Starting into Aerodynamics - Need some help

[Ben Wigg]

So a group of us at Illinois are going to tackle the aero package for the car. We're thinking of doing a front/rear spoiler as well as an underbody. Since the underbody depends largely on the chassis we've decided to start with the front wing and go from there.

We're pretty much brand new to the aero thing and I was hoping that someone on here could guide me in the right direction in selecting an airfoil profile to use as well as how you guys design the spoilers.

I know Dr. Selig has quite a few low Reynolds number airfoils that I've seen referenced on here so we were thinking of using one of those but again we're not sure which ones are good and which ones are not.

As for designing the spoiler itself did you use a wind tunnel or CFD? We were thinking of sticking with CFD if possible.

Thanks for the help, I appreciate it.

[Ben Wigg]

So a group of us at Illinois are going to tackle the aero package for the car. We're thinking of doing a front/rear spoiler as well as an underbody. Since the underbody depends largely on the chassis we've decided to start with the front wing and go from there.

We're pretty much brand new to the aero thing and I was hoping that someone on here could guide me in the right direction in selecting an airfoil profile to use as well as how you guys design the spoilers.

I know Dr. Selig has quite a few low Reynolds number airfoils that I've seen referenced on here so we were thinking of using one of those but again we're not sure which ones are good and which ones are not.

As for designing the spoiler itself did you use a wind tunnel or CFD? We were thinking of sticking with CFD if possible.

Thanks for the help, I appreciate it.

[Mike Cook]

seriously, aero is the biggest waste of time for fsae cars...

[Hector]

Both Steve Fox and Pat Clarke have said that they do not want to see aero. They published this statement in a public design review that you can find online. I've also heard one or both say (don't really remember) that if aero ever started giving teams a dominant advantage, they would have the rules changed to remove the advantage.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">At the typical course speeds (70 kph peak), aerodynamics cannot be justified. These competitions are not about aero; this is a handling competition, not a high speed competition.
-Pat Clarke </div></BLOCKQUOTE>

I'll leave it at that. I won't try and go through the pros/cons of running aero. Just be aware of what some of the top judges have to say about it.

/Hats off to S&T. Sexy car; I'd like to see you guys run without aero someday. Worked in St. Louis over the summer, and almost made the drive to your campus once to see your car and shop.

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Hector:
Hats off to S&T. Sexy car; I'd like to see you guys run without aero someday. </div></BLOCKQUOTE>

I've seen them do just that. With a pretty good driver. It's considerably slower, even at FSAE pace.

Most important thing though: Make sure this is the best use of your time and resources.

[J. Vinella]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mike Cook:
seriously, aero is the biggest waste of time for fsae cars... </div></BLOCKQUOTE>

I know right? http://fsae.com/groupee_common/emoticons/icon_wink.gif

[J. Vinella]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Hector:
if aero ever started giving teams a dominant advantage, they would have the rules changed to remove the advantage. </div></BLOCKQUOTE>

Well, better start taking advantage now. This is not a series, so showing dominance by one team or design theory is hard. When teams only go to at most a few competitions and reliability being such a huge factor it will be hard to prove a trend of advantage.

Formula SAE West this last year was a good showcase of what aero can do. Granted a wing car did not win, but the top autocross result were wing heavy.

I would not at the least be surprised to see a few teams that have been doing aero for a few years just clean up in the coming competitions.

Ben Wigg,

To help you out, starting at the front is a good idea. Get as much out of that front wing as you can. Drag is really not going to hurt you up front. Make sure that you create a GREAT mount to your chassis as cones hit hard. Also you will read all about running the wing as low to the ground as possible (up to a point yes, but this point is relatively low), but really the car dives under breaking and rolls and you don't want to have your wings scraping and coming off.

