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Thread: FSAE Michigan 2013

  1. #201
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    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

  2. #202
    Originally posted by Z:

    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
    Keep back pedaling. "reckon"? C'mon Z you preach more then anyone that we should know our shit before coming out and making a statement.

    As for 90kw, Nobody in FSAE will ever see 90kW unless there engines are pushing over 40% efficiency and .9 Discharge co-efficient throughout the intake and a god of an engine map etc.

    Anyone claiming more then 85-ishhp is obviously using smaller ponies most likely shetlans.

    I'm expecting someone from Swinny or Stuttgart to chime in about now.

  3. #203
    Now that this thread is completely de-railed and turning into quite the train wreck, does anybody know what Maryland's weight distribution was when they were running different size front and rear tires (not sure if they still are or not,) and, you know, winning nationals and what not?

    P.S. While Z sure has the occasional crazy idea, at least you're now thinking about it. And as young engineers, the first thing you should be learning to do is listen to your peers/colleagues/professors and their ideas. Attacking them because they differ from yours will get you nowhere, and you're probably going to end up being wrong anyway since they've been doing this way longer...

  4. #204
    The most powerful naturally aspirated 600cc-I4 with a 20mm restrictor that I know of has 74kW @ front sprocket and a broad usable rpm range, measured on a calibrated Superflow engine dyno.

    Due to the amount of engine work required to achieve those numbers I'm quite sure it's getting close to the limit of what N/A engines can produce.

    I've also heard rumours about a ~85kW turbocharged 600cc-I4 but don't know if the numbers were achieved on a calibrated dyno... Anyway Z's educated guess about 90kW isn't far off.
    "...when this baby hits 88 miles per hour... you're gonna see some serious shit" - Dr. Brown

  5. #205
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    Ok, off multiple sources on the Interweb (all doubtful, but such is progress):

    FORMULA-3 - Many national variations, but typically 2-litre, prod-block, L4, N/A, with 26 mm restrictor.
    So,
    Area = 5.31 sq.cm,
    Quoted Power = >150kW/200hp,
    (with VW engine quoted at 220hp, with "push-to-pass" 240hp available from "special map"?!),
    so,
    Power/Restrictor-Area = 28+ kW/sq.cm, or 38+ hp/sq.cm
    (with 45 hp/sq.cm briefly available, if you believe the VW "ptp" claims).
    ~o0o~

    WRC - Up to 2010, 2-litre, prod-block, L4, turboed, with 34 mm restrictor.
    So,
    Area = 9.08 sq.cm,
    Quoted Power = 300-340hp,
    so,
    Power/Restrictor-Area = 25-28 kW/sq.cm, or 33-37 hp/sq.cm,
    (which is less than F3, probably because of demands of rallying).
    ~~~~~o0o~~~~~

    Anyway, my "derailing" of this Michigan competition thread was intended to get you thinking about how you can do better next comp. Having a defeatist attitude like Moreboost's above will not help (I think that was a late Saturday night post ). More importantly, chasing more power won't help either, IMO. But the other stuff mentioned above could help you get into the record books, which is always fun.

    Z

  6. #206
    As a team without an aero package, a single cylinder motor, a total vehicle weight that Illini has dubbed "Beefcake Jr.", a 50:50 weight distribution, and no clutch:

    Some may say we're doing it wrong. Other's may be amazed that our nosecone is actually aluminum and looks better than a lot of carbon ones. Go ahead and ask about it, we'll pull it off to show you.

    So why do most current FSAE cars have 50:50 weight distribution, and also an unnecessarily large yaw inertia? Because, "Well, err..., that's what everybody else is doing...". It is nothing but mindless copying of the motor-bike-engine-with-forward-leaning-cylinders-that-pushes-driver-forward-and-over-the-front-wheels. Just like the mindless copying of push and pull-rods...
    To finish first, first you must finish. A car that cannot handle is not meant to be on a track. If I need to push the driver over the front wheels so he can 4 wheel drift it through some of the slaloms, so be it. Because the wheelbase is so tiny on these things, having a car that hangs quite a bit off the rear end makes it quite a bit less predictable than when it's put on a road course. The transient requirement is larger, the sweepers are non existent, and those slaloms are killer. Where else will you see cars kick around slaloms as short and quick as these cars?

    Which is another point I'd like to make. These vehicles have a quite a different requirement than what road course vehicles require. Even outdoor karts have some things easier. During those types of racing, you have time to think, "How am I going to take this corner? Turn in, little more, little less, and straight away!" With FSAE courses, they are so narrow and tight, that if anything goes wrong, there needs to be a safety margin that gives stability over control. Has anyone driven 9+ hp indoor karts? It's kinda like that, huh? Even the lower 5hp ones. First thing you see any experienced person do? Push the seat all the way forward. The rear tires are quite a bit bigger than the rear, so what? It's more about pivoting the car and getting it to it's "happy place".

    So far, I've been looking for inspiration from different places than what would be considered normal for most people. What's a good series to consider, F1, Le Mans, F3? The higher echelons where things tend to be dialed in. To. The. Dot. Period. But, lately I've been looking to several SCCA classes, Formula Ford, indoor rental beater karts, and a few production cars. They are cheap, reliable, and sometimes exactly what I'm looking for in these cars.

    To tie back into the Michigan thread. We were very proud that we built our car pretty much to the 'spirit of the rules'. It's cheap, reliable, efficient, and any amateur could fix it with a hammer, tools that resemble hammers, and a welder, barring a few parts that would be made to order, such as uprights. The design review complimented us on many of the qualities of the car, except that we built it to the spirit of the rules. They said that put us at a disadvantage to the other teams that show up running a fully mil-spec wiring harness, <30lb composite monocoque, a weight that is through the floor, MMC brake rotors, Massive drag inducing wings, and running all kinds of crazy gizmos and gadgets that people put on their cars these days. What disadvantage were they speaking of? That we didn't disregard A.1.2?

