FASTEST EVER ACCEL TIME 3.97sec! BATH UNIVERSITY

[RikyTheRipster]

Bath UNiversity achieved the fastest ever acceleration time at FS 2005 of 3.97s over the 75m. The quickest time ever! An unofficial quicker time is also deemed possible. Seems the supercharged R6 could really make the car shift...

[RikyTheRipster]

Bath UNiversity achieved the fastest ever acceleration time at FS 2005 of 3.97s over the 75m. The quickest time ever! An unofficial quicker time is also deemed possible. Seems the supercharged R6 could really make the car shift...

[Kirk Feldkamp]

Which supercharger are they using?

-Kirk

[VFR750R]

I have a strong feeling Cornell has some recorded sub 4 sec times and the record is held by Ohio State at 3.79 or something ridiculous like that from 2001?

[VFR750R]

I guess it's 3.89 from some posts I dug up doing a search for 'ohio acceleration'

[Charlie]

Yes I'm quite sure that's not the fastest FSAE time, though perhaps it is fastest in the UK. Though the all caps do make a convincing arguement. http://fsae.com/groupee_common/emoticons/icon_wink.gif

It's quite a run to get under 4.0s anywhere, and anytome you win an event you've done the best of all your competitors and should be proud. But it is extremely dependent on conditions. We've run lots of sub 4.0 second times at home, on hot asphalt. Detroit, usually, is hard and cold and sometimes wet.

It's my belief (and I hate to say it 'cause I'm an engine guy) that the power-to-weight ratio is only about half the battle in the accel event, which is traction limited for most top teams anyway. Tire selection, gearing, weight bias, and other little tricks get the time down, not so much power.

[Z]

Hmmm? 3.97s ET for 75 metres? That doesn't seem very fast to me...

I reckon that if there was a drag racing class for cars similar to FSAE (ie. 610cc with 20mm restrictor, etc.) that was open to the general public, then the 75m ET's would be closer to 3sec than 4sec. (No offense intended guys http://fsae.com/groupee_common/emoticons/icon_smile.gif.)

I agree with Charlie that power-to-weight ratio isn't the most important thing here. I note that most "standard" FSAE cars have a ~50:50 F:R weight distribution. This is mainly due to the relatively long final-drive (chain) that pushes the engine and driver forward, combined with the short wheelbase that is desirable for the slaloms, etc. This limits available rear grip/thrust. Using a shorter engine package, a more rearward driver position, and about 60% rear weight, would improve Acceleration times much more than extra horses.

Also the type of drivetrain makes a big difference. Big clutches that can be slipped, CVT's, or torque converters are things I would look at. I wouldn't bother with 4WD because rear 2WD works fine - go watch the drag racing.

The Acceleration event is only worth 75 points, but since acceleration out of slow speed corners is important for the 500 point Autocross + Endurance events, it is well worth getting it right (although corner speed is even more important).

Z

[Sam Zimmerman]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
Hmmm? 3.97s ET for 75 metres? That doesn't seem very fast to me...

I reckon that if there was a drag racing class for cars similar to FSAE (ie. 610cc with 20mm restrictor, etc.) that was open to the general public, then the 75m ET's would be closer to 3sec than 4sec. (No offense intended guys http://fsae.com/groupee_common/emoticons/icon_smile.gif.)Z </div></BLOCKQUOTE>
I reckon that is there was a drag racing class for cars similar to FSAE, they would design their cars completely different. After all, 100% of their points would come from the drag racing event, not 7.5%. I would also bet those cars would suck in an autocross.

[VFR750R]

Z, 75m in 4s is not slow and yes a higher rear weight percentage would be a benefit but you also listed why we don't. 550pts in autocross and endurance carry more weight then 75pts in accel. For fun we hooked up the lap timer to my street bike (Honda VFR750F) and I ran a 3.52. That's a case of max weight transfer and traction, and my bike isn't wheelie prone like some modern sportbikes. My bike weighs 485lbs and makes 82hp at the wheel (been dynod) which is almost exactly the power to weight of our 03 car I raced that day. If anyone ever beats that time with a legal fsae car, i'll quit my job and become a suspension guy.

[Mad Ruska]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by VFR750R:
Z, 75m in 4s is not slow and yes a higher rear weight percentage would be a benefit but you also listed why we don't. 550pts in autocross and endurance carry more weight then 75pts in accel. For fun we hooked up the lap timer to my street bike (Honda VFR750F) and I ran a 3.52. That's a case of max weight transfer and traction, and my bike isn't wheelie prone like some modern sportbikes. My bike weighs 485lbs and makes 82hp at the wheel (been dynod) which is almost exactly the power to weight of our 03 car I raced that day. If anyone ever beats that time with a legal fsae car, i'll quit my job and become a suspension guy. </div></BLOCKQUOTE>

VFR750R, what kind of job you have? It is worth, to put a lot of effort into "fire" you out of your job and get hired from your boss? http://fsae.com/groupee_common/emoticons/icon_razz.gif

[Cement Legs]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
Hmmm? 3.97s ET for 75 metres? That doesn't seem very fast to me...