Once you get to the back end do studies on how low you can drop that sucker. Also consider weight (but more CG implications) vs downforce. And of course balance the downforce so your CP is where you want it. Remember the rear wing creates a drag moment that takes force off the front wheels too. http://fsae.com/groupee_common/emoticons/icon_wink.gif

As far as the undertray, the jury is still out in my book. These cars roll and pitch so much and running the necessary springs to control this coupled with some of the surfaces we run on is not the best idea. Do some studied on how much downforce you lose when you roll from the undertray. This is important as when you are in the roll mode you are hopefully cornering and that is where you want the downforce. So...if you are losing it all in that mode...what is the point.

These are things for you to figure out.

Best of luck.

Rambling off.

[Wesley]

Anyone who runs wings is crazy.

[Nice Vans]

Illinois with wings, huh? I like it.

Ditto to John's comments, start with the front and move back. IMO, and undertray may not be the best idea your first stab at aero. It is not easy to prove and will take a boatload of time to develop properly. Shoot for a good set of wings.

A good book to start on is Race Car Aerodynamics by Joseph Katz. Read this as it does help tell a bit about profile selection and where to start from, as well as a basic understanding of how they work.

The rest is up to you. As you can see on the cars, there is not really a similar set of wings out there. Teams run different numbers of setups so you have to find your way.

Good luck, see you guys in Cali

Nic Evans

[Wesley]

So after seeing your 2009 car, we couldn't help but see the following everywhere it went. It's a friendly rendition of your car at Virginia.

http://hphotos-snc1.fbcdn.net/hs257.snc1/10418_723823265307_9619773_41278098_5792655_n.jpg

Another winged car would be nice to see!

[Mike Cook]

Hold on Hector...On one hand, your quote indicates that Pat thinks that aero does not give a car any added performance at our speeds and on the other, you say IF teams get too fast with it they will ban it. So which is it, it doesn't add performance or it does? I'm very confused...

[woodsy96]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mike Cook:
seriously, aero is the biggest waste of time for fsae cars... </div></BLOCKQUOTE>

We put last year's car in the wind tunnel and found this:

http://i308.photobucket.com/albums/kk323/woodsy96/DSC_7280.jpg

Airspeed into sidepod = ~ 10% of free flow velocity.

The other argument is that Formula SAE is supposed to be a learning environment, not an intense motorsport series. An alum from our team did a master's thesis on the aero package of our 2005/2006 car, analysing everything that's been discussed here and that much more again. He now works in the Aero department of the Renault F1 team.

I don't know for certain if he compared back-to-back with and without wings, but on track testing determined a C_l of -2.1ish with a C_d of -0.6ish. Since he left we haven't made/used wings in FSAE (but we strap them on for hillclimbs http://fsae.com/groupee_common/emoticons/icon_smile.gif ), mainly because we feel we can get more performance gains for less effort chasing mechanical grip. Once we have got that sorted I would love to see some wings experimented with again.

And wings look badass http://fsae.com/groupee_common/emoticons/icon_smile.gif.

[Magnarama]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Nice Vans:
Ditto to John's comments, start with the front and move back. IMO, and undertray may not be the best idea your first stab at aero. It is not easy to prove and will take a boatload of time to develop properly. Shoot for a good set of wings.
</div></BLOCKQUOTE>

I'd say it's no harder to prove than any other aero bit on the car. The simplest method would be to run a potentiometer on each damper to get suspension position and then run the car round an oval/square track. Do it at various speeds and then compare the susp posn outputs. It'll be easy to tell if there's any height change from downforce. You then have spring rate and spring compression, so can get the down force at each axle http://fsae.com/groupee_common/emoticons/icon_smile.gif . Course if your aero is unsprung that's a whole different kettle of fish haha.

[Hector]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mike Cook:
Hold on Hector...On one hand, your quote indicates that Pat thinks that aero does not give a car any added performance at our speeds and on the other, you say IF teams get too fast with it they will ban it. So which is it, it doesn't add performance or it does? I'm very confused... </div></BLOCKQUOTE>
Just quoting what I've heard. I'll see if I can find the direct quotes. Also, not sure if that particular portion was said by Clarke or Fox... I'm pretty sure it was one of them. I haven't seen the advantage yet so I wouldn't be too worried about a rule change anytime soon.

