics
You must have read my mind - I am looking at beading machines online just tonight! I just don't know; I seldom use my small rollers. In sheet metal, I use my guillotines a lot, and my folder a lot. But would I use a beader often enough to make it worthwhile? No one can answer that, I know...
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Old 05-05-2020, 10:23 AM   #48 (permalink)
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But would I use a beader often enough to make it worthwhile? No one can answer that, I know...
It's a learned mindset. To a carpenter, everything needs to be nailed together. To a louver freak..................

It will allow a material strength that approaches maximum stiffness the material allows without added stick on structure
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Old 05-05-2020, 10:35 AM   #49 (permalink)
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In "Throttle stop drag testing - including new design front air curtains" (a few posts above) you said a 8% decrease in drag with the edgarwit air curtain. What was the math behind that calculation? Is it only based on the speed change or did you need other factors to calculate that?
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Old 05-05-2020, 10:57 AM   #50 (permalink)
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Those are great design and build standards in those arifoils, hey. Much respect. Enviable. Good luck testing.

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