Anyone done any wing calculations?

[fulltilt]

So I am finally at the point where I am ready to start understanding wings and downforce, even though I am not yet designing the body of my open wheel project. I recently took the rear gas springs off the decklid of my extremely heavy 1994 Camaro road race car to motivate me to take some weight out of the decklid. Boy did it! The decklid weighed around 100 lbs! So I am replacing the glass with lexan (30 lbs) removed the rear factory wing and add-on spoiler (20 lbs) and stripped the lower layer out of the decklid (20 lbs). After struggling to drop even a half lb out of my race bike, I am finding it hilarious how easy it is to take weight out of this tank! So now I want to put that weight back down in the form of: a) a good spoiler to reduce the lift effect on the car, b) a wing to replace the downforce I lost from the weight I removed, or c) a wing to apply more downforce than I removed.

This inspired me to read Competition Car Downforce, By Simon McBeath. A very good read, and has really got the gears turning and got me thinking about ways to apply some of these principles to keep me out of the air with my project car, and hopefully even apply some useful downforce.

There are a couple things however, that are bothering me, and I thought that the formula community may be able to help, as you guys utilize wings heavily. McBeath shows some single element NACA airfoils in the appendix. One is NACA 4415, and there are a couple others. They both correspond to a lift coefficient of around 1.5 for a single element wing at angles around 12-14 degrees. In one example that he works out, a wing with this profile that is 3 ft by 1 ft area, gives 78 lbs of downforce at 100 mph at a lift coefficient of 1, which he uses to take into account dirty air from the car and such. Now, he also has some profiles of multiple element wings that reach a lift coefficient of 3 at the same angles, but I want to talk single element for now.

McBeath provides pictures of a wing on the Mclaren F1 race car that has an airfoil that is unlike the NACA profiles he adds in his appendix in that it is concave on top. It looks much like this wing from Tiger Racing.

http://www.tiger-racing.com/for_sale.html

This wing from Tiger Racing boasts 600+ lbs of downforce at 100 mph (calculated), yet using the formula below for downforce and the area of 12" x 68", I find it difficult to get even a couple hundred lbs with a single element lift coefficient.

L = 1/2 * p V^2 * S * Cl
Where :
L = Lift
p = Density of air ( 1.225 Kg/m^3 at sea level)
V = velocity of air
S = Wing plan surface area
Cl = coefficient of lift.

Now, obviously, this 600+ number could be hype, and no one will ever question it. But I have to wonder if it is accurate, what numbers are they using for their calculations? There seems to be very little information out there on wings supported with real downforce numbers.

I guess I'm just wondering if any of you have done any wing calculations, wing building, or have any experiences that would help. I would love to hear your thoughts!

[FC63F]

Fulltilt,

You have wandered into a very interesting wilderness.

1. You have correctly identified the main issue with aero -- few facts, no math and lots of wild claims.

2. The boast of 600 pounds of downforce is more than highly unlikely in a single element wing system in perfect conditions

3. Except at the highest levels of motorsport, all kinds of claims are made with zero facts to support the claims. There are all kinds of marketers of wing systems and none that I am aware of have actually been in a wind tunnel with valid testing. If they did, they would use those facts to sell their systems. The cost of tunnel time is far to high for the vendors in our space.

4. The Simon McBeath numbers are a rational starting place. You can put together a reasonable approximation of what the wing will do in clean air and when balancing a car derive a starting point as to size, configuration, angle of attack etc. However, air flow over the car is far less than perfect and those variances have to be dealt with on the track to refine the balance unless you are lucky to have big $$ and access to a wind tunnel.

Ultimately after a bunch of tests - you will refine the front and rear attack angles until you now have a baseline. That is at a given attack angle on the rear wing that is supposed to generate x downforece, I need to adjust the front wing to y angle of attack to balance it out. If you have lots of time and $$ you can begin the get correction factors and determine the actual down force generated at the rear across a range of speeds. The assumption is that the front wing being in clear air is generating close to the theoretical level of downforce based upon your calculations

5. I have used the McBeath calcs to set up a series of models which I have used on my CFC car. I have also attempted to utilize 3D Computational Fluid Dynamic calculations and software to validate my numbers with some limited success. That is more than difficult as most of the decent CFD programs require very serious computer power - you desktop PC wll not cut it. There are a couple of higher end 2D PC programs commercially available and are moderately to very expensive. You need 3D cad programming capabilities etc. Point is, that the resources are way beyond most club driver capabilities. If I had that much money - I could buy a ride in more senior series.

