Rear aero project - Civic notchback coupe

[brucepick]

Panel attachment ideas, anyone?

Alternatives to the rubber expansion plugs, or suggestions on using them without ill effects?

[Cd]

Have you considered how large that your blind-spots will be in the new design ?
I threw together a quick Gimp paint-over of your original side shot, and it seems like with your line of sight in the car, you would only need a small section of the Kammback in clear lexan. The stuff is expensive, so this is good.
The rest could be formed in whatever material you decide to use and it could be pieced together in sections to form the compound curves.
The problem that arises is that you would still have massive blind spot along the side of the car. You could form the entire piece in Lexan, but it would be horribly expensive.

[brucepick]

I'm planning a near-horizontal "spoiler", as drawn on the first page. Pretty much what we've called a Bonneville spoiler but going back only as far as the rear bumper. Seeing out via the mirror should not be an issue.

The side panels will intrude on the driver's view but I can redo them in Lexan later. Maybe cut an opening in the side panels where appropriate and put in a Lexan insert. Doing the center panel as a Kamm back going down from the roofline is not my plan (sorry).

Panel attachment ideas, anyone?

[Tango Charlie]

Originally Posted by brucepick

Panel attachment ideas, anyone?

Rare Earth magnets?

[brucepick]

Building it.


Panel resting on supports


After trimming to match defrost wires


Measuring for length of side panel. I cut the panel 55" long.


Side panel taped into position. Will be trimmed approximately as in original drawing (below), the yellow outline.


Original drawing. Yellow = side panel, brown/tan = spoiler panel.

The photo with tape measure rule shows the approximate position of the spoiler plane. It will be close to horizontal, likely not sloped as steep as the drawing. Rear edge position determined by template. Front edge position determined by view out of the mirror. Panel is cut oversize on sides and at rear to allow for adjustment before finalizing.


Rear view of side panel before trimming.

[California98Civic]

Originally Posted by brucepick

Building it.


Original drawing. Yellow = side panel, brown/tan = spoiler panel.

Nice. I just realized two stylistic things I like in your drawing above: the curves in leading edge and the bottom aft edge of the side panels. These mimic the style of the body itself. The rear curve imitating the bumper below it, the leading edge curve tracing the tumble-home pretty gracefully. Well made it could look way-cool.

[brucepick]

Assembled this today.

Question to aerohead:
Do you think I should trim down the "fins" so they end at the height of the spoiler's rear edge?

Here's view from the other side. You can see the artwork printed on the inner surface of the side panel, I got that one at a reduced price!


Did some AB testing. Results were definitely not as good as I'd hoped. Also, seeing a cop hanging out on my test route discouraged me from doing the final "A" part. The car has no cruise control so I just had to do my best to start each coast at the same speed. I attempted to pass a particular speed limit sign at 40 mph, simultaneously putting the clutch in and going into a coast. I recorded the speed at start of coast at the same location each time, and recorded the end speed as I later crossed the same road each time, after about a half mile coast.

Northbound test runs, with spoiler:
START - - - END - - DELTA (MPH)
41.3 - - - - 33.8 - - 7.5
40.0 - - - - 32.4 - - 7.6

Northbound test runs, without spoiler:
START - - - END - - DELTA (MPH)
38.3 - - - - 32.9 - - 5.4
40.7 - - - - 35.5 - - 5.2
40.9 - - - - 34.8 - - 6.1

These tests don't show the results I'd hoped for. Speed loss was more pronounced WITH the spoiler, not without!

Next time I have an opportunity to test the spoiler I'll attach it with 3M's no-residue heavy duty duct tape and take it on the interstate. I found two places where I should be able to do a decent high speed coast.

[3dplane]

I had the same problem with my sedan kamm experiment:
http://ecomodder.com/forum/showthrea...dan-14330.html

I think what is happening is that now your car is poking a larger hole (wake) behind it! The sedan makes us think that the wake is as big as the rear profile of the car. (rear roofline,c-pillars and all the way down perimeter)
However that must not be the case even on my boxy 94 protege!

If the spoiler/kamm thing would extend futher back to the point where the cutoff point will provide a smaller cross section than the original cross section of the trunk/tail area,AND it did that while flow is still attached,then it would help reducing drag but now I'm talking about a boattail.

I think the sides and top of the kamm does not let air to spill in behind the c-pillars/rear widshield and it does not continue long enough to get the small tail cross section to occur like a partial boattail would, therefore increasing the size of the wake.
All I'm saying is that the aerodynamics on sedans (especially your car) is probably a lot better than we think.
A Kamm works on cars with the station wagon style chopped off rear but apparently not on sedans. Sorry man,I kinda went through the same thing.

[California98Civic]

Originally Posted by brucepick

The car has no cruise control so I just had to do my best to start each coast at the same speed. I attempted to pass a particular speed limit sign at 40 mph, simultaneously putting the clutch in and going into a coast. I recorded the speed at start of coast at the same location each time, and recorded the end speed as I later crossed the same road each time, after about a half mile coast.

Northbound test runs, with spoiler:
START - - - END - - DELTA (MPH)
41.3 - - - - 33.8 - - 7.5
40.0 - - - - 32.4 - - 7.6

Northbound test runs, without spoiler:
START - - - END - - DELTA (MPH)
38.3 - - - - 32.9 - - 5.4
40.7 - - - - 35.5 - - 5.2
40.9 - - - - 34.8 - - 6.1

That's disappointing alright, but I don't think it tells you much, at this speed, with only an "A" and a "B" run. Still, maybe you are making eddies worse right now. Here is what the tail of our car looks like with tufts pasted into a light mist of water at abt 45mph:



I'm thinking you could taper the sides more to reduce the eddies and smooth-out the down-wash coming from the roof and c-pillars. I wonder what of the aerocivic's dimensions you could just imitate:

Originally Posted by brucepick

Next time I have an opportunity to test the spoiler I'll attach it with 3M's no-residue heavy duty duct tape and take it on the interstate. I found two places where I should be able to do a decent high speed coast.

I think you need more complete testing too. Get as many runs as possible, not just ABA at higher speeds.

I feel you on the officer, and on the frustrated disappointment. I experienced the same process, as you no doubt recall. You'll improve my failure quite a lot if you get a cleaner and better designed shape that I managed.

[brucepick]

3dplane,
Thanks for posting that.

I'm not sure yet what went wrong with my spoiler. I suspect one or both of these are causing problems:

1) The side fins are causing turbulence, more than the intended benefit. They are supposed to help keep the air in the cavity above the spoiler panel. Very possibly their turbulence is defeating that gain, if they pressurize the cavity at all.

2) Even if I trim the fins down or eliminate them completely, it will still be a project with sharp angled edges. Supposedly not a good thing. The designs I've seen mostly start up front with a rounded rectangular cross section, and as the boat tail extends rearward the cross section becomes more like a circle or oval.