Flat Bonneville-type spoiler

[Pendragon]

Originally Posted by California98Civic

I have photographs. I'm finding myself a little obsessed with this idea now. I "built" this ugly thing (below attached) by simply taping down a 2' by 4' piece of black coroplast. I chose that size only because it is close to what I imagine, and I already had a sheet that did not want to cut. The goal is actually to create something larger, something that might provide a surface at least 40 x 32 inches. The larger surface would extend eight inches aft from where this board is. The larger surface is part of an imaginary concept accommodating a 100w 2.5mm solar panel. Over the weekend I might make side wings. I cut some one inch styrafoam blocks to lift the surface and flatten it a little. I want to do a coast down with it.

Thanks for the pic. That is close to what I had in mind except that I was thinking something running from the end of your rorlplast back to the trunk at about the height of the top of the tail lights...sort of like a reversed wedge (the idea of this is both to provide rigidity so that it does not flop around so much and to see if it cleaned up the airflow somewhat) with something to cover the ends of the wedge and a fence running back to the area of the rear window sort of like the rear window wings of the '66 & '67 GTO or the Porsche 906 series. I would be inclined to have the upper surface of the wedge tilted up something around 5 degrees, perhaps as much as 10 degrees, but this is a gut instinct. I am just suspicious that it being a little bit higher would give it a better chance of picking up the disturbed airflow coming off the top of the car.

I would keep the "footprint" entirely within the trunk lid for purely practical reasons of access to the trunk.

If it shows some promise, you could see about tweaking it after doing some coast down & tuft testing. If you have a video cam it would be very interesting to see what is going on. Please keep posting back.

Cheers

[California98Civic]

Brucepick, with a sixth generation civic, just posted this photo on another forum, I guess not noticing this thread. He says this is an mpg competition car submission:
http://i188.photobucket.com/albums/z...blankplate.jpg

[fusion210]

I was hoping you'd see some decent results.

My spin on it will be using the top half of a trunk lid to make an extension. They're only $20 or so from the junkyard. Bonus points for a color matching one.

I already had two extra ones, all I did was cut out the bracing and the back half. The sides already have rolled edges and I left enough to roll the rear edge so it doesn't pose much of a safety hazard. I'll probably pop rivet it on the top and add a couple braces on the underside.



It can be extended further, it's about halfway on top of the trunk.

To fix the 3rd brake like being partially concealed I'll be adding a 4th one in the rear window.

[brucepick]

California98Civic,
Thanks for bringing this thread to my attention.

I saw this flat spoiler on a diesel-powered Metro at the 2011 Green Grand Prix. The rear spoiler thing is a clear plastic panel, supported by a simple bracket at the center. The car is an X-Prize entry, by BITW Technologies. It scored 106 mpg at the GGP but I have no idea whether the rear plastic panel helped or hurt.

I'll put the pic here, and couple others of that car.

[brucepick]

Now, can someone please explain to me the theory of this thing, if there is one?? There's a lot of discussion earlier in this thread but I can't pull it all together in my brain.

If the panel is dead flat horizontal, could it be helpful? Or is the gain only from providing one surface of what would be a boattail, if the whole boattail were there? If it's a quickie boattail, then I think it needs a downward slope of 10 or 15 degrees, right?

Or is the gain from reattaching turbulent air that's just above the trunk lid? Helping it attach by lengthening the trunk lid??

Or is any gain due to some other effect??

Please, somebody here help out a half-educated aero wannabe.

Thanks!

[Pendragon]

fusion210,

Using another trunk lid is a great idea. Not only does it allow you to experiment without the concern of 'making a mess of it', but different units can be exchanged for testing.

brucepick,

Thanks for joining the discussion.

A couple of questions.

Why the semi-circular shape of the trunk extension?

Can you remove the rear wheel skirts for service or a flat? I would have been inclined to use some sort of quick release fastener, such as a Dzus fastener and, perhaps to have minimized the bulge of the wheel skirt, but that is probably just the result of the experimental nature of the project.

Did you consider a "bump" in front of the wheel to fair it in? There are several projects which seem to have found aero benefits from doing so, but there are non-aero considerations...such as the real world of pot holes and roads that are not exactly what they should be.

Have you done any sort of before/after coast down or tuft testing with the trunk lid extension? Did you consider any sort of fences/end plates? What was your thought about that if you did.

One of your pix shows "BITV Technolog(ies)". Is this a sponsor or a competition?

It looks like fun in any event.

Cheers

[brucepick]

Originally Posted by Pendragon

...
brucepick,

Thanks for joining the discussion.
A couple of questions...

One of your pix shows "BITV Technolog(ies)". Is this a sponsor or a competition?

It looks like fun in any event.

Cheers

The Metro with flat tail extinsion is not my car! It was entered in the Green Grand Prix by BITW Technologies. A quick google search will find their web site.

It certainly was a fun event. My car is the '97 Civic HX that took first in class 2(m) at the GGP. (He said, ever so humbly)

[California98Civic]

Brucepick,

I think the idea is creating a flow of air over the vehicle that closely matches what might be accomplished with a Kamm back. The extended trunk simulates the 15 or 10 degree angles people seek with Kamm backs. That's if I understood correctly.

I attempted an A/B/A test tonight of a design like the pics of my car I posted a few posts back on this thread. The difference was in elevating the surface with one inch blocks of foam. My test was cut short by traffic and cooling weather as the sun set. I got a pair of "A" runs (with mod attached) and a pair of "B" runs (without mod). The average of the "A" runs was 46.88 mpg and of the "B" runs 46.85. It is possible that I overstated one "B" run by 3 mpg through transposing a 6 as a 9. If that is true then the "B" run was 46.10. A difference of 0.88 mpg is not all that much. My speed was fairly low (52mph). I also have attempted several coast-down tests from 45mph, and these too have been equivocal, with a possible but uncertain ever-so-slight advantage to the spoiler. I think the speeds are not high enough for either test. I also think the flat spoiler might be too short. It extends about 9" off the tail for the trunk. I'm thinking I need a longer route, and 60mph to see this for sure, and I might attempt that this weekend. Tips?

[Frank Lee]

Overlay a side-view pic of your setup with the aero template and see to it that your Bonneville spoiler (with or without endplates) extends to meet the template line.

The Bonne spoiler is similar to pickup truck aero with a tonneau in that they both more or less conform to the aero template but not with a continuous surface; rather, that part that falls away from the template (on a pickup, over the box; on a sedan or coupe, behind the rear window and over the trunk) sort of "contains" a rolling wave of air which is not as draggy as the turbulent wake which follows those shapes when they don't conform to the template profile.

[California98Civic]

Originally Posted by Frank Lee

Overlay a side-view pic of your setup with the aero template and see to it that your Bonneville spoiler (with or without endplates) extends to meet the template line.

I was just studying these template again, this time with a well drawn image of my coupe from the 1998 Honda service manual. It looks like the highest point on the car is just ahead of the center pillar. Got freeware in the form of Paint.Net and used Aerohead's template from this site and made this workable image of my car. It does seem I would need a much larger spoiler, no? Would it even be legal?