6. Net - Simon's approaches are a great way to start understanding the areo and to begin to seperate the facts from the myths - single elements wing from Tiger probably makes 600 pounds of downforee when it hits say 700 MPH or is about five times bigger. As for the cambered airfoil, it does not add to the downforce much but it down generate downforce even at negative angles of attack and is more forgiving at maximum angles of attack.

7. Simon has written earlier books - I recommend them as well along with Katz.

Have fun - great subject

David Keep

Reynard 90SF

[Peter Horvath]

You've put a lot of thought into this, Mr. Tilt. But nobody out-thinks Carroll Smith on the subject. Read "Tune to Win".

[Tom Irwin]

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

[fulltilt]

Very nice, exactly the advice I was looking for. I have Smith's fastener book, and Engineer To Win. I put off buying Tune To Win until some point in the future when I felt I was past the coarse tuning, I guess I have overlooked the fact that I'm there. I better pick it up.

This sounds naive even as I type it, but I thought maybe in the $2000 range, maybe they knew what they were talking about! Obviously not. If you dig into their literature, they have a customer that uses it on a C5 that he autocrosses at 55 mph, and boy does he stick to the track!

Thanks guys,
Kyle Verploegen

[Larry]

I've spent a long time in aerospace, and am comfortable making the following statements:
1. There is no single "best" wing. Just as different aircraft use different wings, they are optimized for a particular design point, and any other point is a compromise.
2. This would hold true in racing. You picked an arbitrary 100 mph as a comparison point, and that's probably a good place, but each track will have a place where the wing can provide the most benefit. If you had the time and budget, you could analyze the track and weather and expected velocity at that point, and then design the optimum wing.
3. If you did the above, you might pick up 1/10th over an equally-driven car with a non-optimum wing.
4. As David mentioned, wind tunnel time is expensive. Furthermore, it takes a long time to prepare and instrument for your test program (assuming you can write a good program). Then, you have some data points that are somewhat relevant to racing, but they don't take into account things like terrain effects, effects of other cars, etc. In other words, tunnel data isn't perfect. If it was, aircraft manufacturers wouldn't need to do flight testing.
5. Most claims by race car manufacturers about their wing designs are unsubstantiated BS. I lost out on a lot of sales because, when asked if a new wing would pick up one second/lap, I talked about test sessions and didn't just say "yes." Most people will pay $1,000 to get something they think may make them faster, yet they won't do testing and development work--which will actually pay off, making them faster and better drivers with an expanded understanding of what the car is actually telling them.

Larry Oliver
International Racing Products

[RobLav]

Good comments Larry.

For most of us, there's more to be gained by polishing the nut behind the wheel than there is by adding some new do-hicky. If you buy that do-hicky, then you must also polish that nut.

It's all about marginal benefit to marginal cost...

[John Scott]

Kyle

The aerospace industry relys on computer simulation for most of the aerowork. wind tunnels are too expensive to wast time so they use the tunnel to confirm and refine efforts modeled on the computer.

I have had a lot of fun analyzing our FC wings using a free two dimensional analysis tool called Javafoil. You can get the software from
http://www.mh-aerotools.de/airfoils/javafoil.htm

This tool will give you the coefficients you need for the equation you have.

Larry makes a very good point about testing. We used the results from the simulation to focus our testing into high payoff areas.

You have a much heavier car and the impact of the wings will be quire different than we see in a 1200 lb car where an aditional 50lb on a tire makes a big difference.

