SCCAForums.com

Other than fabing yourself, where can you find some of the large multi element wings in Sm and SM2?

 

How fast do you want to go?  OOPS, I meant how much do you want to spend.

Several links below to get you started.

 http://www.aprperformance.com/index.php?option=com_content&task=view&id=40&Itemid=44

http://www.pennon.com/  

http://www.djracecars.com/carbon-fibre-wings-and-aerofoils.asp 

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Chris
51 SM2

Thanks Glen. :)  I've supplied various APR wing packages to fellow SCCA competitors, including the large SM/2/XP set-ups.

The CF dual elements are only available in 55", and the insert strength is not as secure vs. the aluminum element versions. CF is popular with STS/X/U racers, partially for bling and maybe a couple of pounds less wt. The GT-II models in CF and aluminum versions are ST legal, size wise.

The large SM dual element wing package is 61" wide, with 7.5" width aluminum elements. Cost is very reasonable.

Let me know if you're interested in the complete SM package specs.PM for racer pricing.

Thanks,

Rick 

 

I agree the APR wings are the best bang for the buck, that's what I have  I went with just the standard GT-II sizing, remember it's all about balance, you have to have something out front to balance out the rear downforce.   In a little bitty Miata, I think the GT-II is enough.     

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Chris
51 SM2

Has anyone been able to measure the downforce of their rear wings at a variety of speeds?  Or have the manufacturers sent a spec sheet indicating what kind of general performance should be expected?

Cheers!
 

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Julia Aebersold
97 SM
97 Supra Turbo

You can get an "estimate" with this program:

http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html

Input width, chord, camber, angle of attack, wind (vehicle) speed. It will give you a very rough estimate. Your real life numbers will be lower, but the relationship of speed vs. downforce will hold pretty true.

EVOlutionary

 

Thanx for the link.  My husband pointed that out to me a while back and I just haven't had a chance to play with it. 

 
This is probably pushing the geek limit, but I am thinking of placing foil strain gages (1/2 wheastone bridge config) on the struts of the wing, integrate them into the data system and calculate load values.  I was wondering if anyone (especially A mod) has tried this approach.

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Julia Aebersold
97 SM
97 Supra Turbo

jaebers:

Thanx for the link.  My husband pointed that out to me a while back and I just haven't had a chance to play with it. 

 
This is probably pushing the geek limit, but I am thinking of placing foil strain gages (1/2 wheastone bridge config) on the struts of the wing, integrate them into the data system and calculate load values.  I was wondering if anyone (especially A mod) has tried this approach.

I'd think you would get a lot of/too much noise just from the weight/inertia of the wing as you went over bumps, took turns, jumped on and off the throttle, etc.  A SM2 car is relatively violent.  But if you could do it on a smooth straight public road, it might be worth something.

On a more practical note... more than likely, there are other things to be concerned about data logging before you start worrying about downforce values.  Things like throttle position, steering angle, suspension travel, would be higher on my list.  Using the old school method of putting a bunch of little pieces of yarn on the the wing and then driving at speed to see what the flow pattern looks like might be more useful for a baseline IF you really feel the need for such information.  Just make sure things aren't going super squirrelly.


 

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Jesse
-2002-2006 E-stock 93 MR2 (sold)
-2007-2008 XP Spyder

Hmmm.  I didn't take the noise into account.  I may be able to do some filtering and/or averaging to help ease the sudden hiccups in the data, but I like the approach of driving at speed on a smooth road.

You are correct on the practical note.  A DL-1 system with the accelerometer (multi-directional), throttle position, steering position, rpm, linear pots with video overlay is coming from Race-Technology as soon as the sensor cables are done.

This may be deviating from the thread a bit, but this will be my first time working with shock data and my initial approach is to adjust the things so that bump and rebound velocities are comparable to reduce any induced artificial yaw and/or pitch, while the car is transitioning.  I'm also wondering if FFT's would yield any good info, but I think the data is going to be too noisy.  I'm a bit clueless on how to get as much info as possible from this data.  Any words of wisdom or stories of past experience would be appreciated.

Julia
 

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Julia Aebersold
97 SM
97 Supra Turbo

If you're recording damper position (sounds like it with the mention of FFTs and shock velocity), there's an easier way to measure downforce.

 step 1) put the car on some scales.

step 2) put various weights over the rear axle, and record suspension positions and axle weights

step 3) repeat on the front... this will give you a good corelation between suspension position and wheel load.

 step 4) take the car to a drag strip, datalog speed and suspension position

now just use your smarts to correlate speed/suspension position/stiffness to calculate the lift coefficient.

 

Also, to those of you that are concerned about downforce at various speeds or 'low speed airfoils.'  I'm fairly confident that your Lift Coefficient is going to be pretty darn constant at anything under 100mph.  Hell... it should be pretty constant at anything under 300mph.

Also, the FFT data on shock speed can be pretty usefull for getting an idea where to put the elbow in the curve.  But in the end, after a lot of time mucking with FSAE, I've become a firm believer that while these things matter, there overall contribution to lap time is very small, but it is fun to geek out about.
 

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Jim Reyenga
-Certified National Hack and Car-Whore Extra-ordinare

ChrisSwearingen:

How fast do you want to go?  OOPS, I meant how much do you want to spend.

Several links below to get you started.

 http://www.aprperformance.com/index.php?option=com_content&task=view&id=40&Itemid=44

http://www.pennon.com/  

http://www.djracecars.com/carbon-fibre-wings-and-aerofoils.asp 

Also:

http://g-stream.com/C800.html 

 

Nice looking struts there for sure!

Here's a few numbers to throw out to everyone if that have not already seen them. I requested specific data from them and they sent me their wind tunnel test data at 80, 100, 120 MPH.

