Rear decklid spoiler: design discussion

[mpg_numbers_guy]

Besides length, my guess would be that the sides weren't helping due to not being right at the edge of the car for obvious legal reasons, and the bottom should probably continue straight back from the end of an underbody panel (it may already have been doing that, it's just hard to see from the photo if such was the case).

Vortex generators are quite debatable as to whether they improve or hurt fuel economy, but this article talks about someone fixing a similar detached airflow spot on the rear window and trunk lid of his Mercedes. Might go for an interesting ABA test.

Originally Posted by 19bonestock88

I’m getting to where I wanna redo it though,(though I am thoroughly in love with the look) I shoulda chose some better coroplast, taken more time with my cuts, made my underside supports more carefully...

What do you use to cut coroplast? Unless it's straight lines, I find it pretty hard to get a "perfect" cut on coroplast, no matter what I use. I haven't tried a jigsaw yet though lol..

[California98Civic]

Had a fail with the spoiler prject Thursday/Friday. Expanding foam in a wax paper and cardboard mold had expected difficulty curing but had unexpected difficulty filling the entire void and therefore picking up the full civic trunklid body contour. Bummer. Gonna make an easily removable cardboard version for coast-down testing and dust trails at El Mirage tomorrow.

[Snax]

My thought is that generally a box cavity is a way to simulate the boattail. In effect, the angle of departure for the flow to the trailing edge of the cavity members should not exceed what would remain attached with an actual boattail design, and research has shown that to be an effective design parameter.

[California98Civic]

Originally Posted by Snax

My thought is that generally a box cavity is a way to simulate the boattail. In effect, the angle of departure for the flow to the trailing edge of the cavity members should not exceed what would remain attached with an actual boattail design, and research has shown that to be an effective design parameter.

I understand your claim, but don't really follow that linked article's argument. I am not saying it is wrong. I am saying it is beyond my training. Lemme ask you to comment on the test I did, based on this thread: https://ecomodder.com/forum/showthre...tml#post602571

[Snax]

Just working off my own intuition myself, but I think the reason boxing it had minimal effect over the simple spoiler could be viewed in terms of area. I.e., there is a lot more potentially turbulent air coming off the top of the car vs. the sides. I think that changes as proportions shift with more vertical design areas such as with station wagons and trucks.

[California98Civic]

Originally Posted by Snax

Just working off my own intuition myself, but I think the reason boxing it had minimal effect over the simple spoiler could be viewed in terms of area. I.e., there is a lot more potentially turbulent air coming off the top of the car vs. the sides. I think that changes as proportions shift with more vertical design areas such as with station wagons and trucks.

I just took the whole thing off. It got wet in unexpected rain and even with black paint it warped a bit and it became hard to imagine it was working great. Nonetheless, my average to work was quite a bit lower.

I am going to rebuild and I think I will go with a fiberglass over cardboard build.

[Piotrsko]

I suggest pink house insulation in 1/2" thicknesses. Or Styrofoam since both shape easily.

Dollar tree has 1/4 thick paper wraped foamboard for a buck a sheet that I use for electric model airplanes.

[Snax]

Alumalite signboard material is also a more permanent option that could look nice. I haven't worked with it myself though. Kinda wondering if it wouldn't work out to make some single-sheeted panels as well with coroplast. Don't ask me what it takes to bond polystyrene (polypropylene?) to aluminum though . .

[Shaneajanderson]

Originally Posted by Snax

Alumalite signboard material is also a more permanent option that could look nice. I haven't worked with it myself though. Kinda wondering if it wouldn't work out to make some single-sheeted panels as well with coroplast. Don't ask me what it takes to bond polystyrene (polypropylene?) to aluminum though . .

Prime the aluminum with self etching primer, and use foam safe sikaflex (221?). The stuff is fairly easy to work with but once cured there's no getting it off. It cleans up when wet with plain water too, so that's nice, but it dries quickly.

[California98Civic]

Considering a 6mm high 4'×8' sheet of black polymetal and 3mm high or 4mm high neodymium magnets with countersunk holes in them. Washers, counter sink screws, nuts, and some sort of plastic or rubber insulator for the paint/magnet contact area would complete the kit. Would make underside supports from scrap because turnbuckles seem too heavy and conspicuously like a racecar. People already mistake Black & Green for a drift car (lol).

I could use a hole saw to set the magnets into the polymetal so the sheet is flush with the decklid. Thoughts?