John

[Mike Allison]

"wind tunnel time is expensive. Furthermore, it takes a long time to prepare and instrument for your test program (assuming you can write a good program). Then, you have some data points that are somewhat relevant to racing, but they don't take into account things like terrain effects, effects of other cars, etc. In other words, tunnel data isn't perfect. If it was, aircraft manufacturers wouldn't need to do flight testing." Larry


"However, air flow over the car is far less than perfect and those variances have to be dealt with on the track to refine the balance unless you are lucky to have big $$ and access to a wind tunnel." FC63 F


"The aerospace industry relys on computer simulation for most of the aerowork. wind tunnels are too expensive to wast time so they use the tunnel to confirm and refine efforts modeled on the computer" John

FullTilt, you've opened an interesting thread and I agree with FC63F that you've done some good preliminary work. I also agree that most of the aero claims are unsubstantiated and wildly optimistic.

The main flow, no play on words intended, seems to suggest that wind tunnel testing is too expensive to be useful at Club levels. I would like to ask what that means. How much is "too expensive" for the results gained? Since all of the claims regarding aero seem to be unsubstantiated, including Larry's statement "you might pick up 1/10th over an equally-driven car with a non-optimum wing" , what would be an acceptable price to gain any edge over your competition?

We see that you will buy new tires at $600.00 to $800.00 for temporary advantage. Engine rebuilds or more correctly, modifications costs are in the $3000.00 to $5000.00 range and they wear out and lose their advantage. Testing at a racetrack usually costs $1,000.00 a day when you count tire and engine wear plus consumables and travel. And race track testing involves many variables that aren't often quantifiable.

Information derived in a scientific manner lasts indefinitely, and the advantages gained can be maintained over the competitor that fails to utilize the same or similar methods to find this information. The key lies in the controlled environment, testing only a minor number of variables, with built-in repeatability. No driver variables, no weather changes, track conditions that change, etc.

I admittedly have an interest in wind tunnel testing, and I invite you to visit our website - www.a2wt.com as well as visiting us in person. I am not qualified to speak regarding the science of aerodynamics, since that role is the responsibility of my partner, Gary Eaker. But I can address the economic value of wind tunnel testing.

What do y'all think? Rebuttal? Agreement?

Mike

[FC63F]

Mike,

You pose an interesting questions as to the what is known about the potential improvement and what would the cost be. At this point both are unknown at the club ranks. Lots of opinions but few facts. So - how to sort this out.

1. There are a number of decent books with good science etc that can allow you to work the math and understand the basics - that would get you ahead of 95% of the people racing. There are also a number of cheap simulations - FoilSym for one which can also be useful inb predicting performance. So the first step is to jump into the pond.

2. The second challenge is to take a current design wing (what ever is on the car) and develop a simple improvement plan. Reduction of drag - reduce the amount of HP consumted. Add end plates, change the height of the wing etc. All of this can be modeled and then placed on the car and tried out in the real world. If you add end plate feet - the prediction is 15% increase for example - can you test that - roll down tests, Tests of top speed at the end of a straight ( do you get a couple of hundred extra RPM or do you get nothing measureble. After this period, you know more than 99% of people out there.

3. Hire/find/kidnap an Aerdynamicist for the next step. (PhD Types in Major Universities) and spend some time with that person and show him your test plans, data models, simulations and go from there. You may get if you are really lucky your PhD type to test one or two great ideas in their fractional tunnel - real data. Now you can make some comparisons between the simulations and tunnel. You will need to build some models to test with. One thing to consider is that for the most part - you will not be able to get the whole car in the tunnel without major dollars. Therefore, you have to build small models of the car or maybe full sized wing systems. You will still have trouble testing and improving multiple systems - ie body/diffuser/rear wing systems do to cost structure and tunnel availability. This limits your ability to understand the interaction between car components

4. Final - I hypothesize that there are real benefits in testing and analyzing front wings, rear wings and diffusers. There is downforce to be engineered in and drag to be engineered out of modern cars - how much - I do not know -- and how much cost - I would bet that a very controlled budget of say from $10-20K would get some decent work in number #1 and #2 and yield some useful results. Testing in the tunnel including models and rental time would be the #1 cost elements.

