Wings??

[winnie]

Please excuse my ignorance as i am not completely familiar with the regulations you are competing in but i have a question regarding wings.

I have noticed a couple of teams running large high mounted main wings (my alumni included). The question i have is with such light weight vehicles competing at relatively low speeds, what weight 'budget' would you apply to a high mounted aero device. How many kg of wing mass would you tolerate for a how much downforce? particularily if mounted above the roll hoop? I would have assumed (and it's my pet thing anyway with race cars) that a low CofG would be of great importance to these vehicles?
Just curious, and have been impressed with the thought put into these cars, i'm sure there is a justification.

[winnie]

Please excuse my ignorance as i am not completely familiar with the regulations you are competing in but i have a question regarding wings.

I have noticed a couple of teams running large high mounted main wings (my alumni included). The question i have is with such light weight vehicles competing at relatively low speeds, what weight 'budget' would you apply to a high mounted aero device. How many kg of wing mass would you tolerate for a how much downforce? particularily if mounted above the roll hoop? I would have assumed (and it's my pet thing anyway with race cars) that a low CofG would be of great importance to these vehicles?
Just curious, and have been impressed with the thought put into these cars, i'm sure there is a justification.

[drivetrainUW-Platt]

from our extensive calculations we have determined that downforce is equal to the weight of the wing, thus the bigger and heavier the wing the more downforce one will experience, wings also allow for more sponsor decals as well

[Jarrod]

on the car we ran at Oz last year and UK this year, the CG height with no driver or wings was around 225mm, with wings it was still less than 245mm. The driver position was also reclined a long way. It should be possible to get a wing setup like ours to around 10kg with some work and experimentation. Last years setup was a little over 15kg including mounts etc. I have seen a lot of cars where the driver position will be hurting CG much more than our wings do.

[winnie]

Thank you for the replies, yes i had wondered about the driving position on some of the cars, the driver being a major weight component of the total package of these cars.

PS. I'm ex Monash - pre wind tunnel days unfortunately

[Andy Pate]

A lead weight in the bottom of the chassis would be better than a wing, Producing downforce and Lowering CG - BARGAIN! Aerodynamics for formula student is a bit of a turkey but does makes a good academic project.

[albino_insect]

It seems to me that ground effects systems are a much better compromise for FSAE cars than massive wings. Most designers running real cars in open wheel series would go crazy with ground effects if they could and that is why they are so closely regulated. It seems that there are two camps in FSAE, those with no downforce and those with outrageous wings that have more frontal area than the rest of the car. The ground effects method seems like a good compromise with good downforce with not too much drag. That's my two cents anyway.

[Drum]

FSAE 2004 Rules:

3.7.1.6 Ground Effect Devices - Prohibited
No power device may be used to move or remove air from under
the vehicle except fans designed exclusively for cooling. No
power ground effects are allowed.

[Mark Bacchetti]

I'm assuming albino_insect is referring to an underbody diffuser instead of ground effects. Underbodies are definitely a good deal... your CG isn't hurt and the downforce comes without as much drag penalty as wings. The design can definitely be harder than designing a wing package.

The 2004 Detroit autocross and endurance track was little faster than previous years. Is that making anyone think twice about downforce?

I noticed that Australian teams are starting to incorporate wings into their designs. Looks like UWA and Adelaide have them for Australasia 2004.


Cal Poly Pomona

[clausen]

Andy, you're being sarcastic about the lead aren't you?

We have been hearing that the courses are getting faster - Australia included.

We've done some pretty lengthy venturi tests in our mini-wind tunnel, and concluded that they really arent going to be worthwhile. It's possible to get some measurable downforce with the skirts on the ground, but as soon as you start to get a gap at the bottom of the skirt, downforce drops dramatically. I think we found something like 6kg of downforce at useful speeds, with the skirts touching the ground. Remember the rules say that nothing is allowed to touch the ground except for the tyres.

[Drum]

I agree Paul, I think the Australian track will be quite fast this year. The basic shape of the track does not leave too much to the imagination, looks like it will include a few fast straights and lots of slaloms.

I am guessing that the crest section of the track will be one of the slower sections, although it would be interesting if it was a big fast sweeper (unlikely).

