Rear spoiler fabrication? Any tips?

[beeman]

I think my GTM is asking for a rear spoiler. That is going to be "Plan A" for me. "Plan B" will be a wing, only if "Plan A" fails.
My primary goal is function. I like the idea of low-drag downforce that is easily adjustable. If I buy a wing, APR will be the baseline and work up from there. I don't want anything folding in half at 150+ mph.
The biggest issue for fabricating a spoiler for the GTM is the shape of the rear deck, it would be much easier if it was a flat surface across the upper rear bodywork. I don't mind fabricating a subframe to support the stress on the bodywork.
My ideal solution is an adjustable "wickerbill" type spoiler that can be raised or lowered for different driving situations.

I especially like the C7 Z06 adjustable wickerbill concept.

98588

Here's a similar idea that I found from a racing simulator.

98589

I know tucker298 was working on a spoiler. I really like his design so far, I don't know how far he has gotten on it.
This flat cardboard mockup is very close to what I'm looking to do:
98590

I would love to hear any tips on making something like these work on the GTM rear. Thanks!

[Roger Reid]

Interesting article. https://www.quora.com/What-is-the-purpose-of-a-spoiler-on-the-back-of-a-car

"Spoilers do this job for the car. Their job starts at ~70-80 mph. When the car moves at that speed, the spoilers disrupt (or 'spoil') rapid flow of the air flowing above and below the car, creating wakes behind the car, so that the pressure drag is reduced."

So according to the article spoilers reduce drag leaving diffusers and wings for down force.

[beeman]

In a traditional sense, I consider a spoiler to be a flat (non-airfoil) surface in continuity with the rear bodywork of a car. They are usually used to create downforce, and the drag penalties of the increased frontal area of the device are significantly offset by the decreased negative pressure that they create behind the car. In drag racers, the spoiler is essentially horizontal as they aren't so concerned about rear downforce but want the decreased drag the spoiler causes.

98621

The article you referenced seems to be referring to more modern 'wing' type devices as it states "A spoiler is fundamentally an inverted aircraft wing." but much of the conclusions he draws are accurate.

[Shoeless]

In the article where Ashish started down the road of fluid dynamics, he is pretty spot on, but when he states the following, he totally lost me.

"Spoilers do this job for the car. Their job starts at ~70-80 mph. When the car moves at that speed, the spoilers disrupt (or 'spoil') rapid flow of the air flowing above and below the car, creating wakes behind the car, so that the pressure drag is reduced."

"Spoilers" that are placed on the body of the vehicle and not in the wing area of what I would consider where the wing that APR has available for the GTM, disrupt laminar fluid flow over the surface of the vehicle and may or may not change the fluid dynamics behind the vehicle. When you disrupt laminar flow over a surface you create drag.

The device that Dave shows is more along the lines of continuing the laminar flow across the back of the vehicle to move the drag force that is created by the boundary layer separation (drag) further back away from the car effectively reducing drag.

I guess my Aerospace Engineering background as snuck into this conversation :cool: I still wish I could share pics or even info on the additive manufacturing stuff I'm doing in the aerospace realm these days. Damn ITAR requirements LOL

[beeman]

I highly recommend the book:
Simon McBeath
Competition Car Aerodynamics, 3rd Edition

It is full of amazing data like this, ie the car body creates rear lift with no spoiler, but with a spoiler there is 330lbs (at a cost of only 27lbs drag) to 556lbs downforce with the cfd analysis of 2 spoilers:

https://s15.directupload.net/images/181205/t2y7otmq.jpg

[Shoeless]

That looks like a book I’d really enjoy.

[Cobra 61]

we had a custom wing made from APR and not the one recommended by FFR. I like the looks of it. Earlier versions seem to be in dirty air as being installed to low. We did experiment with wing height to find that balance of effect vs drag. The spoiler ideas and presentation don't seem to have that "exotic look" I did see some work like that on a gto 250 using clear lexan and it actually didn't look that intrusive on a 50 million dollar car! I think it does look a little out of place on the GTM

[Presto51]

To me aero is one of those "Black Art" studies, that the more I learn about it the less I know.

What you think looks like an obvious solution some designer comes along and places another chapter in the book.

Example, the Jaguar XJ220. The designer was quoted as saying the he had to design the car with looks and function in mind, so everything on the 220 worked together to reach the magic speed of 220 mph. They got close, 217 top speed on the Ring. :rolleyes:

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