Bolt-on Rear Wing
 

I am working on making a rear wing element that is attached via the rear tow hook mounts. My models show it being able to supply up to 300lbs of down force. It is fiberglass with a cord length of a foot, 69" in length, and the entire assembly should weigh less than 40lbs. I am wondering if this is something viable for autocross, and if so what class would it be allowed in. I am wanting to make changes to make sure that it will fit in a class.

I am planning on offering it in the normal and a controlled version. The controlled version has electric actuators that will control the angle of attack to apply force when you want it to on the track.
http://imgur.com/a/wRHQI

Here are pictures of it on the car:
http://imgur.com/a/I3nNd

300 lbs at what speed?

How is it gonna stay on?

That's at optimal angle of attack @ 100mph, with optimal airflow. It will never get this high. I also assume that the wing will have to shrink in size. It will stay on with the risers that will be built from aluminum honeycomb to reduce weight and still take the down-force.

Most popular autox classes for the twins are C Stock and STX. Both don't allow for aftermarket wings. Furthermore, most autox tracks don't exceed 2nd gear ~60mph. Not sure how effective/practical your wing is for autox consumers. Probably have better luck marketing to the track guys and or hard parkers.

I know that it will rarely see 100mph, but down-force is usefull accelerating out of corners and the like. I wanted it to be bolt-on for track days so my car won't look like rice the rest of the time. The price point, hopefully just under $1k was also geared towards function at the track.

I'm a mechanical engineer and I hate seeing the stupid wings and all in carbon fiber. This is a functional E423 airfoil design that works well at low speeds. I know it won't fit the standard stock-esque classes, but was hoping there was a "fun" class with some rules.

I was under the impression that in the STX class the wing had to be within the width dimensions of the car, in this case 69." Is there a limit on the height or how far back it sits?

No aftermarket wings in stx period. Hell, an frs with a brz wing isnt even legal.

Ok. Then what is the most common class that allows an aftermarket wing and what are the rules pertaining to it?

SM will allow depending on dimensions. E mod, for the hardcore, has hardly any restrictions

I like the idea. I'd be interested in more details

I found these rules in regards to street mod category, on a 2009 post.

L. Wings may be added, removed, or modified. Nonstandard
wings may only be attached to the rear deck/hatch area and may
not extend more than six inches beyond the widest part of the
bodywork on either side. The total area when viewed from the
top of the airfoil sections of all wings shall not exceed 15 square
feet. The area shall be computed by multiplying the width and
depth of the wing without regard to the curvature of the wing.
Any airfoil shadowed by another airfoil with more than six
inches between them will have its own projected area added to
the wing area calculation. There is no limit on number of elements.

This wing is only 5.75 square feet by those rules.

I am having a hard time finding current information like this in regards to the classes. If anyone here can help me I would greatly appreciate it.

Also, does the 6" rule apply to the the height of the wing from the top of the roof?

It looks like it'd snap off

2013 and draft 2014 rule book links. Allowed mods start somewhere around page 70 I think. Check the ToC

http://www.scca.com/solo/content.cfm?cid=44517

In Section 16. L for Street Modified it states:

Non-OE wings may only be attached to the rear deck/hatch area behind
the center-line of the rear axle.

Wings, and any component thereof, may not extend beyond the vehicle width, as defined by the outermost portion of the vehicle doors, less mirrors, door handles, rub strips, and trim. In addition, no portion of the wing or its components may be more than 6” forward of the rear axle, more than 0” beyond the rear most portion of the bodywork, or more than 6” above the roof line of the vehicle, regardless of body style. For convertibles and roadsters, the highest portion of the windshield frame will be considered the highest portion of the roof; however, a convertible or roadster utilizing a hardtop will use the highest portion of the hardtop as the roof line.

I could, with difficulty, mount the wing farther forward to appease the second highlighted part, but if the mounting location is truly as strict as the first part states then this design would never fit into the modified category. Am I correct in this assumption?

That's how I read it.

I'd love an active wing for the track!

How would it engage?

I'm thinking it would be best to be full on all the time, unless throttle was down past half way, or something of that nature.

I've found that to be bad idea. Having the rear balance and downforce of a car change on throttle or brake application is a recipe for disaster.
For every instance where you put your foot down early, lift past your engagement point, or tap your brakes, you've introduced a new variable to compensate for.

Ask me how I know. -Arduino controlled wings are a bad idea on a racetrack!

Your wing design will introduce an unbelieveable amount of drag.

