FSAE Michigan 2013

[MCoach]

The disappointing thing is that FSAE is supposed to be an "educational competition". All these useful lessons should be passed on to each new intake of students. On the face of it, we should expect FSAE to have the fastest rate of improvement of all types of motorsport. Relatively liberal rules, hundreds of universities around the world, thousands of research theses each year, all with the singular goal of building "the fastest possible autocross car, ever!". But it ain't happening...

Honestly, I have to blame the Design event as being a major reason for this almost complete lack of progress. Too many newbs have (or are given?) the impression that their job is to impress the DJs with their "mini-F1" car...

When are you students going to learn some engineering?

I just want to address the negative view on the progress of this student design series:


Not everyone is a genius, blessed by the Flying Spaghetti Monster with the Chapman touch to turn any car into a rolling puff of air. Not everyone is writing their PhD thesis on the "super advanced ultimate controls, make car go super fast system" that they are finishing up this term after dedicating 8 years of their life to FSAE.

This, as anything else in the world, has evolved, and has made its progress, both good and bad. Students are exploring different avenues, deriving their own formulas of how to tackle this problem. Is their a correct answer for how to tackle this? Probably not. Is it the one that wins? Sounds reasonable, but only if it still addresses the key point that this is a design competition meant to encourage teams to learn along the way. I feel that THAT is the most important aspect of this. It's like a big science fair for college kids, just bigger toys, and they actually get to play with them. If you insist that there is only one solution to solving this problem, then in your mind, there is only solution, but there have been many different winners and concepts that have come through this program, all with their trade offs. Want to criticize someone on putting a 1lb part half a meter in the air? go ahead, but I'd rather put the rest of the car closer to the ground under that 1lb part.

Not everyone is building an all out autocross car either. Sound ridiculous? Sure, it does. Why wouldn't you want to be the fastest? Because this is such a cumulative point event, it's more important to very well in all areas than be the team that only dominates 1 event.

This isn't life and death, have a little fun with it.

[rjwoods77]

Fun fact that I should throw in based on the last couple posts. The 2007/2008 UB FSAE car used a Satchell Link solid axle with a pullrod and rocker arm connected to each birdcage...

http://www.eng.buffalo.edu/Stu...a_web/images/car.jpg

...and in two separate conversations with top tier design judges one of the very first things they both asked is why I didn't just tie in direct acting dampers off the birdcages and into the chassis. Looking back at it I could have done so and saved myself a bunch of grief in the design of the car.

[VFR750R]

Z, I appreciate your observation that FSAE cars are slow to develop but do you expect them to have a linear progression in performance? I would say performance is more likely to go asymptotic with unchanging rules.

Tires are the most important, and the limiting case here. I don't think you could come up with a purely theoretical FSAE car to run in the 3's in skidpad with the currently available tires. Even if you simulated a car with zero CG height and impossibly low overall weight. Aero is measurable, and would be even better on such a car, but it's a lot easier to calculate something than to implement it.

And likewise, tires and surface play a significant role in accel. I think much like your skidpad times, your 'analysis' is making a lot of assumptions here. First being power; 90KW is a ridiculous crank power level for a 20mm restrictor engine. How are you simulating "right launch technique"? What traction limit are you assuming for the cold tires. I don't doubt your assumptions gave you the results you calculate, but a 65% rear weight bias (with driver) 350lb car with 67HP is probably un-achievable.

I would agree though, that some teams and team members focus on unimportant details and ignore some fundamentals that would result in a faster car. But, I would say, that's part of the learning process. A lot of times, you can't dismiss an idea until you've allocated at least some resources to it, and even at the professional racing level, most ideas don't make it to the racetrack. It can sometimes seem like there are no good ideas, and other times there are so many reasonable ideas that limited resources have to be allocated based on other criteria.

I disagree with the idea that only out-of-the-box innovation will lead to learning how to be an engineer. You also shouldn't so easily dismiss the development of the current FSAE car, of close to 30 years now, to mindless 'monkey see monkey do'.

