Sample Wind Tunnel Test

[A2WindTunnel]

What type of information can you learn in a wind tunnel?  This is a question that the majority people ask since a wind tunnel is not a place often visited by most people.  I will post some data (okayed by customer) from a A2 Wind Tunnel in house study to illustrate what information can be learned from each run. 

A run is a term used in the tunnel which is a single test run.  Every time you make a change to the model you then do a run to measure the effect of the change.  This consists of a tear of the balance where the weight of the model and balance are zeroed out so that when the air/fan is turned on, the balance is measuring the aerodynamic forces in 6-components: Drag, Lift (front & rear), Side Force (front & rear), pitching moment, yawing moment, and rolling moment.  All of these forces are studied to analyze what is happening to the shape, whether it is a car, motorcycle, or cyclist. 

Below is a sample test of a Camaro in the wind tunnel.  I just want to show 3 simple configurations (baseline + 2 tape configurations) and explain what the results were for this particular car.
 
Camaro Configuration:  I will be vague with the information of the cars configuration because the customer didn’t want too many details given about the car and set up.  It is not a Landspeed car, but can be illustrative to what information you could learn in a wind tunnel and how it applies to any type of racing. 

TEST CAR:
1997 Camaro SS:
-Larger rear spoiler
-Wide performance wheels
-Road Racing Series

[A2WindTunnel]

Attached is the data sheet that we provide each customer from a test.  You will need Microsoft Excel to open the file to view the data. 

[maguromic]

Thanks for posting the spread sheet.  Its very interesting.  But I thought in one of your earlier pots you said that taping the seams had very little effect, but in this test their was a significant reduction in CD versus the baseline. 

[A2WindTunnel]

Again, this is a very simple illustration of information learned at a test.  I realize some classed have rules against taping up the front end etc… and I am not advocating that this is all you have to do to reduce drag or all you could do in a wind tunnel session.  More important is the change in Drag, Lift (-Lift = downforce) front and rear, and how reducing the drag will change the HP required to achieve that speed.  In the column labeled HP (AeroHP).  That is how much horsepower it will take just to move this car through the air at 200mph (minus rolling resistance and any losses through the drive train).  You can see a 39HP reduction when fully taped, and this would be the same as adding 39HP to your engine. 

These are very simple modifications, and you have to look at the big picture... not just thinking with this drag# & HP engine I will go XXX mph.  Look how imbalanced this car is.  At 200mph in the baseline configuration it has 625lbs front lift, and -766lbs downforce on the rear.  One end is lifting as you increase speeds and one is pushing down with increased speed.  How would you correct that at the track? Adding weight to the car to balance an aero imbalance?!?! 

I know there will be lots of questions about this data and I will try to help answer any questions.  Please understand that I am doing this on the side from doing my regular duties at work (sometimes late hours), and sometimes that means that I am busy wind tunnel testing and not on LS everyday.  Part of getting on LS is to help educate people and I hope this is appreciated and not slammed by any members because I don’t have time to play the games.  I have had some really good PM’s from members thanking me for trying to help educate (while not giving away anyone’s speed secrets or information), and I hope these members enjoy this post because it is the most complete information you will find on the web about wind tunnel data to my knowledge. 

Dave

[A2WindTunnel]

I don't recall ever saying that tape has little effect (could you help me remember the topic).  The front end is very sensitive on cars and there are big gains to be made.  All cars differ in how well things help and hurt the aerodynamics and that is why a lot of times you can't generalize because one change that helps one car might hurt another.

[sabat]

Great info, thanks for taking the time.

You once posted that you would comment on the use of broad-coverage front fenders on motorcycles, but probably got distracted with "working" or some such.  Can you share any insight, for a guy on an unfaired bike?

Dean

[sabat]

Also, is it possible to operate the wind tunnel with the rider aboard the bike? How is it supported?

[maguromic]

I don't recall ever saying that tape has little effect (could you help me remember the topic).  The front end is very sensitive on cars and there are big gains to be made.  All cars differ in how well things help and hurt the aerodynamics and that is why a lot of times you can't generalize because one change that helps one car might hurt another.

I may be wrong, but I thought  some time ago their was a discussion on here about smoothing the joints on a body.  Thanks for posting the information. Its been very educational for a non aero guy like me.

[Howard]

Thank you for all the interesting information. For whatever it's worth, back in the late 80's I was running a 60cu. in. streamliner and when I built it I tried to get a good panel fit and alignment.
One year at World of Speed we made a run, returned quickly to the staging area and taped all the body seams with the thin, clear, 2" wide "Scotch" tape.
On the next run which was probably within an hour, we saw no increase in clocked speed. Very little change. (Normal deviation in runs.)
We found that interesting and had a real fun time getting all that tape and sticky crud off the car.
Howard
#448 back then

[Larry Forstall]

I have seen the future of LSR and it is the wind tunnel. Gone is the guesswork, trail and error of attending multiple meets (OK if you are from SoCal as Bonneville is "next door"). The few hours it takes to test ideas with the help of the tunnel staff guarantees a faster, safer race vehicle. As an old timer I can hear my words that such testing is not the hot rod spirit. Go to the great white dyno and run. Well this is the 21st century and electronics rule the world, traction control is allowed and speed gained through air management is just another tool. The beauty is body improvements are a one time expense as they never break. Dean: You will run out of boost. To go faster the tunnel will quickly tell what tuck is the most efficient, what bike attitude is best and how much you will gain by moving the radiator to the rear. (Much less drag). Since the mid-seventies I have traveled 166,000 miles from the East Coast to race on the Salt. Nice to have the tunnel "next door". 

[Woodstock]

Great post, A2.
Wind tunnel testing is the way of the future and for some of us can save a lot of time as we approach the upper end of the age numbers while playing on the salt.
The tunnel allows you to make changes as you go and realize positive results.... you can also go the other way, too. Been there, done that!
It's a lot cheaper to go back to a previous configuration in the tunnel than on the salt.
Immediate testing results will save you money up front and finalize the optimum body configuration.  This eliminates that part of the equation and lets you focus on HP and weight distribution.

Bruce   

[Dynoroom]

I like the way Larry thinks. The trouble is all the usable full scale tunnels are back east. So I guess its test and tune on the salt for us "left coasters" 

[maguromic]

I like the way Larry thinks. The trouble is all the usable full scale tunnels are back east. So I guess its test and tune on the salt for us "left coasters" 

Thats why on my roadster I did a lot of CFD work.  The next best thing to a full scale tunnel.  But by no means a substitute.

[Stan Back]

Huh?

[maguromic]

Stan, CFD is Computational Fluid Dynamics.  First you build a computer model then you wrap it with a mesh(the tighter the better) and run it and see how the flow works on it.  The only problem is you need almost a supercomputer and the software package is very, very  expensive. To get around it I got the Stanford University Engineering School involved. After seeing the results I had to change my way of thinking.  Dont want to high jack this good thread, soon I will post on build diaries some results.
Tony