Hatin on wings and monocoques

[Jersey Tom]

Yup, Jersey Tom is bringin the hate on two of the most prominent things in high-end Formula racing recently. Or at least their application for FSAE teams.

Allright fine well I'm not really bringing all sorts of hate necessarily but I would not personally put them on a FSAE car. I've always been a skeptic of everything (which IMO is required of all engineering, especially at this level), and being an alum now, I am even more so.

Anyway. Not knocking the teams that use them, but I'm curious to see other team's analytical justifications of monocoques or enormous wings.

Monocoque

Did a quick model of a chassis goin into a turn as two rotational spring mass damper systems (F&R end of car with susp) linked by a torsion spring (frame). Idea was since the rear load transfer and slip angles are initiated by the front, the speed at which they do so (and turn in) is in a big part affected by chassis stiffness. Put a step roll moment on the front end and watched as it and the rear end moved around. Not the best model of what's going on, but not a bad ballpark. At 1000 ft-lb/deg the response was very quick, on the order of .01s, which I deemed good enough. Beyond that it was a point of diminishing returns getting response to thousandths of a second. Very attainable with a steel frame chassis.

Steel frame materials - $350, fairly quick and painless other than the stupid large gaps I had to weld at times, and seemed a lot more bulletproof and easier to analyze than a carbon tub. It amazes me sometimes that after this, and after not even being able to vacuum resin infuse a flat carbon plate this year, some people are still considering trying a vacuum infused monocoque at CU.

In testing we could make damper adjustments and either end of the car would be plenty sensitive to them, and the car was very neutral and predictable through turns and slaloms so I feel pretty happy we have a stiff enough chassis. There's definately large potential weight savings with a tub, but that assumes you can do good accurate analysis of one, which as I understand is a nightmare.

Wings

Now I don't doubt the importance of aero, and I've been looking at it for a project car I intend on building in Ohio. Running some idealized numbers, on wings with fairly high aoa's (near stall, tho admittedly single element), I find it hard to believe the claims I hear walking around of multiple hundreds of pounds of aero download at 60mph. Perhaps this is with some massively efficient venturi diffuser, though I'd want to see pressure sensors on the top and bottom of the car to be convinced of it.

Beyond that, even if you had an appreciable amount of download at low speed, the thing that I think kills it for FSAE cars is the wild high load sensitivity of FSAE tires (6x higher rate than I'd expect to see on a GP car from even the early or mid 90s). Even if you can get some appreciable increase in available down force, the roll off rate of the tires lateral grip capability makes the increase in available lateral force small.

Beyond the usual headache of problem solving and fixing issues on a new FSAE chassis every year, and figuring out mechanical balance, I would think that having to figure out aero balance and how to get enough performance out of the package to make an appreciable amount of difference would take a lot of valuable time.

But that's just what I think. Other thoughts?

[Jersey Tom]

Yup, Jersey Tom is bringin the hate on two of the most prominent things in high-end Formula racing recently. Or at least their application for FSAE teams.

Allright fine well I'm not really bringing all sorts of hate necessarily but I would not personally put them on a FSAE car. I've always been a skeptic of everything (which IMO is required of all engineering, especially at this level), and being an alum now, I am even more so.

Anyway. Not knocking the teams that use them, but I'm curious to see other team's analytical justifications of monocoques or enormous wings.

Monocoque

Did a quick model of a chassis goin into a turn as two rotational spring mass damper systems (F&R end of car with susp) linked by a torsion spring (frame). Idea was since the rear load transfer and slip angles are initiated by the front, the speed at which they do so (and turn in) is in a big part affected by chassis stiffness. Put a step roll moment on the front end and watched as it and the rear end moved around. Not the best model of what's going on, but not a bad ballpark. At 1000 ft-lb/deg the response was very quick, on the order of .01s, which I deemed good enough. Beyond that it was a point of diminishing returns getting response to thousandths of a second. Very attainable with a steel frame chassis.

Steel frame materials - $350, fairly quick and painless other than the stupid large gaps I had to weld at times, and seemed a lot more bulletproof and easier to analyze than a carbon tub. It amazes me sometimes that after this, and after not even being able to vacuum resin infuse a flat carbon plate this year, some people are still considering trying a vacuum infused monocoque at CU.

In testing we could make damper adjustments and either end of the car would be plenty sensitive to them, and the car was very neutral and predictable through turns and slaloms so I feel pretty happy we have a stiff enough chassis. There's definately large potential weight savings with a tub, but that assumes you can do good accurate analysis of one, which as I understand is a nightmare.

Wings

Now I don't doubt the importance of aero, and I've been looking at it for a project car I intend on building in Ohio. Running some idealized numbers, on wings with fairly high aoa's (near stall, tho admittedly single element), I find it hard to believe the claims I hear walking around of multiple hundreds of pounds of aero download at 60mph. Perhaps this is with some massively efficient venturi diffuser, though I'd want to see pressure sensors on the top and bottom of the car to be convinced of it.

Beyond that, even if you had an appreciable amount of download at low speed, the thing that I think kills it for FSAE cars is the wild high load sensitivity of FSAE tires (6x higher rate than I'd expect to see on a GP car from even the early or mid 90s). Even if you can get some appreciable increase in available down force, the roll off rate of the tires lateral grip capability makes the increase in available lateral force small.

Beyond the usual headache of problem solving and fixing issues on a new FSAE chassis every year, and figuring out mechanical balance, I would think that having to figure out aero balance and how to get enough performance out of the package to make an appreciable amount of difference would take a lot of valuable time.

But that's just what I think. Other thoughts?

[Ashley Denmead]

Here's my main thoughts:

Sometimes its not all about performance in seconds on the track. We must remember that FSAE is an educational exercise as well as a good way for us to release our creative talents. As an engineer i agree with your arguments against monocoques and wings to some extent. We've built monocoques for the last 4 years and mainily for the weight benefits initially but the experience and what you learn in the field of composites is very worthwhile and has set quite a few of us up post university. So in summary maybe the teams with monocoques and wings dont always do them for track speed reasons! It could be that their university is heavily into composites or aerodynamics and sae is a great teaching/learning tool. It could also be that an individual student wants to learn some particular skills.....so many considerations other than the ones you mentioned.

Ash

[Kyle Walther]

did you see the autocross scores? as soon as the organizers opened up the course just a little bit, the aero cars took off. It's hard to look at that 1.2~1.5 second gap and tell me that aero does not work.

But like Ashley mention this was a learning experience. The only reason we have wings in b/c a highly involved member wanted to use wing development as a capstone. And from that capstone he landed a pretty sweet job. So, right there i would say it was worth the added complexity and weight.

[Maverik]

Yah, I was about to chime in on the same thing... as soon as I saw the autocross this year I knew UTA and OU would be up there. Clearly the aero works, but anyone see the cone shovel UTA used in the skidpad?

[Jersey Tom]

I am looking at the autocross scores right now. UTA and OK did very well, yes, but there's also a bunch of schools up there without wings.. UWA, Wisconsin, Helsinki, Florida.. who always bring damn fast cars. Same goes for skidpad, and for endurance.

In endurance, the biggest event and the one I'd tune the car for the most, UWA was a second per lap faster on avg than Wisconsin, who was a second and a half faster than Cincinatti, etc. Extremely quick (and well driven) non-aero cars.

Clearly those cars are all fast, but that doesn't necessarily correlate to aero working, especially with large variability in drivers, track layout and conditions, car setups, etc. To be convinced that the aero was really doing its job rather than just talented drivers or setup engineers I'd love to see pushrod load data from a gradual acceleration run from say 0 to 70 mph, and then numbers from a high and low speed skidpad.

And I completely agree that its an educational experience foremost and I'm all for trying new things, but I'm a numbers guy and wanted to see some analytical stuff behind it all. Mostly I wanted to start some good discussion.

[Ben C-M]

I think your analysis of the effect of chassis stiffness isn't representing whats actually going on very well. A compliant chassis is also going to affect weight transfer in a corner. Basically the effect that this has is reducing the effect of modifying the roll stiffness distribution. With a very compliant chassis, changing an ARB setting will have virtually no effect.

You're definetly right about diminishing returns as the stiffness is increased, but any team should be doing a full analysis to decide on a suitable stiffness, then decide what the best way to achieve that stiffness is. Furthermore, your selected stiffness of 1000 ft.lb/deg would be at the contact patch, which means you'd need a significantly stiffer chassis because of deflections in the suspension, upright, hub, wheel and tire.

The other big thing to consider is what resources a team has available to them. Some teams don't have the facilities/aren't allowed to weld in their shop, but have extraordinary access to carbon fiber and layup facilities.

As for wings, every year the viability of wings is going to be different. If there's a fast track like the autocross was, winged teams will be viable. If it's a slow track, they wont be.

An interesting change to the rules would be to allow teams to add/remove wings for different events.

[Mexellent]

I think there is only one good reason not to run wings: Its a ton of work.

If you are going to do an aero package you need a guy who lives and breathes aero. Youre also going to need to give him a very powerful computer, and alot of time (multiple years).

We have taken our cars to the wind tunnel in the past to make sure that we are making the downforce we designed for. I can fetch the aero guy if you really want me to.

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I think your analysis of the effect of chassis stiffness isn't representing whats actually going on very well. </div></BLOCKQUOTE>

It certainly isn't. But with none of us having any formal exposure to this sort of thing and trying to figure it out on our own it was a first initial stab to see what was going on. I agree that compliant chassis' mean the front and rear ends aren't sensitive to setup changes, which is why I pointed out with our chassis makinig small damper adjustments very definately noticeable so I'm happy with our frame.

And yes certainly 1000 would be hub to hub, which is why we engineered the actual framework to 1400.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The other big thing to consider is what resources a team has available to them. Some teams don't have the facilities/aren't allowed to weld in their shop, but have extraordinary access to carbon fiber and layup facilities. </div></BLOCKQUOTE>

This surprises me. I wouldn't have guessed. I've been to schools that have both but haven't seen a place where composites dominates with little access to metalworking.

Mexellent - I'd just be curious to see what actual test numbers you have for vehicle download at competition speeds (40, 60, 80mph say). And really whats important beyond that is the increase in lateral grip you'd expect with very sensitive tires.

[Scott Borg]

Jersey Tom, I can get you DAQ logs from Cal Poly Pomona's 2004 car, which ran wings.

Photos here:
http://www.csupomona.edu/%7Efsae/photos/2004/index.htm


We did some acceleration / top speed runs, similar to what you're describing, with linear potentiometers mounted on each damper to measure downforce produced. I was pretty new to the team at this point, so I don't know what the results of the calculations were, but I can give you the raw data if you'd like it. We have an AIMsports data acq.


I'd be happy to trade this info for a datalog that shows one of your cars shifting gears during an acceleration or endurance run. I'm looking to compare shift times to our pneumatic/electric shifter, so it would help if you've got RPM, engine speed, and longitudinal acceleration plots.



By the way, our drivers loved the wings, we measured faster lap times and increased lateral g's (about 0.2 higher IIRC) on autocross courses. The main reason CPP quit building winged cars was the extra manufacturing time weight added to a car that is usually a bit heavy and behind schedule. Also, most of the recent FSAE track layouts have seemed unfriendly to winged cars.

Scott Borg
scborg@csupomona.edu

[John Stimpson]

Tom,

Where did ths $350 value come from for a spaceframe? Our steel is all donated, but we easily have $1500 in tubing making up our spaceframe, and that doesn't include scrap generated in tube fit up.

