I thought I would post this as some positive feedback. It appears that the recent changes to the rules have improved FSAE quite a lot. I am mainly referring to the aerodynamic changes allowing sharper trailing edges, more plan area, and moving wings. A couple of main design considerations have changed:

- After removing most of the advantages for 4 cylinder engines through more points to fuel economy, aero returns some of that advantage by allowing teams with more power to take advantage of more downforce (due to being able to carry more drag). The recent changes have made it possible for cars to have too much drag relative to the power, which is a good thing. This might have a side effect of more teams trying to do custom engines.

- Aero development simply can't be ignored now. While teams may not decide to make aero packages some of their competitors will. As a result teams almost by default have to consider whether or not to run aero, rather than dismissing the possibility all together. Aero should be more prominent in design discussions. This is good as a fundamental area of mechanical engineering is in the forefront of students minds.

- for cars that go aero weight is now even more important, given that your downforce divided by your car weight will be the grip modifier.


Going over the trade-offs there are now a number of very competitive concepts that will largely depend on your competition. For example if there are no winged cars a single car can take economy points, without losing too many dynamics. A high powered, high aero car might put a decent enough points gap to nullify it, where a non aero four might not. There seems a big increase in valid approaches:

- Lightweight single aimed to reduce fuel use as much as possible with high mech. grip
- Single with high aero to maximise normalised aerodynamics, but maintain low fuel use
- High powered four with maximum downforce to go as fast as possible
- Light(ish) four to have high accel, mech. grip, and coast a little on endurance to reduce fuel use
- Custom lightweight engine to have low fuel, low weight (with or without aero)


I applaud the recent rules changes in opening up the potential concepts. I still am very critical of the ones that came before:

- Change in fuel economy scores pushing to singles and low fuel use rather than efficiency (Germany did this well though)
- Templates!! Removed one of the fundamental trade-offs in chassis design of driver comfort vs. weight/packaging
- More mandated tubes making tube chassis' more uniform and generally unnecessarily improving the relative performance of monocoques


When Carroll Smith was still around he was making noise about fundamentally changing the rules to cause a bit of a shakeup. This was in response to the convergence of US cars to a norm (i.e. 95% of teams trying to be Cornell). I would say the recent aero changes have done that and we are now in the middle of an exciting time in FSAE.

Comments? Thoughts?

Kev

Nice points made there Kev, although you are hardly going to stir up much response when you open with a line about positive feedback. Where is the controversy in that?

As far as the rule changes go, you seem to have missed the point that Monash can now fit an even larger weather shelter to the back of their car. This is a crucial point as their ever-expanding team no longer fits inside a standard pit tent. Given your sensitivity to Melbourne weather Kev, how did you miss that?

As a team that's been using wings for a while, definitely think it's a good thing that people are finally starting to catch on to the benefits of wings. Anything that draw more branches of engineering students (most likely aerospace) to work together on a project is a positive. For too long, too many people were very closed-minded about them. "You just don't go fast enough, they're useless" The same people usually turn right around and contradict themselves by saying "and think how much drag you're adding!" If we don't go fast enough for the downforce to matter, we don't go fast for drag to matter either. You can't have it both ways.

I think the rule change is especially good for the design event. In our past experience it seems like having wings puts you at an unfair disadvantage in design. A team could put absolutely 0 thought into aerodynamics and the judges are too willing to accept an answer of "we just don't think its worth it" and not dock any points.

Meanwhile a team that does put a lot of effort into designing a good wing package just opens themselves up to get docked unless you have overwhelming test data to change the judge's pre-formed opinion about wings. IE last year year we had a ton of CFD results comparing different profiles & configurations but couldn't get access to a wind tunnel before competition so the judges just refused to believe any of it.

Hopefully with wings becoming more established that will even out a bit.

I really wish that was the case Kev, but there are a couple of reasons why I think that this new golden age of engine and aero diversity will not come to pass.

Firstly, there is little to no current overhead in the amount of aero cars are able to run. Specially in the Aus comp where track design has forced our track widths to the limits of stability, with a consequent decrease in vehicle plan area and wing span. A four cylinder car does not have access to more aero than a single, in fact I would argue they are less able to generate DF due to the narrow package of singles and the flow on effect of being able to run greater diffuser angles, i.e. Maryland's carbon rear keel concept).

