Skid Pad Speed

[sub0]

Hi there,

I can't find any data on the skid pad speed of a reasonably fast car, no speed logged in our files http://fsae.com/groupee_common/emoticons/icon_frown.gif. Can anyone do me a huge favor and help me out? Doesn't need to be super-accurate or anything, just something to work with...

Cheers

[Francis Gagné]

mean speed = 2*pi()*R/t

where
R is mean radius of car
t is time for a complete revolution.

You can also work it out from lateral acceleration data and radius with basic physics.

[sub0]

Thanks for your quick answer. I was completely off.

What are skid pad times for good teams though??

[Chris Craig]

Record is around 4.9s
Most good teams are running around 5-5.2 secs

[sub0]

hm.. that comes out to about 2.5g?? seems like quite a lot

v=2*pi*r/t

r=15.25 m (neglecting car width)
t=5 s
v=19.16 m/s

a=v^2/r
a=2.45

is that correct? I just have some old data suggesting something like 1.3g for an 2007 race car, that seems like a looooooot less.

EDIT: Using the diameter instead of the radius makes things really ugly. Now 5s turns out to be 1.2 (conservative as no car width was assumed). Better http://fsae.com/groupee_common/emoticons/icon_wink.gif

Thanks for your answers!

[ed_pratt]

Hi sub0,

remember that the skidpad we use is figure of 8 - check the rules for the exact sizes on page 115

ed

[Chris Craig]

radius is 9.125m if you went round exactly between the two circles, 15.25 is inner diameter of circle

If you use that it gives an lateral acceleration of about 1.4g which sounds acceptable

[sub0]

one more question... neglecting aero forces
f=ma=umg, so a=ug
Therefore a=1.4g gives about u=1.4. Sound like quite a lot... (or do I have a mistake in my approach?)

[Chris Craig]

i'm guessing u is the normalised acceleration?

if so then this seems about the maximum you'd ever achieve in figure of 8, not unreasonable, Monash were getting around that mark in UK this year however most teams are running around 1.2-1.3

[sub0]

normalized acceleration? u is supposed to be the greek mu, the coefficient of friction

[Chris Craig]

I get you. 1.4 for a coefficient of friction isn't too high i'd say around 1.5 was about the usual you'd be expecting from a warm FS tyre possibly even higher dependent on your design.

[sub0]

Well thanks a lot for your help. Really great!