That said, I'm really torn between a spaceframe and a tub. There are a lot of pros and cons to both. I did 99% of our spaceframe this year, and for a number of reasons, but mostly because I'm a proud welder and want my welds to look perfect, I'm anal retentive about fitup. There is also considerably less warpage in your frame if your fit up is good by the way. Anyway, I'm pretty competent at tube fit, and I have hundreds of hours in our spaceframe to get it just right. I easily have 40-50 hours in welding on it as well, and damn, its TEDIOUS to weld these things... Don't know about you, but my weld quality is mostly dependant on how close I can get my face to what I'm welding on. We have a number of chassis nodes with 7 tubes at the node, and each tube has a minimum of 3" of weld length around the circumference, thats over 21" of tedious, painful welding, which I don't do all at once, to minimize warpage.

I don't know composites very well at all, but it seems to me that once you have a good mold, its far less tedious to get your tub. Again, I may not be speaking intelligently here, but it seems that a tub is considerably less work. But, when you realize you've forgotton something on the chassis, its terribly easy to weld it onto the spaceframe...not so terribly easy to add/incorporate it to the tub. What if you bang up the car a litte??? The tub is now scrap and you try again. A steel chassis can be repaired (not always of course).

Clearly, weight is a big concern with FSAE cars, and the tub is a good bit lighter. The mass of our chassis is about 35kg, and I know a tub can beat the hell out of that.

If (and this is a huge if) the team could design a tub that was "modular", meaning bolt on suspension points that were fairly adaptable, the tub design could be used for a number of years... We have a shop with a 5-axis gantry CNC that will carve out any tooling board mold we want for free... I'd love to see a sweet mold made that we could make tubs from. We lack an autoclave however.

I dunno, I certainly don't hate on the monocoque... I'm jealous I think, I wish we could/would do it.

[Jersey Tom]

All of our tube is purchased. We used to get it in the huge lengths from one or another alloy tube retailers around here. Order would usually be $1100+

Then we found Chassis Shop's prices. Absurdly cheap. Big saving on shipping as well going with 8' lengths shipped UPS rather than the full lengths shipped on a truck. I am 95% certain that all our chassis tube amounted to $350 this year. Blew my mind.

Believe me I feel ya on the frame welding thing, I got to weld our whole thing this year. Fitup and visability were definately key. I went with shade 8 and 9 helmets which I cleaned off and put new polycarb on, and it made a huge difference over old nasty shade 10s. Fitup obviously very important. I didn't do the fitup on the tubes, so I'd be goin along all happy on some good fitup stuff and then get in on the other side to see .125-.250" gaps and would be all sorts of pissed off, at 3am with no one else around. Think the worst node I had was an interior, hard to reach one.. 6-7 tube node with .035, .049, and .065. Fitup ranged from good to pitiful.

But I digress.

Getting a good tool and mold for a tub is the first step. But (a) designing the ply orientation right (b) being able to analyze it accurately [as opposed to a simple beam element model] (c) getting the layout right (d) ensuring all the layers are well laid-up and laminated... is very difficult. Screwups are costly. For example I know of one team who had to scrap an entire tub because when they went to lay out the prepreg they unrolled it on the shop floor.. which hadnt been swept in some time.. and none of the layers laminated together worth a damn. Oops! With regard to analysis, I know a team who projected the stiffness of a carbon drivecase to be 5000 ft-lb/deg and it wound up being about 500.

The only benefit I see is the weight. I think our frame weighed in at 58-60 lb, full 8-10lb reduction from last year. For the cost and time investment I see better places it could go.

[BrendonD]

This is a great thread.

First off let me say that I am a freshman and I know absolutely nothing compared to some of you and what I am about to say is completely my own opinion based on what I have heard/done.

It is unlikely that we will run a monocoque. Ever. That being said here's why I personally don't want to run a monocoque. We have a brilliant group of guys working on the car right now, and we change things up quite a bit based on how things can be intergrated with each other. (hell, we talked about running colin chapman frame members). With a monocoque things are really set in stone, and unless you build in adjustability of the suspension in the tub, which sounds like a huge pain in the ass, you're stuck with whatever suspension geometry you chose when you gave the hard points to your composites guys. So many things have changed on our car this year I can't tell you.

A steel spaceframe is also much more available to be built for us. Granted our Solar Car team has a bunch of carbon fiber, but they also think they are going to make their space frame out of 6061 T-6 tubing. (I don't even want to talk about it...) Steel tubing is relatively cheap, pretty easy to weld together, and if you know what you're doing it can go together pretty easily. I've already put some serious thought into making a car from scratch over the next few summers, and I'd absolutely use steel over a tub, it's just so much easier to make it do what you want and integrate more parts into the chassis. I'd also feel you learn so much more about manufacturing when you actually have to MAKE your car from scratch and not just figure out how to bolt stuff to a tub.

Just my thoughts.

[VFR750R]

After being on a team that makes a steel frame and seeing a team do a tub, I feel the steel frame is the way to go.

It is definitly no less work to make a tub and for such a small car it has no measurable increase in performance. Since you still have to bolt a steel rear sub frame to it, you now have a hybrid and have to figure out a way to reliably assemble the two and maintain your stiffness. I believe thier tub alone was supposed to be twice as stiff as our steel spaceframe, but with subframe, measured through the suspension, the tub had no stiffness advantage. It could be that our suspension design had better load paths to the frame, but that in itself is proof that a tub is only as good as what you bolt to it. Weight wise it would have been very close although I don't know the exact weights. Even if the tub was lighter, how light does it have to be to be an advantage?

Once you've made your tub, now you have to attach things to it. If you did a good job of mocking up where things will go, and designed hardpoints into appropriate places it still won't be easier to package things then a steel spaceframe.

The particular team I saw, had trouble accessing their pedal bay, and had spilled brake fluid into the bottom. I don't know what brake fluid does to epoxy, but I know it won't degrade 4130.

Back to hybrid frames, you still have to have steel roll hoops. With a steel spaceframe you can use these required roll hoops to help your stiffness, with a tub, it's possible to have them contribute, but in most cases its an add on contributing nothing to the frame but weight.

I've never talked to the guys from Penn state, but I remember talk of a full titanium tube frame. That seems like at least as good an idea as a tub...until 2004 when the rules committee insisted steel be the only choice for the roll bars. The frame would be nearly as strong as a 4130 frame but would also be less the 60% the weight. I've not seen a tub in FSAE weigh only 60% the weight of a comparable steel frame.


Last, in 2003 we crashed our car hard into a granite curb. there were 19 out of 60 frame tubes buckled or bent. Not to say a tub may have had suffered less damage but we were able to replace all the tubes and come to competition less the 10 days later. If there was major damage to a tub, you'd have to lay up an entire new tub.

[Jersey Tom]

The only reservation I'd have about a titanium frame is the loss in weight would come with a loss in rigidity as titanium is considerably less stiff than steel, appreciable if the frame is built from a strength standpoint.

Tungsten frame. Oh yea!!

[Chris Allbee]

A note on wings: Done right, they are fast and not much of a weight penalty. And thats fast on ALL circuits. Granted the difference between winged and non-winged cars will be less on a tight and slow circuit. However, done correctly the aero car will be faster. Problem is you can't just slap wings on a vehicle without considering the stiffness and balance of the suspension and expect it to be easy to drive fast. However, make an honest effort to to it right and you can end up with a fast car that is balanced well and easy to drive quickly. Its a lot of work, but it is well worth it once its figured out (at least to some degree). And as for not seeing a lot of benefit from using 1 element wings...try mocking up some of the configurations you see at comp with one of the free programs out there (Java-foil, etc.) and see the difference. Its not entirely out of the realm of possibility to see 70% of the vehicle's weight at 50-60mph.

I can go on and on about the benefits of aero, but i think our first enduro driver made the best case for it in detroit. One hand holding a faulty switch, electrical system failing, shifting and steering with the other hand, and still putting down an average lap within 4.5 seconds of UWA. That would have been good enough for 10th in endurance. ONE-HANDED!

[Alan]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VFR750R:
Since you still have to bolt a steel rear sub frame to it, you now have a hybrid and have to figure out a way to reliably assemble the two and maintain your stiffness. </div></BLOCKQUOTE>

I may be mistaken but I believe both UWA and RMIT have fully composite chassis.

[Charlie]

<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 can go on and on about the benefits of aero, but i think our first enduro driver made the best case for it in detroit. One hand holding a faulty switch, electrical system failing, shifting and steering with the other hand, and still putting down an average lap within 4.5 seconds of UWA. That would have been good enough for 10th in endurance. ONE-HANDED! </div></BLOCKQUOTE>

Vehicle performance, especially in that type of situation, is never a case for a particular subsystem that happens to be on the car.

The only way to evaluate it is to hold constant as many parameters as possible... engineering should teach you guys that.

Using that logic than RMIT has proven singles are the best, while Texas A&M have proven that superchargers are the way to go, etc etc.

There's not much worse a comparison that to say X FSAE car with this sytem was better than X FSAE car with a different system because one was faster. There are likely to be few similarities between the cars. Most notably, the driver, and if it applies, the tires.

Unfortunatley, rarely have any teams done a true aero test. It's a pretty difficult test to perform. Cars designed for aero are more likely to be faster with wings than without.

To say proper wings make a car faster on ALL courses is a bit ambitious, to say the least.

[John Stimpson]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:
The only reservation I'd have about a titanium frame is the loss in weight would come with a loss in rigidity as titanium is considerably less stiff than steel, appreciable if the frame is built from a strength standpoint.

Tungsten frame. Oh yea!! </div></BLOCKQUOTE>

I **LOVE** welding titanium, but again, thats me having a huge hard-on for welding... Its extremely time consuming to do, any way you do it. It would be very difficult to do in a fully inert atmosphere (read: enclosure), which is fine, but that only adds to the massive time consumption of welding. The Ti that I welded this year, which were our rear subframes (small spaceframes), control arms, tie/toe links and pullrods takes approximately 30 times longer to weld than steel. Being that I had over 50 hours in the steel chassis, I can't imagine 1500 hours for a Ti chassis. But damn, that would be sooooooo hot! I've been half jokingly planted the seed to the rest of the team to do it, mainly so I can come back to weld it. I don't see it being so hard to interface a tie chassis with steel front/main hoops. I can picture a bunch of double-lug joints with capping plates like this:http://i138.photobucket.com/albums/q243/stimpsonjohn/2007%20Kettering%20FSAE/Titanium/DSCN3158.jpg

As you mention though Tom, the stiffness of Ti is crap. 16000 KSI vs. 29000 KSI, just a tick better than half. Thats a problem. Not to mention that Ti is so friggin tough. Its hell on cutters and abrasives. Theres a stout learning curve to work with it. For example, when you grind it, you MUST have very sharp abrasives to keep the heat out of the Ti. If you push too hard, and/or have dull abrasives, you oxidize the Ti and destroy its properties. We haven't even touched on cost... LOL I figure a Ti chassis would cost over $10,000 between cutters, abrasives, argon, filler rod and material...and thats if you have someone that REALLY has a knack for tube fit-up. You do *not* want to mess up a $300 section of Ti by making it 2 or 3mm too short. (Fit-up MUST be impeccable)... Heres a pic or two of some of our Ti (shameless bragging). ;-)
http://i138.photobucket.com/albums/q243/stimpsonjohn/2007%20Kettering%20FSAE/Titanium/DSCN3039.jpg

http://i138.photobucket.com/albums/q243/stimpsonjohn/2007%20Kettering%20FSAE/Titanium/DSCN3063.jpg

[Chris Allbee]

Done correctly there is not a reason why extra download can't be a benefit on all but the tightest of courses. That's what adjustments are for. You can adjust your spring rates and dampers and roll-bars to make the car perform better on tight courses, fast courses, wet tracks, dry tracks, etc. Aero is no different, just another variable to deal with and it has its attendent advantages and disadvantages. I wasn't saying that that situation was the only validation for having intentional aero devices (yes, intentional), but that the use and tuning of the aero allowed us to develop a car that could perform to high levels without it being difficult to do so. Call it a crutch, laziness, or whatever you will, but it was a design decision we made, tested, and developed our car to take advantage of. We have done back to back testing on many of our cars (most designed without aero in mind) and the aero package always came out on top.

