At 12:29 PM 2/26/2006, Byron Short wrote:
>Hey John,
>
>Long time no see! Hope all is well with you!
Ditto.
>I agree with you that transitional g's are much higher than
>sustainable g's as measured on a skidpad. I think I even agree with
>how much you say they differ (20-25%). But with that said...
>
>Transitional g's are real g's, aren't they? They are higher than
>sustainable, skidpad g's for a several reasons, including the fact
>that they result from a temporary increase in force on the tread
>beyond what the car can produce in steady-state. This is
>conceptually similar to aerodynamic advantage in that in both cases
>you have a higher force on the tread without a higher mass in the
>vehicle. Because the friction remains a constant, you get a higher
>lateral g. Of course, with aerodynamics, the effect is
>long-lasting, while with transitional dynamics it's fleeting. But
>it's still real, isn't it?
Yes, they are are real, but I'm a subscriber to the philosophy that a
slalom is a different animal than a corner when it comes to
safety. Remember that the persistence of these peak g's are
relatively short, but they can cause the dreaded 'excess sideslip'
which helps neither your speed through the slalom or your
stability. You certainly can still lose control in a slalom
(actually more likely due to all those bespoken dynamic effects), but
the trajectory of the vehicle is more likely along the line of the
slalom. In a corner it is likely to be tangent to the path.
>Slaloms are completely negotiable using the peak g levels, not the
>steady state g levels. This is backed up by empirical observation
>of times and application of the slalom formula.
To quote Ed McMahon: "You are correct, sir". But see comments on
previous paragraph. I believe we would agree that a higher max
slalom speed compared to max cornering speed would be acceptable.
>So I agree with your assertion that steady state g's and those
>reported in autocrosses are two different things, although I
>disagree that it's an instrumentation issue, and agree instead with
>your intimation that it's more because of the nature of "peak" g's.
Remember that the instrumentation inaccuracy and roll correction is
added to the pile - AND trying to keep the geekosity to a minimum,
the dynamic roll angles are greater than the steady state roll angles
compounding the overestimation.
>But this brings me to a small quibble with your final statement,
>that we should use the steady state numbers rather than the peak
>numbers for course speed calculations. While the slalom is the
>best/easiest example of where you will be misled if you use the
>steady state number, it's in fact the nature of solo that the best
>drivers out there will create the dynamics that create high peaks
>and utilize those peaks in driving the course. This will occur in
>all kinds of places, including the exits from nice, simple steady
>state turns. The throttle can be applied to change the dynamics of
>the vehicle in a way that would be totally unsustainable on a
>skidpad (hence I think it meets your definition of "peak") but which
>is nonetheless, true and real and effects the speeds accordingly.
We are in violent agreement, but you were perceptive to pick up on
the nuances unstated in my post. I was not really including slaloms
in the cornering rule, more noting the largess of the estimated g's.
>(Okay, I'm gonna go hide now, because if the Geekmeister unloads all
>of his geeky-geekness on me I'll crumble into a pile of protoplasmic
>psuedo-geekitude. Be nice to me John...use small words.)
I like it when you talk like that :-)
John
>--Byron
JACircuits Autocross Timing Systems
http://www.jacircuits.com
- Timing the SCCA Solo II Nationals since 1985
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