Looking forward to being suprised though...

[Mark Bacchetti]

Paul, did you account for a ground boundary layer in your small scale wind tunnel tests? Remember, the air in ground effects is moving at the same rate is the ground itself, ie no boundary layer. A moving floor should make a difference in wind tunnel tests.

Ground effects are very attractive to other forms of racing because they operate at much higher speeds, where drag is a larger issue. I'm not saying it's not a factor here, but when is the last time you saw F1 teams running the same angles as UMR and us?

I seem to recall someone from UTA mentioning that they broke an undertray because it made so much downforce once. Anyone from UTA care to comment?

With our 2000 car, I've been told that there was a noticeable difference between available power at high speeds (50+ mph) with and without wings. A few weeks ago we were autoxing the 04 car and broke our wings on a cone strike, so we drove the rest of the day without. The most noticeable difference was in braking distance, but high speed stability and grip were also very apparent. There was no large effect on acceleration at high speeds though. At the (traditionally) low speeds of FSAE, you can argue against wings and I can understand why you feel that way. But at an autocross course, it was a ~3s difference on a 60s course.
If FSAE is truly heading in that direction, wings should become a serious factor in performance of the top teams.

[clausen]

Hi Mark,

I'm actually in suspension, so I'm not sure how the guys accounted for the lack of a moving floor.

Speaking of UTA, I'm interested in why they moved away from that floating undertray system. Does anyone from that team post on here?

[JPaolicchi]

Wings are a good thing. Our car had them in 1991 when we won the endurance race. But they must be carefully designed and fabricated to be very light. A 3 foot by 6 foot wing can weigh around 15 lbs if built out of carbon fiber.

Here is the math:
The 2003 results show that an average autocross speed for top team = 40 MPH (59 ft/sec). From driving the course in my Sentra I know that several of the turns are 40+ MPH.

Force = 1/2 x desity x velocity2 x coef lift x area = 1/2 x .00238 x 59^2 x 2.5 x 18 = 186 lbs of down force.

186 lbs is a lot of down force for a 600 lb car.

A coef of lift of 2.5 is possible with a multi element wing at these speeds.

ground effects don't work becuase the maximum lift coef for ground effects is 0.6 max.

[DJHache]

Allrighty, but by the same token,

Fdrag=1/2 x desity x velocity2 x coef drag x area = 1/2 x .00238 x 59^2 x 2.5 x 12 = 124 lbs of drag

Now this is a brute calculation, but at the wheel, you've got
power = Force*velocity = 7332ft.lbs/sec or roughly 13 horsepower of drag to overcome... and that's only for the wing

I also think its hard to back up the need for an extra 186 pounds of downforce when tire data are so difficult to come by. As far as anyone knows, the tires don't want that much additional weight.

[Denny Trimble]

Extra normal force (downforce) creates extra lateral force capability, and if your mass to move laterally (vehicle mass) doesn't increase much, you pull more lateral g's.

Maybe the tires don't want it, but they'll have to learn to take it http://fsae.com/groupee_common/emoticons/icon_smile.gif

[nathan s]

One thing to not forget about when considering wings is the lateral force from the moment that the mass of the wing creates around a turn.

I was really wanting wings until the chief engineer sat down with me and we did some calcs on it. We figured out that we didn't go fast enough to gain any real benefit from wings. We even used an upside down 747 wing (coeff of lift of .7 I think) and couldn't get enough downforce to help around the turns.

[Rob Davies]

747 wing has nowhere near the lift coefficient of a multi element wing. From my reading the multi elements allow a great camber and also the gap between the elements reduces in size from top to bottom so the air gets lower pressure as it goes through it and this effects the whole underside of the wing positively. I think a triple element wing can get lift coefficients of over -3

[John Bucknell]

Javafoil (http://www.mh-aerotools.de/airfoils/javafoil.htm)

Play with this some, and your eyes will open.

[Marshall Grice]

Just to clear up some of the math above. Your Cl's should be higher then 2.5 and Cd's should be much lower then 2.5 otherwise the wings wouldn't be worth it. Ground effect and tires have very interesting effects on wings. Overall i'd say 200lbs of downforce for 25lbs of mass is a fair trade. If only we could get that kind of benefit from our battery we'd be set.