As far as the singles and super-chargers out there, they are the best solution...for the packaged they were engineered with.

And it is alright to say one racecar is better than the other because of times on track, if thats what the product was designed to do. As far as I'm aware its ok to rate designs by performance....i think thats why they have us drive the things in the first place...not sure though....maybe i should look at the points allocation again....

Wings aren't the only way to do it, and it can be done adequately in many other ways, but I'm fairly convinced that a well-done, light, and properly powered aero car has the potential to clean up the track pretty soundly. Do i think that Aero has progressed to that point in FSAE? No, not really. But the potential is there.

[VFR750R]

I'll second that Charlie, just because X team does Y doesn't mean it's why they're fast. It could even be the case that Y makes them slower but Z more then makes up for it. Or you can't make Y work without invisible Z. (I hope that explaination is not too obtuse)

I see it all the time in Nascar. Team X has Company Y's rocker arms and they are faster then us, so we need 'those' rocker arms.
It's an error in logic to assume a single part to be the reason for an assembly of thousands of parts to have ultimate performance.

That said, small winged cars make sense. Lets say at 60mph you can get 100lbs of downforce. If your car is like Cornell's perenial heavyweight (~650 with driver) you can expect an increase of grip of 15%. If you have a lightweight single of 500 with driver, that increases to 20%. Since the tires friction coefficient (for FSAE)is not very load dependent, both cars stand to go just as fast without wings, but with wings, the advantage goes to the smaller car. The only thing left is a course fast enough to have 60mph corners has enough grip to put down the 20 more hp afforded by the 4 cylinder turbo cars. And before you guys say it... a T A&M type car with supercharger and wings...could logically have an advantage.

[John Stimpson]

In my mind, its pretty clear aero is the way to go, but only if the team has already developed a chassis/suspension package that works. The aero is worthless if your chassis/susp sucks. It takes a long time for a school to gain enough empirical insight and knowledge to have a solid idea of what is going to work well and what won't. Until that gets hammered out (meaning years, and a handfull of good chassis/susp guys over the course of those years), why bother with aero?

Ultimately, I'm in agreement with those saying the proof is in the pudding, and this year's comp, with an open AX, proved aero is where its at.

[JuicedH22]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:
project car I intend on building in Ohio. </div></BLOCKQUOTE>

wait.... you're coming to Ohio?.....


NOOOOOOOOOO!!!!



j/k http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Since the tires friction coefficient (for FSAE)is not very load dependent </div></BLOCKQUOTE>

Interesting comment.. from the data I am looking at I would call it moderately to fairly load dependent.

And indeed I will be coming to Ohio, taking a job with Goodyear later in July.

Also, nice lookin Ti welds John. Real nice argon coverage. The one time I dabbled in it I didnt have any purge or trailing shield so I had to literally do a dab at a time, let it cool, move on. Came out real nice and shiny silver though. Once I got decent at it I got big into Aluminum welding this year. So clean and cool lookin.

[VFR750R]

Interesting. Is this for Hoosiers, Goodyears or both. Although we tested with our car over a considerably small range, almost all CG and weight sensitivity tests we did showed changes in performance smaller then our inherent variabitlity in our test methods. For instance a CG test we did in 01; where we added weight to the rollbar hoop, raising the CG to the point of toppling over during skidpad, and the times stayed within hundredths of baseline times. Obviously a kind of test like this has flaws, we didn't change the roll stiffness of the car or camber ect., but considering we just added weight, not moved weight the car already had, we assumed that the tires couldn't be very load sensitive.


Although the Goodyear tires have been changed and improved tremendously since then, I believe the hoosiers are very similar in construction and compound no?

[rkellz007]

VFR, interesting comments on the CG testing you had done, though not totally surprising. I have wanted to do a similar set of tests for a while but keep finding other things to investigate that take priority.

As for what the TTC data shows, I spent a considerable amount of time combing through stuff last fall. It was a bit of a revalation to me to find how far 'down' in the linear portion of the normal/lateral force curve we (appear to) operate in FSAE (I was at the time particularly interested in the 13-7 Hoosiers, though it seemed to apply to most of the 13s we have data for). Especially since all of the common literature spends a lot of time on the evils of increased load due to load sensitivity.

Probing further we did find that although the marginal (sorry, past life in finance and econ, cant get away from the jargon) pound of normal force produces an almost linear increment of lateral force, more and more of this lateral force is sucked up by drag (we live in a less linear region of SA) and overcoming same.

Tom is a smart guy and this might be one of the differences in what he is looking at and what the rest of everyone sees. Could explain why he now has a job at GY...

Ryan

[Test Driver]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">There's not much worse a comparison that to say X FSAE car with this sytem was better than X FSAE car with a different system because one was faster. There are likely to be few similarities between the cars. Most notably, the driver, and if it applies, the tires. </div></BLOCKQUOTE>

I agree on the point of wrongly assigning all credit for winning on any one Aero/Mechanical/Electrical system. However on similarities, I disagree. For the last fifteen years or so, the level of refinement has definitely gone in the positive direction, however, we can't say the same about innovation. We basically have the same type of cars showing up year after year with nothing really earth shattering about them. Sure we see the occasional interesting bits like the WW V8 but for the most part, the cars that do well are quite similar. I don't even think the single/monocoque winning car last year is that revolutionary.

Likewise, I think that the drivers themselves are not similar in capability. This is especially apparent when looking at the top teams. And this year, it is even more telling of how drivers are the single-most important part of the whole system. I'd say, they're even more important than the tires.

UTA has a driver that if I'm not mistaken, has twice won national AX championships (plus a background almost impossible to duplicate by other schools). They also espouse autocrossing at the regional level. This helps teach driving skills not associated with a single turn of the wheel. Skills that promote fast initial laps like reading lines, memorizing courses/corners and visualizing laps make for fast times the first and second laps out. Once a few laps are done, then the gap closes and these skills are not as important. I believe some of this borne out by the progressively quicker times the winning cars had when compared to UTA's times during endurance. Although, UTA did bow out of endurance so this might have been a contributing factor.

It's too bad that Kansas did not have a good chance at AX this year as I understand they have quite a talented shoe.

Cheers.

Ramon

[BuffRacing]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Since the tires friction coefficient (for FSAE)is not very load dependent </div></BLOCKQUOTE>

Interesting comment.. from the data I am looking at I would call it moderately to fairly load dependent.

And indeed I will be coming to Ohio, taking a job with Goodyear later in July.

Also, nice lookin Ti welds John. Real nice argon coverage. The one time I dabbled in it I didnt have any purge or trailing shield so I had to literally do a dab at a time, let it cool, move on. Came out real nice and shiny silver though. Once I got decent at it I got big into Aluminum welding this year. So clean and cool lookin. </div></BLOCKQUOTE>

Remember when I wanted to cut that golf club head in half and reweld it? It's still in my car, i might do that when i get back. Who else is welding next year?

[Wesley]

I believe the UTA's pro driver autocross times were within... say three tenths of OU's time.

And within seven tenths of our second driver, whose autocross experience is limited to FSAE.

But saying the driver is reponsible for the car going faster seems like saying a car goes faster because of part or system X. http://fsae.com/groupee_common/emoticons/icon_razz.gif

[Test Driver]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Wesley:
I believe the UTA's pro driver autocross times were within... say three tenths of OU's time.

And within seven tenths of our second driver, whose autocross experience is limited to FSAE.

But saying the driver is reponsible for the car going faster seems like saying a car goes faster because of part or system X. http://fsae.com/groupee_common/emoticons/icon_razz.gif </div></BLOCKQUOTE>

So, what part or system X do you swap between your drivers to account for the 4 tenths time difference and does the slower driver complain? http://fsae.com/groupee_common/emoticons/icon_razz.gif http://fsae.com/groupee_common/emoticons/icon_razz.gif

Ramon

[Kurt Bilinski]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VFR750R:
I'll second that Charlie, just because X team does Y doesn't mean it's why they're fast. It could even be the case that Y makes them slower but Z more then makes up for it. Or you can't make Y work without invisible Z. (I hope that explaination is not too obtuse)
</div></BLOCKQUOTE>

What hasn't been mentioned is the enormous difference the driver plays in this. I'm sure that putting the fastest car's driver into the slowest car, will show a Huge improvement. Yes, a car with better parts has the potential for better performance, but it all depends if the pilot can make use of it.

In other words, there's a ton of performance to be had by using a good driver - far more than what one part can add. If one's not available on the program, see if you can find someone on campus. Of course everyone think's they're a great driver, so they'd have to provide background info to prove it.

[Superfast Matt McCoy]

The Oklahoma approach, low budget and simple:

1. find a dedicated aerospace student and have him design a good aero package
2. set up mock dynamic events in a parking lot
3. drive without wings
4. drive with wings
5. repeat with second driver
6. compare times
7. enjoy faster car
8. stop speculating on forums

[conekilr]

I like that method. However, most aero people here cannot compute when you flip a wing profile upside down so we do it ourselves.

[John Valerio]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Superfast Matt McCoy:

3. drive without wings
4. drive with wings
</div></BLOCKQUOTE>

thats a bit too simple though. i don't know how you guys run your wings, but unless all your aero mounts unsprung you need:

3a. redesign suspension

data or lap times wont be worth much unless you at least consider your wheel, damping, and roll rates. and thats assuming you have a good mechanical balance to start with. and the faster the track the bigger the difference will be.

[Superfast Matt McCoy]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by John Valerio:

thats a bit too simple though. i don't know how you guys run your wings, but unless all your aero mounts unsprung you need:

3a. redesign suspension
</div></BLOCKQUOTE>

No it's not and no you don't. If you want to make the most of your aero you need to do some suspension setup, but we did this test on our 2006 car, which was never designed for aero and we changed nothing but the addition of a front and rear wing. The difference was significant, our wings are well worth it, even with no suspension changes. Stiffer springs and some other minor changes makes aero even better, but i'm not talking about even better. I'm talking about with vs. without.

[KU_Racing]

I am a spaceframe guy, through and through. I respect the teams that design and build monocoque cars, but I would vote against it for my team. Carbon is easy to lay up to a moderate quality level, but the curve up from there is pretty damn steep. Not having access to an autoclave is also a big problem. Having done a couple of carbon nose cones in the past, as well as a fair number of carbon/kevlar remot control boats, Id say that a monocoque would be a HUGE undertaking. For the level of quality that I would want, It would be a very long design process, followed by a lot of test layups, followed by a very intricate final layup to do the actual race monocoque. I greatly prefer the ease of manufacture, as well as the flexibility, of a tube frame design.

[John Valerio]

fair enough. my point was just that you won't be comparing the fastest each setup can be. i guess we run stiff enough and slow enough that just throwing wings on won't dig you into the ground.

[VFR750R]

The driver can be huge or almost unimportant. For instance, in FSAE you have top level drivers that get lots of seat time and come from racing backgrounds...against kids that are still wrenching on brand new cars up to the point of the dynamic events. Obviously for a single class of racing the discrepency is huge.