So, neglecting drag considerations for a second, the 4s will never be capable of achieving the same specific downforce as a lighter single car, assuming all other aspects of the design are equal and the cars are developed and refined to the same level.

With regard to the drag issue, DRS (drag reduction system) and moveable aerodynamics will provide additional advantage to the aero cars. They effectively get to have their cake (downforce) and eat it too (low drag). If designed and implemented well, the lower power Aero singles will not suffer the drag penalty of carrying an obscene amount of wing. Neither will the Aero 4s. So in the straights, both these aero cars will have performance comparable to their non-Aero competitors + 20 kg. That level of weight is only just outside the competition "noise" limits discussed previously, and well within the driver variation for most teams.

This means that the Aero cars will have a significant advantage over the non-Aero cars in all cornering and braking segments, and only a slight weight disadvantage in the straights.

Furthermore the lighter weight single aero cars will have a significant advantage over the heavier 4 cylinder aero cars in all cornering and braking segments due to their higher specific downforce. Assumed lower fuel consumption is an added bonus.

Perhaps sadly, on this basis, the archetype of a high performance, high scoring Formula SAE car for the current rules seems both crystal clear and rather singular:

It is a lightweight, single cylinder car, with maximum aero and DRS capability. Anything less (or more) and you will be bringing a knife to a gun fight (all other things being equal... which they rarely are).

This is obviously just my personal opinion, but it is backed up by our team's point sims. Kev, I would suggest you program a DRS option into your point sim (if you havent already) and see the effects.

Time will tell...

Scott

PS: How good would downforce cake taste?

Scott,

The points sims long ago indicated that a four with aero (by the old aero rules) was the best option before increase in fuel economy points. But we rarely saw teams adopt that approach. The recent change offers such an advantage to aero teams that we will definitely see an increase in aero vehicles.

The single lightweight aero with DRS concept you present is not ideal. It is entirely possible to build a top power engine for the weight and packaging of a single. Hence the single cylinder engine choice already shows compromise to reduce required resources. As has already been the case aero (and DRS) requires extra resources, so while on paper the standard single or four may not be as good it may be easier to implement them well. I wouldn't predict their demise in competitiveness too soon.

You and I have been around long enough to know that it doesn't really matter which concept is the theoretical "best" but rather who can implement a concept that is good enough very well. This is where resource allocation and team knowledge and skills creation plays a big part.

The other effect that comes into play is the thrid team effect. It is easy in the points sims to compare one car concept to another, or even a field of sensible cars. What may need to be taken into account is the outlier. If we assume that there are two teams and for the sake of it we assume equal driving ability:

Lightweight single with aero and DRS (Monash 2012 in current direction)

High powered four with aero (no DRS, but flaps able to open) (Monash 2012 returns to four and has Cornell Alumni do their engine)

On the comparison they should come close to equal on skidpan (now being limited by wheel lifting). The four takes accel easily. The single takes autocross and endurance (not by much) and takes fuel. In comparison the single has quite easily trumped the four.

Now we add other cars to the competition. In the mix we have a super lightweight single. It is a reasonably quick car but plays to conserve fuel in enduro. It uses a ridiculously low amount of fuel rendering the fuel advantage of the previous single meaningless. The gap closes.

There is also a high powered four (great mechanical grip) with a crusty old driver who has FSAE cars moulded around him. The driver manages to peel out a super fast autocross time based on abnormal driver ability more than having the ideal car. Now the autocross advantage has been eroded. The gap is even closer.

At this stage the sacrifice in accel points now becomes an issue that it wasn't before. The lightweight aero single still has the edge, but it has been significantly reduced, making the two concepts much closer and well within the points "noise" due to preparation. Interestingly on the strategic front the aero four is likely to be in front at the start of the final day. It is always good to be in the lead at any stage in an event. It could be weather that decides the winner. By the way when it rains the four by necessity had implemented a good traction control system, the single hadn't (a very common approach for both teams) this alone makes the four faster in the rain.