[Paul V.]

Hi everyone,
I am the moron who was playing with the 747 example so let me explain the fact that I was just playing with some figures without books or calculators, I just inserted that # for a figure. That said however, I am quite curious about some of the figures presented. Has anyone physically measured downforce on the wings in the turns? I noticed that the Java sim applet has some quirks . Most notably at real high angles of attack, (since the program explicitly states it does not model Laminar flow separation)you can induce extraordinary Cl without the realistically high Cd. I wonder if this is any relation to FOIL SIM which is also notorious for these shortcomings. I am not saying this is impossible, or that I don't believe it, just it is in that grey area that I (we) would test if I had the resources and were not in a rebuilding year with 9 active members on the team.
I am no authority on this, but I work at Computational Fluid Dynamics Research Corporation (CFDRC). Some of you may use the software we developed CFD-ACE or the like. We do Aero analysis for Defense, F1, Le mans, and other teams all day long, and our stuff gives inaccurate data at times. ( and it takes 100 hrs. of Cluster CPU time for most SIMS). I've added some pics from the site below (sorry couldn't use any racing ones).
In short before I would put anything that involves a potential performance tradeoff (ie a 20+ lb weight with 100s of lbs of drag on a 3ft moment arm) involving Aerodynamics on a car in competition, I would test, test, test. And not just in CFD or in wind tunnels. I love Aero effects, and love to see teams explore them. I have just seen some (by no means all [kudos UTA]) teams use them on blind application of rules of thumb. We should not be so arrogant to think that so many of the top teams have not thought this through and are to dumb to realize their benefits. I would love to see why Cornell GT, Wollongong, and others do NOT use these. (Sometimes I sit and dream about having CALSPAN at my disposal but I digress.) Rock on to anyone who has wings that work. I hope we can get there in the next couple of years.
http://www.cfdrc.com/bizareas/autochem/images/auto_grid.jpg

Paul Vaughan
Univ. of Alabama Huntsville FSAE

[Mark Bacchetti]

Has anyone read the October issue in Racecar Engineering on UMR's 2004 wing package? The article starts to uncover some interesting low speed aerodynamic concepts that may impact the future of wing design in FSAE. Definitely worth reading.

-Mark
Cal Poly Pomona

[NJM.]

I just wanted to add some stuff that we learned at NC State when I was there in grad school. As part of a masters I built a set of front and rear multi element wings to test at autocrosses and we did some straight line coast down testing. The wings were not light at all since the main elements were built from scrap MG Lola LMP wings which were shortened. The LMP wings were built for 1000+ lbs. of downforce so they have some serious internal spars. Everytime we have taken the car to an SCCA autocross event it is definately much faster with the wings. The corner speeds average around 45 mph at those events compared to the fsae course corner average of about 30 mph. On our fsae style (25 mph avg. corner speeds) practice course the car with wings has been only slightly faster and maybe not necessarily worth carrying around the wings for the acceleration and skidpad events. At speeds below 30 mph the effects on cg and the weight overcome any extra downforce for our setup.

Looking at lift and drag, a CL of 2.5 should be easily achieveable. Our package produces a car CL of approx. 2.5 with no underbody and the wings no where near the limit of the rules. As for drag, the only drag that matters is the induced drag produced by the component of downforce, and this matters only slightly. I wrote a SAE paper on that subject that may or may not be helpful. I can probably email you a copy if you want one. On a SCCA style course you might actually get into the drag/downforce trade off but with speeds seen on an fsae course you should not even think about drag unless you are trying to attach a barn door to the front of the car.

I am attaching some plots from our straight line testing as well as a picture of our car. The straigt line testing was done by accelerating on a long straight road up to 80 mph then pushing in the clutch and letting the car coast down to about 50 mph or until we ran out of road. I would encourage any team with wings to do some of this testing as it is the most accurate way to simulate drag and downforce and if you can strain gauge your pushrods you can get really accurate df numbers. If you look at the first graph which is the car decelerating with the wings on you can see the ground speed go to 80 and then a slightly non linear deceleration to 50 mph. You can also see that with the speed increase the 4 wheel positions are going down due to downforce and as the car decreases speed the car rises back to its normal ride height. You can also see the front and rear downforce increase and decrease as speed falls off with the front decreasing non linearly and faster than the rear df due to ground effect falling off with ride height increase. From this we can calculate the car CL of about 2.5.