I reckon that if there was a drag racing class for cars similar to FSAE (ie. 610cc with 20mm restrictor, etc.) that was open to the general public, then the 75m ET's would be closer to 3sec than 4sec. (No offense intended guys http://fsae.com/groupee_common/emoticons/icon_smile.gif.)
Z </div></BLOCKQUOTE>

And Massey Ferguson builds nice tractors... http://fsae.com/groupee_common/emoticons/icon_razz.gifhttp://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[Z]

Hmmm, so does that mean that you can't build a FSAE car that has good acceleration AND cornering performance? Does this fall under that cliche that "racing is all about making compromises"?

Since VFR's bike could do 3.52, with the same power-to-weight ratio, similar overall length, and less tyreprint area available than a typical FSAE car, can anyone please explain why an FSAE car couldn't do similar or faster times? And why that car couldn't corner fast?

Sensible, well thought out responses prefered, rather than vitriolic diatribes directed at cynical old farts, please http://fsae.com/groupee_common/emoticons/icon_smile.gif.

Z

[Denny Trimble]

I'll take a shot at that http://fsae.com/groupee_common/emoticons/icon_smile.gif

The VFR has a wheelbase of 56 inches (or so I read on the first search result). This is close to the minimum wheelbase for FSAE (60in). However, the VFR with rider has a cg height probably in the 24" range (just guessing), meaning it will be fairly easy to get 100% vehicle weight on the rear tire under full forward acceleration.

An FSAE car must have a lower CG to pass the tilt test (and to corner well), so the only way to get most of the weight on the rear tires in an acceleration run is to have an extremely rearward static weight distribution. Anti-squat and spring/damper settings can play tricks dynamically, but I'll stay away from that for now.

So, if you build an FSAE car with 80% rear weight (don't feel like doing the calcs at the moment), you might get front wheel lift on acceleration, which is great. Making it corner well in a steady state corner is even possible. But, in my opinion, getting it to handle well in transients (slaloms, corner-entry) would be difficult. The turn-in phase of slaloms and corner entries is initiated by the front tires applying a lateral force, which starts to rotate the car about its CG until the rear tires assume a slip angle and start generating a stabilizing force. With only 20% static front weight, there wouldn't be much front lateral force available to yaw the car to initiate a turn.

You could trail-brake the hell out of the car to help get dynamic front weight, and a high CG would help this as well.

But overall, I'm skeptical it could work well. I guess that's something to play with in a more advanced simulation (or with lots and lots of ballast!).

[VFR750R]

That's exactly why the VFR can run the time it does. Weight transfer. My VFR won't spin the tire on launch and actually my gearing is a little off for this; it'll do 60 in first gear. But no, my VFR won't come close to out handling an FSAE car, even a bad one. This one may shock some of you, but motorcycles corner like ass. Steady state cornering they can be good but never better then a car designed to turn. The only advantage is power to weight and weight transfer.

[John Bucknell]

I have a 94 VFR750 as well. I've crashed six times (mostly on roadcourses) because it doesn't want to turn - thank god I've never tried to autocross with it....

On the other hand, there are bikes out there built to turn. Show up at a go-kart track sometime when they are running supermotards. That's hilarious. Even better, mini-motos at an indoor kart track (but they don't have any power).

[Chris Boyden]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Sensible, well thought out responses prefered, rather than vitriolic diatribes directed at cynical old farts, please </div></BLOCKQUOTE>

Here we go again...... http://fsae.com/groupee_common/emoticons/icon_razz.gif

How about sensible, well thought out critiques, instead of pompous dissection of peoples cars and stultifying pontification?

[Z]

Denny,

Thanks for your well thought out response. Please don't take this as a "pompous dissection" of your post, just my way of seeing things http://fsae.com/groupee_common/emoticons/icon_smile.gif.

RE: ACCELERATION
================

Yes, bikes certainly can accelerate hard. Even when they are quite front heavy it is hard work for the rider to keep the nose down - too much rear load transfer!

You suggest that for an FSAE car to get similar acceleration/load transfer it would have to have "an extremely rearward static weight distribution". I don't think it has to be so extreme. For example, say in round numbers, wheelbase L=1500mm (shortest possible and least dragster like), CG height H=250mm (low for good cornering), and tyre CF=2.0. The appropriate (and approx.) equations are:

Acceleration, A=(CF x L x Rs%)/(L - CFxH)

with A measured in units of "G", and Rs% = static rear percentage.