In summary, many quality engineers have gone through FSAE; you don't think one of them has thought about having higher rear weight bias, you think you are the only one in the world that thinks that might be an advantage, and none of them have thought it through and tried to implement it?? Be careful making the assumption that you are the smartest one in the room...

[Z]

Well, it is bucketing down rain outside, so I may as well have another go at this... Also, with Michigan just over, some teams might now be thinking "How can we win next year?".

But firstly, the expression "mindless 'monkey see monkey do'..." is an insult to monkeys. Monkeys are very independent and perceptive thinkers. I have seen baboons regulary outsmart university educated H. Sapiens. It is we who should really call ourselves Homo Mimicus. But now I am getting off-topic...

I can understand that many of you students don't understand "The Theory". That is your teacher's fault. But all that I say below, and in most other posts, is based on "The Practice". All this can be found in the history of motorsport. I am sure that the average baboon would pick this stuff up after one day at a racetrack. Unfortunately, I guess you guys have to rely on Google, for which you have my sympathies...
~~~~~o0o~~~~~

ACCELERATION EVENT - As "engine and turbo guy" VFR750R should know, the maximum power that any restricted racing IC engine has ever made is about 40 hp or 30 kW per square centimetre restrictor area. So the maximum power you can hope to get in FSAE is about 90 kW (at the crank).

With 50:50 weight distribution, typical CG height, rear wheel drive, no aero, and a lightweight car, this 90 kW engine will spin the wheels almost all the way down the track (ie. traction limited all the way). With the typical tyres available these days, and a typical track surface, which give a typical Mu = ~1.5, this car will get ~3.8 second times. Most importantly, MORE POWER = NO BETTER!

The "right launch technique" I mentioned above (and as any baboon would tell you) is to get almost all the weight onto the driven wheels. So with RWD you want to be "popping a wheelie". Front-engined drag-cars do this by raising the CG, but this is not good if you also want to go fast around corners. So the obvious solution, as seen on by far the majority of racecars (ever !), is to have more rear weight, and bigger rear tyres.

For FSAE I suggest 60%R as a starting point. The general packaging layout to achieve this has been posted many times on these pages. Side-winder engines are NOT needed (where did that come from, Charles???). With this weight distribution and an average power FSAE engine, 3.5 seconds is reasonable. Geez, it is not that hard!

For the Acceleration event itself, it may be beneficial to give your lightweight driver a "booster seat" (ie. like kiddies have, but intended to raise overall CG). Rear anti-squat also helps. To understand why the first ~10 metres are most important, draw a graph of car velocity (y-axis) vs time (x-axis). Acceleration is the slope of the curve, distance traveled is the area under it. (Hint: At any given time you get more area under the curve if the curve starts off steeply...)

VERY IMPORTANT! Longitudinal acceleration is not very important for overall points in FSAE. Much more important are lateral acceleration (see below), and yaw acceleration. You get greater yaw acceleration if the car has lesser yaw inertia. Squashing the driver and engine backwards (eg. for more rear weight) can lessen the whole package's yaw inertia.

Lateral and yaw acceleration are not dependent on engine power (to first approximation), but they have the greatest affect on overall points. Do the simulations and tests!!!!!
~~~~~o0o~~~~~

SKID-PAD - No, VFR750R, "Tires are [NOT !] the most important...". In the hundred+ years since rubber tyres were first used in racing their maximum "coefficient of friction", or Mu, has increased from about 1, to about 2. These numbers correspond to attainable horizontal "Gs" of the car. A few years after racers discovered aero downforce the horizontal Gs doubled. Then a few years later they tripled, then quadrupled...

The practical limit for Gs due to aero is the driver passing out. This is never reached because the organising bodies keep changing the rules to restrict aero, and thus to restrict cornering Gs and speeds. (BTW, this is why aero on all current racecars is so inefficient (ie. high drag and low downforce), because it allows the cars to keep their noisy, high revving, high power, "sexy" engines, but still be slow and safe).

