Neil:
Looking at the car, I see nothing obvious that would suggest a rear aero
lift probability-- but we all know that aerodynamics can fool you! Rear
aero lift is the first thing I would investigate, if I was working on
that car.
I can tell from the front tire prints that there was plenty of downforce
(aero, I suspect-- rather than ballast) in front-- which could, of
course, lever the downforce off the rear tires, if the difference is
great enough and if the center of this downforce is ahead of the front
axle.
DrMayf was talking about the tires possibly "planing"; I think this
(theoretical) effect might also contribute, if the drive-tire downforce
is insufficient (factors to be considered would the tire footprint area
and the "firmness" of the salt surface).
Even in the excellent conditions we had this summer, I suspect that the
tire/salt CoF is not more than 0.70-- so quite a bit of downforce is
required to produce big thrust from the tires. Some competitors have
ways to monitor the downforce on the drive tires; I suspect that every
crew could benefit from that kind of data.
Russ
"Albaugh, Neil" wrote:
>
>
> Russ;
>
> RE: "...there was one very lightweight car (that I can identify, from
> the front tireprints) that was definitely wandering a lot-- and the
> back tire tracks were faint. ..."
>
> I'll wager that car's problem was aerodynamic lift at the rear.
>
> Regards, Neil Tucson, AZ
>
> -----Original Message-----
> From: rtmack [mailto:RTMACK@pop3.concentric.net]
> Sent: Saturday, December 15, 2001 7:40 PM
> To: DrMayf
> Cc: land-speed@autox.team.net
> Subject: Re: High Speed Traction A few thoughts..
>
> Mayf:
> interesting theory, doctor! I think that some were definitely having
> traction
> problems that were not hydroplaning-- because they were digging-in,
> not riding
> the surface (not "planing"). However, there was one very lightweight
> car (that I
> can identify, from the front tireprints) that was definitely wandering
> a lot--
> and the back tire tracks were faint. I have heard since then that the
> team was
> having difficulty getting the car to "hook-up" on the "big-end". I
> wonder if
> they might have been "hydroplaning", as you call it. I think it is
> possible that
> the cars with not a lot of downforce (relative to area of the
> footprint of the
> drive tires) may be doing something like that. That might also
> explain why the
> cars whose drive tires are not "digging trenches" seem to leave tracks
> that
> wander around more-- if they are "hydroplaning", they get
> batted-around with
> every little gust, every little bump.
> But that particular car was only in the 250mph range, so tire
> centrifugal growth
> (shrinking the footprint--??) would not be so much a factor as with
> the big-power
> guys. As a matter of fact, I think the "shrinking the footprint"
> part doesn't
> relate to increased hydroplaning tendancy: given the same tread
> pattern (and
> depth), the same vehicle, and the same tire pressure-- a wider tire
> will
> hydroplane (on wet pavement, anyway) quicker than a narrower one. The
> narrower
> tire tends to "cut-through" the water (or salt??) like a V-bottom
> boat, while the
> wider tire acts more like a ...well, more like a hydroplane. Note the
> difference
> in the "rain tires" on the F-1 cars. They are narrower (as well as
> having deep
> tread).
> But the disfiguration of the tire cross section due to centrifugal
> force-- and/or
> the action of the centrifugal force against the salt surface-- could
> be
> contributing to the problem in some other way. Is the centrifugal
> force trying
> to push the car away from the surface? That is-- is the centrifugal
> force of the
> tire "countering" (to some degree) the downforce (whether aero, or
> ballast) built
> into the cars? What do you think about that possibility, Mayf?
> Russ
>
> DrMayf wrote:
>
> > Dan, hit your delete key now! Don't want you to get bored..lol
> >
> > I wonder if the car tires are hydroplaning? That is at high speeds,
> the
> > tires are expanding and becoming pretty rigid from centrifugal force
> on the
> > outer plys. This makes for a pretty small foot print I suspect. Add
> to that
> > there is loose salt on the hard stuff. So I think that the tires
> could
> > possible hydroplaning or skating on the loose salt. Why? Well, have
> you eve
> > driven in sand? Go slow and you sink, but go faster and you skate
> across.
> > Add a bit of moisture and maybe the "hydroplaning" get even more so.
> Anyway
> > to test this?
> >
> > just a question...
> >
> > mayf, the red necked ignorant desert rat in Pahrump...
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