Rear Wing

[Cattrax]

I may be getting a little ahead of myself (car is go-kart stage) but I want to build a rear wing for trackday use. To keep it simple I plan to use a straight (not twisted) section and mount it fairly high. There may be a little advantage to a twisted wing at moderate mounting height but the rear of the GTM greenhouse slopes so gently I think a high straight wing will serve my purpose. I am currently considering an E423 airfoil profile. It has good lift (downforce) to drag ratios and the angle of attack is fairly forgiving. It is popular in motorsports. The plan is to lay it up in fiberglass or fiberglass/carbon fiber mix over a foam core. I have most of the equipment (vacuum pump, gauge, degassing pot, etc) to vacuum bag or vacuum infuse it. The processes look do-able.

Any words of wisdom? Have you tried it? Length will be car width. Recommended width? 12"? 18"?

Thanks for any help.

[mikeinatlanta]

I would skip the vacuum infusion and go with a standard wet layup and bag it. Would also skip the carbon.

[crash]

I build wings for racing purposes, and have found that an aluminum internal structure is required. Mine are out of fiberglass for economy and typically run up to 150 MPH without issue. Every wing is specific to the application and there are a lot to them. Upright mounts are pretty critical and must be very strong. Hence the internal aluminum structure. They may look simple, but get complex in a hurry. The APR wings I have found, seem to be really good "bang for the buck". If I was wanting a simple, single element, mid speed wing, I would talk to APR.

[mikeinatlanta]

Agree with crash. Rule one in composites is to never build what you can buy. Unless you just want the satisfaction of doing it yourself, you are guaranteed to spend more building one than buying one, especially if you place any value on your time.

If you insist on fabricating one, I would suggest buying a prefabbed foam core. Cutting a quality core isn't as easy as it looks. Once you get the core, you can beef it up with a carbon and glass spar, then coat the whole things with three layers of 181 E-glass.

[Cattrax]

Thanks for the replies Crash and Mike.
I am sure APR makes good products but... There 3D wings have a 10 degree twist. This seems a little much for a wing mounted at any significant height on the GTM. The specs on their straight wings read: "71" long, lots of downforce, low drag, $1500". The price is right and perhaps if I called them I could find out what profile they are using and the chord length. I would understand if they said the profile was proprietary. If building a wing appears to be too much of a hassle I may give them a call.
Flying Foam has a good selection of 2pcf foam profiles including the E423. The maximum length available is 60" but I assume I will need to add stiffeners at the mounts anyway thus 3 short pieces will work. Any recommendations on chord length for trackday use? I may look around for a Viper ACR at the next trackday and do some measuring.
Thanks again.
Ken

[mikeinatlanta]

Any recommendations on chord length for trackday use? I may look around for a Viper ACR at the next trackday and do some measuring.
Thanks again.
Ken
Nobody can know the answer to this question without knowing and testing your exact combination. I suggest going with what looks good to you and adjust as needed. Having no practical knowledge of GTM aero, I expect any decent and properly placed wing would produce more than enough downforce that front/rear balance at speed will be an issue on a street car lacking proper front aero.

[VRaptor SpeedWorks, LLC]

The specs on their straight wings read: "71" long, lots of downforce, low drag, $1500".
Ken

If you go to this page:

http://aprperformance.com/racing-product/gt-250-adjustable-wing/

About half way down the page there is a red button you can click next to where it says "CFD Data....." that should tell you about everything you need to know.....

BTW, if you do decide to go with an APR wing, I can probably get you some good pricing on it. :D And I do have wing stands here in stock for the GT250 wing for use with my Universal Wing Mount system.

[Presto51]

Just a suggestion:

Read the thread http://thefactoryfiveforum.com/showthread.php?6157-GTM-roll-cage-modifications-and-race-car-build-log

And reach out to John, I think he can help answer some of your questions on set ups and aero development.

Ron

[kabacj]

Hey Ken

I've used both the Gt 250 and the Gt 1000 from apr.

The 1000 makes way more downforce. That's a technical analysis BTW. Haha.

Seriously the 1000 makes more downforce than you can balance out unless you take some extreme measures. (I'm working on that)

More power to you regarding making your own wing , but my highly technical seat of the pants analysis says that more than 500 lbs or so is too much unless you make corresponding changes up front. So If you plan on going big realize that you will need downforce up front too.

All that said both I and team PDG pull 2 Gs in the corners without anything crazy.

Good luck on the project. Looking fwd to see what you develop.

John

[Cattrax]

Ron,

I was hoping John would pipe up. His thread is the first one I look at to see if there are any updates. He has done great work. I will try to search his thread for wing info. Yep, APR double element wing shows up.

Ken