Notchback Rear Aero / Big Wing

[Series8217]

I'm going to a track day on the Roval course at Auto Club Speedway in Fontana next weekend, so I am rushing to implement a rear aero solution that adds downforce and aerodynamic stability (by moving the center of pressure toward the rear).

I purchased a Nascar Car of Tomorrow (COT) wing from Ebay. This is a 54" carbon fiber wing from Crawford Composites. They were $3000 new, but can be found secondhand for $500 to $1000. The wing uses the LNV109A airfoil. NASCAR stopped using these and switched back to spoilers because these wings generated a large amount of lift when traveling backwards (i.e. during a spin) which increased the probability of cars going airborne (1).

This type of airfoil is extremely well performing but is sensitive to imperfections in the surface (2). Luckily mine doesn't have any rock chips that I could find. We'll see how long it lasts..

There are two wings available -- one was used on show cars only, and is not really a structural part. Don't buy one of these. You can tell if it's a real race wing because it has CNC machined aluminum ends (you can see this with the endplates off), and 6 fasteners hold each of the mounts on. There are only 4 on the show wings. I think the show wings also don't have a slot for the gurney flap.

Carbon fiber endplates are available in two different configurations: curved and straight. The curves ones are aerofoils set up to pull toward the left. Duh, NASCAR! They also include a 1" aerofoil extension on each side, giving a total wing span of 56". The straight endlplates are not aerofoils themselves, but they do still have the 1" extensions. I don't have these right now, so I'm stuck with some aluminum endplates that the previous owner made.

The mounting plates are about 38" apart. This coincidentally lines them up perfectly with the end of the bumper crush structure on the 87/88 Coupe/Formula rear bumper.

I finished the steel bumper adapter brackets last week:











I mocked up the wing position on some perforated angle steel, and played around with some cardboard mockups for the upright shape.

This is one of the early mockups:



The wing is as far forward as possible without interfering with the opening of the decklid. The decklid misses it by 1/8". I could lower the wing but then it would have to go even further back. It's currently 11" above the decklid if I remember correctly. It's just slightly higher than the roof.

I settled on a design for the uprights but I'm not super happy with it. I'll finish them off and see how it looks; I can always make new ones later. I need to get this project done in the next couple days so I don't have time to be picky about the design. I cut the uprights from 3/8" 6061-T6 aluminum. I still need to drill the holes and trim them a bit -- hopefully I'll have that done in the next couple days, but I want to finish my harness bar first. I bent the tubing today and cut 4 of the 6 brackets, so I should be able to knock that out tomorrow.

The reason I mounted it so far back and high is to improve the chance of it ending up in relatively clean airflow.

Once I have finished my smorgasbord of projects, I'll get tape some yarn to the rear clip and see what it's actually doing.

[The Dark Side of Will]

I purchased a Nascar Car of Tomorrow (COT) wing from Ebay.

The wing uses the LNV109A airfoil.

The reason I mounted it so far back and high is to improve the chance of it ending up in relatively clean airflow.

"Any time you can raid a NASCAR parts bin, do it." - from that shock comparison article. NASCAR has some serious stuff. The mechanical analysis that goes into making a pushrod valvetrain stable and durable at 9000 RPM is pretty tough.

Getting the wing out of the dirty airflow coming off the vertical rear window will be the tough part.

Have you seen this? http://fierofiberglass.com/Product%20Pa ... hback.html
I've heard the quality and fit are not very good, but it could be a starting point. You could set it up so that it's easily swapped for the stock decklid; then you just swap it on for track days.

Do you work with a brake and laser or water jet cutter?

[ericjon262]

I purchased a Nascar Car of Tomorrow (COT) wing from Ebay.

The wing uses the LNV109A airfoil.

The reason I mounted it so far back and high is to improve the chance of it ending up in relatively clean airflow.

"Any time you can raid a NASCAR parts bin, do it." - from that shock comparison article. NASCAR has some serious stuff. The mechanical analysis that goes into making a pushrod valvetrain stable and durable at 9000 RPM is pretty tough.

Getting the wing out of the dirty airflow coming off the vertical rear window will be the tough part.

Have you seen this? http://fierofiberglass.com/Product%20Pa ... hback.html
I've heard the quality and fit are not very good, but it could be a starting point. You could set it up so that it's easily swapped for the stock decklid; then you just swap it on for track days.

Do you work with a brake and laser or water jet cutter?

unfortunately, those hatches are for gt's and won't fit the notchbacks. not impossible to make one, but it would be a major undertaking.

[Series8217]

I purchased a Nascar Car of Tomorrow (COT) wing from Ebay.

The wing uses the LNV109A airfoil.

The reason I mounted it so far back and high is to improve the chance of it ending up in relatively clean airflow.

Do you work with a brake and laser or water jet cutter?

