Russ,
Poor communication is man's worst enemy, I stand corrected. by your
definition, I was talking about "plumes." Even so, I should have said
not all rooster tails are not from wheel spin, I realize that spinning
wheels do contribute. Quite honestly, I have not looked for what you are
explaining as "rooster tails", I will be a better observer in the
future.
Tom, Redding CA - #216 D/GCC
rtmack wrote:
>
> O.K. Tom, Bryan, Glen, Pork.Pie, Rick, DrMayf--
>
> I am finally getting around to all those comments about "roostertails"
> (although I did comment to Tom already as part of a broader-scope response)
>
> First, I apparently need to explain to you all what a roostertail IS. In
> terms of racing (whether boat, bike, or car)-- it describes the media kicked
> up into the air by the driving mechanism. It was so-named because of the
> SHAPE. I assume you all know what a rooster is. Think about the shape of his
> tail when he is standing in his typical pose: it makes an ARCH-- sort of a
> "rainbow" shape.
>
> Do you see the salt making a vertical arch-shape behind blunt-tailed cars
> cruising across the salt at 200 mph (or so)?
> ...no, I thought not.
>
> Do you see the salt making a vertical arch-shape behind front wheel drive
> cars?
> ...no, I thought not.
>
> Do you see the salt making a vertical arch-shape behind jet cars?
> ...no, I thought not.
>
> Do you see the salt making a vertical arch-shape behind open tires that are
> just rolling (not spinning)?
> ...no, I thought not.
>
> The cloud of salt beind the vehicle in all these cases (when viewed from the
> side, 100 yards or more away) is pretty much a horizontal band that grows a
> little and becomes more transparent the farther behind the vehicle. (There is
> a little more vertical component to the salt from open tires-- but this is
> pretty thin (if the tires aren't spinning), and can't even be seen from much
> of a distance when the salt is as good as it was at Bonneville this year.)
>
> What you guys are calling "roostertails" are not what I was talking about, at
> all. (And see, you've gone and mislead the German guy!). What you are
> talking about is what I call "plumes". They don't have a "roostertail" shape,
> and they don't come from the source that racers always have always associated
> with the term "roostertail" (or just "roost", to us dirt bikers).
>
> I didn't mention all these other sources of salt clouds behind the vehicles--
> these PLUMES-- because I have seen so much written about it (on this list, and
> elsewhere) that I thought everyone would know about the masking effect of the
> turbulence clouds, and that you would have to take those factors into account
> when looking for airborne salt from wheelspin. I want to assure you that I am
> satisfied that I can recognize the difference (up to about a half-mile, I
> would guess, in salt conditions like this summer at Bonneville) in airborne
> salt from (severe) wheelspin and airborne salt from turbulence.
>
> I spent some time studying the runs-- and looking at data-- because I was
> interested in this wheelspin problem. On open-wheeled cars-- lakesters and
> roadsters-- it's easy to tell, because you can make-out the especially dense
> arch of salt from the drive wheels (sometimes, within a more transparent cloud
> created by the turbulence). On full-bodied cars (and FWD cars), it is harder
> because the bodywork distorts the shape, and you usually can't see much of an
> arch. On Earl Wooden's car, for example, I saw the usual semi-transparent
> horizontal turbulence plume-- seems like it was just a little higher than his
> roof, a few feet behind the car-- but the (opaque) salt surface appeared to be
> 6" to a foot higher behind the car than in front. I believe that this
> illusion came from (a very dense suspension of) airborne salt due to
> wheelspin. Look at the film again, and see what you think. (It was actually
> about 2 miles earlier when I saw the car go by, looking from the other side).
>
> I am sure that this airborne salt from wheelspin is much easier to discern
> under some conditions than others. If wheelspin percentage is small, the
> "roostertail" will be harder to see. If the tires are lightly-loaded, I
> suspect that the tires won't "dig-up" so much salt-- so again, the pattern
> would be harder to pick-out. In either case, a driver might be audibly "on
> and off the throttle", and you might not be able to see significant difference
> in the salt cloud. But for the high-horsepower, high-downforce machines, I
> think you can usually see changes in the salt cloud if there is significant
> wheelspin.
>
> The most off-putting thing about all these responses is that you all seem to
> be implying (and I am sure you know better) that wheelspin does not produce
> airborne salt. Any of you who actually believes that--Tom, Bryan, Glen,
> Pork.Pie, Rick, DrMayf-- I invite you to participate in an experiment with me
> next August at Speed Week. The plan is to have you all assemble on the salt
> behind my Silverado so we can conduct the test. I will then do my best
> burnout (ol' Gandalf doesn't have a whole lot of power), and we will take an
> opinion poll as to whether airborne salt ("ROOSTERTAIL") is produced by
> spinning tires.
> Best Regards,
> Russ Mack
>
> Tom Bryant wrote:
> Rooster tails on the salt are not from wheel spin - it is caused by
> the vacuum created behind the car. The severity of the rooster tail has
> much to do with how much loose salt is on the course. I say this because
> of experience in a low HP car that rarely spins its wheels but generally
> carries a tail from about the one mile.
>
> "Bryan A. Savage Jr" wrote:
>
> > Russ,
> >
> > I believe Tom is correct:
> > > 1. Rooster tails on the salt are not from wheel spin - it is caused by
> > > the vacuum created behind the car. The severity of the rooster tail has
> > > much to do with how much loose salt is on the course. I say this because
> > > of experience in a low HP car that rarely spins its wheels but generally
> > > carries a tail from about the one mile.
> >
> > and this is why.
> > 1) An aerodynamic change Howard made to the old 448 reduced the rooster
> > tail from 20-30 feet to 6-10 and the speed went from 240 to 250. There
> > was absolutely no other change. Two sequential runs about two hours apart
> > at World of speed.
> >
> > 2) While I was on patrol in 1986 I noticed that the rooster tail didn't
> > disappear when the driver shut off the engine and it didn't vary
> > when the driver was on and off the throttle trying to control wheel spin.
> >
> > 3) Front wheel drive cars have rooster tails.
> >
> > My conclusion from these observations is that salt is lifted into the air
> > by wake turbulence resulting in what we call a rooster tail.
> >
>
> Glen Barrett wrote:
>
> >
> > Back when Arfons, Breedlove and other jet cars were running they all had
> > giant rooster tails and no tire spin. We have checked the clocks with a pick
> >
> > up truck and other vehicles and they had small rooster tails and no tire
> > spin.
>
> Pork Pie wrote:
> A rooster tail comes from nothing other than this turbulences behind the car,
> if
> it's a streamliner. The reason why you can see this, is the salt which is
> flying
> in this turbulences.
>
> Rick Hammond wrote...
> Not to cloud it more, but I would think that a wheel could throw up it's own
> rooster tail even by being pushed/pulled rather than driven, especially if
> there
> was increased downforce as well. Not sure if it would show up the same for a
> front open wheel, or if the air flow around and past the rear wheels would
> have
> it's own effect?
>
> Dr.Mayf wrote:
> Watched most cars at speed have rooster tails. My thoughts are two: 1) that
> salt inherently sticks to the tires and is flung off and the faster you go
> the more is thrown up farther, 2) tires flex a lot, especially when they are
> overloaded and this also picks up salt and throws it into the air. The under
> body low pressures and the pressure at the aft end of the car expands the
> rooster tail further.
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