The second plot represents the car with no wings. In this config the car actually produces a little lift which would be expected from the carbon tub and the big low pressure coming out of the cockpit hole. The deceleration rate is linear with speed and there is no suspension deflection when the car is decelerating.

In my experience, I believe wings can improve lap times in fsae especially if the courses are getting faster with fewer tight corners. I believe a car that has a bad suspension to start with and the best wings still cannot beat a car with sorted suspension (ie Cornell). I do believe a team like Cornell could put wings on thier car and go slower until they developed their suspension package to hold a good aero platform at cornering attitudes. These cars are just a big complex system of bottlenecks you cant just bolt anything on anymore and expect speed improvments without understanding the whole system.

For teams running a front wing in ground effect or a underbody, what changes in your suspension package have you made to help improve your aero platform? Do you run stiffer across the board? Do you look at corner entry, center and exit attitudes and try to optimize your aero platform for a given section? I know in NASCAR our suspension package is more important for its aero effects than it is for its grip effects on many of the tracks. We compromise balance and grip with our shocks and springs all the time to get the nose down on entry and keep it there through the corner.

Sorry for the ultra long post.

Noah McKay
Aero Engineer - Richard Childress Racing


http://home.triad.rr.com/wmracing/fcar_wings_1.jpg

http://home.triad.rr.com/wmracing/wings_on.jpg

http://home.triad.rr.com/wmracing/wings_off.jpg

[Denny Trimble]

Noah,
Awesome post, thanks for sharing your information!

[Charlie]

I second Denny's thoughts. Car looks pretty good with wings!

Noah, check your PMs.

[RickyRacer]

If you could email me a copy of the paper, I would appreciate it.

[Jarrod]

very impressive Noah, that is the sort of test we have always planned, but haven't got around to doing, maybe after comp this year. Our biggest issue is the fact that we mount our wings unsprung, so measuring downforce isn't quite so easy, but there are ways. I would greatly appreciate a copy of that paper. Did running the suspension stiffer for the aero affectyou much in terms of low speed grip?

jpham1 at student.monash.edu.au

[Jon Huddleston]

Sorry I didn't reply sooner guys. For the question "did UTA break their undertray from too much downforce?" No, only front wing endplates have broken from high speed cone impacts. Funny story though, we pulled the floor of our windtunnel platform off the base at around 40mph. "Why did UTA go away from floating undertray?" We went with a new package this year that has conventional chassis mounted undertray with "split wings" that connect independently to each susp belcrank. We call it unsprung aero or aero-into-belcranks. The floating undertrays of '02/'03 was a great idea and made more downforce than our current package. But, with the new package we were able to drop 30 lbs and lower the ride height by atleast an inch. So this loss of downforce has been more than overcome by the increase in performance. '04 was more than 2 seconds faster at SCCA Nats and that has become pretty much the norm at local autocrosses. Oh yeah, and were pretty sure the carbon wheels help out a bit too! Our website should be updated in the next couple weeks with photos.

[Joel Miller]

We here at UWAM are just getting started on aerodynamics this year and have nearly finished manufacture of our first set of wings. We will be doing some testing soon after the FSAE-Aust, getting it ready for the 05 US competition. We've found that these wings can be made pretty light, and I think an aero pack for ~7kg is very achievable.

We've got have a more rearward weight bias than most (~57%) so more rear wing is in order. With a more rearward COP, the car should be less sensitive to front wing ground effect variations caused by roll or pitch.

Regarding the earlier discussion on undertrays, our studies corroborated what Paul at Uni Adelaide and others have said: venturi tunnels seem to have little worth in FSAE. This is mainly (I think) due to the small track width of the vehicles and thus the limited width of the tunnels. Our CFD work suggested that about an undertray would generate only 1/4 of the downforce of a good set of wings. I think that UTA are doing it the right way: theirs weighs almost nothing and does not compromise ride height.