Net the concept of testing in a tunnel is very seductive - but you need to be really well organized and diciplined. I have a couple of freinds who are Aerodynamicists PhD students at the U of M who have been helping my efforts but we still have not het been into a tunnel at this point. We have used various simulations and their brain power to identify improvement opportunities. At this point, we have not yet been to a tunnel

Regards

David Keep

Reynard 90SF

[Mike Allison]

David,
I'm asking a real world question. Are club racers willing to spend any money at all for wind tunnel testing? Our FULL SIZE wind tunnel, A2 Wind Tunnel, charges $490.00 per hour to test. ( www.a2wt.com )

If you have access to PhD aero students, we have a place where they could get their rocks off.

My question again, what price glory? People pay to have engines dyno'd, shocks dyno'd, double, triple, zoom bang whiz adjustable shocks and $490/hour is expensive?

I'm not fully understanding. What price is cheap enough?

A group that pooled their funds and did a massive test on a specific car/chassis would learn bunches for little individual cost.

Just wonderin'.

Best regards,

Mike

PS-models are very expensive if you want the kind of accuracy you need for scale model testing.

[fulltilt]

At a first session price of $345 for two hours, I'd be tempted to throw the Camaro on and see what effect a spoiler or front splitter really makes. Of course, as an engineer, much of that value would come from satisfying curiosity. However, I wouldn't be willing to travel very far to do so. Is it just me, or does the website not mention location anywhere?

It's funny, I have actually started paying more attention lately to the "bling wings" that I see around town, just before laughing and dismissing them as a joke of course!

I have also been thinking, as I have a rear decklid on the Camaro, it probably wouldn't be too hard to rig some kind of poor man's load cell on each side. Hmmmmm........

[FC63F]

Mike,

Had to think about your proposition before I could respond.

1. Distance would be difficult to overcome but if there was a local (200 miles or less)

2. Need to have a plan for the test - I would think that for the fee. you the tunnel owner would have to help (consult) with the club user so that they could get high value. I would be wary of blowing $500 on a poor test design. Maybe you put together packaged tests - the $300 dollar test, the $500 dollar test plan, the $1,000 dollar plan etc. I suspect many club racers would need assistance in design

3. Using the tunnel - Helping to make sure the tests go as designed - a service necessary to make sure time is effeciently used

4. Data interpretation - what does the data mean to the racer and what should his next steps be. This would need to be provided to the club racer in order to make the data actionable.

Lastly - I think this is an interesting idea but offering the tunnel bt itself is not enough - there is a need for services to design, manage the test and interpret the data which many club racers would have difficulty accomplishing on their own.

Thoughts??

David Keep

Reynard 90 SF

[Mike Allison]

David,
I'll be the first to admit, our website is not as informative or interactive as it should be. soon to change, however. We've hired a very good computer/tech person recently and he will be improving that area, on both of our sites. BTW...We're in Mooresville, NC

One of the areas we have to be concious of is the "sanctity of data". We don't want to compromise our integrity with the suspicion that we are "sharing" hard earned (and paid for) information. You wouldn't want me selling your discoveries to the next customer that waltzes in.

At A2 we do offer interpretation and suggested approaches to problem solving. We don't go in and reshape a wing for you. At AeroDYN (our big brother tunnel) we offer zero advice since we are renting our facility to professionals, big budget NASCAR Teams.

We recognize the need to assist the beginner but need a way to sort out the beginner from an informed lower tier racer. It is a difficult balancing act. We do provide a few names of consultants that can jump start an aero effort or "hire on" for long term development.

"2. Need to have a plan for the test - I would think that for the fee. you the tunnel owner would have to help (consult) with the club user so that they could get high value. I would be wary of blowing $500 on a poor test design. Maybe you put together packaged tests - the $300 dollar test, the $500 dollar test plan, the $1,000 dollar plan etc. I suspect many club racers would need assistance in design"

I like this idea a lot and need to give it more thought as to how we could do that. Perhaps some form of added value package to the original fee? Optional extras?

I appreciate your interest and will discuss them with my partner after the Holidays. Hopefully you and all the others tuned to this thread will give us more input. We want to provide a means for the underfunded racer to utilize this form of testing. So far, we are a non profit organization, although not by design. I think we'd be happy with breakeven.