    "A1.2 Vehicle Design Objectives
    For the purpose of the Formula SAE competition, teams are to assume that they work for a design
    firm that is designing, fabricating, testing and demonstrating a prototype vehicle for the nonprofessional, weekend, competition market"

    I'm pretty sure a non-professional, weekend, competitor doesn't have room in their budget to replace the chassis on their car just because it has started to delaminate from just sitting out in the sun too long. Maybe a few do, but, not the general market.

    In conclusion, there is more than one way to consider how points can be rewarded. We've been working on our static events for a long time, but only recently starting to improve on our dynamic events. We plan to continue on campaigning a car that meets the spirit of the rules, but that is our take on it. To all of the teams competing at the Lincoln competition this week, we wish each and every one of you the best of luck. We will see you there!
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  7. #207
    Originally posted by Canuck Racing:
    Now that this thread is completely de-railed and turning into quite the train wreck, does anybody know what Maryland's weight distribution was when they were running different size front and rear tires (not sure if they still are or not,) and, you know, winning nationals and what not?

    P.S. While Z sure has the occasional crazy idea, at least you're now thinking about it. And as young engineers, the first thing you should be learning to do is listen to your peers/colleagues/professors and their ideas. Attacking them because they differ from yours will get you nowhere, and you're probably going to end up being wrong anyway since they've been doing this way longer...
    At risk of not only de-railing but building new rails on this thread. I'll keep it short.

    Your assuming us young engineers are not thinking about it, and it fits with the common practice on this forum that nobody besides x,y,Z person is thinking and everyone else is just asking silly questions. If theres one thing FSAE has taught me over the years is don't believe anything your told. Go and find out, some of my professors would have me believe that air is in compressible. Wasn't meant as an attack, still disagree. Just because someone has been doing something longer doesnt mean they have been doing it right. - This is not a personal attack on anyone.

    -

    Z - all those power - restrictor comparisons on the same fuel for all engines correspond to 45% efficiency. I still find that hard to see in an sae engine. Would love to be proven wrong maybe the AMG-sae engine or the Zengine will blow my doors off.

    Also, getting pretty sick of the" you should be at x lat g, y this and that by now" your all stupid students who dont think. It doesnt even matter so long as we can explain why/why not. I reckon (to put it on Claudes terms) a C class car with an A class team (a class being blokes who know what is happening) will mince an A class car with a B class team every time. Its happened to me! More important to me (as a previous leader) was the education of my team then the performance of the car. It takes 3-4 months for the students to understand what the previous car did and by then your already behind the 8-ball to go into redesign and knowledge carry-over is one of the hardest things to implement.

    Im not at all a suspension guy, have never really payed too much attention to it, but on the subject of getting people thinking or somebody please enlighten me. Why does maximum achievable Lat g even matter? My lap sim will tell me .1 g is worth Xx more points then anything else. But am i ever reaching this g on an sae track? am i ever reaching steady state Wxfer? which brings me to the age old argument over RC heights and diffs but i think this has been had way too many times here.

    I think i put down some rails.

  8. #208
    Originally posted by Charles Kaneb:
    Good luck designing the 65% rear weight distribution car, or finding two tires, one with twice the cornering stiffness of the other, that otherwise have identical cornering characteristics (not just the lateral vs vertical force functions but identical paths to operating temperature from cold). If you are anywhere near the minimum wheelbase, and are opposed to building a big heavy car with a big heavy four-banger engine, you will have to start with a "sidewinder" engine and its compromises and be very careful with your driveline part selection to get anything like 65% of the weight on the rear tires.
    We built 3 cars with 40/60 weight distribution. They launched unbelievably hard. The rear tires on our 375 lb single cylinder 40/60 car had the same corner weight as on our 450 lb 4 cylinder 50/50 car. We had little trouble finding 13" tires with the proper cornering stiffness distribution, and I didn't do the math on the 10s (data wasn't available for multiple widths of 10s back in 2007 when I last did the analysis), but our last 40/60 car was on 10s and I believe they matched cornering stiffness as well. I did a few other rough size correlations and guessed that the two size/rim combos of 13s we picked would have very similar heating rates, and they did handle consistently during tire warmup. And this was all done without any excessively fancy gew-gaws or impossible to find engines; it was the same YFZ-450 that many other teams use, and a 63" wheelbase. It was a tight squeeze, but doable.

    For that matter I believe Maryland pulled off something like a 30/70 weight distribution with 10" front and 13" rear tires, which by my rough estimate from numbers I've seen would give a good cornering stiffness balance. And they cleaned house at SCCA Nationals. Funny thing is back when I was doing the cornering stiffness analysis I joked about running 10" front and 13" rear, everyone else thought it was pretty funny. Kudos to Maryland for pulling it off.
    Dr. Adam Witthauer
    Iowa State University 2002-2013 alum

    Mad Scientist, Gonzo Racewerks Unincorporated, Intl.

  9. #209
    Well, good to see some people have brought us back to earth a bit. We should all remember that absolute performance is irrelevant. It's a competition/race, it doesn't matter how fast you are (or how many points you get), as long as it's more points than your competitors. Every year there is only one team that gets to walk away and say they did it better than everyone else. As long as your rate of progress is equal to or better than your competitors, the rate of development also doesn't matter.
    'engine and turbo guy'
    Cornell 02-03

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