Nascar on the other hand is the epitome of US motorsports and every driver has already proven themselves otherwise they wouldn't have gotten that far (Micheal Waltrip and Kenny Wallace excluded). In 2005 all 5 roush drivers were in the top 10 in points at the end of the year. In 2006 only 1 was. Right now, every single Hendricks driver has one a race and they've one all but 3 races this year. The equipment makes a bigger difference then the drivers. In 2005 Jeff Gordon missed the chase, this year he's leading the points. Did he change, no, his cars have changed. And this is why Nascar continues to screw with us, and give us stuff like the COT to deal with. They don't like teams being able to one up each other, which makes no sense because once you nueter the teams ability to make changes then all you have is a bidding war for the best driver and everyone else might as well go home.

[Charlie]

I think the subject is FSAE. http://fsae.com/groupee_common/emoticons/icon_razz.gif

Besides, you are also talking about oval racing. At least on the 1.5 and bigger oval tracks (Indy excluded), the driver plays a very small role.

Road courses are a different story.

[Kurt Bilinski]

When I worked FSAE West last year I saw first hand how important the drivers were. For example, at the skid pad competition, several drivers took too many laps, or didn't switch to the other half of the pad. In the acceleration competition, it was easy to tell who knew how to shift and who didn't. In the autocross, I was one of the cone chasers, and I replaced cones over and over because drivers forgot where their wheels were and turned in too early.

The best that suspension, tires, and wings can do is perhaps make up some time after these errors occur. Isn't it better to get a driver who's less likely to make the errors in the first place?

Putting a kid in the car who hasn't slept in 48 hours, who drives a Honda Accord, and putting him into something that weight 1/10 as much with tons of power and grip is a huge component of the overall package. If the driver has no experience, it's pretty clear what's going to happen.

I realize not every college has a Schumacher willing to drive the car. My point is that it's worth some serious effort to find someone on campus that had at least driven a formula car. You guys are building something similar to an aircraft, and having a pilot who knows how to handle it is a huge part of the package.

[mtg]

Bump to help push the religious spam down the page.

[Figlio_del_Diavolo]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:
Also, nice lookin Ti welds John. Real nice argon coverage. The one time I dabbled in it I didnt have any purge or trailing shield so I had to literally do a dab at a time, let it cool, move on. Came out real nice and shiny silver though. </div></BLOCKQUOTE>
I believe John did the vast majority of his Ti welding in open air one dab at a time. A judge said it looked like jewelery in fact. http://fsae.com/groupee_common/emoticons/icon_cool.gif

As for the topic at hand, it seems to me the level of work required in designing and constructing a monocoque chassis would be a drain of resources for many teams. The money spent getting it right could be better spent in improving other parts of the cars that would help more for what FSAE cars must do. Now I'll be the first to admit I lack the level of immersion in the FSAE program that many of you have, but it is how I look at things.

If you have a good base program, then an aero program seems like it would def be worth the effort. However, taking the plunge into the black art of aero does not seem like a wise choice if the basic prgram is not sound.

Then, onto the topic of drivers as part of the package. I think that they can make a considerable difference in the equation. Like others have said, with a very limited amount of run time on the actual competition course picking out and visualizing the line you must take to make your car work best is a huge deal in the auto-x. Over the course of the endurance I'm sure it will have a great impact as well. It is the same in all forms of motorsport though. A top notch driver will almost always make mediocre machinery look good and make good machinery look great.

[KU_Racing]

I agree with figlio. Ive always thought that a good driver can do a hell of a lot with a bad car, but a bad driver can do next to nothing with a really good car.

[Kurt Bilinski]

A perfect example is in autocross. With a inexperienced driver, but the same car, tires, and track, the driver's time a year later will be on the order of 10-20 seconds faster. That's a Huge amount of time. Most importantly, the skills the driver learns are, for the most part, transferable to anything he drives. The whole point is, don't underestimate the importance of the driver.

[Figlio_del_Diavolo]

You don't even need a year to see the difference. http://fsae.com/groupee_common/emoticons/icon_smile.gif With Kettering's last minute finishing of the car, the only seat time I got prior to running in the auto-x was in a wet parking lot on used slicks. My times were not competitive to the majority of schools, but thats not suprising with the out-of-the-box setup (aside from a caster adjustment to reduce wear on drivers' arms). However, I was able to drop about 3 second from one run to another, even with the ill handling (lifting inside fronts under cornering loads). Such is racing I guess. Our setup change for the endurance was worlds better than the initial setup, but our rear right wheel bearing decided to explode while testing it in the practice area less than an hour before we were to roll off.

[Bill Kunst]

if driver/pilot/rider didn't make that much of a difference, then what is up with The Doctor? When V. Rossi left Honda for Yamaha, everyone thought he was a fool to go to the slower bike, yet he rode it faster.

As for the mono vs steel, how much weight is saved?

[js10coastr]

I've got an idea, lets have a bunch of universities come up with what they think is the best way to solve this problem, and then we'll meet once or twice a year and have a "competition". At this competition we'll have professionals from the motorsports industry judge the designs, and then we'll race the cars. That'll prove what's the best design and what matters the most...

...oh wait...

[MalcolmG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by js10coastr:
I've got an idea, lets have a bunch of universities come up with what they think is the best way to solve this problem, and then we'll meet once or twice a year and have a "competition". At this competition we'll have professionals from the motorsports industry judge the designs, and then we'll race the cars. That'll prove what's the best design and what matters the most...

...oh wait... </div></BLOCKQUOTE>

I don't know you...but I think I love you

[Ashley Denmead]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by js10coastr:
I've got an idea, lets have a bunch of universities come up with what they think is the best way to solve this problem, and then we'll meet once or twice a year and have a "competition". At this competition we'll have professionals from the motorsports industry judge the designs, and then we'll race the cars. That'll prove what's the best design and what matters the most...

...oh wait... </div></BLOCKQUOTE>



ROFLMAO.....perfectly said

[KU_Racing]

In that case, lets determine what percentage of the top 10 finishers over the last few years have been steel tube frame cars with no downforce.

Sweet.

[Kyle Walther]

then can we normalize it based on the amount of steel space frame no down force cars at competition.

[benjo]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by js10coastr:
I've got an idea, lets have a bunch of universities come up with what they think is the best way to solve this problem, and then we'll meet once or twice a year and have a "competition". At this competition we'll have professionals from the motorsports industry judge the designs, and then we'll race the cars. That'll prove what's the best design and what matters the most...

...oh wait... </div></BLOCKQUOTE>


Hahaha, thread over.

[Chris Allbee]

I wouldn't say that having a couple judges look at the car can decide which is the best. Look at what happened to UWA. They were in a design line where the judges harped on people for not using 40 year old design techniques. They also had their own way of looking at things. One of the judges turned his nose up at the concept of using shock histograms as part of a valid tuning strategy. I'm sure some other judges would have like to skin the man alive for that. The judges are human just as you and I are, they make mistakes and have their own pre-conceived notion as to what a good design is, and they don't always agree. This can be especially detrimental in prelims when there isn't a lot of communication between different design judge groups. But hey, thats part of life in general, sometimes you get the shaft, suck it up and deal with it and go show the judges the worth of your car on track. I think UWA did a damned fine job of that. Just remember, general consensus isn't proof and it damned sure isn't fact, just a shared opinion.

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">One of the judges turned his nose up at the concept of using shock histograms as part of a valid tuning strategy. </div></BLOCKQUOTE>

Really??? Did he give a rationale for that? I'd love to hear it.

[Magnarama]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by John Stimpson:
In my mind, its pretty clear aero is the way to go, but only if the team has already developed a chassis/suspension package that works. The aero is worthless if your chassis/susp sucks. It takes a long time for a school to gain enough empirical insight and knowledge to have a solid idea of what is going to work well and what won't. Until that gets hammered out (meaning years, and a handfull of good chassis/susp guys over the course of those years), why bother with aero?

Ultimately, I'm in agreement with those saying the proof is in the pudding, and this year's comp, with an open AX, proved aero is where its at. </div></BLOCKQUOTE>

This is exactly how I feel on the topic. In my opinion aero can only work with car that has already been 'sorted' for a couple of years. I also feel that the design process would probably be over 2 seasons as in the 1st season the initial aero package should be designed for the previous years car and then tested to buggery to prove that it is a valid concept. In the second year the aero should then be integrated into the whole car's design. I know some people would really disagree with me(ie the current adelaide suspension team for sure http://fsae.com/groupee_common/emoticons/icon_razz.gif ) but that's what makes this competition so unique, that people really can try stuff 'out of the square' rather than just follow a set formula.

Having said that though I haven't yet seen what I would call a fully thought out wing setup. Pretty much all of them look to me like the airflow over the entire car hasn't been taken into account. Rear roll hoops and front wheels especially. The turbulence from the driver/roll hoop would significantly effect the efficiency of the wings and having multi element wing sections in front of tires is pretty pointless in my opinion, due to the high pressure areas formed just in front of the rotating tyre.

[Jersey Tom]

I will add, that when I was originally lookin at this stuff it was based on tables in Milliken and the old Chaparral, ie a single element symmetric airfoil.

Numbers sure change when you go to non-symmetric, thicken it up and throw in a bunch of camber!!!

[mtg]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jersey Tom:
I will add, that when I was originally lookin at this stuff it was based on tables in Milliken and the old Chaparral, ie a single element symmetric airfoil.
</div></BLOCKQUOTE>

No wonder why you thought wings sucked- Indy cars don't even use wings that mild.

The multiple hundred pounds of downforce @ 60mph is pretty easy to achieve on an FSAE car- we proved that in a full scale wind tunnel in 2004 and then measured a similar level of downforce on a test oval with linear pots on the springs. I remember driving that sucker at 86 mph (drag limited top speed) with so much downforce that the slightest blip in the pavement made the chassis scrape the pavement (and this was with "F-stiff" springs).

This was shortly after the test:
http://wwwcgi.umr.edu/cgi-bin/cgiwrap/formula/imagefolio2.3/imageFolio.cgi?action=view&link=2004%20Events/2004%2012%20car%20Michigan%20test&image=Race%20Car0004.jpg&img=&tt=

[Jersey Tom]

I still say you lose a heap of grip from the load sensitive tires, among other things, but its interesting to see one can actually throw down that much downforce.

86mph drag limited top speed.. thats a mighty amount of drag.

[mtg]

If you look at the results, I wouldn't say we were "losing a heap of grip"

http://www.sae.org/students/fsae2004results.xls

[flavorPacket]

pshh, you were only fast cuz you were f stiff. aero had nothing to do with it...

[Jersey Tom]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">If you look at the results, I wouldn't say we were "losing a heap of grip" </div></BLOCKQUOTE>

If you look at the controlled tire test data, I would say you are indeed losing a lot of grip.

[Marshall Grice]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> If you look at the controlled tire test data, I would say you are indeed losing a lot of grip </div></BLOCKQUOTE>

Are you implying that their car has less grip by adding wings?

Sure the Mu is not as high as a non winged car but they're operating at nearly double the normal force!

[VFR750R]

Well maybe that should be clarified as not getting a one to one benefit between downforce and grip. 1 pound of downforce reduces the coefficient of friction but not enough to actually lose grip.
I don't think there is a tire on the planet that actually loses grip with downforce, it just doesn't always get you as much benefit as it would initially seem.

The controlling factor for aero is still more normal force then actual car weight, which always results in improved traction. For it to not work out you'd have to lose mu at the same rate as increased normal force. For instance 500lbs of downforce plus 500lb car. Mu changes from 1 to .5.

Plus, aero force is not subjected to weight transfer. if you have 50lbs per tire it doesn't bias towards the outside tires during cornering like weight does. This means the more aero the more even the distribution of normal forces across all tires. It can mean orders of magnitude more normal force on the inside front for instance at corner exit.

