Rear Wing for CSL Trunks

[C///M]

While I love the CSL trunk lid on a street car, I didn't plan to run one on a race car, but the recent E46 M3 I picked up to build into a w2w car already had a carbon CSL trunk on it that I figure I'll just keep.

At first I wanted to slot the trunk and have the mounts bolt to the rear frame in the trunk floor, but it's looking like that may be against my class rules; I still have to confirm.

That said, anyone familiar with wings that can mount to the CSL trunk lid? Jack Haberman's orange M3 that VAC built appears to have a nice setup so I'll probably reach out to them to ask.

Trying to find a high efficiency swan neck/top mount wing would be cool, but most of the BMW specific mounts call out not fitting the CSL trunk curvature.

Sent from my Pixel 6 Pro using Tapatalk

[Obioban]

https://euroconnex.co/products/wing-risers-for-csl-trunk

[C///M]

https://euroconnex.co/products/wing-...-for-csl-trunk

Thanks I've seen them. Unfortunately they appear to be much shorter than I'm aiming for.

Sent from my Pixel 6 Pro using Tapatalk

[bigjae46]

I could be wrong but I think the regular trunk lid is better with a wing. The airflow across the underside is the most important for downforce which is why you would go with a swan neck. The duckbill on the CSL trunk could cause some high pressure interaction with the low pressure under and behind the wing which negates the efficiency of the wing.

[C///M]

I could be wrong but I think the regular trunk lid is better with a wing. The airflow across the underside is the most important for downforce which is why you would go with a swan neck. The duckbill on the CSL trunk could cause some high pressure interaction with the low pressure under and behind the wing which negates the efficiency of the wing.

I'm certainly no expert, but ducktail spoilers are supposed to create vortices along the rear glass and trunk lid that pushes the air off the car and causes it to flow more smoothly over the rear of the car. This is generally why high wings are more efficient so they get smooth airflow higher above the car.

So according to the basics, trunk spoilers should allow a wing to be more efficient, not less.

That said, the size of the spoiler and height of the wing would be important when working together. Not exactly the kind of thing you can really figure out without a wind tunnel.

I wouldn't think the trunk lid style would matter much with a high enough wing. All that said, this is only based on the reading I've done; I'm not in the field nor do I have a physics education.

Sent from my Pixel 6 Pro using Tapatalk

[bigjae46]

I'm certainly no expert, but ducktail spoilers are supposed to create vortices along the rear glass and trunk lid that pushes the air off the car and causes it to flow more smoothly over the rear of the car. This is generally why high wings are more efficient so they get smooth airflow higher above the car.

So according to the basics, trunk spoilers should allow a wing to be more efficient, not less.

That said, the size of the spoiler and height of the wing would be important when working together. Not exactly the kind of thing you can really figure out without a wind tunnel.

I wouldn't think the trunk lid style would matter much with a high enough wing. All that said, this is only based on the reading I've done; I'm not in the field nor do I have a physics education.

Sent from my Pixel 6 Pro using Tapatalk

The underside flow creates a lot more downforce than the flow over the top of the wing. The underside is the low pressure side and interacts with the flow off the rear window, top of the trunk lid and if the wing is setback far enough it will interact with the recirculation bubbles coming off the rear of the car.

Raising the wing increases downforce because the low pressure underside of the wing has less interaction with high pressure flows coming off the rear window to a point. If you have a flat wing, the pressure differential between the top and bottom sides become higher at the edges as you raise the wing. This will cause more drag and different pressures across the wing. In most cases if the wing is still getting airflow off the car then it will have a more consistent pressure across the wing so you get a better lift to drag ratio.

With a flat wing, you will generally not want the wing in free air. It should be designed to interact with the airflows off the car. Also if the wing is setback far enough, you can improve extraction from the rear diffuser.

You'd have to test the air pressure on the bootlid but I would suspect that the duckbill generates high pressure on the duckbill which adds downforce. But the low pressure region under the wing will interact with that high pressure region and cancel each other out. Air flows increase as pressure drops. So the duck bill could improve air extraction over the car but I think it has more to do with the air flow behind the car.

The result will probably be less overall downforce with a bump in drag. Probably won't be significant.

[TeddybearCup]

At the wing height you're aiming for, I would expect the lid shape to be inconsequential. I run a 9livesracing wing on a 370Z and I have a spoiler on the car. The wing makes a lot of downforce even at 0 degrees. I have a large splitter with the large professionalawesome ramps to sorta balance it out (wing still does more IMO).

I'm in the same boat, though I have a cheap CF CSL style trunk and I don't trust it holding up to downforce from a good wing with normal mounts. I can design mounts for a shop to CNC and use with flat cut uprights. Let me know if you have the desire for that route. CNCing wouldn't be cheap.
You could then easily make uprights from the trunk mount to the wing itself.
Personally, I'd print mounts because I trust my prints to handle hundreds of pounds of force, but I realize most people view printed pieces with more skepticism than I do, having not handled prints designed and printed with strength in mind.

Outside of a large and contoured mount, most people would just chassis mount with a carbon hatch or trunk, unless you have a trunk reinforced specifically for aero loads.