rtmack wrote:
> Our TCs do not need to respond to as many different things as a road
>racer.
> We are going straight, and the wheelspin probably varies in a fairly regular
> sinusoid (due to the fact that the expansion cracks in the salt are (in any
>given
> year) fairly regularly spaced. Even if they weren't, the same cure would
>apply--
> basing corrections on a "trailing average" of the wheelspeeds. The program
>can
> include an algorithm to make "progressive" correction, thereby damping the
> response. No need for a system that "jumps" around.
>
You can integrate the analog signal for an average deal or just apply a low
pass filter
with a real big cap that works way down in frequency..8 or 10 hz is easy enough
to do so
the changes are gradual.. adds about 1.00 to the simple version so now we are
up to
11.00....
>
> Most of the fastest LSR cars seem to depend more on ballast than on aero
> downforce. Lately I have come over to this idea (although it sounds
>archaic). The
> biggest factor in causing the tires of our high speed machines to spin at
>steady
> speeds is aerodynamic resistance-- that is, the resistance of the car to going
> forward (most of which is aero-- only a small fraction is tires, at 300+mph)
>becomes
> greater than the friction force of the drive tires. You cannot add ANY aero
> downforce without increasding aero resistance, as well (whether you use the
>body, or
> a wing). In effect, in aerodynamics "there is no free lunch." Since aero
> resistance is our biggest enemy, aero downforce can't be our best friend.
> Weight, of course, hurts the accelleration. But if it is used cleverly,
>that
> is all it hurts; it doesn't slow the top speed. And we usually have a lot of
>room
> to accellerate these days (thanks to "Save the Salt").
>
weight is the biggest problem to go fast once you get into the 300 range.. do
the math.
Plus it hurts you from the very start to the very end but in different ways. At
the
start it takes more to get moving at the end the rolling resistance is
substantial. On
the Golden Rod (I use only for example as it was well documented) the rolling
resistance
was 90% of the power required...
The real problem is the coefficient of friction on the salt. From what I have
learned
and information I have gathered from data acquisition systems on different cars
and
talking to many who have a clue is that the best you might hope for is 0.61 g
acell
rate. Funny this number is the same whether it was a 1100 lb car with 1500 cc
engine or
Tom Burklands car from what he told me... So if you get to that point the only
way to go
faster is with distance... or in the case of most cars they will hit terminal
velocity
before the 4 mile marker as they are out of power with that acell rate, the
speed equals
the power available. The other little bit of info is that the best rates of
acceleration
do have some slip on the order of 5 to 10% so if you run a TC you would want to
allow
about 15% and have it pull power out only to that point. Doing it this way i
suspect it
would be much smoother as you are never really trying to have it hunt for zero
slip.
>
> >
> > You said...
> > So the question for traction, is not a question for a traction control -
>it's a
> > question of the compromise of downforce and resistance.
> > If you got enough power you can increase the downforce, which will
>eliminate the
> > traction/grip problem.
>
> If you do this, I think you will soon get into the realm that Tom
>Bryant
> theorized was the cause of Earl Wooden's tire failure: you simply overload
>the
> tires-- too much downforce + torque (see Tom Bryant's response to this
>thread). I
> think the first thing to do is to minimize the resistance so you don't need
>to ask
> the tires for so much (the True/Costella car that you worked on appears to be
>a good
> example of this idea).
>
All the Goodyear stuff that was labeled for LSR use has a speed load rating why
not just
believe it..Add what down force you can until you exceed the rating then back
up a bit
and that is what you have to work with.. BTW a tires grip does not always
increase with
force applied to it. There is an optimum amount and when you exceed it you get
on the
other side of the curve too. Read "Fundamentals of Vehicle Dynamics" Thomas
Gillespie
from SAE press..
>
> > Thanks for your response; you are new to the list, but appear to be one who
> > consistently has something intelligent to say.
>
> Russ Mack
>
Dave Dahlgren ( who does understand exactly what we are doing or at least
trying to
accomplish)
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