2015 FSAE Rules

[Kevin Hayward]

Just did the calcs ... around 3.1s (obviously close to accel times of the electric cars now). The big point here is that for these 4wd electric cars the tyres only need to provide a mu of 1.5 in all conditions, which is pretty reasonable. The power is controlled through the motor controller, which is the ultimate traction control. No gear changes to sap power. No need to play around with weight balance or COG height.

The power limit comes into effect after the first 1.8s (42% of the run).

This was done for a 200kg car. Change it to a 300kg car the time drops a whole 0.1s to 3.2 seconds (getting closer to where we are now) and the power limit comes into effect after 1.2s (62.5% of the run). The power limit for electric cars is effectively limiting how long you can have the extreme acceleration.

I have heard of 1.7g accel from the electric AWD drive cars, and obviously believable. In this case the run would be improved (with a 300kg car) to 3.1s, with the power limit coming into effect after 0.9s. (71% of the run)

So the AWD electric cars can do the ultimate times that Z suggests, but with a lot less effort, and on the power limit nearly the whole time. All the calcs here (Z's as well) are not including the effect of drag, which obviously slows things down, and will almost completely account between the difference of 3.1s to what the electric cars are currently doing. Also allow for a margin teams will be running to ensure they do not cross the 80kW limit.

Please note that I didn't crack open my proper sim code, and just did this roughly on excel. But I think the results are fairly clear, and close to expectations.

Of concern is that if the AWD electric cars are dropped to only 50kW of power they will do the run in about 3.45s, allow a couple of tenths for drag and we are still at 3.65s and they only need to worry about grip for less than 0.6s. Even with a big drop in EV power we will not be seeing the petrol cars faster than the EV's without doing a lot of work.

Kev

[tromoly]

I'm sorry if I missed something. But I don't think it's physically possible. The lightest car ever built was (I think, correct me if I'm wrong) the DUT06 at 120kg with a single cylinder (45bhp). I'm not sure what the lightest 4 cylinder (which has more power) was, but I'm guessing it's not less than 175kg.

Lightest US car was UC Berkley, last year their car weighed 275 pounds/~125kg with a Swissauto 250 karting engine that put out 35hp.

[BeunMan]

Lightest US car was UC Berkley, last year their car weighed 275 pounds/~125kg with a Swissauto 250 karting engine that put out 35hp.

That is (with the current rules) more what you can expect. The lightest GFR/DUT singles were around the 138-145 kg with about 45-50bhp if I remember correctly. I know there are some more teams running the (W/Y)R450 and in the 140-150kg range which gives around 0.30 - 0.36hp/kg in terms of power/weight ratios. The value DMuusers mentioned for the DUT06 was at the time when side impact structures were there just for rules sake and not there to protect the driver. Which is lighter of course. The lightest 4cyl stuttgart cars (both quite light and powerfull) generate about 85hp at 185 kg according to their specs on the website, which amounts to 0.45 hp/kg which is even better. So the 60kW option would be more near the 170kg without driver than the 130s mentioned.

Or you just do the 75 yard accel like some years back at FSUK. That way you should be able to get in the low 3s on accel.

[Dylan Edmiston]

The 2015 rules are expected to release late August.

From a Facebook post:

[Menisk]

A big thing I found surprising in my messing around with acceleration of a 4 cylinder was how little gears and wheelspin really affected times. We seemed to gear taller than most teams at FSAE-A with a 1st gear that ended at 78km/h and 2nd at 105km/h. The majority of our acceleration runs were between 3.95 and 4.00 seconds as we messed around with winding the launch control from being restrictive to barely doing anything at all. The fastest runs we put down were when we were dropping the clutch at 10,000 and holding a 10,000 rev limit until 35km/h. Hardly a well calculated map. We ended up somehow posting a freak run of 3.82 amongst all the 3.95 - 4.00 runs, but I'm not convinced it wasn't a timing error or just pure dumb luck that we parked on the oddly sticky part of the strip.

There were a few people that mentioned our fast gearshift times as helping a lot. We were running a 45ms cut on full throttle upshifts and only shifting once on the accel run. For the heck of it I did 2 runs at comp with no launch control and no gears. I started in 2nd, dropped the clutch at 14,200 and fishtailed my way to the end. We posted a time of 4 seconds flat. At best our "launch control" and use of another gear may have gained us 0.05 but I imagine you could get more by fitting a billet headrest to your car, which if you do the calcs still does jack all compared to static rear weight bias. Also by the time we get to ~70km/h, we're nearly at the end of the run. At that point even 300ms with no torque to the wheels is going to do bugger all to the time after we just spent a second or two clawing at asphalt trying to get our lump of a car moving.

As far as I'm concerned, so long as you have some sweet anti-squat, static rear weight, low driveline inertia and enough power to keep the wheels spinning for the first half of the run you'll win. Every bit of testing I've done with the R25B 13x7 Hoosiers tells me that for the most part more slip is more grip. I'd be inclined to guess at somewhere in the order of 30%-40% slip is where you'll make your max longitudinal.

Also for those that feel you need a light car to win accel, we weighed in at 240kg with a 50/50 weight bias. We simply aim to get the weight as rearward as we can, that's where we ended up with a "conventional" layout SAE car. Also we have a dyno printout that says 59.6hp.

[Jonny Rochester]

That is an enjoyable read Menisk, and I tend to agree with the spirit of what you are saying. One should understand gear charts and spreadsheets, but just as valuable is to understand the weighting of that info, especially as tyres are spinning as you say.

"More slip is more grip" will ruffle a few feathers on this forums, and I love it!

I believe UTAS did well in acceleration in 2001/2002 with a very heavy car, but a pro had dyno tuned the 4cyl engine several times to get the most from it.

[Shuff]

I believe UTAS did well in acceleration in 2001/2002 with a very heavy car, but a pro had dyno tuned the 4cyl engine several times to get the most from it.

Dyno tuning for acceleration times... Hmmm, I get where your coming from, but, you tune some things on the dyne, the things that get the times are done on the track, not talking about launch/trac control either.
Just something to think about

[AxelRipper]

I've just been trying to figure out why none of the "Acceleration Specialist" teams have just said the hell with it and gotten some Jr Dragster tires.

[Dunk Mckay]

I've just been trying to figure out why none of the "Acceleration Specialist" teams have just said the hell with it and gotten some Jr Dragster tires.

Cos they still need to finish Endurance on them? Also do they not need a reasonable amount of heat in them first? (they may not, but if they do....) That's something that will be difficult in series where tyre warmers are banned.

[mech5496]

Regarding heat, I found this:

http://www.mickeythompsontires.com/s...?item=ETDragJr

"Requires little or no burnout". Plus they come in a FSAE-friendly 19/8-10 size. Finishing endurance (and takcling corners) is a whole different issue, and definitely a more serious one though...