Like I said, I won't be getting into the specific pros/cons of aero because I think the subject has been beat to death and I'd be adding nothing new to the conversation. My post was simply to make others aware about how design judges feel on the topic.

[Hector]

Ok, so they may not change the rules, just the course layout http://fsae.com/groupee_common/emoticons/icon_razz.gif

From FSG 2007 design review,found here (http://www.formulastudent.de/academy/pats-corner/design-reviews/)

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Fox: Ok, what wins this competition? Horsepower or handling? *Raises hand* Handling? Horsepower? Oh, thank you, the handling hands win. It is a handling competition, isn't it? You rarely get over, how fast here? 60, 70 kilometers an hour? Are you going fast enough as 60 or 70 kilometers an hour for a very extended period of time to justify the aerodynamic work that some teams put in? Or are you generally going slower where the aero forces really aren't that big and it is very difficult to generate good, effective down force.

Clarke: Let me tell you another little secret. If a car, if a team, does come up with a really, really effective down load car, like an aerodynamic car, and they start to go around the track at speeds that we see as being maybe a little dangerous, guess what we're going to do? We're going to move the cones out and slow you down. So all that aerodynamic work went for *laughs*...

Fox:...Nothing. We're not saying that we don't like seeing an aero car. What we are saying is that you need to take a good hard look at what this competition is. You need to build the most useful tool that wins this competion. It's not a high speed event, it's not a gran prix.
</div></BLOCKQUOTE>

Take it as it is.

[Hector]

Ok, so they won't change the rules, they'll just change the track layout.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Fox: Ok, what wins this competition? Horsepower or handling? *Raises hand* Handling? Horsepower? Oh, thank you, the handling hands win. It is a handling competition, isn't it? You rarely get over, how fast here? 60, 70 kilometers an hour? Are you going fast enough at 60 or 70 kilometers an hour for a very extended period of time to justify the aerodynamic work that some teams put in? Or are you generally going slower where the aero forces really aren't that big and it is very difficult to generate good, effective down force.

Clarke: Let me tell you another little secret. If a car, if a team, does come up with a really, really effective down load car, like an aerodynamic car, and they start to go around the track at speeds that we see as being maybe a little dangerous, guess what we're going to do? We're going to move the cones out and slow you down. So all that aerodynamic work went for *laughs*...

Fox:...Nothing. We're not saying that we don't like seeing an aero car. What we are saying is that you need to take a good hard look at what this competition is. You need to build the most useful tool that wins this competion. It's not a high speed event, it's not a gran prix. </div></BLOCKQUOTE>

From FSG 2007 design review.

[TorqueWrench]

I remember that Design Review video and its a requirement for our members to watch it.

Another way to see if a diffuser/undertray would be worth it due to the conditions in the corners would be to set up a CFD and run it. Before people start yelling "physical testing" and such, I am simply saying that it would give you a ballpark idea of what would happen.

So turn the wheels, set your wheel speeds correctly, throw some body roll in and some wind going in from the side to approximate conditions and see what happens. I don't know what it does, but would definitely like to see.

[Ben Wigg]

Alright well thanks for the input so far. We're already throwing around a bunch of ideas. We're not investing a lot of manpower in it so far. It's just me and another guy working on it.

I have a question about importing the airfoil data to Pro/E. How the heck do you do it? We're using one of the airfoil data files from the UIUC Airfoil database and I cannot for the life of me figure out how to get it to import.

[Chris Allbee]

In recent times there has been at least one or two good sweeping corners that can last up to 5 or 6 seconds at speeds of up to 50mph. Yes, I have competition data that shows it. In these types of corners aero cars can gain an easy 0.5 sec advantage in that corner alone. Thats 11 seconds for the whole endurance.

We have done back-to-back testing that shows this. There are other benefits to the driver that aero can provide, but I do not believe either Mr. Clarke or Mr. Fox would car to entertain them as design reasons. It involves "soft-engineering". Which as we all know is a load of BS. I mean, really, when was the last time you heard of a company spending precious R&D dollars to add features to a car that existed simply to improve driver feedback and or comfort?