I admit that the big hit strategically is the potential of losing fuel points. This is in reality a weakness in fuel use rather than fuel efficiency, the same scenario does not play out the same way in Germany. To my mind the only dynamic events you can realistically design to win are skidpan, accel, and endurance. Autocross is too dependent on driver skill and can be stolen by freak drivers, and fuel use is too dependent on lap times and can be stolen by a coasting car.

So while I largely agree with you in theory that the lightweight aero car is dominant, I would imagine in practice the concepts will not be as far away in points. The points gap by Monash at Melbourne was as much to do with team preparedness, vehcile development, and a good driver squad as it was having the better theoretical conept (which they also had). We cannot forget Stuttgart's recent world dominance with a theoretical "less optimum" vehicle.

So I return to being positive about us entering a period of increased vehicle diversity and points being traded between concepts.

Kev

quote:

This is obviously just my personal opinion, but it is backed up by our team's point sims.

Don't worry Scott - it's not just your team's simulations that say that. Even as the Australian track layout discriminates against aero more and more, year on year, it'll be a long time before the gains are lost.

--
Pete,
Ex-UTS.

quote:

Originally posted by Pete Ringwood:

quote:

This is obviously just my personal opinion, but it is backed up by our team's point sims.

Don't worry Scott - it's not just your team's simulations that say that. Even as the Australian track layout discriminates against aero more and more, year on year, it'll be a long time before the gains are lost.

--
Pete,
Ex-UTS.

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.

quote:

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.

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.

Kevin,

Let me start with some shouting.

1. High downforce DOES NOT IMPLY high drag!!!

(And, turning volume down a bit.)

2. Under the old rules, a lightweight aero car, done right, would have DOMINATED.
~~~o0o~~~

Regarding #2 above, I recall Carroll Smith saying something similar 10+ years ago.

So I don't think the rule changes have really changed much at all, other than perhaps providing an even bigger incentive for the teams to go "aero" (a necessary push to get the teams out of their ruts). In fact, I think as soon as one of the teams "does it right", the rules will change back to less aero.
~~~o0o~~~

But the important point is #1 above.

I reckon the "downforce=drag" myth is a result of the motorsport regulatory mechanism that only allows grossly inefficient aero, mainly for safety reasons. That is, cars go faster because of more downforce, so things get more dangerous (or more costly to upgrade tracks), so rules are changed to give less downforce and more drag (ie. less efficient).

I would argue that with liberal rules a true "aero" car will have LESS DRAG than a non-aero car. By definition, non-aero cars don't bother with things like streamlining, and open-wheelers naturally have high drag. But any rational attempt to generate downforce requires some attempt to control the airflow over the car, and this is easiest if the car is "streamlined". Obvious example = wheel-pods! (BTW, high mounted rear wings = "air brakes"!)

So a simple analysis of the Dynamic events strongly suggests an aero car (even under the old rules). There might be break-even in Acceleration, because slightly more weight from aero panels, but slightly less drag. But the biggest first-order performance differentiator in the other events (SP, AX, and E) is DownForce/Weight, so a lightweight car is strongly favoured. Thus even Acc benefits from going "aero" (see below re: lightweight engines).
~~~o0o~~~

The increasing points awarded to Fuel Efficiency is an yet another incentive to go aero. Quite obviously FE benefits from low drag, and as noted above, good aero (both Cl and Cd) comes from smoothly controlled flows.

I think one of the main goals teams should be setting themselves is the "constant speed car". Namely, high enough corner speeds that they don't have to accelerate hard onto the straights, and then brake hard for the next corner. Again quite obviously, the braking is just dumping valuable energy into the atmosphere, which is not good for FE. The easiest way to get high corner speed is a lightweight car with high aero DF. (And a bonus is that you do NOT need a gearbox, so even less weight! )

So a lightweight aero car is win-win for Fuel Efficiency.
~~~o0o~~~

For the reasons given above, and IMHO, Drag Reduction Systems are a wank (more mindless mimicking of the "real racecars" in F1.)

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.