Rear dynamic percentage, Rd% = Rs% + (A x H/L)

So, if;
Rs% = 50%, then A = 1.5G, and Rd% = 75%
Rs% = 55%, then A = 1.65G, and Rd% = 82.5%
Rs% = 60%, then A = 1.80G, and Rd% = 90%
Rs% = 66.7%, then A = 2.0G, and Rd% = 100%

These are just rough calcs ("back of an envelope") but they do give a reasonable idea of what happens. You can plug different values in and see that an "extreme" rear percentage is not really necessary.

In fact, some more calcs suggest that with 40F:60R, sticky CF=2.0 tyres and road (most important at launch), a good power/weight ratio (more important after launch), and, most importantly, the right sort of drivetrain, then a sub 3.5 second run should be possible.


RE: CORNERING
==============
You say of a car with Rs%=80% that "making it corner well in a steady state is even possible". I agree. Basically this is just a matter of bigger rear tyres. (Eg. if Rs%=60%, then the rear tyres should be ~1.5x as big as the fronts.)

You then say "With only 20% static front weight, there wouldn't be much front lateral force available to yaw the car to initiate a turn". True, but the front tyres only need to provide a smaller force! You can think of this as either there being less "mass" on the front wheels that needs to be accelerated sideways, or as the front wheels having a longer lever arm to yaw the car about its CG. Roughly speaking, the yaw moment available, due to the front wheels about the CG, is;

YMf = Xf x (Cf x Fd% x TotalWeight)

with Fd% = front dynamic percentage (which for no longitudinal acceleration = Fs%=Xr/L),
and Xf, Xr = distance front and rear wheels from CG.

So, with no longitudinal acceleration YMf is proportional to (Xf x Xr)/L. This is a maximum when Xf = Xr = 0.5L (ie. 50F:50R), but it only drops slightly for small changes in F:R distribution. For example;

Xf=0.5, Xr=0.5, =&gt; YM=~0.25
Xf=0.6, Xr=0.4, =&gt; YM=~0.24
Xf=0.7, Xr=0.3, =&gt; YM=~0.21
Xf=0.8, Xr=0.2, =&gt; YM=~0.16, etc.

There is a lot more to it than this - think about the different behaviour of a 40F:60R car during braking and accelerating. But putting it simply, when a very rear heavy car with a high CG accelerates hard out of a corner, the dynamic front weight drops significantly and the car does suffer from "power-on-push". This is quite common with rear-engined, high CG, off-road cars, but it isn't really that bad! At most it requires a change in driving style - point nose down exit straight before accelerating hard. It is less of a problem with less extreme rear biased cars. But any disadvantage is offset by better corner exit acceleration, and the corner entry behaviour can be very good (eg. under braking with Xf=0.6, Fd%=0.6, =&gt; YM=0.36).

You say that you are "skeptical it could work well". If all the above theory in not convincing enough, then consider the history of racing. If this rear weight thing didn't work, then all those rear biased mid-engined racecars, from the 1930's Auto Unions to most every modern formula car (except FSAE), shouldn't work! And the rear-engined Porsche 911 (sometimes ~30F:70R) should be even worse! But these rear heavy cars have actually been quite successful.

I note that while most current F1 cars are around 43F:57R, because that's the ratio of their maximum allowable F&R tyre sizes, Renualt have (apparently?) gone for a higher rear percentage. Seems to be working for them.

Z

[Denny Trimble]

Z,
I agree with your numbers, though we see coefficients of friction of around 1.6 (sustained) with Hoosiers on the Detroit surface, which means a car with a 1500mm (59in) wheelbase and 10in (250mm) cg height needs a 27/73 static weight distribution to get "full load transfer" on launch. A car with a 64" wheelbase, for reference, would need a 25/75 weight distribution to do the same (still 1.6 CF, 10.0 CG height).

Your numbers on yaw moment show a fairly significant decrease as the weight distribution is shifted to the rear. FSAE courses are all about turn-in, slaloms, corner-exits. There are hardly any "steady state" corners, which makes transient performance that much more important.

Rear-biased cars can do well in FSAE, but there's not much reward for going past 40/60. Also, it would require a major change in vehicle layout to get a 40/60 weight distribution with a 60in wheelbase (sidewinder, rear-engine single http://fsae.com/groupee_common/emoticons/icon_wink.gif ).

[adrial]

Denny,

That coefficient of friction of 1.6 you mentioned was, I assume, measured on hot tires?

Do you know what it is for the tires when cold? (as they are for our acceleration runs)

[Denny Trimble]

Correct, that's what our car does on hot tires. On cold tires, I think around 1.3 (as indicated by skidpad results) is more appropriate.

[MikeWaggoner at UW]

I'd saying going by the best skidpad may be more accurate, 1.6 G's. I'm assuming a driver could do a good heatup accel run, and then do a good accel run.