In 2002 Carroll Smith was encouraging more teams to go aero (Scott Wordley has a video linked somewhere). A few years ago the FSAE aero rules were freed up. But still very few cars are getting under 5 seconds in SP. Come on guys, take the hint.
~~~~~o0o~~~~~

PUSH & PULL-RODS - On the "Suspension Design" thread I recently listed the dozen or so excuses that are given for using these, and why those excuses are nonsense. The only excuse (I won't call it a reason) that was supported by other FSAEers had a defense that went something like this;

"If we are silly enough to buy really expensive dampers, and if we are silly enough to build really fragile wishbones, and if we are silly enough to crash this super-fragile car in testing, then we might save the cost of a new damper.....".

So, summarising this argument, if you are really stupid (I figure 3 x silly = 1 x stupid), then you only have to stupidly pay for your new wishbones... Err, or something lame like that...

Anyway, the really important point here is that no one gave a compelling argument as to how push/pull-rods make your car go faster. That is, push/pull-rods give (next to) NO PERFORMANCE ADVANTAGE AT ALL. (Well, in an indirect way they might help a bit with aero, but they are by no means necessary...)

Bottom line here (and in keeping with MCoach's post above), is that using "pushrods-to-springs-on-top-of-the-nose" is a lot like wearing your baseball cap backwards, and upside down, or whatever... I reckon you will have a lot more fun, and win a lot more, if you just learn to play baseball.

Z

[VFR750R]

Look, I don't want to get into a pissing match of performance can's and cant's, but it's pretty obvious that not one team has ever achieved 90KW, and I know several teams that have had cylinder pressure tuned engines and all the bolt on electronic goodies one could ask for. Some of these engines have seen similar development as seen on professional racing efforts. No professional engine shop says "well an ALMS engine makes xHP/cm^2, so a cup restrictor engine should make XX-HP".

Your 30KW/cm^2 is by your own admission a guess, an assumption of what is achievable, based on another configuration of engine in another series. Can you verify the output of the engine that creates that claim; can you verify the engine was not leaking air to achieve it? It's fun to think about what-ifs, but when the highest verifiable output is in the range of 70KW, you think these engines are ~30% off their potential?? And I know of several professional applications that are highly developed and competitive that do not reach 30KW/cm^2.

This kind of activity is nothing more than a kid saying "why doesn't GM make a 2500HP car that makes 5000lbs of downforce, for $8000. GM is dumb for not doing it, I'd buy one.

And I'm actually getting a bit upset that you are insulting pretty much everyone in the series. Sure there are teams that get many of their designs by bench-marking others, and not every team is equal in abilities (and budgets), but you are claiming expertise over every area of the car, and critiquing a lot of work and accomplishments and trivializing the knowledge required to succeed.

I wonder, since you are such an expert, why didn't your teams' FSAE car get into the 3's in accel and skidpad, make 90KW, and make the driver pass out from all your downforce... I await your excuses about how you are only one man and if you had 30 of you on your team, it would have been easy to accomplish said goals.

[MCoach]

I wonder, since you are such an expert, why didn't your teams' FSAE car get into the 3's in accel and skidpad, make 90KW, and make the driver pass out from all your downforce

VFR750R,

Z has not been a participant in this competition nor a mentor for any team that I am aware of.

In fact, here is picture from the younger days:

http://fsae.com/eve/forums/a/t...010404621#5201040462

And a few articles he has written:

http://www.smithees-racetech.com.au/ackerman.html

http://www.slashdocs.com/yxurz...n-erik-zapletal.html

http://www.theoryinpracticeeng...ced%20suspension.pdf


Erik,

until we can talk in terms of compromise and structured thoughts, it makes it very difficult for anyone to take you seriously. Start treating people like colleagues and less like monkeys. While it may be on the limits of possible to reach these theoretical maximums that you've called reasonable, as I've mentioned, some of us have other goals in mind. We've made 60 hp (44.7 kW) to the wheel on our FSAE car from our 450cc motor. Assuming a 5% driveline loss, that's 104kW/L. Should we shoot for that magical 90kW/cm^2? No, to us the amount of fuel we need to carry nor an available motor to reach that is worth the weight they bring. I prefer the straw hat to a baseball cap anyway.

[RenM]

90 kW is totally beyond the limit of what is achievable in FSAE. Comparing FSAE Engines to other restricted engines is more like comparing apples and oranges.

If you use a naturally aspirated engine you will need at least 4 cylinders for a rather constant air mass flow through the restrictor. However this results in very small cylinders which them self create increased thermodynamic and mechanical losses. A very high compression ratio without compromising the combustion chamber is also not possible due to the very small stroke.

Going for a turbocharged 2 cylinder engine will also not be able to yield 90 kWs because of the bad efficiency and high back pressure of the small turbochargers needed.

[Z]

VFR750R,

You should really read what was written before getting your knickers in a knot.

So, for the third and last time;

1. "... the maximum power that any restricted racing IC engine has ever made is about 40 hp or 30 kW per square centimetre restrictor area."

In the next few months Ian Bamsey's "Race Engine Technology" magazine should have a wrap-up of this years Le Mans' engines. There he normally gives his well reasoned (IMO) estimates of their power. Typically, all these 5,000+km engines produce about 35hp/sq.cm. Engines requiring less durability have produced more. But the point is, 30 kW/sq.cm is about the UPPER LIMIT. Good engineers should know their limits...

2. "...Most importantly, MORE POWER = NO BETTER!"

The whole point of my above two posts was to make clear that FSAEers should NOT be chasing more power. A medium power car with ~60+% rear weight will out-drag the top horsepower car with 50:50 weight distribution.

3. If you have well reasoned arguments as to why 50:50 weight is best for FSAE, then please share them. And while you are at it, you might let us know why the vast majority of rear-drive racing cars have got it wrong for all these years, by putting more weight, and fatter tyres, on their rear wheels.
~~~~~o0o~~~~~

