Hi Folks,
why I joint this e-mail list? Now I'm sitting the whole night here on my lap
top
to write comments and during the day I sleep in my office and when my boss is
coming along the way, I got marks from the keyboard on my forehead.
Smiling. Honestly I enjoy this discussion.
Rooster tail, need me a while to understood what the heck you guys means with
this.
Glen, at first, Art Arfons Green Monster or Craig Breedlove's SoA can't have
wheelspin problems, due to this, that this cars used thrust power - jet engines
- they was simple pushed forward, there was no power which went over the wheels
to the ground. Sometimes they didn't touch anymore the ground, so as Art during
his last record in 1965 - some years ago I saw a fantastic picture from this
"flying mile". This was the reason, that in the FIA rules stand now, that all
four wheels has to be on the ground.
Howard is bloody damn good in aerodynamic. I got a wonderful dicussion at Black
Rock (in 1997) with him, when I was there with the Thrust Team. I think I
bother
the Thrust team a little bit, when my good old friend John Ackroyd start to
discuse his problems he got with Craig's SoA Sonic Arrow with me.
I discused with Howard exactly this aerodynimac problem which cause this,
what you call a rooster tail (funny name for that).
And we got the same opinion about the reason and how you can solve them.
There are two main problems on streamliner.
One is the rear end - how the bottom line went up into the air,
the other is how the body tapered on the rear end.
To the first problem.
If the bottom line of the rear end goes into a to big angle upwards, than the
airflow is collapsing under the rear end and create turbulences.
The car can't go properly out of the air. I see the big questions marks now in
the faces.
I will try to explain. It's like diving into water, so your car is diving into
the air, behind your car, in the worst case, the air collapse. If you watch a
motorboat, you can see how good this boat is gliding in the water - a bad shape
good a real rough water wave behind the boat end, a good one creates soft and
smooth wave. The air is doing the same, you only can't see it. In a wind tunnel
they use smoke to show this. If the air can't rip off properly from your (car)
rear end, than you will loose a lot of speed - due to this that the air (tries)
to create a vaccum behind your car - which "stops" you to go forward.
Howard got this problem in the beginning with his car, after he changed the
shape of the rear end, this problem was gone.
The second problem is the "tapering" of the rear end.
If you look on the Golden Rod, you will see that this car goes smaller on the
rear end, there is a reason for.
When you dive into the air, the air tries to go back to the place, where it was
come from, so fast as possible. But, sorry, there is the body from your car in
the way. but if you tapered the body from the front to the end (wider in front,
smaller in the rear) than the reaction of the compressed air is not so
"agressive".
If you can't tapered the car from the front to the rear, so you can taper the
rear end.
The most cars shows a so rear end - only some of them got a mistake in the
design.
When I walked around in the pits, I saw a this rear ends, but I also so that
the
most of them (if they done it) reads aerodynamic books about aero planes.
Why - thet got rear ends with a 7 degrees tapered shape.
But this is wrong. For the car aerodynamic you need 6 degrees.
A German guy, named Willibald Kamm, investigate this more than 60 years ago.
Kamm was Professor for aerodynamic in Stuttgart, where they done also the
aerodynamic for the NSU Dolphine and NSU Baum'sche Liegestuhl (Flying chair).
It may be surprise, that there is a different between an aeroplane (7)and a car
(6).
The different comes from where this body's are.
A plane is in the air, means the air is complete around this body (shape).
The airflow has only to work around the body.
A car is on the ground (and so as we hope all, he stays there). When the car
body splits the air, the air will be also compressed as by the plane. With one
different. When the air is pressed to the side, the air smash also to the
ground
surface, for us it's the salt. From there the air (bounce) back into the air.
But there is the other air, which is gliding along the car, on a other level
above the ground. So this air on the side of the car is not only gliding
backwards, there is also a up and down moving.
This creates a turbulence, which by 6 degrees rip off from the end of the car
without problems. When you got 7 degrees, the air collapse behind the car and
produce a underpressure area behind your car - and this slows you down.
Don't ask me why.
Aerodynamic is a very strange thing, and if you ask 10 aerodynamic experts, you
will get 10 different opinions.
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.
By an open wheeler, this will be a part of the reason.
But what I saw at the salt, for me it looks that it comes also from the salt
which stucks at first on the tire, and is than thrown away. The airflow and the
salt is building up a rooster tail, too.
This for today.
See ya
Pork Pie
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