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Denny Trimble:
Also, it would require a major change in vehicle layout to get a 40/60 weight distribution with a 60in wheelbase (sidewinder, rear-engine single http://fsae.com/groupee_common/emoticons/icon_wink.gif ). </div></BLOCKQUOTE>

Denny,

Or turn your 600/4 engine back to front, so the exhaust pipes are above the differential, reverse engine rotation, and use a chain drive from a (bearing supported) extension of the output sprocket, with driver moved maybe 0.5 metres back. (I think this has been done at least once?)

Or that simple single cylinder... http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

[Chris Boyden]

Haven't some teams that run the Yamaha YZF-600R flipped the head to put the exhaust towards the back? Is it the centrally located timing sprocket that makes that easier to do?

[scooter2131]

UCSD did that last year so that they could package their supercharger better. I have no idea what mods they had to do to adapt the reversed head, but a central timing sprocket is the most logical for attempting a project like this. I'd love to hear from someone at UCSD as to how they went about turning the head around, as i'm sure many on this forum would.

[Denny Trimble]

I think Z's point is to flip the entire engine around, so that the tranny is under the driver's back and the diff is somewhere under the exhaust. The "diagonal" lines of seatback and engine angle line up better this way. But, there's that little issue of getting the chain power around the sidecover of the engine, its widest point, and to a diff.

[Chris Boyden]

Ohh..I see now...that would really squish things up. While hypothetically possible to reverse the engine rotation, it seems like too much work, starter rotation, etc.... A two gear drive with the extension could accomplish reversal.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">driver moved maybe 0.5 metres </div></BLOCKQUOTE>

Kansas State 03 or 04(i think) did a side engine air cooled single or twin with an AL frame.
They didn't pass braking, so we didn't see it run.
It was a superlightweight car ~300 lbs with a high rear weight distribution. I'll do a search.

[Chris Boyden]

Kansas State in '03
Actually weighed 361 lbs.

http://fsae.com/eve/forums?a=search&reqWords=KSU&use_for...orum_scope=125607348 (http://fsae.com/eve/forums?a=search&amp;reqWords=KSU&amp;use_forum_scope=on&amp;fo rum_scope=125607348)

[Travis Garrison]

I think Kettering did exactly what Z is talking about in 2002...there may be more examples but I've got a photo (non digital sorry) of a car (yellow I believe) with the engine flipped around like that and a relatively trick dual runner intake...

-Travis Garrison
UW FSAE

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Boyden:
A two gear drive with the extension could accomplish reversal. </div></BLOCKQUOTE>

Yes, that's an option. Or perhaps a spur gear drive built into the differential unit, with a ratio of ~3:1. Then a chain drive from the engine to the diff unit, with a ratio of ~1.3:1 and larger sprockets for less chain load. These sprockets would be changed for easy overall ratio changes. To get the chain past the engine sidecover would require a ~4-6" extension of the engine output sprocket, which would have to be supported by a bearing at its outer end.

This is more complicated than a "standard" layout, by the extension shaft and gear pair, but it gives a shorter car overall, and more rear weight for better corner exit acceleration.

Z

PS. (Edit) Then next year fit a bespoke engine/drivetrain (with easier drivability (auto transmission), better fuel economy (turbo'd single), lighter weight, etc., etc.) into the same small space. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[EliseS2]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:

Or turn your 600/4 engine back to front, so the exhaust pipes are above the differential, reverse engine rotation, and use a chain drive from a (bearing supported) extension of the output sprocket, with driver moved maybe 0.5 metres back. (I think this has been done at least once?)

Or that simple single cylinder... http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z </div></BLOCKQUOTE>

Our team had 44/56% with a Honda F3 and a 60in wheel base. I think that by moving the radiator, oil resivior, lightened frame, battery, and all sorts of smaller stuff reaching 60% is possible without resorting to a sidewinder single or a reveresed four cylinder.

[Storbeck]

Michigan Tech did the backwards engine for a couple of cars, the last one was 2002, it was yellow, probably the one that Travis remembers, it had a dual runner intake. The motor ran backwards and there was a short extension from the output shaft, about 6" to get the chain around the mag case.

The backward motor idea was ditched in 2003 for simplicity and reliability. I'd love to go back to a backward motor with a two gear box just as Z described, the packaging would be great.

There was also a Michigan Tech sidewinder in I believe 99 or 2000.

I'm told the 2002 car was quite fast, it's still around, I'd love to get it going again but the effort to get a motor running backwards for a practice car is just not available.

[Frank]

have two sets of front suspension pickups..

the "acceleration set" is 10" forward of the "normal set"....

problem solved

[Denny Trimble]

Right, never mind "steering", that luxury.

[Travis Garrison]

Storbeck,

That's probably the one...sorry about the school confusion there...

-Travis