MCoach,

I like monkeys. They are a lot of fun.

As above, I reckon the 60hp you are getting is more than enough to do well in FSAE. In a simple, lightweight car, with about 60% rear weight, and the right launch technique (front wheels almost lifting), you should be able to set a few Acceleration records. And that's always fun! More importantly, the rest of the package would be a good starting point to do well in the other Dynamic events. (Hint: just add that aero-undertray.)

BTW-1. That first car I built in your top link was simple, strong, had 50:50 weight distribution that gave great handling (on equal size tyres), and was all-round pretty good. Its weakest point was that it lit-up the rear tyres too easily! Every other RWD car I've built has had a lot more rear weight, which, all things considered, I reckon is better.

BTW-2. One of your other links managed to spell my name wrongly in three different ways! Now you know why I keep it simple here.
~~~~~o0o~~~~~

RenM,

I reckon a 20mm restricted, <610cc engine could get close to 90kW (at the crank, no accessories, etc.). But as before, I reckon that would be a pointless exercise in FSAE.

(Note that said engine, probably a single with big plenum and bespoke turbo, would have to have all bearing sizes minimised, oil/water pump flows minimised, 2-ring piston(s) with tiny skirts, gear drive to cams (?), CR on the edge of detonation, DLC everywhere, and quite a few other things. But the biggest influence on max power would be the fuel. Ie., use the one with highest energy release for a given amount of air breathed.)

Z

[RacingManiac]

For simple curiousity, I wonder what the weight distribution of the current Le Mans Prototypes are...running basically now squared tire setup...

[Z]

RM,

I am quite sure that there are LM cars nowadays that run close to 50:50 weight distribution. This is mainly due to the ACO mandating that only certain size tyres are allowed. Some teams choose to use the wider "rears" all around, so they have to set their weight distribution accordingly (the name Nick Wirth comes to mind?).

In F1, way back during the 1,000+hp turbo era, the tyre rules were much more liberal, and 70%-rear-weight with monster rear tyres (20" wide) was the norm. Tyrell even went the six-wheel route, with 4 x tiny 10" fronts (still available from Avon?). In the 1990s Max Moseley decided he didn't like this look, so for purely aesthetic reasons he imposed rules mandating a very close range of tyre sizes front and rear. The weight distribution had to follow and ended up around 55R:45F.

Whenever the rules are free, RWD racecars end up with more rear weight. A good current example is Bowlby's DeltaWing (built as a completely rules-free concept car), which I believe has at least 70% rear weight, maybe closer to 80%.

Z