My New (to me) Civic! “Prius Killer”

[freebeard]

According to #7 you have attached flow all down the back window. Instead of a step and flat top, why not a concave curve and eleiminate the step.

There is a race car (I always forget) that used a concave spoon-shaped afterbody to get downforce without a wing.

[JacobLeSann]

Like that? It’s an idea. I’d say the “whale-tail” on the 911 has a spoon shape too. Makes sense to me.

Mainly, I feel like I’m standing confused at a metaphorical crossroads. Julian Edgar teaches that tufts on my car’s rear glass represent true flow. aerohead and other members on this site believe that the tuft flow is actually a symptom of downwash and vortices from the C-pillars. Vman455 (who has a website that I’m now obsessed with) seems to shoot somewhere in between.

so, accordingly, I have three ideas in mind for rear windshield aero:

-create a bonneville type spoiler, to smoothen airflow. This looks to have the cleanest tuft-flow. I could use a device such as a vortex generator or a wing to channel energy into the boundary layer, according to Ford and Mitsubishi cars; but wouldn’t that just cause drag in itself? I’d have to do it properly enough to make the gain higher than the cost.

-create an add-on kammback or fastback. The one in that older “ECOfamily Civic” thread is a nice design. But that adds weight, complexity, presumably noise, etc. Would be annoying to mount it when I don’t want to screw into the body at all. I’d need plexiglas for rear vision and it would likely fog or scratch….blah blah (I’ve beaten that idea to death before)

-create an artificial fastback, and capture air into a bubble, which will force air to flow over it. That’s more or less what the drawings in my last post show. I’m not sure if this is best, but it could be. According to aerohead, this needs to have zero porosity. Hm.



Vman455 makes a great point when speaking of testing:

“The air doesn’t care about what you think it should do, and you’re most likely wrong anyway.”

Yet, the people who disagree with him are also respectable, with many credentials; so I’m going to observe any ideas I have.

[freebeard]

Like that? It’s an idea.

Somewhat. It is a concept supercar with the whole top rear shaped, rather than an add-one. I found it again once, but failed to add it to my albums.

[JacobLeSann]

When reading what you’re describing, I imagine something like the Re Amemiya Lotus Europa. I love that car. But I’m also curious as to what you’re describing. Post it here if/when you find it!

[freebeard]

I have access to a scanner, so I decided it would be easier to draw a sketch.



Imagine an hypercar than looks like an old sway-back horse.

[JacobLeSann]

I’m at a rather lacklustre point of development right now, but here’s some pics of what I’ve been up to. I added a rising edge around the sides and rear of my original spoiler, much like a Porsche 911 Turbo “whale-tail”. Seems to work good. I also tried an opposite idea, making a big trunk extension that attempts to modify the existing backlight angle. Seems to work good as well.

Seems. That’s a big word. Waiting for a nicer day with less crosswinds. Im noticing one side of the rear windshield is attached while the other detached. These alternate based on which direction I am facing on the road.

W.I.P!

[JacobLeSann]

freebeard, I don’t think I’ve tracked the exact car you’ve drawn, but it kind of looks familiar to me as well. It looks like some newer wing designs are picking up on similar ideas:

https://www.motorsport.com/f1/news/c...ings/10324304/

And here’s some *slightly* similar images floating through my mind. The Insight belong’s to Julian Edgar. Fins remind me of the Kamm cars.

[JacobLeSann]

Here’s what I’ve done lately. I’ve read in Edgar’s book that an EBLA of 10-12 degrees is quoted as being best by Adrian Gaylord. I guesstimated that angle and took a hardwood flooring sander to a laminated stack of foam sections. The way the trunk is setup, I can actually get the front edge of my “wing” pretty close the rear glass. I sanded the leading edge more than I really needed to, but it seems to work very well. Flow is cleanly attached, so far as I can tell.

I used a very long tuft to try and measure the proper EBLA of the car, and got confused. It was evenly spaced 2” or so above the surface of the “wing”, and did that consistently.

I cut/taped another piece, adding more height with the same angle. Yet again, it looks like the tuft is 1-2” above the “wing”. Even if adding a bit more height is a better idea, I don’t think I want to as I can’t see much of anything with the extra 1-2”. It’s much more practical without.

Am I simply looking at the boundary layer? I hope that’s the case, but I’m not too sure. If anybody could explain this to me I would greatly appreciate it.

[freebeard]

Am I simply looking at the boundary layer?

I can't think of another explanation. If you progressively shorten the tuft maybe you'd learn something?

[Piotrsko]

Comment: if you shorten the tuft eventually the tuft mass will be too stiff to respond. Perhaps change to fluorescent colored very thin sewing thread. Afaik, the boundary layer is still thought to be only molecules thick and any taping of tufts will affect that.

Traditionally, smoke or dust or exotic concoctions are used to show affectation of the boundary layer to airflow.

You are definitely looking at the transitional layer which for all intents and purposes would be close enough. Remember there are airfoils which are known to be turbulent but are lower drag than laminar.