underbody tunnels

[Maverik]

Agreed, I think the real question of aero in FSAE is whether you have the means to truly develop any sort of aero package... ie design tools, manpower, fabrication tools and techniques... if any of those are lacking, the package likely won't do well and the overall car will suffer from lack of development in other areas of the car. Aero definitely works, but only when the rest of your car has its act together. Who cares about having more downforce into a corner if your suspension can't handle it?

[Scott Wordley]

Downforce is not something that "happens" at 60 to 70mph, we all know its a v^2 relationship.

There are numbers published for the aerodynamic performance of FSAE cars, they are not hard to find. With them you will also find wing profiles, CFD, wind tunnel and on-track measurements.

If anyone thinks that 60 kg of downforce is of no benefit at 60 km/h (yes kilometers per hour) then I suggest they leave aero to the hand wavers out there.

Scott

[CappyUMD]

I also recommend mulsannescorner.com and Competition Car Downforce by McBeath. I heard Race Car Aerodynamics by Katz is good, and a bit more technical.

At the speeds we're running I think the aero package to have is high downforce comparable to A-mod autocross cars. Drag is negligable because there are no straightaways or large radius turns (never achieve anywhere near drag limited top speed). However weight of the package is a huge issue, and it's tough to make large wings weigh nothing.

As far as tunnels go, they'll probably stall when using aggresive diffuser angles unless you employ vortex generators. You'd want to use 3D CFD to design vortex generators though.

[Marshall Grice]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Downforce is not something that "happens" at 60 to 70mph, we all know its a v^2 relationship. </div></BLOCKQUOTE>

only true if the airfoil is not stalled.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Drag is negligable because there are no straightaways or large radius turns (never achieve anywhere near drag limited top speed). </div></BLOCKQUOTE>

You'd be suprised how much drag can be produced at our speeds. We have had configurations of our car drag limited to &lt;60mph. To say that amount of drag has no effect on typical FSAE speeds is misleading.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Who cares about having more downforce into a corner if your suspension can't handle it?
</div></BLOCKQUOTE>

Downforce makes pretty much any suspsension work better. Although i agree that cutting team resources will bite you in the ass. But not because your suspension can't handle it.

[CappyUMD]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marshall Grice:
You'd be suprised how much drag can be produced at our speeds. We have had configurations of our car drag limited to &lt;60mph. To say that amount of drag has no effect on typical FSAE speeds is misleading. </div></BLOCKQUOTE>

What kind of engine are you using? Let's assume the car has the same amount of power as the Honda 600 F4i which has a top speed of about 160 mph. The car would have to be 19 times as draggy in order to have a top speed of 60 mph. I realize that the car with wings has at least twice the frontal area and a higher drag coefficient, but I still don't believe it.

[mtg]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by CappyUMD:
What kind of engine are you using? Let's assume the car has the same amount of power as the Honda 600 F4i which has a top speed of about 160 mph. The car would have to be 19 times as draggy in order to have a top speed of 60 mph. I realize that the car with wings has at least twice the frontal area and a higher drag coefficient, but I still don't believe it. </div></BLOCKQUOTE>

Marshall's right, I've tested the drag limited top speed on a couple aero FSAE cars and you can set them up to be drag limited at pretty low speeds. There was also full scale wind tunnel data to back that up.

Also keep in mind mechanical drag. Motorcycles have much less mech. drag than an FSAE car with 4 larger tires and lots of toe angle. Then there's the power loss in the drivetrain, which is more complicated on an FSAE car (I don't remember seeing any CV joints on a motorbike). Then there's that pesky restrictor...

[awhittle]

Your design goal is to develope a car to market as an autocross car. You would never be able to sell cars without aero. You can not win on an autocross without aero. All of the fast/quick autocross cars now running in A-Mod have aero packages.

AW

[Maverik]

Im really starting to enjoy reading the responses here, most are well thought out. In regards to the suspension, what happens if you choose crappy dampers that bottom out from the downforce generated into a corner... woops. There was an A-Mod aero car a few years back I think it was called the phantom that had so much drag that it was limited to ~80 mph, but it could almost sustain speed through corners due to the immense amount of downforce gained. If you saw the thing, all it looked like was an A-mod car but with ginourmous aero! Supposedly it won almost every race it competed in.

[awhittle]

see http://www.napylon.com/Phantom.htm

To look at the car would not strike you as anything revolutionary. Everything is very well done. As I remember it was around 300 hp. Most of the top autocross cars top out around 100 HPH and I cant think of any that are shifted more than once wile on course. Most are CVT. Most if not all of the top cars run tunnels and close to the full size on wings.

AW

[andyman61]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by awhittle:
Your design goal is to develope a car to market as an autocross car. You would never be able to sell cars without aero. You can not win on an autocross without aero. All of the fast/quick autocross cars now running in A-Mod have aero packages.

AW </div></BLOCKQUOTE>

Hmm, this is something we've pointed out, but apparently section 1.2 of the rules (or whichever one states of purpose of building an FSAE car) is being ignored these days.

As stated before, you have to have everything done right on the aero package to consider running it. You have to have multiple forms of testing to show you know what you did and you have to be able to build it properly (light, strong, accurate). Pretty much like anything else on a car that you want to be competitive. They're definately not something you want to be slapping on last minute, it has to be considered as an integral part of the package from the word go.