Simple stuff, but probably a leap too far for most teams. It would require some imagination....
~~~o0o~~~

I think it is a shame that the whole event, regardless of the rule set, is biased towards the building of unnecessarily complicated chassis and suspensions, and away from aero and engine design, where the real "efficiencies" are to be found. Bring last year's chassis and you are penalized 50+ points. Bring last year's off-the shelf engine, then platinum plate your titanium grumlinks, and you are rewarded with extra Design points.

I think the design and build of a lightweight, efficient, maximum horsepower bespoke engine (~120hp, given ~3 sq. cm restrictor) is quite achievable for many FSAE teams (easiest as a single!). The "limited resources" argument is countered by developing it over a number of years, and more importantly, stop wasting time on ridiculous suspension rockers, paddle shifters for the gearbox (which becomes redundant), bespoke CVs/axles/wheels, etc., etc.

FSAE is graduating thousands of chassis/suspension engineers each year, but who is going to design the next generation of lightweight, fuel efficient engines. Oh yes, they are going to be electric motors, so I won't be able to drive into town anymore...

Z

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

quote:

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.

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?

quote:

Originally posted by Kevin Hayward:
... you can always take any car you are suggesting and add a wing which would be more drag...

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

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

quote:

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"

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.

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

quote:

Originally posted by bob.paasch:

quote:

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.

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.

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.

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

quote:

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

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

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...

quote:

Originally posted by theTTshark:
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.

I'm sorry that you felt my last paragraph was condescending, that was not my intent.

For many years the FSAE rules read differently:

"1.2 Vehicle Design Objectives

For the purposes of this competition, the students are to assume that a manufacturing firm has engaged them to design, fabricate and demonstrate a prototype car for evaluation as a production item. The intended sales market is the nonprofessional weekend autocross racer...."

Some people complained about the premise. Some, like you, felt the FSAE autocross course should be representative of an SCCA course. Others felt fuel economy/efficiency an unnecessary part of the competition, after all, weekend autocrossers don't care about fuel economy.

What did SAE do? They dropped the above wording, and replaced it, making the purpose of the competition explicit. You are designing cars for FSAE dynamic events.

Of course they kept the "weekend autocrosser" premise for the presentation, the market for selling cars to other FSAE teams is pretty small (actually, given the rules, precisely zero ).

To tell the truth, when I think of the cars that Kansas has brought to competition, I see cars that are designed to win FSAE competitions. They also happen to be good at SCCA autocross. Not the other way around.

Now, back to our regularly scheduled pot stirring.

quote:

Originally posted by Z:
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).

Easy to pontificate from the armchair, but in practice, very difficult to implement. Aero undertrays on FSAE cars are complicated by:

1) inability to use any kind of side skirt to seal the sides
2) typically rough FSAE autocross and endurance surfaces that cause a lot of variation in vertical distance to ground for sprung undertrays
3) nasty vehicle dynamics considerations for unsprung undertrays
4) high yaw rates means that when you need the downforce, the air is coming in at an off angle. This complicates simulation (you now need a full car model) and becomes nearly impossible to physically validate under controlled conditions.

Now back to the original question:

quote:

Originally posted by Kevin Hayward:
I thought I would post this as some positive feedback. It appears that the recent changes to the rules have improved FSAE quite a lot. I am mainly referring to the aerodynamic changes allowing sharper trailing edges, more plan area, and moving wings. A couple of main design considerations have changed:

- After removing most of the advantages for 4 cylinder engines through more points to fuel economy, aero returns some of that advantage by allowing teams with more power to take advantage of more downforce (due to being able to carry more drag). The recent changes have made it possible for cars to have too much drag relative to the power, which is a good thing. This might have a side effect of more teams trying to do custom engines.

- Aero development simply can't be ignored now. While teams may not decide to make aero packages some of their competitors will. As a result teams almost by default have to consider whether or not to run aero, rather than dismissing the possibility all together. Aero should be more prominent in design discussions. This is good as a fundamental area of mechanical engineering is in the forefront of students minds.

- for cars that go aero weight is now even more important, given that your downforce divided by your car weight will be the grip modifier.

In my opinion, the new aero rules go too far. I think there was already a substantial advantage to aero under the old rules. Most teams declined to do aero due to logistical considerations. Under the new rules, again IMHO, aero is going to be necessary (but not sufficient) to win a major competition. The better teams will adjust, the lesser teams will fall further behind. Anyone can run CFD, but there will be an even larger advantage to teams with wind tunnel access.

That said, we're of course working on bigger wings.