Effects of rule changes

[Kevin Hayward]

Z,

While I agree that high downforce does not have to equal high drag, you can always take any car you are suggesting and add a wing which would be more drag and more downforce. A car with "maximum" downforce will have higher drag.

You can start with any car and figure out how much drag you can deal with and then try and get as much downforce as efficiency as possible.

Kev

[Gruntguru]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
But there is a big benefit possible from "active aero", IF some LATERAL thinking is applied. So, instead of the "lift" acting downwards, do it sideways! Fit a vertical wing (or two+), like on a sailboat, and steer it to give a centripetal force into the corners. It could be mechanically linked to the steering wheel, or electro++ controlled for more "optimal" performance on gusty days. This not only helps the tyres push the car into the corner, but since the aero force screw is likely above Cg height, it counteracts body roll and lessens LLT. </div></BLOCKQUOTE>
I had thought about this concept previously and some quick calcs show that the emost efficient utilisation of downforce is a combination of lateral and vertical. The optimum ratio depends on mu. The optimum DF angle to vertical ranges from:

45* for mu = 1 (and a 41.42% improvement in "aero" grip) to
34* and 20% for mu = 1.5, and
27* and 12% for mu = 2.0.

So "tilting wings" somewhere in the future?

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kevin Hayward:
... you can always take any car you are suggesting and add a wing which would be more drag... </div></BLOCKQUOTE>
Kev,

And you could also add a parachute, which would be even more drag!

I repeat, aero cars should have LESS drag than non-aero.

(Maybe I'm biased. I own four Citroen DSs, and two Tatra T600s. One day I'll get one of them roadable!)
~~~o0o~~~

Gruntguru,

I figure your calcs above are based on the assumption of a constant amount of aero force.

My thinking was that the team would extract as much downforce from the undertray as practical (ie. from the plan area of the car). Then they can go after yet more aero force from vertical "sails".

Is there a max vertical height for "aero devices" in the rules? Or for non-aero, ahem, "bodywork"? If not, then the sky is the limit! (Although I would start with about 1 metre high, just to get a feel for it.)

Z

[Kevin Hayward]

Z,

Maybe I should have phrased my response better to account for pot stirring.

Present any drawing, picture, concept of any car and I guarantee that us idiots can add downforce to it (including your super low drag FSAE aero car). I can't guarantee that it will come free of drag. At some point the additional weight/drag/COG height will outweigh the benefit of the added downforce, but that would almost certainly be past the point at which the aero car has less drag than the non-aero.

It is entirely possible to design a car using aero to have lower drag and higher donforce than one without. It will not however have the maximum possible downforce, and most likely not the best balance of downforce to drag for the competition. It is easy to see that the points in the competition are much more sensitive to downforce than drag, so even the inefficient downforce devices add points.

...

I would love to see someone take on the moveable vertical sails. There would be some interesting hurdles to overcome such as driver visibility and cockpit templates, but it would make for a very interesting car.

...

Lastly the Citroen DS and the Tatra T600 are both fantastic cars. If only we lived in a world where carmakers were more concerned with true engineering in personal transportation rather than selling new body shapes on old platforms by marketing a lifestyle. Where are our interconnected suspension systems and lightweight vehicles?

FSAE may actually be the only area of new cars (including racing) where average weight has declined in the last couple of decades.

Kev

[Gruntguru]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:My thinking was that the team would extract as much downforce from the undertray as practical (ie. from the plan area of the car). Then they can go after yet more aero force from vertical "sails" </div></BLOCKQUOTE>
The optimum "angle from the vertical" for application of DF applies to any DF for which the angle of the force vector can be varied. In other words if you have an undertray that generates 500N (vertical only) plus a wing that generates 500N in any direction you like, the optimum angle for the wing will still be given by the above calcs - ie not horizontal. Of course all this assumes constant mu and neglects any benefit of reducing lateral weight transfer.

[Z]

Kevin,

The key reason for my "pot stirring" here , is to counter the myth that aero downforce comes with an unavoidable cost of increased drag. Or, for that matter, with much more weight, higher CG, etc.

The above myth comes from the ubiquitous high mounted rear wing on formula cars, which is an abomination.

So, all FSAE aero students;

1. Get that picture of the "high rear wing" out of your minds.

2. "Streamline" your car (good for Fuel Efficiency ). Try a central cigar shaped fuselage, and add four tear-drop shaped wheel-pods at the corners. (And as long as there is nothing specific against these wheel-pods in the rules, DO NOT accept any arbitrary "spirit of the rules" bulldust bans from the scrutineers.)

3. Generate ALL your downforce from an "aero undertray". This approach is relatively lightweight, it lowers CG, and it generates negligible drag for tyre popping downforce (the rotating wheels will give more drag).
~~~o0o~~~

Regarding vertical sails, I suggest doing a thorough job of the aero undertray first.

When many other teams also have good undertrays, then you might start thinking about, oh, say..... extending those four wheel-pods upwards, multi-flapping them, and steering them......
~~~o0o~~~

All those classic cars, and none of them yet driveable....

Due to some poor "life decisions" I have the better preserved cars stored in my uncompleted house, while I live in a rented hovel! Better get busy laying more bricks...
~~~~~~~~~~o0o~~~~~~~~~~

Gruntguru,

Picture an end view of the car, and a rectangular box as wide as the car, going from ground up to the sky. Now imagine a planar wing (seen edge on) spanning that box from side-to-side, but at any angle. Obviously the closer to vertical the wing is, the longer it is, and the more aero force that it can generate.

Now what is the "optimal" angle of this wing?

I'd say that the vertical component of force is constant (because the wing spans side-to-side), but the horizontal component increases indefinitely as the wing gets closer to vertical.

But I would NOT want really tall sails on a gusty day.

