Landracing Forum
Thrust-powered Land Speed information => Discussions on absolute land speed records => Topic started by: J79 on May 06, 2016, 08:05:13 PM
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http://www.bbc.com/news/science-environment-34200629 (http://www.bbc.com/news/science-environment-34200629)
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I read the article. Thanks J79.
Questions, questions!!!!!!!
Do I now have to start building a suspension for my liner?. :-D
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I'd like to see the survey results of most likely to be used lake beds in the US as a comparison, ie Bonneville, Black Rock, Diamond Valley, Alvord. Keep in mind that since we live on a sphere, the earth curves at 8" every mile, so the surface is never perfectly flat.
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The day before the accurate survey is needed, you walk the line with and put a 16 oz beer can down every 34 paces (this is 100 feet for most of us.) Then, early in the morning before the heat waves, you lay on your belly and look down the row of cans. Some cans will stick up more than others. This tells the flatness of the route and where corrections need to be made. All that laser stuff is for folks that have more money than talent.
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And YOU get to empty the beers the night before! :-o :-D
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Mickey Thompson addressed the problem of course smoothness.
He wrote, "...the fastest that a shock absorber can work on a two-inch bound and rebound is a very fat fraction of a second. ...If I'm going several hundred feet per second, what earthly difference does it make what the springs and shocks did a thousand feet back? They're just starting to react to a condition that existed long ago and far away. What's the good of suspension if it doesn't know what hit it until it's maybe a quarter mile down the course?" (Challenger: Mickey Thompson's own story of his life of speed.)
Multiply this by a factor of 2 1/2 and it raises more questions about suspension and the course.
Will Willis
#6302
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Mickey Thompson addressed the problem of course smoothness.
He wrote, "...the fastest that a shock absorber can work on a two-inch bound and rebound is a very fat fraction of a second. ...If I'm going several hundred feet per second, what earthly difference does it make what the springs and shocks did a thousand feet back? They're just starting to react to a condition that existed long ago and far away. What's the good of suspension if it doesn't know what hit it until it's maybe a quarter mile down the course?" (Challenger: Mickey Thompson's own story of his life of speed.)
Multiply this by a factor of 2 1/2 and it raises more questions about suspension and the course.
Will Willis
#6302
I always love when folks use this quote to validate not using suspension.
The very next land speed record car Mickey Thompson built, Challenger II (the car his son Danny is currently going to try to set the LSR with) has suspension both front & rear. I wonder why?
It must be because his original statement was in error.
:cheers: :-)
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Man-o-man that's a sight for sore eyes. So was hearing Danny's 406 run a couple of years ago - a sound for starved ears. :-D :-D
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I think you're bang on Mark. :cheers: :cheers: :cheers:
Pete
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Mark;
"Could it possibly be because a car without suspension has a "wheel rate" of nearly infinity? Component and chassis flex "reduce" the rate somewhat. (Suspension guys, please point out my error if I am wrong here.)"
You need to add in the tire spring rate; the result is not really infinite but it is very high. The whole car will bounce around instead of just the wheels and suspension- tough to control and a very uncomfortable ride!
Regards, Neil Tucson, AZ
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Tom Burkland's 294 mph Datsun logged rear suspension travel and found .050" travel at high speed . Without light weight wheels and irs suspension seems futile for fast lsr cars .
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John;
Effective bump performance in a suspension depends on the sprung/unsprung weight ratio. You're right about needing lightweight wheels- the rest of the unsprung mass (tires, uprights, brake rotors & calipers, part of the suspension control arms, etc) needs to be lightweight, too. Practical considerations usually dictate how light you can go. Of course, a heavy car can get away with heavier sprung components.
Regards, Neil Tucson, AZ
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I suspect a good fraction of the "effective" suspension travel occurs in the tires only, since the wheel inertia, shock absorbers and spring rates does not allow it to accelerate fast enough to follow the surface.
It would be very interesting to see a very fast frame rate video of the tire contact patch of a 200+ mph car at speed with suitable visual markers present to see how much suspension compliance actually is confined to the tires.
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Craig Breedlove and others have said that when you're going extremely fast,
that little general elevation changes in the ground result in an airborne vehicle
much of the time during the high-speed part of the run -- which, of course,
makes steering pretty iffy. I think this is one reason that cars will have to
rely on aerodynamics acting on the steered wheel(s), and possibly also on the
fuselage as well.
People who generally aren't car buffs will look at something like the Blue Flame
and say "That's not a car - it's a rocket with wheels." Well, yeah -- it is a rocket
with wheels. But it's self-propelled, and carries a driver, and can be steered, and
is not restricted to running on rails like a train. So the Blue Flame is a car. Many
folks have trouble thinking outside their ho-hum daily lives. And it's a rare (but
admired!) breed of person who designs something new and improved, but technically
within the rules.
As speeds increase and it therefore becomes increasingly difficult for the wheels
to stay in contact with the ground, should/can we expect to see these vehicles
designed to purposefully lift the wheels from the ground at speed, and use wings
to support the vehicle, with only some "token wheels" rolling along, and touching
the ground much of the time? If so, what should the rules be, and how would
they be enforceable? I'm just extrapolating, folks. I think we can all agree that
the current (recognized) and recent (recognized) absolute land speed records
were set -- and recognized and accepted, perhaps without much thought given
to the fact that at times, the entire vehicle may have been briefly airborne during
the record-setting runs!