I am interested in the suggestion that drag almost doesn't matter in FSAE. Have any aero teams found that due to induced drag, going for extra downforce isn't worth it? Does fuel economy reductions compromise any of the aero teams? Or are the biggest gains in FSAE aero to be had from getting the most thumping downforce possible?

Noah:
Top post. I'd love to read your paper. Please send it to millej02@tartarus.uwa.edu.au and uwafsae@ee.uwa.edu.au Thanks.

[jaywong]

G'day from Adelaide

Noah, could i please have a copy of the paper too.
jay.wong@student.adelaide.edu.au

Admire people who are pro-wings. After all, it's all a learning curve for us.

Was wondering if anyone has experience in 2-D grid generation of multi-element wings using Gambit. Struggling a little.

Cheers

Jay Wong

University of Adelaide Racing Concepts

[Big Jimbo]

Brilliant post mate, very interesting and detailed. Would really appreciate a copy of the paper if you were able to send it, would love to read on into the topic.(Skeltz84@hotmail.com)

-James

University of Herts

[NJM.]

James,

Just sent you a copy of that paper. Any teams doing any wing research? Wollongong? UTA? that they would like to share. Any experiences or data from FSAE 05? I hope to have some CFD of our wings to post soon if anyone is interested.

Noah McKay
Aero Engineer - Richard Childress Racing

[andyman61]

I'd appreciate a copy of the paper if you could send it to aadpn6 at umr.edu

We haven't done any wing research yet for the 2006 car, but I'm sure we'll have started by the time the summer's over. I hope to see more teams running aero at future competitions!

[kwancho]

I'd also like a copy of the paper.
kwancho at stanford.edu
Not for our first car, but something we might want to look into for the future.

[nathan s]

What the heck, I might as well ask for one too. My guys will probably be interested in it. Could you sent it to nsandmeyer @ chargermotorsports.com. Thanks,

[Dr. Bob Woods]

Noah,

I just read your posts on FSAE.com. Good work and thanks for sharing. I
would like to have a copy of the paper.

-Dr. Bob Woods, UTA
Woods@mae.uta.edu

[Alastair Clarke]

Noah,

Any chance of a copy of the paper as well?
clarkea7 at cardiff.ac.uk

Thanks

Alastair

[Wizard]

Noah,
While you sending out emails could you send me a copy also.

ekm24@drexel.edu

Cheers
Eric Moyer
Drexel Racing

[Agent4573]

I'd like a copy of it too while you're at it.
paul@hatespeople.com

[TG]

Could you please send a copy of the report to saeasu@asu.edu

Thanks.

[Matt Gignac]

I'm starting to feel left out here...

Could you send it to matt.gignac(at)gmail.com also?

Thanks, and those wings look sick!

Matt Gignac
McGill Racing Team

[RiNaZ]

hey noah ...
glad if you could send me a copy too ... at

mohdnurm at erau.edu

thanks a bunch!

[Gunman]

Noah's email addy seems out of date...anyone have his paper, or an updated email, that they could share?

Thanks,
dkieffer(at)moslerauto.com

[NJM.]

Dave, Rinaz, etc.

Sorry if you were waiting on a paper that never came. Been busy with work blah, blah. Anyway, I haven't been to the site in a while and a friend told me to check out this post. Anyway, my paper is now online at:
SAE 2002-01-3294 (http://home.triad.rr.com/wmracing/sae_2002-01-3294.pdf)
I hope somebody gets something out of it. I haven't looked at wings in a while since working on a NASCAR team. I still like wing discussions and would really like to see more informaion/testing results like those I shared in this post much earlier. By the way I just read a paper by Cornell in a Fluent Automotive CFD Confence Book. Great paper, very general. As soon as a sorted car like Cornell shows up next year with wings and wins walking away, everybody will have to have them. Wings represent the last small percent of perfomance envelop that is now open because cars like Cornell have gotten near the limit of performance in thier current configurations. Thats my prediction anyway. I hope somebody, and not Cornell (sorry Judd and Jazzy), proves me right.

Thanks for the interest in the paper.

Noah McKay

[Gunman]

Noah,

Thanks for the link.

-Dave