[Jersey Tom]

Interpreted wrong. I dont mean that by adding wings you lose overall available cornering force. But mu for these tires goes down quick with normal force. So one might think by adding quite a bit more 'aero' weight to the tires you'd be absolutely flying around the competition, but in actuality the dividends paid aren't nearly as high.

[Kyle Walther]

so you agree it pays dividends you didn't have before.. and therefore makes you faster...
How is it a bad thing again?!?

[Jersey Tom]

Hey, easy. There's benefits in running a monocoque, there's benefits to running an aero package. Don't think anyone has argued that. Certainly its a good research and design experience. I just don't feel either is a huge return on investment for the time invested, at this level anyway. It's not like F1, GP2, IRL, Champ, FA, etc where if you dont run aero you don't even have a shot at qualifying. For the time and money involved there's a million other things that I feel the time could be better put towards.

Most of all the idea behind the thread was to start some good damn discussion and to hear some opinions and facts on things, which can be lacking when the forum comes down with religious propaganda and all sorts of other malarky.

[John Stimpson]

This could be totally off topic...or maybe not?

I did some testing last year for my Vehicle Systems Dynamics class... We tested our '06 car in slalom and skidpad using different tires, and different combinations of tires on different corners. I wrote an SAE paper on it, but I can't remember the title to search it by. I'll save you the trouble. Bottom line was, adding ANY amount of extra grip to ANY corner, even if only one corner, made the car faster.

You want ALL the grip you can get. Even if it biases the car, the car will still go faster, although it can take a bit of getting used to.

To bring it on topic, it seems to me that aero, and the associated downforce ADDS GRIP, which makes the car faster. (&lt;----thats a period right there) Not to say that balancing the car aero-wise doesn't make it faster yet.

[BrendonD]

So is the next step trying to find tires that will allow the aero dividends to be paid out higher?

[Scott Wordley]

Its been a long time since Ive read a thread that has sufficiently motivated me to reply, but this one did.

And not for any good reasons.

Regardless, i was pretty impressed by some of the numbers, facts, measurements and competition results that people have produced to argue against the "its all to hard, and if I can't be bothered no one else should" mentality that kicked off this thread.

I'm not going to bother talking about the monocoque side of things because there are others more qualified to counter the views expressed here or ignore them, as they see fit.
Anyone can see that if you have the time, the carbon and an autoclave sitting around then a carbon tub might be a good option for a stiff, light chassis. If you dont, you're probably better off with a space frame.

A few comments, mainly regarding aero:

Tom said:
"Running some idealized numbers, on wings with fairly high aoa's (near stall, tho admittedly single element), I find it hard to believe the claims I hear walking around of multiple hundreds of pounds of aero download at 60mph"

How many FSAE cars do you see running around with single element wings? (with the exception of old school calpoly?) Try multiplying your numbers by 3 and see where that gets you.

Tom said:
"the thing that I think kills it for FSAE cars is the wild high load sensitivity of FSAE tires "

The TTC data is not everything. If it seems ridiculous maybe it is? Do your own testing like several teams have. Maybe even do it on a variety of real road surfaces (rather than sandpaper), under different ambient weather conditions, with transient corners of various radii (rather than one endless corner), using a FSAE car with pyros, accelerometers, wheels speed sensors, slip angle sensors etc. You might find some interesting things. Write a few papers and a PhD thesis on it and go work for Honda BAR. One of our guys did. Would be good reading for your new job im betting.

Tom said:

"I would think that having to figure out aero balance and how to get enough performance out of the package to make an appreciable amount of difference would take a lot of valuable time."

It depends on how you value time on a FSAE project. I tend to think time in FSAE is best spent on the areas which will will yeild the biggest increase in performance for the minimal amount of time (money and effort). I think you siad this later in the thread. So which areas do you think are valuable? Or are you talking about "valuable" time in reference to the time that the car is finished, reliable and ready for tuning. If, in this sense, you have less than a month of "valuable" time then I would suggest that your doing something wrong. A design "saving" of 10 kg will never compensate for a car that is not tuned or a driver that cannot drive it to its limits.

Ashley said:

"Sometimes its not all about performance in seconds on the track."

I understand where your coming from, but I think to be a good team (like Deakin is) it should be. With so little resources available to each team, they should be targeted most efficiently to maximise competition results. If done properly the learning will come as a result of this. When people here harp on about wanting to "learn" for their own ends and give nothing useful back to the team it usually ends in tears, costs and little actual learning. Thats why we are racers and not pure scientists.

Tom said:

"To be convinced that the aero was really doing its job rather than just talented drivers or setup engineers I'd love to see pushrod load data from a gradual acceleration run from say 0 to 70 mph, and then numbers from a high and low speed skidpad."

Such data is published by (have a guess where?) and freely available. Have a guess who published it... hahaha. Also some good papers from cornell (CFD) and NC. If Noah still reads this board, I was at Aerodyn in NC recently and ended up talking about you. Weird.

Ben said:
"every year the viability of wings is going to be different. If there's a fast track like the autocross was, winged teams will be viable. If it's a slow track, they wont be."

Very true. In light of the extremely tight endurance track last year (oz), we will be going to this year's competition with a cost report addendum that reads: removed wings -minus $600. We will then look at the track theyve laid out and decide what to run. Just in case.

Charlie said:

"Vehicle performance, especially in that type of situation, is never a case for a particular subsystem that happens to be on the car. "

Exactly.

"The only way to evaluate it is to hold constant as many parameters as possible... engineering should teach you guys that."

&lt;The sound of crickets in the night&gt;

VFR750R said:

"Although we tested with our car over a considerably small range, almost all CG and weight sensitivity tests we did showed changes in performance smaller then our inherent variabitlity in our test methods."

A simple, well thought out test with a clear result. Nice.

Matt McCoy said:

1. find a dedicated aerospace student and have him design a good aero package
2. set up mock dynamic events in a parking lot
3. drive without wings
4. drive with wings
5. repeat with second driver
6. compare times
7. enjoy faster car
8. stop speculating on forums

I would suggest:
9. come back to forums with data
10. realise few people are actually interested in data
10. attempt to avoid overly long forum rant
11. fail attempt

John Valerio said:

"i guess we run stiff enough and slow enough that just throwing wings on won't dig you into the ground."

This comment brought back an old memory. A couple of years ago we lent our very first set of wings (from 2002) to UWA to test with. They sent us back photos of the underside of their car badly scraped from their first test (they had hurriedly mounted them to the chassis). Our current (2006) wings make almost twice as much downforce. They also told us that the lifted nose they ran for several years was to potentially package a front wing. Havent seen one yet for which Im glad, they are already too fast for my liking http://fsae.com/groupee_common/emoticons/icon_smile.gif

kb58 said:

"The best that suspension, tires, and wings can do is perhaps make up some time after these errors occur. Isn't it better to get a driver who's less likely to make the errors in the first place?"

I believe this too. Which is why we have already competed in 6 hillclimbs this year. Drivers and car set-up/understanding have improved measureably.

js10coastr said: it all basically

Chris said:

"Look at what happened to UWA."

I thought it was really sad what happened to UWA. It kind of felt like the design results took the competition win away from them. Im not knocking the other cars in the finals, they looked nice but the judges must have been blind to overlook the yellow car. It was significantly different from the previous one in many important details, many of which will be copied by other teams. And those boys KNOW that car. To be honest I think a slightly diffent paint scheme might have won them the comp. Maybe they just need to ship 2 cars to comp, the current and previous years so as to illustrate the differences? At least they proved their point on track.

Magnarama said:

"I haven't yet seen what I would call a fully thought out wing setup. Pretty much all of them look to me like the airflow over the entire car hasn't been taken into account. Rear roll hoops and front wheels especially. The turbulence from the driver/roll hoop would significantly effect the efficiency of the wings and having multi element wing sections in front of tires is pretty pointless in my opinion, due to the high pressure areas formed just in front of the rotating tyre."

Some interesting ideas here. Some comments. FSAE cars need chassis, drivers, engines and wheels. It is hard to move or resize such parts significantly without performance losses. It is possible, to some extent, to clean up the flow about these bodies. This is difficult due to the very bluff nature of FSAE cars (wide, short and high) and often requires considerable extra weight in body work, with the gains (primarily drag reduction) becoming marginal. These gains on the optimised body are completely dwarfed by your wing drag (if you run them). For instance the addition of wings doubles the drag force of our car. So what you might say is that some people have taken such an integration into account, done a whole lot of work, figured out how to design a good nose cone, realised engine covers are a joke, learnt to minimise the frontal area of the car even if that resulted in asymmetry (I hate empty, functionless sidepods), and that ultimately the weight and complexity of crazy intricate streamlined bodywork outweighted any drag gains and then happily ignored it. Consider also that a good front wing massively deflects to flow up above the driver's shoulder, so bodywork and stuff below this height dont matter much.

Rear roll hoops can be faired (sp? ie have a fairing added) to try and improve flow to the rear wing but it doesnt seem to help much. Mounts on the underside of the wing dont seem to do much at the angles we operate. The driver's head is a problem. You can lift the wing to get it above the driver's head, which is great for downforce (goes up) and lift/drag ratio (goes up), but bad for CG height. It also means you need MUCH more front wing to balance it because the drag component of the rear wing is also trying jack the front off the ground, and it just got a longer lever arm. A lower rear wing does the opposite of all the above. It was interesting to see that UTA have finally gone away from the narrow and low mounted rear wing, our wing packages are very similar these days. Both also unsprung which we have always believed is a must for maintaining mechanical grip.

As for multielements in front of the wheel, consider these things. We have VERY little span to work with, generally about 1400mm. If you subtract 2 wheels (200mm each) and a nose cone (300mm) that only leaves 700mm of wing, or more accurately 2 x 350mm wings (apects ratio effects are significant. Thats not a lot of wing, and you would quickly gather by reading our rules that due to the small allowed package space (and the competition for this space), that your front wing is your limitting factor on how much BALANCED downforce your car can produce. There are 2 very good reasons why teams lift their nose cone (to allow a partial low angle wing here) and also run wing in front of the wheels.

1 You get twice as much wing
2 3D flow effects

Number 2 is not obvious, but we have pressure tapping data that shows the centre of our front wing under the nose (which is just a mainplane) is working harder than anywhere else, because it is being "pumped" by the flaps on the sides. We have also cut down a wing from the outside in increments to see if this region of the wing was working, and found it was. Remember our tires are only 200mm wide, they are not F1 tires, the stagnation zone is much narrower and lower (due to smaller overall diameter) so not such a bother for the wing. Also how can you take advantage of the stagnation region to make downforce?. The front endplates are crucial so think about what they should be doing and how much span you can afford to sacrifice to do it properly. Then wonder how ground effect impacts on all this. Keen to hear your thoughts and have a good chat at competition. Will you guys need any wind tunnel time? let us know.

mtg said:

"The multiple hundred pounds of downforce @ 60mph is pretty easy to achieve on an FSAE car"

I wouldnt say its easy, but it is achieveable. We happened to be in the wind tunnel with our 2006 car this very day, and measured:

a net 70 kg downforce (or 154 pounds) at 100 km/h (60 mph)

May I remind you that our tunnel has no moving ground simulation which means the front wing is measuring low. Our on-track work suggests another 10kg, for a total of 80 kg (or 176 pounds) is a more accurate number.

May I also mention that the bare car (no wings) generates about 10kg of lift (which the wings are counteracting), meaning that the wings themselves are actually producing 90kg (198 pounds) of downforce.

End of disclaimers and footnotes.

And no, we dont design the wing for 100 km/h we design it to work at the average track speed of 60 km/h where you generate more like 60kg of downforce. This is one fifth of our total vehicle driver weight which is significant.

