Flat Bonneville-type spoiler

[cfg83]

Pendragon -

Originally Posted by Pendragon

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Out of curiosity, try moving "the template" forward. I think you will find the result interesting. I think, but it is just my opinion that "the template" misplaces the rear because of the choice of both the airfoil and the position of the leading edge, but that is just my opinion.

...

Cheers

Our resident aero-expert aerohead has stated that the template has only one correct location on the car. Locating the center of roof camber and centering on that is critical.

That is *not* to say that I have it correct either, but it is very important.

CarloSW2

[aerohead]

Originally Posted by cfg83

brucepick -



I'm not an aero-wizard like aerohead, but I think this is good. I would also employ the blue-line solution. Along California98Civic's comment, here is an example for a hatchback that is similar to an XR4TI spoiler, albiet not a biplane (cosworth?!?!?!?) :



The blue-line solution could be a custom spoiler or maybe an adaption of an existing adjustable spoiler.

Here's another example that fits the streamline template (but extends beyond the bumper) :



CarloSW2

I don't know what it is but I like it! Could it be a Cozworth Sierra?
With a top foil like Mercedes did with the 190 EVO,and running the mid-wing all the way to the glass,we'd capture some nice vortexes inside,forcing the air to go over and around.
And it doesn't jeopardize pedestrians like the longer foil on the car below.
I really think the gas pump would have words with it.
Thanks for images!

[California98Civic]

Originally Posted by aerohead

I don't know what it is but I like it! Could it be a Cozworth Sierra?

You got it right: Sierra. Here's another image, showing the spoiler from another angle.

[aerohead]

Originally Posted by California98Civic

Well, Pendragon, wonder no more, because I just tested it. Drag and/or downforce added by the angle might just be what caused a decline in MPG. Across my 18 mile "course" at 16.5 throttle steady:

A (no mod): 51.7
B (mod): 50.4
A (no mod): 52.0

This was so dramatic a difference I could see it just a few miles after starting out. Slower speeds were another obvious indicator. Clearly, this design does not work, possibly for the reasons you suggest, though there are others here who might know more and might comment. But I will say that at 60mph it was difficult to keep the leading edge of the assembly taped flat onto the trunk lid surface. Even though it was just 2-3" behind the base of the rear window, it would separate and flap in the wind like a parachute. I taped it down hard with duct tape and started again. I should have tuft tested first. The air does not move the way I thought.

Next, I want to try a less aggressive approach, combining ideas you (Pendragon) and Brucepic and probably others have already suggested. That tiny "kamm" type add-on at the top of the window (for cleaner separation) and a small, flat spoiler that does not extend beyond the bumper and that is flat or slightly angled downward.

EDIT: Added previous long flat design photo, the over lay of both angles, and flat spoiler test results on the long flat spoiler, for reference: http://ecomodder.com/forum/showthrea...tml#post241134

California,does the fabrication in the thumbnail photo follow your red line,or fall off as in the photo?
Also,do you think the area on either side of the spoiler,between the end-plates and sides of car is in turbulence?
You may have created two longitudinal vortices above the tailights as the spoiler does not extend out to that region,and the downwash off the roof is not supported there with the existing voids.
I've never seen a rear spoiler which wasn't full width.It's hard to tell everything from photos.

[California98Civic]

Originally Posted by aerohead

California,does the fabrication in the thumbnail photo follow your red line,or fall off as in the photo?
Also,do you think the area on either side of the spoiler,between the end-plates and sides of car is in turbulence?
You may have created two longitudinal vortices above the tailights as the spoiler does not extend out to that region,and the downwash off the roof is not supported there with the existing voids.
I've never seen a rear spoiler which wasn't full width.It's hard to tell everything from photos.

Thanks for chiming-in, aerohead. This latest version follows the red line. The previous fairly flat spoiler is in the photo. It showed a 0.60mpg gain. This one showed a 1.35mpg loss. Some of the photos of Civics with spoilers (racing cars) others posted here were contained to the trunk profile. It was a source of inspiration. I think these may be more about generating downforce, however, no? As for turbulance between the endplates and the tail-lights, I have to admit I simply don't know. I'm thinking of something smaller now. Foils really. Street legal and all. What do you think?

[aerohead]

Originally Posted by California98Civic

Thanks for chiming-in, aerohead. This latest version follows the red line. The previous fairly flat spoiler is in the photo. It showed a 0.60mpg gain. This one showed a 1.35mpg loss. Some of the photos of Civics with spoilers (racing cars) others posted here were contained to the trunk profile. It was a source of inspiration. I think these may be more about generating downforce, however, no? As for turbulance between the endplates and the tail-lights, I have to admit I simply don't know. I'm thinking of something smaller now. Foils really. Street legal and all. What do you think?

We're kinda in the shadows on this.If the original foil had been horizontal you would have been very close,if not on the 'line.' I did this on my CRX,but also extended the hatch buttresses along the 'Template' line out to the foil and went ahead and enclosed the foil to create a short boat tail.It added only a foot to the car but got the Cd to 0.235,added 8 mph to the top speed and pushed me immediately to over 60 mpg at the old double nickel speed limit.
Basjoos has seen 90 mpg with his AEROCIVIC.The air loves his car!
Seems like the racing Civics would be trading mpg for downforce.
Danika Patrick just lost the Indy 500 because of her front wing and the extra fuel consumption it cost her for the downforce setting she was comfortable with( not to mention a bunch of yellow flag laps which destroyed her pitstop strategy).
If a Civic can carry speed through the curves and chicanes due to the wings,then they've got an edge.
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On current production cars you'll notice that the trunklids are a lot higher .The air likes this.
You could construct a 'hollow' projection which runs above the trunklid,from the backlight,out to as far as the bumper,which has sides which wrap down to meet the sides of the car.It would be like the 1982 Pontiac Trans Am Firebird,only full-length.
You'd be able to look right through it.The air would re-attach onto the back of it,capturing a vortex above it like Lamborghini,Porsche,Lotus,and Ferrari have used with their backward facing step backlights.
Just thinking out loud.

