Hi Folks,
here some information to the mails of the last days.
There was 4 reasons why the Mercedes with his Air brake was banned -
first the safety - the car went so unstable (lost contact) on the
front wheels that they got a hard time to steer the car around the
corner. Second - they not only lost the speed, they also lost
sometimes the brake, which was not good for a car behind. Third - due
to much higher brake rate there was all the time the risk that a other
car crashed into the racer to the not so effective braking and at
last, turbulences - this air brake produce a so high (vaccum)
turbulences (like this special wing the cart series use on high speed
tracks that the cars can run faster in the windshade of the forward
car to overtake easier) that it increase the risk of #3 and also make
the behind car very unstable like a hard cross wind.
A comment to Mayf's calculation.
at first a simple calculation to get a feeling what "destroying speed" means.
If someone crash with his car into a wall and comes in a time of 0.1
second to the halt from a speed by 35 mph (50 kph), the driver - if he
weights 150 pounds (I know that this is not american standard) normal
- his weight will increase to 3000 pounds. This is the force which
goes on the drivers body from the deceleration.
So now to Mayf's.
It's a very interested calculation and may be to low (this is not a joke).
The problem is, how much force goes on the square inch of the cross
section of the rope (and of the bracket/bold/welding threat aso.).
Mayf saw this correct, that the power which will be create comes from
the resistance area of the chute, from the speed (when the chute
explode in the air) which "runs" against the chute and from the
airflow over and behind the car.
The airflow over the car is incredible - see a Golf convertible - the
soft top produce by higher speed a real bubble shape.
But I miss something (may be I missed it by my bad English, when I
read his article).
The force goes in two direction - there is not only resistance from
the moving forward speed against the chute (and the force on the
rope/bracket aso.), which is a extreme deceleration (or opposite like
this example with the car, crashing against the wall) from running
against the wall of air. Depends on what kind of airflow the body of
the car produce this wall is "harder" or "softer".
There comes now a second direction of power, exactly opposite of the
"stopping" chute, this is the weight of the car which is still pushing
forward. This has nothing to do with this if the car is only rolling
or still under power. Only the pushing weight of the car produce a
enormus force on the rope. So better the aerodynamic of the car is, so
higher is the product from moving speed and weight. Jeff Shipley was
two years ago very surprised, when he shut down the engine to the end
of the fourth mile and he still went an average only 15 mph slower
than the fourth mile thru the 5 mile. This was only the weight and the
aerodynamic of the car which allowed the car to stay on speed.
A heavy car is much more (negative) affect from this weight issue than
a lighter car - here the example Al's # 76 and Tom's # 411. Which
holds by Al, can be ripped of by Tom.
This number of the opposite direction force on the rope/bracket is
different by all car's due to the different weights and
aerodynamic. Also the percentage of the weight front/rear creates a
affect - a front engine is pushing more forward than a rear engine.
What also effect the force is the chute type and size.
A open chute so as Art Arfons used on his Green Monster or Carl Heap
on his Phoenix, creates a much softer resistance than a closed one. I
don't know if someone tried ever a open chute as the first (highspeed)
chute on a real fast streamliner. Would be interested what experience
he got with them. The rope length is also important. Due to this that
the most parachutes start to "turning" the rope like a screw threat a
longer rope can eliminate the rolling effect against the car - or more
important against a streamline bike. A short rope can may be eliminate
this real hard stopping from a chute which is open before the rope is
stretched, but can produce also the effect that a half open chute
close (collapse) again due to bad airflow behind the car.
May be Mayf can check his formula and find a idea how he can modify
them with my input (opinion) of the opposite force of the car. Would
be great to see the result and it would not surprise me, if the force
increases.
See ya
Pork Pie
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