But then again, i must say, taking a sharp corner, foot to the floor, in this car at 110 km/h is one of the funnest thing ive EVER done. Can post the video of last weeks hillclimb for those interested. Coicidentally on a steep hillclimb track we find we are drag/RPM limitted at about 116km/h, or the top of 4th gear, not sure for a flat track.

John Stimpson:

Has obviously thought about what we do in FSAE and said a lot of things that I completely agree with, particulary:

"Adding ANY amount of extra grip to ANY corner, even if only one corner, made the car faster.
You want ALL the grip you can get. Even if it biases the car, the car will still go faster, although it can take a bit of getting used to."

To give an example of this at last year's comp one of our team members asked wollongong how much time their turbo car spent at WOT during endurance. They said 0%, ie they never even ASKED for the maximum power they had availbale. If this isnt a grip limitted formula i dont know what is. Gains will come from dealing with this problem ie:

UWA: Kinetic suspension, better wheel control = more grip = faster

RMIT: Smaller engine, less power, lighter car, more useable power for less weight = more grip = faster

Aero teams: More wing = more grip = faster

Same problem different solutions.

End of Rant


New website address:

www.monashmotorsport.com (http://www.monashmotorsport.com)

[PatClarke]

Bravo Scott !!!

Encore! Encore!
http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Pat

[ad]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Scott Wordley:
To give an example of this at last year's comp one of our team members asked wollongong how much time their turbo car spent at WOT during endurance. They said 0%, ie they never even ASKED for the maximum power they had availbale. If this isnt a grip limitted formula i dont know what is. </div></BLOCKQUOTE>

Good point Scott.

I would like to add a few comments, and im sure Pete (PeteM) will correct me if im wrong;

-From what i remember maximum throttle opening was about 75%
-This may have been limited because of front brake issues.....

Pete any suggestions?

[Chris Allbee]

Charlie said:

"Vehicle performance, especially in that type of situation, is never a case for a particular subsystem that happens to be on the car. "

My original comment was not to be taken as that was the ONLY reason to have aero on the car. I can see that in trying to avoid a long protracted discussion only baits people. That example of still performing well under those horrible conditions was meant to highlight one of the attributes that our car (as a system of interworking components, each tested and developed over the last 3 years) has gained from the addition of aero. That attribute being increased grip. I'll say it again, increased grip. Say what you want about aero not doing a damned thing at low speeds, but on a low speed skid pad (i.e. competition) we placed 4th. The use of wings also allows a team to balance the car differently at different speeds. Done properly you can increase stability and make the car EASIER TO DRIVE.

Think about it: If you have an amazing car without aero that is setup to 100% of its theoretical capability (i.e. all the equations say it should pull say 2.0G on a 50 diameter skidpad), it will most likely be "twitchy" and a handful with an amateur driver at the wheel. So let us say that he's only comfortable taking it to 70% of its limit that give you only 1.4G acceleration.

Now let us say that you added wings (through a rigorous design and testing process so that the car set-up is appropriate) and the goal was to increase stability at that 50 ft diameter cornering speed. And it just so happens that you get an increase in "theoretical performance" up to 2.2G, only a 10% increase. However, with your amateur driver the extra stability available cornering at that speed allows him to be comfortable pushing the car to 75% of its limit means you are now cornering at 1.65Gs. Its a performance gain, whether you want to criticize the added weight or not the result is still faster cornering.

And yes, I know that there is more to going around than cornering. With the introduction of a hell of a lot of drag it begins to argue for using more powerful engines and even turbo devices.

When we added aero, one of the goals was to make the car easier to drive faster. When setting up the car in this manner, you reduce the "theoretical maximum potential" of the vehicle, but we developed the aero to help compensate for that. And as our drivers get better we are able to open that envelope up even more.

Not every team has a professional driver, so whatever can be done to make the car easier to drive fast is most likely going to pay dividends out on track (if that is your goal). I realize not everyone believes that building a race car means trying to be faster, for some the mental masturbation is enough.

The example I gave was meant to illustrate how relatively easy it is to drive our car quickly around a track, and the way in which we implemented our aero package was a key ingredient that allowed us to obtain that goal.

And I will say it again: Holding other variables constant while implementing and tuning subsystems, vehicle performance IS a viable selection and judgement criteria for the worth of that system on the car. I don't know about the rest of you, but our team builds a Performance Vehicle (read: race car) and we make design decisions and tune to improve the performance of that vehicle in its defined operating environment (read: on track). So you design, build, test, refine, test, and tune (ad infinum) and if it marks an improvement in the product under its required service conditions...how is that not a valid way of measuring the worth of a system? I'm not claiming that is the ONLY justification of the system, or the ONLY way we measured its performance on the vehicle. I never claimed it was the ONLY justification we had. But the proof is in the pudding, and at the end of the day (read: 2 years development) every driver (new and old) was faster with the aero.

If you don't like it, fine. We have a nice flashy OU tail light for you to look at while you're behind us.

DISCLAIMER: Before the bitching starts about 2G being unrealistic in a 50ft diameter skid pad....The numbers are for comparative and illustrative reasons only, not to be taken as data for true on-track performance. Thank you and have a nice day.

[James Waltman]

Scott, Good to see you still hangin' around.
Great post.

For anyone that wants to read more of Scott's rambling, I would suggest the following SAE papers:
2006-01-0806 Aerodynamics for Formula SAE: Initial design and performance prediction
2006-01-0808 Aerodynamics for Formula SAE: A Numerical, Wind Tunnel and On-Track Study

[BStoney]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Scott Wordley:
Ben said:
"every year the viability of wings is going to be different. If there's a fast track like the autocross was, winged teams will be viable. If it's a slow track, they wont be."

Very true. In light of the extremely tight endurance track last year (oz), we will be going to this year's competition with a cost report addendum that reads: removed wings -minus $600. We will then look at the track theyve laid out and decide what to run. Just in case.
</div></BLOCKQUOTE>

Scott:

Do they let you see the enduro track prior to competition in Oz?? In the US, you don't know what the enduro layout is until the morning of enduro (we do only have 1 enduro here though, unlike the 2 in Oz). I didn't know if you had a different setup for comp there, could be interesting if you can do as you stated above with the wing removal...

[Pete M]

I don't think i'd be prepared to say that aero is a waste of time in FSAE. Thus far Wollongong haven't considered it something worth investing significant effort into. That said, we've had feasibility studies and a CFD thesis or two on the topic. It's just never made it on a car.

To offer an analogy, i think aero vs no aero is similar to forced induction vs naturally aspirated. A turbocharged engine will likely be more powerful and have more area under the curve than the same engine naturally aspirated. However, it will also likely be heavier, more complex, and less responsive. On a wide-open track with gentle, progressive throttle application and significant time at 100% throttle, the turbo engine will likely be superior. However, on a very tight track, where using all the power available is difficult, and the response of the engine becomes more critical, the best solution is much less clear. A typical SAE track is right on the border between aero being an advantage and aero not being an advantage. If the track is fast, the aero cars get a slight advantage. If the track is slow, that advantage largely disappears.

However, i think those pushing the benefits of aero need to realise something: the teams not running aero didn't just take a holiday instead of making wings, they were doing other things. Our time is limited and we all have our different ideas as to the best approach. And considering the remarkable absence of winged cars in the number one spot recently, i don't think it's too much of a stretch to say that whatever the non-aero teams are focusing on instead of wings is at least as beneficial as the aero they could have been doing.

As for Aus 06, it is true that the only event that we saw appreciable time above 80% throttle was acceleration. The track didn't really suit our engine package as well as some in the past have, but that wasn't the main reason. The real reason is that the car had less than a day of testing before comp. Neither the car nor the drivers were at their best, so we are fairly wary about drawing conclusions from it.

[Wesley]

I've said it before, and I'll say it again.

The design decisions a team makes should be a direct result of that team's past experience, and current know-how.

If that extends to the addition of wings for a performance gain, the addition of a turbo for a performance gain, or the reduction of weight via carbon monocoque for a performance gain, then the decision to pursue one or all of those options lies within the capabilities of the team.

This is a performance competition. If you want a well engineered, reliable, production car that is theoretically and actually proven, reliably sturdy and well-designed, and will take anything you throw at it without pushing the limits of what is and what isn't known, enter a Honda Civic in the competition.

The most basic facts about the universe are learned through observation. If you can observe a difference in performance, no matter what the paper says, you are ahead of the team that runs simulation after simulation up until they have to throw it together at the last moment.

I've only been to competition once. But from what I learned and what I've heard from others, the difference between those who win and those who don't is practical, real world experience - whether it's proving a combination works, or improving driver ability and confidence.

This competition takes place on the track and in the shop. The lab is useful, but we don't draw up our cars in modeling software and email them in to be run on a digital track.

And if you haven't noticed, I'm biologically unable to make a post less than three weeks long. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[VFR750R]

I think most people agree aero is worth nothing to something performance wise but the only negatives are weight, and cost, and time, which are all worth something. If your team doesn't have the time to do the fundamental tuning of the car, it's stupid to work on wings. If your car is running months before competition, you should at least be doing some work on the subject. Make it a 2 or 3 year project.

Wow Scott, what a rant. Way to nit pick every other persons responses.

In defense of our CG testing, fuck you with your assumption we did a shit test. Our results were clear and we learned from the test, my point was it was not a win or lose the competition type result. It was small change in performance. It gets factored in when we build a car, but it gets a points sensitivity rating just like everything else we do. We build cars to maximize points, and I think history shows we're not stupid in doing that.

Other than that, I agreed with most your post. There is a lot to consider in wing design, another reason to start as soon as you can and make it a continuous developement that you can pass along year to year. In fact, that's how every system of the car should be looked at. But almost every other system HAS to be on the car, that's why wings/turbo/drysump have been such hotly debatable subjects over time. Most teams that have them have proven their worth, otherwise they wouldn't run them, but the fact that they aren't required to run top ten or even win, they are contested.

[flavorPacket]

scott, I'd love to hear how reducing body roll reduces weight transfer (unless you care WAY too much about track change).

If anything, a low roll-gradient car (UWA) should exhibit more weight transfer because it can exploit outside camber thrust better and create more force.

[Ashley Denmead]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">"Sometimes its not all about performance in seconds on the track."

I understand where your coming from, but I think to be a good team (like Deakin is) it should be. With so little resources available to each team, they should be targeted most efficiently to maximise competition results. If done properly the learning will come as a result of this. When people here harp on about wanting to "learn" for their own ends and give nothing useful back to the team it usually ends in tears, costs and little actual learning. Thats why we are racers and not pure scientists. </div></BLOCKQUOTE>

nice journal paper there scott very well said. My comment was of course taking the devils advocate approach from the very first post of the thread. As you would well know our cars are very much oriented towards track speed in the last 4 years that ive been involved.

my comment about performance in seconds on the track actually came from thinking about you guys and the facilities you have available and the people who give you money to build the car. Although after your post i wouldnt dare conclude that your design decisions arent for "seconds on the track" reasons....just possibly another reason to do it and it looks great from the universities point of view given their courses etc.

I've been trying to persuade the team to get their act together and come to the hill climbs.....hopefully they will soon so we can have some more fun with you guys...

Ash

[drivetrainUW-Platt]

My $0.02

I was a corner worker for autocross this year in Detroit at the last leg before the finish line. It was a very tight corner with lots of cars hitting the brakes hard and some skidding out of control as a result. UTA's brake light never came on through the corner and they were hauling ass. I do not think that they were going more then 15-20mph so I do not atribute the wings. My point, they have darn good drives and a very well handling car.