[California98Civic]

Originally Posted by aerohead

If the original foil had been horizontal you would have been very close,if not on the 'line.' I did this on my CRX,but also extended the hatch buttresses along the 'Template' line out to the foil and went ahead and enclosed the foil to create a short boat tail.It added only a foot to the car but got the Cd to 0.235,added 8 mph to the top speed and pushed me immediately to over 60 mpg at the old double nickel speed limit.

This is exceedingly cool and tantalizing, but I have the reality of the Cali Highway Patrol, which pulled me over re: my driver side mirror delete today. I got off with a warning. That's actually my second warning. If I had a foot long projection I think I'd catch more trouble. I already run tint where I am not supposed to. I need a strictly legal solution here.

Originally Posted by aerohead

On current production cars you'll notice that the trunklids are a lot higher .The air likes this. You could construct a 'hollow' projection which runs above the trunklid,from the backlight,out to as far as the bumper,which has sides which wrap down to meet the sides of the car.It would be like the 1982 Pontiac Trans Am Firebird,only full-length. You'd be able to look right through it.The air would re-attach onto the back of it,capturing a vortex above

I have noticed this about the trunk lids. I like this idea a lot. I recently took apart the rear deck inside the car and I could attempt this, lifting the third backlight a little higher easily. In fact my first effort at a "spoiler" was maybe not altogether off from this idea... see old attached photo. It was just a 2'x4' sheet of 4mm thick coroplast taped down. I could elevate it a little and shape it in the spirit of the 82 TransAm. I could mount it to the lower window and cut it to curve around the the side, yes? Any further thoughts before I act on this idea?

[brucepick]

I like the idea a lot too. I eyeballed where I think it would be on my '97 Civic coupe. Horizontal panel starting at about the 6th or 7th rear defroster wire, counting up from the bottom. It will go straight back, level, to a point even with the rear bumper. Might need to be adjusted up or down a bit depending on exactly where the template curve is. I like the idea of side panels; building them might be a challenge.

As for the center brake light - here's my plan. I'll do this before I cut even one piece of material for a spoiler. Get a brake light assembly from a truck stop or a parts store. They sell them. Just a plastic housing with a red lens and a bulb holder. Tape it to the trunk lid, center, all the way back. With that in place you can experiment with different spoiler panel setups.

[California98Civic]

Originally Posted by brucepick

Get a brake light assembly from a truck stop or a parts store. They sell them. Just a plastic housing with a red lens and a bulb holder. Tape it to the trunk lid, center, all the way back. With that in place you can experiment with different spoiler panel setups.

Ooooooh. That's a good idea. So simple. I just now raised the light inside the cabin several inches. It's an ugly deal, but you can't see it through the black tint very much. Yours is a better deal. If you had 10mm coroplast you could maybe thread the wire through its lengthwise voids. 10mm coroplast would be stronger material in the wind too. I think even the 4mm will get bent-up over time. If I do this, I might double-up.

[aerohead]

Originally Posted by Pendragon

With the plate/spoiler angled up to intersect "the template" with a shorter overhang of the rear of the car as shown in the diagram, I have to wonder just how much additional drag will be created.

Out of curiosity, try moving "the template" forward. I think you will find the result interesting. I think, but it is just my opinion that "the template" misplaces the rear because of the choice of both the airfoil and the position of the leading edge, but that is just my opinion.

If you take a look at the current Subaru WRX five door which has an aero add-on at the top of the rear window and compare it with the four door notch back I think you will notice that there is a trend toward establishing a sharper separation point which basically creates a Kamm back on two box designs. The wing on the notchback is probably more of a styling feature to look like the actual rally cars than something which actually does something beneficial at normal highway speeds, but who knows. It is all a matter of drag and few of us have the capability to quantify it on different model designs.

I have seen ads for add-on affairs for SUVs which have a narrow slot to allow air to get to the underside of the wing at the top of the vehicle which were supposed to help keep the rear window clear and improve the air flow in general. As with all such things, a fair degree of skepticism is probably in order.

Chevy has been running ads for its Equinox, which uses a similar approach, claiming that it has the same Cd as a Corvette ZO6. (The truth is that they are both about 0.34-0.36 which isn't all that wonderful, but sounds nice and besides it is an improvement for a SUV.) One or the other of their ads even talks about the Kamm back aerodynamic treatment. Once again, it is as much marketing as anything else, but there is some truth to it.

The Subaru with the trunk mounted wing does illustrate how you could mount some end plates on the trunk lid and position things pretty much however you wanted. The ones on the Bonneville cars are more in line with what I would think to be low drag designs though.

Cheers

Pendragon,sorry,I'm late catching your post.
The wind tunnel investigations from which the 'Template' are derived mandate that a departure from its geometry of curvature will guarantee flow separation and the attendant drag increase.
We're given an extreme amount of latitude in a vehicles fore-body,but once we get to the point of maximum cross-section we've gotta play hard ball.
Boundary layer stability is feeble at best and laminar flow will trip into full blown turbulence without a thank you or a by your leave.