It may be that there should be a rule that limits the use of hardware or design
intended to intentionally (I know that this is a mushy, hard-to-prove word) lift
the vehicle at high speed. Or not. Actually, it may be very nearly impossible
for any land speed car (or bike) to keep any part in continuous contact with
the ground at (say) 600+ mph. An extreme example would be something that
looks like a jet fighter aircraft flying with the main fuselage just a couple feet
above the ground, and a tiny little wheel (say about 2 inches in diameter?) on
a relatively stiff trailing link, with the wheel touching the ground most of the
time. Seems silly, don'cha think? But how can the existing (or future) rules
specifically prohibit this? Should they?
I suppose that technically we may be able to have enforceable rules that would
allow an official "judge" to measure the marks left on the ground by the wheel(s),
and conclude with reasonable certainty that the wheel(s) were in contact with
the ground for a majority of the measured mile. But I also don't believe that I
will live long enough to see the day when land speed racing is like this.
I do, however, like to encourage out-of-the-box thinking. I admire designers,
builders, and racers who are good at it. This is what keeps progress alive,
thus resulting in new land speed records. And as we should all know, "records
are made to be broken".
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There's always the old "not within the spirit of the rules" which can usually be invoked. That's why it's wise to check with the tech director for the sanctioning body before you try something totally off the wall.
Pete
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Craig Breedlove and others have said that when you're going extremely fast,
that little general elevation changes in the ground result in an airborne vehicle
much of the time during the high-speed part of the run -- which, of course,
makes steering pretty iffy. I think this is one reason that cars will have to
rely on aerodynamics acting on the steered wheel(s), and possibly also on the
fuselage as well.
...
As speeds increase and it therefore becomes increasingly difficult for the wheels
to stay in contact with the ground, should/can we expect to see these vehicles
designed to purposefully lift the wheels from the ground at speed, and use wings
to support the vehicle, with only some "token wheels" rolling along, and touching
the ground much of the time? If so, what should the rules be, and how would
they be enforceable? ...
It may be that there should be a rule that limits the use of hardware or design
intended to intentionally (I know that this is a mushy, hard-to-prove word) lift
the vehicle at high speed. Or not. Actually, it may be very nearly impossible
for any land speed car (or bike) to keep any part in continuous contact with
the ground at (say) 600+ mph. An extreme example would be something that
looks like a jet fighter aircraft flying with the main fuselage just a couple feet
above the ground, and a tiny little wheel (say about 2 inches in diameter?) on
a relatively stiff trailing link, with the wheel touching the ground most of the
time. Seems silly, don'cha think? But how can the existing (or future) rules
specifically prohibit this? Should they?
The (2014) FIA International Sporting Code has a loose definition of automobiles and other vehicles:
13. Land Vehicle, Automobile, Special Vehicle, Ground Effect Vehicle
Land Vehicle :
Vehicle propelled by its own means in constant contact with the ground either directly by mechanical means or indirectly by ground effect, and the motive power and steering system of which are constantly and entirely controlled by a driver on board the vehicle.
Automobile :
A land vehicle propelled by its own means, running on at least four wheels not aligned, which must always be in contact with the ground; the steering must be ensured by at least two of the wheels, and the propulsion by at least two of the wheels.
Special Vehicles :
Vehicles on at least four wheels which are propelled otherwise than through their wheels.
Ground Effect Vehicle :
Vehicle whose bearing on the ground is maintained by means of a pressurised air cushion.
/end
Not sure how a given vehicle is classified, or by whom...
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The (2014) FIA International Sporting Code has a loose definition of automobiles and other vehicles:
13. Land Vehicle, Automobile, Special Vehicle, Ground Effect Vehicle
Land Vehicle :
Vehicle propelled by its own means in constant contact with the ground either directly by mechanical means or indirectly by ground effect, and the motive power and steering system of which are constantly and entirely controlled by a driver on board the vehicle.
Automobile :
A land vehicle propelled by its own means, running on at least four wheels not aligned, which must always be in contact with the ground; the steering must be ensured by at least two of the wheels, and the propulsion by at least two of the wheels.
Special Vehicles :
Vehicles on at least four wheels which are propelled otherwise than through their wheels.
Ground Effect Vehicle :
Vehicle whose bearing on the ground is maintained by means of a pressurised air cushion.
/end
Not sure how a given vehicle is classified, or by whom...
These definitions were revamped/replaced in 2015:
Automobile:
Vehicle running in constant contact with the ground (or ice) on at least four non‐aligned wheels, of which at least two are used for steering and at least two for propulsion; the propulsion and steering of which are constantly and entirely controlled by a Driver on board the vehicle (other terms including but not limited to car, truck, and kart may be used interchangeably with Automobile, as appropriate within types of competition).
Special Automobile:
Vehicles on at least four wheels which are propelled otherwise than through their wheels.
No "Land Vehicle"; no "Ground Effect Vehicle".
As discussed in another thread, this has the unfortunate (and unintended) side effect that statements referring to "Automobiles" could be read as not applying to "Special Automobiles".