Along the lines of aero, noone has mentioned that UTA autocrosses during the summer, which would mean tons more track time than FSAE. They win and the wings definitely help there. They dont just "slap" on some wings and see if they work, this is shown by there active angle of approach(or whatever technical term they have) as the suspension moves through its travel.

[Peter7307]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by KU_Racing:
I greatly prefer the ease of manufacture, as well as the flexibility, of a tube frame design. </div></BLOCKQUOTE>

One additional point is the ease of repair if and when the car is shunted or has an off track excursion.

Pete.

[Scott Wordley]

A few things

BStoney:

When we have arrived at competition the last couple of years we have often found that there is both a map of the endurance autocross track in the printed event booklet and also they usually have the cones layed out. They remove some of them on the straight for acceleration on the Saturday. Otherwise the course is usually sitting there for us to see from Thursday onwards, and we do Endurance on the Sunday.

VFR750R:

Sorry, but I think you must have misunderstood me, I was not saying you did a shit test at all, quite the opposite. As I said it was:

"A simple, well thought out test with a clear result. Nice."

and thats exactly what I meant. I have a huge respect for what you guys have done over the years, and Im guessing a lot of it comes down to little ideas like this that can quickly dispel all the conjecture and give you a direction. These are exactly the kind of tests I try and encourage our guys to come up with. For the last 2-3 years Ive been trying to get someone to do a proper weight/CG Height/Polar Moment of inertia sensitivity test much along these lines. Our idea is to take the bare car and add say 20, 40, 60 kg to it. Weights will be added low and centrally (low CG, low PMI), low and at extremities (low CG, high PMI), high and central (high CG, low PMI) and high and at the extremities (high CG, high PMI). So 12 different configurations in total. Of course we measure the car/driver's CG height and PMI for each config. We then go drive skid pan, acceleration and a track and note the performance differences. We then get real data which tells us in real terms, EXACTLY how sensitive the PERFORMANCE of these cars are to weight, CG height and PMI. We then know (or can better estimate) where our time and resources are best spent.

flavourPacket said:

"scott, I'd love to hear how reducing body roll reduces weight transfer (unless you care WAY too much about track change)."

You (and the rest of my team that pointed this out) are totally right, I had meant to delete that.

Ash:

Yeah I know man, I just get a bit sick of people carrying around the idea that we ONLY run wings because we are Monash and have a wind tunnel, and there for it is good advertising. I have seen several team with wings specifically for advertising purposes, but believe me we are not one of them, and like i said I would pull them off in a moment if i thought they werent making the car faster.

Just on this point, we have done a lot of work to measure what wings do for our car. Out of curiosity, can anyone tell me exactly how many competition points their turbos/tubs/wings are good for? Perhaps an idea for another thread... how people go about benchmarking the competition and determining/estimating how a particular design feature (or lack thereof) will affect their competition scores. Im sure many teams must do it, as VFR alluded to?

Oh, James, you might have missed the new one published this year.

2007-01-0897 Aerodynamics for Formula SAE: On-Track Performance Evaluation


Also Phil was nice enough to post some of our in-car videos from the other weekend. Check em
out.

http://www.youtube.com/watch?v=h-uYfH726Q8&mode=related&search=

http://www.youtube.com/watch?v=asy46w9mA1I&watch_response

Look for the speed in the right corner of the ADL.

Yes I got slightly on the grass, but we were the only car there not to lift for that corner.

[Big Bird]

Firstly, Jersey Tom - great thread. I've been following it since you first posted, it has been a damn good read. Unfortunately end of semester here has meant that I haven't had time to properly respond, and I didn't want to only throw in a lightweight one-liner (as with Wes, I'm physiologically incapable - those familiar with my previous posts will agree).

I am so glad to see people finally talking about points sensitivity (VFR both here and on another thread, Scott). I don't know how you can make an objective decision about your design direction without quantifying the trade-offs. You simply can't have everything in this game - you are never going to build a car that has the most power and the most downforce and the lightest weight and the best fuel economy. There are too many contradictions there. So you need to find a good mix somewhere that is achievable with your own resources & capabilities. How you can fight your way through this maze without some guiding principles is beyond me.

For what it is worth, the RMIT design change a few years ago came from a simple acceleration sensitivity analysis - we found that a 1% increase in cornering acceleration scored around 7-8 times as many points as a 1% increase in acceleration, (and from memory it was around 10 times greater than for a 1% increase in braking). The meaning? We could trade off a good bit of straight line performance without much penalty - and then hopefully make up for it with manouevreability and lesser complexity of a smaller lighter engine. The figures were for a track that we had dimensions for (2001 Oz Endurance track), and the figures I quote are from AutoX / Endurance only - but I have seen very few tracks or data to radically contradict our initial finding. A simple constant acceleration lapsim will get you started.

As for the composite tub argument, I'll side with those who argue it is as much about resources than any performance gains. The latter are arguable, but we have had success with both composite and spaceframe chassis. I doubt our team could ever build a 145kg car without carbon, but I have no doubt the lads could build a 165kg car using no composites at all. And I would be very surprised if that weight difference would amount to much points wise.

In response to one of the earlier comments, I know of two unis where it is actually significantly easier to build from composites than from metals - ourselves and Delft in Holland. We have a composites lab and autoclave about 50 yards from our team workshop, to which we have almost around-the-clock access. Our metalworking facilities are around a 45 minute drive away, and are only accessible at occcasional pre-booked times between 9 and 5 on weekdays. So carbon is the go - at least until we run out.

As for scientific principles (the comments that development requires holding everything else constant and changing one thing at a time) - I certainly won't argue that scientific reduction is not a good tool, and hasn't made great advances for mankind. But as with all tools we need to use our judgement where it is useful and where it might hinder us. A purely scientific approach would never have led to the RMIT change in philosophy a few years back. We would have had to independantly and consecutively prove a whole string of changes, including the less powerful engine, the 10 inch tyres, the smaller brakes, the radically different suspension geometry, the radically different weight balance - and it is very likely that any one of these tested in isolation on our old 4 cyl car would have been a step backwards. But thinking holistically (instead of reductively), as a team we managed to go back to first principles and piece together a completely different jigsaw puzzle that worked. Science is great for refining advances along the road already being travelled, but sometimes stepping back from that path and starting again opens up very different paths that can be equally as worthy.

As for aero, I think I'll leave that for another day - a full thread in itself! But I will say in particular that I'm glad to see Scott speaking about the drag effect of the rear wing and the moment it creates around the rear wheel. On short wheelbase cars it is a significant effect. I've seen many arguments primarily relating to downforce values, (a science that others would know volumes more than I do), but from a vehicle dynamics point of view the argument is pretty thin until you look at the COMPLETE range of 3D inputs that the aero devices are providing. Only then can you truly start understanding their complete worth.

Cheers all, gotta go.

[SR-Mike]

Excellent thread guys, some very intelligent and well informed points so far.

I don't think there will ever be a common consensus on the suitability of technologies such as wings, monocoques, turbos etc in these cars because of the huge variation that exists in resources available to each team. It is regrettable but still a fact that not all teams have the resources available to them to produce the optimal vehicle design but of course they still have the ability to produce the optimal competition package (more than simply the design) for their particular resource situation. So basically each team has a different problem to solve, which is why the "my solution is best and I've got numbers to prove it"� argument is good but doesn't always universally apply to every team.

If you are in the game of winning then as mentioned points sensitivity studies should be a fundamental starting point for all conceptual design decisions but this should be accompanied by a detailed risk analysis that considers the available resources and what effect they have. Poor risk management results in the all too familiar sight of teams finishing their cars at the comp, or not getting there at all.

The real points that separate the potential winners from those who just take part are gained with these initial conceptual decisions and then with the project management to ensure everyone is pulling in the same direction thereafter. The detailed design and development work, although obviously still absolutely fundamental just determines how close to this potential maximum you're going to get.

I know that when I was involved these decisions were made at the start of the year of the competition but i would be really interested to know how many teams took a longer term planning approach than that, 2 or even 3 years down the line. I think this type of team thinking would give huge returns keeping team member continuity and motivating new ideas over such a long period could be an issue.

Cheers,
Mike
Uni of Strathclyde Motorsport 01-06

[VFR750R]

Sorry Scott, that's the problem with forums as a form of communication, sarcasm can be implied or not based on the reader.

Our CG/wieght distribution test was almost exactly how you describe. And every few years I'd say we end up repeating it, with a slightly different twist.

As far as points sensitivity for a turbo, we take into account cost based on the last competition.
We do laps with the wastegate on and off, with our best comp level driver and our worst, and adjust lap times based on our weight sensitivity results assuming we can remove the weight of the turbo and accessories. This gets a percentage better rating that can be applied to the last competitions breakdown of times and points. Obviously this is only possible if your car already has a turbo, but older cars can be retrofitted with enough time. Multiyear teams should always consider putting the effort into testing with old cars rather then assuming design changes incorporated into a new car will be faster, and I know most do.

We do accel runs with and without the turbo hooked up, we have also done boost sensitivity tests on both endurance and accel courses.
We've also looked at cars that have made secondary design and we look at our history there and feel it is an advantage in design (but mostly because we have the data to back our decision).

We also have a lap simulation program written in 2000 by a team member using the turn radius, widths, and lengths of straights given by the rules. This is where we have done wheelbase and track sensitivity studies were it is not realistic to do physical testing on.

We also have a sim for acceleration, so we can test gear ratios, power curves, weight distribution, weight, with varied Mu's.

Are the sims the tell all, no, but they allow you to consider wholesale changes that, like Big Bird said, are not possible changing one thing at a time.

And big bird is so right in the possibility of being at a local optima in the optimization of a teams car. No matter what you do, you may not be able to go faster with small changes, but with large wholesale changes in design you'll find new optima that may or may not be at a higher performance level. But, big changes takes BIG balls and effort. I've mentioned this before that Cornell's worst enemy maybe the fact that we've been so successful with our current overall package. We may take a long time to risk our success on a 350lb car with no turbo/4 cylinder or a monocoque. In the meantime, teams are already developing this direction and we'll be behind the curve if we decide it's better.

[BStoney]

Scott:

Wow, that really provides a HUGE advantage to ALL teams competing to be able to plan for the weekend. Interesting approach...wonder how/if that would change anyone's outlook on coming to Detroit??

[AeroGT3]

Good post by Scott. I'll add a few comments.

I think Aero can have significant benefits from downforce, but also by balancing cars that are difficult to tune through other means. It's another selling point to have aero for high-speed stability if you can position your Cp correctly.

There are definite benefits to aero if they can be designed correctly, but i think too many teams rush for wings without pursuing a tray first. there is infinitely more potential in a tray if your car's geometry allows for one. often less weight, CG penalty, drag, etc.

I'll also add that a lot of aero teams run overly aggressive wings angles and neglect 3-d effects a little too much.

I'd love to hear even the 2-D Cl's and Cd's coming off these massive bricks, because there's really not much else other than drag to be had with more than 2 elements.

A proper 2-d cross section can have Cl's of 3.5+ with Cd's under 0.1. Proper optimization and iteration will get you a lot further than throwing on more elements at alphas over 60.

[Pete Marsh]

Ben,
I don't know how the officials would take to adding or removing stuff after tech for a performance gain but one team here took there wings off after they found they couldn't fit around the hair pin corner with no dramas from the Michael Royce. I wouldn't put a lot of value in the track map either, My memory of the event was I was suprised by the track when I walked it on Saturday because it was much tighter than the drawing looked.
You guys should come down here to Aus so we can get you that round of beers we owe you! I guess while your here you may as well have a run in the local comp and we can both try and beat that anoying little red RMIT thing that wins everything.