Also, when generating "lift" these sails will also suffer from vortex drag (unlike the undertray). This drag could be used to deliberately slow the car for corner entry, countering nose down pitch from the normal brakes, while the "lift" initiates cornering by leaning the car inwards. All this started by the driver pressing the "left" or "right" button on the steering wheel...

Z

[theTTshark]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by bob.paasch:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by theTTshark:
It's funny that the tracks are so aero unfriendly considering we are building cars for SCCA Autocrosses. In case you haven't seen one, think of a course on concrete big enough that even Corvettes can stretch their legs, and you have the SCCA National Championships. In fact I challenge any non-aero car to come to that event and try to win it. </div></BLOCKQUOTE>

From the 2012 FSAE rules:

"A1.1.1 To give teams the maximum design flexibility and the freedom to express their creativity and
imaginations there are very few restrictions on the overall vehicle design. The challenge to teams is to
develop a vehicle that can successfully compete in all the events described in the FSAE Rules. The
competitions themselves give teams the chance to demonstrate and prove both their creativity and
their engineering skills in comparison to teams from other universities around the world."

We are not building cars for SCCA autocross. We are building cars for FSAE/FS competitions. Most of those competitions take place at venues without the room to build a SCCA Nationals course.

I have no problem with a team deciding to build a car to compete at the SCCA Nationals, but IMHO they then lose the right to complain about tight FSAE/FS courses. The FSAE/FS course are what they are, if you want to win, design to those courses. </div></BLOCKQUOTE>

I completely understand that there are specific rules for the courses that we run, and I understand why these rules exist. I understand that we have to take into account space limitations, but better courses have been made in spaces even more limited than what the Michigan and the old California venues are. I should also correct my previous sentiments about the difference between SCCA and FSAE courses. It isn't just the speed of the tracks (because sometimes the courses we run average out to around 35mph), but what is quite possibly more important than that is the flow of the courses. Last year's California course is a perfect example of random corners being thrown in just to produce a "FSAE" course. I think what we're going to see is that even in the existing rules of how courses can be constructed we're going to get courses that are much more fluid than ever before. At least that's my hope.

Besides that we also have rules like C4.1.1 that indicate we are indeed, at least from a marketing perspective, producing these cars for the SCCA.

C4.1.1 The objective of the presentation event is to evaluate the team’s ability to develop and deliver a
comprehensive business case that will convince the executives of a corporation that the team’s design
best meets the demands of the amateur, weekend competition market, including Sports Car Club of
America (SCCA) Solo, and that it can be profitably manufactured and marketed. (See also A1.2)

Granted this is just for presentation, but it instills the point that we are building SCCA autocross cars. The rules that you cite indicates that we are building cars for FSAE competitions. Here would be my counter-point to your analysis of rule A1.1.1: If the business aspect of FSAE is to build a car for SCCA autocross, doesn't that indicate that we should at least take SCCA autocrosses into account? Obviously many will say no, but still it raises interesting talking points about the way these events could head in the future.

I normally wouldn't write a response this long but I find that your last paragraph is a bit condescending (maybe not in intent but certainly in writing over the internet), so I feel especially driven to write a full response. I have no problem with someone disagreeing with my opinions regarding Formula SAE course design (or anything for that matter because at the end of the day everything is just an opinion except for the basic rules of nature), but we're always going to have people complaining about this and that especially in a competitive event like racing. It is not our job as engineers to say to those complaining that they do not have the right to complain, but it is our job to investigate and discuss these outside options to potentially find solutions to problems we hadn't thought of ourselves. I find that in every complaint, there is at the bottom of it, a problem, even if it is microscopic. As I have discussed above, the courses are what they are not because of the rules, but because of poor course design and implementation. At it's core this is indeed complaining, but on another level this leads to a discussion about where the future of courses can lead even within current rule sets. Which could lead to courses that are arguably easier for everybody to drive. I think the point here is, yes we all can't have it our way, but we are all entitled to our opinions. That's why I'm so interested in why you believe that my opinion should be silenced.

BTW, I believe that at least on a dynamics level we have proven that we can win or come close to winning on these autocross tracks, as your team has as well.

[Fantomas]

Don't get me started on course design.
Some of the FSAE/FS course designers really just throw them together without even driving them themselves. So they have no chance of getting rid of passages which are not fluent etc.
The hard 90° turn at FSAE-MI2011 was probably one of the best examples for this.
It also seems as if some of the competitions do not care about rule compliance of the course.
Track widths are to narrow, slaloms to short, etc.
Track safety is another thing, that should be mentioned: Fire extinguishers miles away, no radio for the marshals, marshal posts at the most dangerous places or walls of shame/little monaco kind of setups.

There is a lot room for improvement.

Fantomas

[ed_pratt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
But there is a big benefit possible from "active aero", IF some LATERAL thinking is applied. So, instead of the "lift" acting downwards, do it sideways!.....
Z </div></BLOCKQUOTE>

Nice topic,

Surely we can make drag work to our advantage is we use active aero? i.e. DIS??!

Using a similar concept to the one proposed by you in the beam axle topic, how about under braking having an increase in the angle of attack for the front wings? We get extra deceleration from the increased drag and greater normal force to the tyre from the additional compression of the suspension?

Am I way off base here?

Ed

[Mike Cook]

I pretty much agree with Scott and Kevin entirely. Not much to argue about.

The Downforce advantage of a single cylinder outweighs the power advantage of the a 4cylinder car. It will be interesting to see how our tr12 car compares to the tr11. The TR12 certainly has more downforce, but far less power. With out a boosted engine, i'm not convinced it will beat the TR11 car on a SCCA course.

Z,

I like the way you think outside the box, but, just because people don't post all of their calculations, doesn't me they didn't do them...