Wind Tunnel Smoke Testing

[Peter Jack]

Dave, thank-you for your clear explanations and your educated opinions on getting the best use out of the tunnel. Your contributions to lsr are greatly appreciated. 

Pete

[WhizzbangK.C.]

Yes, thank you very much for taking the time to give us a detailed and well stated explanation. Like I've said before, I'm a VERY low budget racer, who won't be able to afford tunnel testing unless I hit the lottery. I appreciate any good info I can get that might help my SWAG designs to work a little better. 

[fredvance]

When I went to A2 with team Forstall, earlier this year, Dave's knowledge and expertise was incredible. Having someone so willing to help was invaluable. I looked into going to one of Texas A&M's wind tunnels, last year, and they would take us, but did not particularly want motorcycles. With that kind of attitude i didnt think it would be worth the time and money.

[A2WindTunnel]

You guys are all welcome! Our main goal at A2 is to help our customers (and non) understand what wind tunnel testing is all about and how to use it as a tool.  You don’t necessarily have to have the best too in the tool box, but if you know how to use it then you can see an improvement on the track.  A tire iron isn’t as good as an expensive impact, but you can use it to get the job done. I don't find a great deal time to write on here but glad that it is helping some people understand.

Dave

[A2WindTunnel]

I haven't posted any current video's of our AeroDyn Wind Tunnel so here is one for anyone interested to view.

http://www.youtube.com/watch?v=EWsermqAx_Y

D

[maguromic]

Thanks for the link.  With the automated ride height control in the tunnel, could you simulate a given track?  Tony

[A2WindTunnel]

In the wind tunnel you are always trying to control variables.  Teams will use the automated system to perform ride height matrix (pitch, heave, roll) and see where the car likes to be from an aero standpoint.  By aero I mean the best balance front to rear downforce vs. drag.  Once they determine an attitude they will work with springs and shocks to get the cars stance where they want it and a suspension package to get the car working at optimum with aero grip as well as mechanical grip. 

With a splitter on the front, these cars are very sensitive to height changes and the cars like to run just off the track surface.  With so many tracks there is always variation in speed, corner banking and track surface conditions, that every track with have its own spring and shock package. What they also do is take all the wind tunnel data and load it into a program with shaker rig data.  A shaker rig is a tool like a wind tunnel or engine dyno that holds the car at the chassis, and tests the suspension components of the car to see what different shock and spring packages will create at the wheel (load).  If they are at the race track and the spring package they initially thought would work is bottoming the car in the corners they might bump up the spring rate in the front.  This will raise the front of the car, but they can look at that program and determine for example; that mechanically the car needs to run ¼ higher in the front, but what will this do to the aero?  After they plug all the numbers in they can then determine how the change will affect the car from an aero & mechanical stand point and make a decision based on the results.

Attached is a link to an older video of a shaker rig.
http://www.youtube.com/watch?v=hqyUwCTIGQg&feature=related

D

[A2WindTunnel]

Thanks for the link.  With the automated ride height control in the tunnel, could you simulate a given track?  Tony

Tony, that was a very long answer to your question.  Yes any track can be simulated.  A racecar running at Daytona will have a different attitude than one running at Charlotte (super speedway car vs. downforce car). 

Teams have track data and one component of the data they log (during practice) is shock travel or frame height from surface (real time) and they can determine a straightaway height along with corner entry and corner exit (and anything in between).  They can then look at the heights in the wind tunnel to see what the car is doing from an aerodynamic stand point for a given track.  With the automated ride height system teams have run ride height matrix as big as a hundred points (heights) to get fine detail of aero vs heave, pitch, roll. 

[Rex Schimmer]

And who said NASCAR was low tech!!!???

Rex

[Kix]

I have always been curious if there has been any testing done regarding how a wind tunnell (air being forced past a stagnant object) compares to an actual object forcing itself through stagnant air?

Kix

[A2WindTunnel]

I have always been curious if there has been any testing done regarding how a wind tunnell (air being forced past a stagnant object) compares to an actual object forcing itself through stagnant air?

Good question.  The NASCAR Teams spend a lot of time performing what we call straight line testing or coast down testing to validate what they learn in the wind tunnel.  This is very difficult to do right because of the number of variables involved that must be kept track of to compare changes on the car. In a wind tunnel we control many factors but in straight line or coast down testing you are at the mercy of the natural conditions such as wind, wind angle, temperature, and pressure that are constantly changing throughout the day.  The car needs to also be highly instrumented as well to keep track of variables such as temps, heights, ground speed, relative wind speed, yaw angle (relative to wind), any incline or decline in surface, etc…

This type of testing has been going on for years and teams do correlate what they see in the wind tunnel to the track.  You need to be smart enough to know what you are correlating, to the wind tunnel used for correlation.  Example: If you have an underbody change or inner fender change you need to be correlating to a wind tunnel with boundary layer control on the floor and rotating wheels (such as AeroDyn or Wind Shear).  If it is an over body change (nose, hood, wing, spoiler) something like A2 could be used for the correlation.

I posted a video about a year ago but will post it again.  The video only talks about them testing and not so much of what’s involved.  You will not find a good video because teams are tight lipped about the procedures used for any type of testing or R&D.

NASCAR straight line test
http://www.youtube.com/watch?v=qM11-Qm5QOQ

To illustrate how hard it is to get adequate data, notice how the engineer says they get 12 coast downs per outing.  That means that it takes 12 coast downs for one change on the car (think fuel, tire costs, time, $$).  They have to do this because of all the factors involved and seeing how consistent they can detect the change.  In a wind tunnel one change can take minutes to know the answer.  So teams will test a large number of things in the tunnel and then narrow it down to the changes that worked to then validate in a straight line test.

[Kix]

Thanks for the reply, I thought that might be the case... I asked that question because I recently saw videos of the Ganassi Coast Down Tunnel in the old train tunnel and wondered if they were experimenting between the two......

This is all very fascinating, I hope this thread lives on a long time and people keep posting ideas here on how to test the basics before spending the big bucks on the Wind Tunnel!

We are running a GMC Sonoma and have learned a lot by following S10s and Sonomas down the freeway on rainy days.  Not exactly the same thing, I know, because the weight of the mist is much heavier than air, but it sure is neat to watch how the air flows around the cab/bed depending on wether the bed is open or closed with a tanneau cover.


Kix

[A2WindTunnel]

New Video of  a Lakester in A2

http://www.youtube.com/watch?v=c-072fOM84g

D

[Elmo Rodge]

Thank you very much. That is one helpful video for me. Wayno

[Tman]

I agree Wayne. I will be watching that one a few more times