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Allbee:
I mean, really, when was the last time you heard of a company spending precious R&D dollars to add features to a car that existed simply to improve driver feedback and or comfort? </div></BLOCKQUOTE>

Or developing FWD cars.

[Wesley]

exFSAE, I'm unsure if you're trying to say that FWD was developed to improve driver feedback or comfort?

If so: I really don't think that's the case. It just makes more sense on a production level to consolidate all your drivetrain into a package you can lift up in one operation. Plus easier to reduce driveline losses.

If not: I don't know what I'm talking about.

[Chris Allbee]

I think exFSAE is just trying to point out that not all engineering decisions involve just trying to optimize the performance numbers. Most of the time engineering has nothing to do with making some new widget faster,lighter, and more fancy and seems to be the continuous focus in SAE competition.

Most engineering that deals with any type of consumer product usually focuses on trying to figure out all the retarded ways people will misuse your product and then thinking of ways to prevent the lawsuit that comes afterward.

[MalcolmG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Allbee:
Most engineering that deals with any type of consumer product usually focuses on trying to figure out all the retarded ways people will misuse your product and then thinking of ways to prevent the lawsuit that comes afterward. </div></BLOCKQUOTE>
That sounds like FSAE, except the people who are going to misuse it are your team mates and you're not trying to avoid a lawsuit, just trying to avoid having to make it again.

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Allbee:
I think exFSAE is just trying to point out that not all engineering decisions involve just trying to optimize the performance numbers. Most of the time engineering has nothing to do with making some new widget faster,lighter, and more fancy and seems to be the continuous focus in SAE competition.

Most engineering that deals with any type of consumer product usually focuses on trying to figure out all the retarded ways people will misuse your product and then thinking of ways to prevent the lawsuit that comes afterward. </div></BLOCKQUOTE>

Yep. Focusing on figuring out all the retarded ways people will misuse your product is a huge deal as a race product supplier!

Plus just trying to be a smartass with where (I'm assuming) you work. Know 7 or 8 people down there. Not much RWD action!

[EPMAl]

I agree with Clark and Fox on the principle that this competition is about handling and not power but still, at the speed we go, isn't the whole idea behind aerodynamic work to improve handling? I don't see why downforce couldn't be use for that purpose.

To woodsy96, jut out of curiosity your Cl and Cd data has been collected at what speed?

[woodsy96]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by EPMAl:
To woodsy96, jut out of curiosity your Cl and Cd data has been collected at what speed? </div></BLOCKQUOTE>

Those figures were calculated using car data gathered from the 2006 FSG competition (shock pots). It was slightly lower than the half car aero testing which gave a C_L of around -2.2, which was tested between 10 and 14 ms-1.

[Scott Wordley]

Just read this thread again.

Interesting quotes in retrospect particularly:


<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Both Steve Fox and Pat Clarke have said that they do not want to see aero. They published this statement in a public design review that you can find online. I've also heard one or both say (don't really remember) that if aero ever started giving teams a dominant advantage, they would have the rules changed to remove the advantage. </div></BLOCKQUOTE>


Was wondering what happened here...

Apparently if aero cars starting getting too fast they were going to downsize the course, or restrict aero further. In fact we have seen exactly the reverse happen...

Perhaps the lesson here is that you should design your car based on what you think will work best for the rules as they stand, rather than base your design choices upon which hand Steve Fox decides to raise (no offense to Steve, or Pat).

[Neil_Roberts]

In my opinion, the aerospace industry is in dire need of engineers who have learned the lessons that FSAE teaches. So, I'm in favor of anything that makes FSAE relevant to aero majors. Of course there is a natural overlap between motorheads and wingnuts, but that's usually not enough to recruit aero majors into FSAE. It's certainly not enough to get most aero faculty interested.

Here is a data point to consider: all of the design semi-finalists at the 2010 FSAE California event had at least one aero downforce device.

Full disclosure: I've been a frame and aero design judge at California every year, so I'm admittedly biased.