[BStoney]

Pete:

It sure would be interesting if that were commonplace (changing thinds for performance gains), b/c to me, that would be the same as being able to change to a softer tyre compound for skidpad, accel,autox and then run a tyre that takes a bit longer to heat up but is more consistent for enduro...I guess that is another thread in and of itself.

Right on! Yea, We'd love to come down to Oz..would be a hell of a time I'm sure...December time frame is very hairy for us as the Oz Comp is right during our Fall Quarter finals time..but we might be able to work something out in the future. We'll see what kind of run we can give the boys from RMIT over in England here in about a month! Should be a great competition over the pond...

[Steve Yao]

Having been the organizer of a few autocross events, I can state that what looks good on paper can make for a tight and confusing course in reality. I would bet the course map was technically correct.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Pete Marsh:
Ben,
I don't know how the officials would take to adding or removing stuff after tech for a performance gain but one team here took there wings off after they found they couldn't fit around the hair pin corner with no dramas from the Michael Royce. I wouldn't put a lot of value in the track map either, My memory of the event was I was suprised by the track when I walked it on Saturday because it was much tighter than the drawing looked.
You guys should come down here to Aus so we can get you that round of beers we owe you! I guess while your here you may as well have a run in the local comp and we can both try and beat that anoying little red RMIT thing that wins everything. </div></BLOCKQUOTE>

[terra_dactile]

VRF750R,
Your comment about making big changes need for big ball reminds me of our ETS 2005-2006 car, going into the UK competition in the 2004, everyone on our team would have said that a light weight single cylinder car was a waste of resources, we went there and got our asses handed to us by RMIT and Delft who had used this idea to make very competitive well balanced packages.
Our 2004 car weighed 510 lbs and had around 80 some horsepower from a naturally aspired Yamaha R6 engine, in 2005 uk comp we had a 365 lbs car with not one peice that could transfered from one car to the next, this was really shooting ourselves in the foot, the car handled great on the track but the engine change has taken three years to see a possible benefit from.

Your comment about being behind others who have persude the light weight option is one that every team asks, however what is so great about SAE is that you never know untill your try and compete, that is what is so great about competitions, no matter how prepared, every thing comes down to a few days that decide wether your decision have been wise, what I really like about your team is that you can be strong year after year after year. In my four years at ETS I have competed six times, we have won 1st place in design 3 times, 2nd place once and 4th the other time however untill this year we had never had finished a freaken endurance race.

It has been really great to chat with you guys over the years, its awesome to be such fierce competitors on the track but still be so open to help eachother by giving personal example of thing your team has learned over the years,

Jude Berthault
ETS FSAE 2003-Current
Team Captain

[repeatoffender]

Even though this is getting more off topic;

but has anyone considered that a light small single, vs say a 410lb four NA of equal times on the autocross may nip everyone in fuel economy?

One area not many teams focus on?

[Kyle Walther]

the point comparison between fuel eco. vs. autocross time is

.4 of a gallon in fuel = about 2 seconds in the autocross.

both worth about 30 points

or over a second per lap in the endro

......
so you have to be considerably faster.. by alot to afford to run a four banger.

[benjo]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Scott Wordley:

"The multiple hundred pounds of downforce @ 60mph is pretty easy to achieve on an FSAE car"

I wouldnt say its easy, but it is achieveable. We happened to be in the wind tunnel with our 2006 car this very day, and measured:

a net 70 kg downforce (or 154 pounds) at 100 km/h (60 mph)

May I remind you that our tunnel has no moving ground simulation which means the front wing is measuring low. Our on-track work suggests another 10kg, for a total of 80 kg (or 176 pounds) is a more accurate number.

May I also mention that the bare car (no wings) generates about 10kg of lift (which the wings are counteracting), meaning that the wings themselves are actually producing 90kg (198 pounds) of downforce.

End of disclaimers and footnotes.

And no, we dont design the wing for 100 km/h we design it to work at the average track speed of 60 km/h where you generate more like 60kg of downforce. This is one fifth of our total vehicle driver weight which is significant.

But then again, i must say, taking a sharp corner, foot to the floor, in this car at 110 km/h is one of the funnest thing ive EVER done. Can post the video of last weeks hillclimb for those interested. Coicidentally on a steep hillclimb track we find we are drag/RPM limitted at about 116km/h, or the top of 4th gear, not sure for a flat track.

New website address:

www.monashmotorsport.com (http://www.monashmotorsport.com) </div></BLOCKQUOTE>

Scott, this might be a bit much to ask, but I'll never know if I don't. Would it be possible to see some of this data? Even if its old, would be interesting to have a look at. Alternatively could you point me in the right direction of others who have done similar testing?

PS. Great post http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Bryan Hagenauer]

http://fsae.com/eve/forums/a/tpc/f/125607348/m/50510609...10703811#21010703811 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/50510609711?r=21010703811#21010703811)

[benjo]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bryan Hagenauer:
http://fsae.com/eve/forums/a/tpc/f/125607348/m/50510609...10703811#21010703811 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/50510609711?r=21010703811#21010703811) </div></BLOCKQUOTE>


Thanks mate, appreciate it!

http://fsae.com/groupee_common/emoticons/icon_smile.gif

[wingman]

Old School Cal Poly Huh... That's a stinging compliment, it's only been 10 ye....

HOLLY CRAP!! I'd laugh but I might get a HERNIA!!

I'm going to have to change my screen name!!

You guys have gone way beyond anything I ever did, my toupee is off to ya!!

Sure is nice to see some familiar names.

My 2 cents

Scott has WAY too much time on his hands or was sitting twitching at the keyboard trying desperately not to post, oops couldn't stop it.... �

Aero (event old school single element) done even fairly well will make the car more drivable for less experienced drivers (less twitchy, more predictable) but at the cost of weight and drag so it's a toss up. (may not be worth it given the newer options of the light weight single cylinder configurations and the comment about fuel milage)

All the analysis in the world means nothing without proper fabrication and implementation onto the vehicle

If done properly, Aero will cause other systems on the car to fail that you didn't expect (i.e. sustained high lateral Gs = oil starvation in the old days... )

Aero has historically been a detriment in design given the lack of time to properly justify it to the judges which sacrifices justifying other critical systems...(may or may not still ring true)

If you question implementing aero even for a second, it's probably not the way to go for your car. (Unless you are passionate about and committed to it, it's not worth the time)

Time to go remove my dentures!! Good luck everyone.

Old School Aero

[Paul Garcia]

Our team has the resources for a carbon chassis so wouldn't we be cheating ourselves NOT to use them! I don't see the disadvantages when you commit to developing a multi-year composite program that can streamline this construction. The finished product is a lighter, stiffer car that looks amazing.

The benefit of OU's wings were again demonstrated in California. They were not only the fastest car there but they proved their engineering justification by winning Design. I'm sold.

BTW the original post stated high load sensitivity of our tires but failed to site any data. A quick glance at my numbers shows variation of normalized lateral force from 1.7-2.1 between 350 and 50 lbs respectively. I am interested if this is "much more sensitive" than another series' tire. I would suggest the wing teams look at the data and decide (to run Goodyears) for themselves.

Paul
Jayhawk Motorsports

[CappyUMD]

It seems that people are coming to different conclusions about tire sensitivity. Univeristy of Maryland does not have TTC data, but independently we had Hoosier 20.5 X 7" tires tested a couple years ago. The data shows roughly a 7% drop in friction coefficient from 50 to 330 lbs normal load. I would consider this low normal load sensitivity. Higher temperatures at the 330 lbs normal load probably explain why there is not a bigger drop in friction coefficient (I have my reasons for this suspicion though it hasn't been verified).

This low sensitivity means that if you stiffen up your suspension, throw on 10 pound aero package, and create 100 lbs or so of downforce, you will acheive higher lateral acceleration. To me it also says that reducing car weight isn't that important for increasing lateral grip in non-aero cars. However it is important for impressing design judges, increasing power/weight ratio, and lateral grip in aero cars (higher downforce/weight ratio).

In the past Maryland has investigated aero packages, but lately we've realized that the rest of our car needed attention first. For those designing aero I recommend 3D CFD with a full car model instead of wind tunnel testing. Wind tunnels can be useful for verification but testing many changes is much easier in CFD. If you have a fluid dynamics professor that specializes in CFD talk to him about mesh density and the CFD settings you will need for greatest accuracy.

I think teams should consider aero if their car is already reliable, light, and their program is mature enough that they don't need people spending their time elsewhere. As far as aero costing more points than it earns you, I think people have already mentioned increased weight, increased suspension stiffness, increased cg height, increased drag, increased cost, and increased build time. I would also like to point out reduced fuel economy, increased roll over tendency (from higher cg and lateral acceleration), more parts to fall onto the track during endurance, and increased weight from beefing up suspension components if your safety factors were low.

Also a full width front wing effectively lengthens the car, requiring you to adjust your racing line. This requires you to tighten up your turn radii which can hurt you in really tight courses. It would be interesting to hear what portion of cone hits are done by the front wing.

[Kyle Walther]

eight autocross runs (two second place times, a third place time, and a fifth place time.)
and 23 laps of endurance.

0 cones 0 off course.

the car becomes soo much more forgiving and easier to drive that you don't need to push it to the ragged edge to do well.

[Superfast Matt McCoy]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kyle Walther:
eight autocross runs (two second place times, a third place time, and a fifth place time.)
and 23 laps of endurance.

0 cones 0 off course.

the car becomes soo much more forgiving and easier to drive that you don't need to push it to the ragged edge to do well. </div></BLOCKQUOTE>

I actually hit one cone in Detroit endurance, but I hit it with the back tire.

In cali endurance I was driving over the base of the slalom cones several times. If you hit a cone with the front wing, you probably would have hit it with the tire anyways.

If your drivers are not hitting cones, it's safe to say they won't start hitting them when you add aero. If your drivers are hitting cones, you need to fix that first, because it's costing you more time than you will get back with aero.

[VinceL]

Quoting Cappy UMD

"increased roll over tendency (from higher cg and lateral acceleration)"

Icreased roll over tendancy probably won't be an issue since the downforce you are creating is pushing the car down, and hence, preventing a roll over.

Another thing to add to this discussion is that the more downforce a car creates, the more sensitive the car's total acceleration capability will be to mass. Even if you assume the coefficient of friction of the tires is constant.

[Kyle Walther]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Superfast Matt McCoy:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kyle Walther:
eight autocross runs (two second place times, a third place time, and a fifth place time.)
and 23 laps of endurance.

0 cones 0 off course.

the car becomes soo much more forgiving and easier to drive that you don't need to push it to the ragged edge to do well. </div></BLOCKQUOTE>

I actually hit one cone in Detroit endurance, but I hit it with the back tire.

In cali endurance I was driving over the base of the slalom cones several times. If you hit a cone with the front wing, you probably would have hit it with the tire anyways.

If your drivers are not hitting cones, it's safe to say they won't start hitting them when you add aero. If your drivers are hitting cones, you need to fix that first, because it's costing you more time than you will get back with aero. </div></BLOCKQUOTE>

i'll give you one cone in detroit..but you were driving with one hand

[CappyUMD]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VinceL:

Icreased roll over tendancy probably won't be an issue since the downforce you are creating is pushing the car down, and hence, preventing a roll over.

</div></BLOCKQUOTE>

Good call, I missed that. In fact if the tires have any normal load sensitivity, the roll over tendency should decrease.

[Gruntguru]

What about low speed corners?

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by CappyUMD:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VinceL:

Icreased roll over tendancy probably won't be an issue since the downforce you are creating is pushing the car down, and hence, preventing a roll over.

</div></BLOCKQUOTE>

Good call, I missed that. In fact if the tires have any normal load sensitivity, the roll over tendency should decrease. </div></BLOCKQUOTE>