What are you using for CFD analysis?

Is the wing dedicated specifically toward this car? It seems you're using a pre-existing blade design. Why not tailor it specific to the FRS/BRZ body?

Probably a bad idea to have it controlled by throttle; such as opening up at 50% throttle, but I think push button to open the wing slot and at the time the brake is applied for the wing slot to close is fine (DRS anyone?)

I'm more concerned with the fence plate shapes you have on the diffuser design...which has bothered me ever time I've seen those images. Why unnecessarily slow the air down and increase pressure (which is the opposite of what a diffuser is designed to do)?

The diffuser doesn't look like that anymore. The first picture on the second set has the verticals flat now, but that is a different project.

Unless someone else knows of a loophole or a hidden rule, I don't think this wing will fit into any SCCA classes because of the mounting location. So I'm just going to build it for fun.

phastafrican; The control system is going to be an option I've built with my own custom custom non-arduino system that uses latter logic. It will have brake pedal, gas pedal, and G-senor inputs, and much more user friendly than arduino. Again it will be an option to the fixed position wing.

CSG Mike; The CD/CL is .0136 at optimal angle. This is very low. The aerfoil design is very similar to most "GT" style wings. I think most of the wings on the market are pretty crap and overpriced. They are more for show than function.

It's very easy to get a high drag/downforce ratio in free-flowing air over just a blade.

What have you modeled this in to get your data? Without data, it's just another generic wing.


Since you haven't picked up on it, this is why I'm questioning you: your mounting solution introduces more drag than the wing will ever make, even at maximum AoA at the verge of stalling. I don't need to do any CFD to know that, simply due to the design.

Simply put, wings are not allowed for SOLO II competition with production cars (even in Modified class), spoilers are what's allowed...

CSG Mike; The data is from table sets for the wing profile. It is a well documented profile and I did the calculations for a reynolds number of 100,000 and Ncrit=9, for sea level air. This gives a maximum Cl/Cd of 156.5 @ 6.25 degrees. This does not take into account the mounting solution and I understand it will have a constant drag coefficient that I have yet to calculate.

Sounds like you're committed to testing this out. Looking forward to the results. It's not a novel idea, but your approach appears innovative.

What kind of CL is the wing making at that angle, and does your calculation of drag include induced drag? That sounds unbelievably high for the aspect ratio and profile shown...

It does take into account induced drag. The optimum angle for down-force is around 13 degrees and the induced drag almost doubles the drag because of it. CL @ 12.5 degrees = 2.0391.

These numbers are optimal and with perfect, laminar airflow. The conditions will be much less optimal on the car, but It's good to start with a nice optimal design to get a better real world one.

This sounds like you are getting a head of yourself. Are you pulling these Cl and Cd numbers from a table? Also you state that these numbers are optimal with perfect laminar airflow. You know that most cars start to transition to turbulent flow at around 60mph. The airflow will not be laminar on this wing at 100mph. I bet that wing stalls at 13 degrees.

A wing will work very different on the back of a car than in free stream air. I have done extensive work with this using cfd. If you want some help with this, let me know. My background is an engineer specializing in fluid flow and heat transfer.

As I have stated before. I know that there is turbulence, I know that these numbers are optimal. I know it will never hit these numbers.

This thread was started in an attempt to understand if this was applicable to autocross. I am still engineering the design and was trying to make sure the form fit before I did "get ahead of myself"

No it isn't applicable in autocross then is the answer. You would have to have a huge multi-element rear wing and something crazy in the front to balance it out. I would look to FSAE cars to get an idea.

Sorry, free flowing data has zero use on a car. It's anecdotal at best. The air flowing over the wing isn't smooth.

Seems you're just pulling existing numbers, not doing the modeling yourself.

Laminar vs turbulent shouldn't make much of a difference to the lift values (though it will change the drag), and turbulent airflow is actually more resistant to stalling than laminar is. I do agree though that freestream numbers don't mean a lot for a wing mounted on a car. I also agree that even if this wing can make 300lb of downforce at 100mph, it's pretty useless at autocross - that means that it's only making 75lb at 50mph, and 27lb at 30mph, both of which are much closer to the cornering speeds seen at a lot of autocross courses.

The rules change based on what specific class you are in, even for modified.

Wings are allowed in the Street Modified classes and X Prepared. But as noted the mounting for this would be illegal, the wings have to mount to the trunklid.

the other day i saw an s2k with the exact same design wing. It looked like a dirt track race car