I made these with a band saw and a vice.

I have a sheet metal guy that laser cuts and bends and would do these for cheap but these are the prototypes.

[Series8217]

"Any time you can raid a NASCAR parts bin, do it." - from that shock comparison article. NASCAR has some serious stuff. The mechanical analysis that goes into making a pushrod valvetrain stable and durable at 9000 RPM is pretty tough.

Getting the wing out of the dirty airflow coming off the vertical rear window will be the tough part.

I'll go into this more in my post-trackday analytical update, but the curved edge at the back of the notchback roof (the fastback roof has a sharper trailing edge) contributes to filling the rear notch area with turbulent air. If the edge is sharpened and straightened to allow clean flow separation this could improve the performance of the wing, and possibly also help suck more air from the decklid vents to improve engine bay ventilation and the effectiveness of the front splitter (by drawing more air from under the car and thus increasing underbody airflow velocity). However it may also contribute to rear lift generation. Such a modification would also greatly increase the size of the wake (more drag) which may be why GM didn't make the clean break in production. I wish I had a high resolution 3D model of the notchback Fiero to do some CFD on that.

[Series8217]

Finished shaping and painting the uprights and mounted everything last night.

With force applied by hand, the bumper beam is deflecting more than I'd like (but the 3/8" 4130 steel brackets I made are sturdy) so I'm going to add some reinforcements tonight. The top of the brackets are attached to the relatively thin sheet metal of the bumper beam, which is unsupported on the front edge. I think I can just need tie that edge into the frame or box the beam to make it sturdy enough.

[Shaun41178(2)]

found these don't know what program was used or if accurate

[Series8217]

Ooh, very interesting! Thanks!

Looks like my wing might actually be high enough and far enough back to be in pretty clean airflow.

[AkursedX]

Would some Airtabs on the edge of the roofline help smooth out the airflow??

[The Dark Side of Will]

The Evo doesn't have a very steep angle on the rear glass, but still uses Vortex generators.

[Series8217]

Would some Airtabs on the edge of the roofline help smooth out the airflow??

No, that's not what those are for. Vortex generators impart additional energy into the boundary layer to delay flow separation. Here's a basic primer from AutoSpeed: http://www.autospeed.com/A_3058/cms/article.html

On the notchback Fiero, the body ends past the roofline, so flow separation is going to occur no matter what. The air can't make a 90 degree turn, remain attached to the rear window, then make another 90 degree turn and remain attached to the decklid.

We can, with minor modifications to the trailing edge of the roof, determine whether the air separates cleanly, or breaks off with a lot of turbulence and fills the wake a bit (as it does stock).

The Evo doesn't have a very steep angle on the rear glass, but still uses Vortex generators.

Autospeed ran an article about how Mitsubishi developed the vortex generators for the Evo: http://www.autospeed.com/A_3059/cms/article.html

[Series8217]

Looking at this again, I don't think that model is meshed correctly (if the wireframe by the roof is showing the mesh used in the calculations). In fact, since there isn't a lot of detail at the rear roof edge (which I think is important) it may be modelling the case where there's a sharp trailing edge.

It also could be that the trailing edge doesn't matter because the boundary layer is thick enough back there that the shape isn't all that important.

[Series8217]

Some pics I took while in pre-grid at Auto Club Speedway over the weekend:

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[Series8217]

Photographer's pics... (CaliPhotography)

Fuck yeah.

Some awesome shots by CaliPhotography:

Finish Line - NIC_7100-08-03.jpg (131.97 KiB) Viewed 6816 times

[The Dark Side of Will]

Awesome!

[CincinnatiFiero]

Car looks great!

[Series8217]

Thanks

All the low angles make it so you can't see how bad the paint is on the top of the car...

[CincinnatiFiero]

Who cares? You've got serious aero and putting it to serious use that more than 99.99999% of any car owner can say, let alone fieros.

[Series8217]

Finally replacing my wing stand prototypes with some good looking parts I created in Solidworks.

The new wing stand design:


The new stand integrates the adjustment holes so I won't have to use the bulky, ugly separate brackets anymore.

Also new adjustable endplates:


I got the wing endplates from the laser cutter already and the wing stands from the water jet vendor. I routed an aerodynamic profile into the stands with my table router and a template routing bit. I need to sand and paint them. I'm also thinking about milling some nicely profiled pockets into the stands to reduce the weight a bit. They're ~4 lbs each right now, but there's a lot of extra material in the middle for cosmetic purposes only.

This is a render of the parts on the car:

[The Dark Side of Will]

and the wing stands from the water jet vendor.

I'm also thinking about milling some nicely profiled pockets into the stands to reduce the weight a bit. They're ~4 lbs each right now, but there's a lot of extra material in the middle for cosmetic purposes only.

Steel?

Feature creep... should have had the water jet guy do the weight relief