APR Wings:
GTC 500 Wing (This is their big 3D Parabolic wing)
     80 MPH generates 149LBs of Downforce with 27LBs of Drag
     100 MPH generates 230LBs of Downforce with 44LBs of Drag

GTC 300 Wing
     80 MPH generates 200LBs of Downforce with 30LBs of Drag
     100 MPH generates 317LBs of Downforce with 47LBs of Drag

On the foilsim program...
maxing out the various settings (-20 degrees, -25 camber, 8 square foot etc) at 60MPH will get you 391LBs of downforce, at 80MPH you get 696LBs of downforce.

I would bet APR's 60MPH numbers are not very good IMO. That's why we have been researching some other alternatives...

If anyone wants the Excel files for these two wings I'd be glad to email them to you. Shoot me a message at info@doubletimejazz.com with a subject line of APR Wings or something like that.

Good info, it's odd that the larger GT500 generates lower numbers?

The parabolic wings were designed for higher speed applications and don't generate near the downforce (or drag) that the dual element APR wings do. Which makes the large dual element wings more suited to AX speeds. 

Jreyenga:

If you're recording damper position (sounds like it with the mention of FFTs and shock velocity), there's an easier way to measure downforce.

 step 1) put the car on some scales.

step 2) put various weights over the rear axle, and record suspension positions and axle weights

step 3) repeat on the front... this will give you a good correlation between suspension position and wheel load.

 step 4) take the car to a drag strip, datalog speed and suspension position

now just use your smarts to correlate speed/suspension position/stiffness to calculate the lift coefficient.

 

Also, to those of you that are concerned about downforce at various speeds or 'low speed airfoils.'  I'm fairly confident that your Lift Coefficient is going to be pretty darn constant at anything under 100mph.  Hell... it should be pretty constant at anything under 300mph.

Also, the FFT data on shock speed can be pretty usefull for getting an idea where to put the elbow in the curve.  But in the end, after a lot of time mucking with FSAE, I've become a firm believer that while these things matter, their overall contribution to lap time is very small, but it is fun to geek out about.
 

 

Thank you for the input.  That way will be a lot easier than mounting gages to the wind struts, but I may "geek out" and put them on at a later time.   Once I get the system installed and get familiar with the software then I may ask more detailed questions once after I start putting the pieces together.   Okay, I'm dense........what do you mean by "put the elbow in the curve"?

Julia

 

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Julia Aebersold
97 SM
97 Supra Turbo

I wouldn't trust the numbers on Foilsim for high angles of attack.  Was that number for a single element?  I'll dig through my simulations when I get to work tomorrow to quote the numbers, but I don't recall them being that high.  I may or may not have spent a fair amount of time playing with the company's CFD to optimize a dual element wing (plausible deniability on the internet).  Any idea what the CL for that foilsim wing is? (I'm too lazy and had too many beers tonight to calculate it), but that number seems quite high.

The APR wings are a good value.  We intend to run them initially, but I obviously have a design I want to construct when the free time, energy, and money align for that project.  Custom wings are still pretty pricey if you do them yourself.  I expect to spend around $700 or more to build a composite wing doing all the design, engineering, and construction my self.

As for the 'elbow' on the shock dyno.  There is usually a blow-off from low-speed to high speed damping.  The FFT can give you an idea for what velocities constitutes track induced movement (generally high speed) and what velocities are from driver inputs.  But the guys at places like Koni know WAY more about that than I and can build you a pretty darn good damper without any of that information.

 

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Jim Reyenga
-Certified National Hack and Car-Whore Extra-ordinare

Building your own composite wing isn't that hard, just a bit messy...

http://forums.freshalloy.com/showpost.php?p=1461240&postcount=277

 APR's number seem a bit optimistic to me, but if the actual numbers are even 2/3 of those, they're still a pretty decent bargain.

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--Jason Rhoades

Jreyenga:

I wouldn't trust the numbers on Foilsim for high angles of attack.  Was that number for a single element?  I'll dig through my simulations when I get to work tomorrow to quote the numbers, but I don't recall them being that high.  I may or may not have spent a fair amount of time playing with the company's CFD to optimize a dual element wing (plausible deniability on the internet).  Any idea what the CL for that foilsim wing is? (I'm too lazy and had too many beers tonight to calculate it), but that number seems quite high.

The APR wings are a good value.  We intend to run them initially, but I obviously have a design I want to construct when the free time, energy, and money align for that project.  Custom wings are still pretty pricey if you do them yourself.  I expect to spend around $700 or more to build a composite wing doing all the design, engineering, and construction my self.

As for the 'elbow' on the shock dyno.  There is usually a blow-off from low-speed to high speed damping.  The FFT can give you an idea for what velocities constitutes track induced movement (generally high speed) and what velocities are from driver inputs.  But the guys at places like Koni know WAY more about that than I and can build you a pretty darn good damper without any of that information.

 

You're right Jim, my husband was quoting for a single element, but I am not aware of the lift coefficient (CL). Truthfully, I haven't even used the foilsim software.  Aero and CFD is an area I'm not proficient, but I have had an idea about making a wing using a rapid prototype model and bond the materials to the wing (similar to the link in the other post where the fella is laying up his own).  It just might be time to get use the university's CFD software and get up to speed.

On the shocks, I have a great contact with Koni and they are only 1 1/2 hours away from me, so I just might pay him a visit and buy him a meal in exchange for info. As for the FFT, if the shock is suppressing the high speed velocities (bump or rebound is set too high) are you also relying on pitch & yaw data?

 Julia
 

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Julia Aebersold
97 SM
97 Supra Turbo

CI is -5.326 from the foilsim program. 391LBs DF at 60MPH, 8 sq ft, -20 degree angle, -25 camber %

Those numbers are a fantasy far greater than APR's.

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--Jason Rhoades