Happy New Year to All

Mike

[Larry]

Around 10 years ago, I was excited about the prospect of using a wind tunnel. I went to the University of Maryland, where they have a very nice, large wind tunnel, and met with the head of the aero program, and we discussed my ideas. They were doing work for Ford as well as a variety of low-speed (below 200 mph) projects. These are the main points that I found:
1. Productive use of a tunnel takes TIME. You have to bring in the test article, and it has to be clean (to avoid damage to the tunnel from debris). The article has to be lashed down to the test stand and then instrumented to record the data. You are probably starting hour #3 by now. You may want to use strain gauges, manometers and/or scales. Of course, you need recorders on every instrument to get the maximum data and value.
2. Just what do you want to test? Downforce, drag, downforce/drag vs angle of attack? All of the above at various speeds? You have to write your test program explicitly. If you try to wing it, you're still paying by the hour.
3. Tunnels are semi-accurate. They are not perfect. You get drag off the walls, swirl effects from the air, etc. This is why you confirm tunnel data with flight test data...and of course, you use the tunnel data as step one in confirming your calculations.
4. OK, now you have a bunch of data points. Just how do you propose to use it in racing? Are you going to map each track, calculate segment speeds and then run calculations over each segment with various wing configurations to come up with an optimum configuration? (Yes for F1, not likely for FC...unless you have 5 or 6 aero guys to crunch numbers for you).
5. Model testing is wonderful, but proportionate in value to the accuracy of the model. A good model will cost as much as the car.
6. You can test a nose or a tail, and you'll get some info, but it may change completely when you attach the rest of the car.

I would LOVE to have the time and budget to play with a tunnel and a car! I'm sure that I could eventually find a nugget of value. But in the current environment, I'm quite certain that I can find more benefit in other areas for less time and expense.

Larry Oliver
International Racing Products

[Joefisherff]

There was a great article on this about 2 years ago in SportsCar detailing Neil Porter's work in a wind tunnel with the DB6's. It gave a great play by play on preparing for the wind tunnel test, test scenarios, results, some of the things they tried and the results. The results were born out in a national win in FF so I think there are benefits, but to Larry's point, it takes a lot of pre-planning and helpful wind tunnel personnel to realize the benefits. Maybe Neil or someone could jump in with the date of the magazine for those who are interested.

[M.L.Sauce]

Before I built my FF, I built a 1/10 scale wind tunnel.I used a digital gram scale for drag.I built 4 models.The models were not finished out in paint but were sanded smooth so all areas that licked the air were consistent.The amount of info from this was staggering.I found out a few of the basics of aero dynamics.I had a friend who knew two guys who worked in the wind tunnel at Lockheed and they helped us to keep from making too many of the big mistakes.We have done dynamic testing since the car was completed with tufting and oil tests.The car is as good down the straights as any other car in the class.My wind tunnel although not near what any F1 or even Pro team would consider adequate taught me alot. I have since used a computer program that is designed for Gliders because they deal with similar air speeds of the small open wheeled race cars.The wings that we all thought were so great that come on most English racecars are not really that great.If you want a good wing try a NACA 4412 air foil or something like it.

[racer27]

http://www.compufoil.com/product_cf.shtml

is a link to some wing modeling software, primarily used by model builders.

[EYERACE]

the other year my child wanted to go to the orlando science center.......wow....cool even....because eye discovered they had enclosed in a plexiglass box about the size of a suitcase > a small wing section with a fan and smoke trail set up for demonstration purposes. this model wind tunnel was placed at "child eye height" which is about only three feet off the ground. this child's height is also a reasonable idea for a child's attention span. they can walk by push a button, jiggle the lever and then go off to the next thing that has whistles, bells and lights. so eye had to sit on the floor and stretch up a little if i wanted to stay and play. one could vary the fan speed and vary the wing angle of attack and watch the smoke trail vary........i must have sat there for a half hour studying the results. my kid got mad at me for not running around the center with them after a while.

eye then went home and trimmed all wings to virtually flat on the FC - maybe add a couple of degrees tops for a short "technical" course.

eye used to laugh at the "rice box" with the aggressive tilted wing in the past but now i laugh longer, louder and deeper too. by the way, eye'm going back to the science center again some day but this time with a couple of small levels and a laser pointer to shine through the smoke and a chair.