rec.autos.simulators

You're absolutely right, and I agree with you that improving car construction in the area of crush zones would be the simplest, least expensive, and most rewarding place to start improving safety.

When you say Martinsville is not a high speed track, everything's relative.  From what I understand, the severity of a barrier impact can be expressed with a physics formula:

IS = .5m(V sin J)

where IS = impact severity, m = mass, V = velocity, and J = trajectory angle (the angle between the line of the car's motion and the barrier face).  The heavier the car, the worse the impact.  The faster the car's going, the worse the impact.  And the more "head-on" the car hits the barrier, the worse the impact.  While Martinsville doesn't see anywhere near the top speed of some other tracks, it shares something with Loudon in that the turns are sharp and the wall at the end of the straight is at a very high angle to the straight.  So even though the speed might be lower, the trajectory angle is probably higher and that can still make for some *** impacts.

I think it was the year before they put in the chicane (Inner Loop) on the back stretch, I'm guessing late 80's, early 90's.  I believe the man's name was J.D. McDuffie, a Dave Marcis type owner-driver.  I remember my favorite driver at the time (Geoff Bodine) had a similar incident a year or so before that where at the end of that long back stretch he hit the brakes for Turn 5, cut a front right tire down, and went straight off into the grass ending up in the catch fence.

I find myself attracted to every kind of racing except sprint cars (that crab-walking around corners just doesn't seem right) and drag racing, and enjoy good races at all levels from Winston Cup at Michigan to hobby stocks on a third-mile dirt.  I just don't think it's speed per se that builds a fan base, it's competition.  So to treat increased speed as inevitable and work around it seems unnecessary.

I was calling MY friends beer-swilling idiots, not yours <g>.  But it does appear that when you initially wrote "an awful lot of NASCAR fans", what you really meant was "a former racer ... and long-time NASCAR fan".  No big difference, just a matter of perceived multitude I guess.

At any rate, the Earnhardt report can be viewed or downloaded from http://www.nascar.com/SPECIAL/er/download/.  The first part is just a summary of the conclusion, all the details of the who and how and why of the investigation are in the appendix.  As a complete layman with just enough knowledge of physics to be dangerous, it seemed pretty complete and thorough to me.  (FWIW, I'm not an automatic defender of NASCAR, I think some of their moves have been as idiotic as some of the CART and FIA decisions.  I just think they have probably been unfairly criticized concerning their handling of the Earnhardt case.)

If you collide head on at 60mph with an object and the deceleration to zero
takes .1 second you are at about 27 G. At .2 second you cut that in half. At
.05 second you double it and get 55G. The crumpling of metal increases the
time of deceleration. Less crumple = less deceleration time = more G force.

A collision with a wall at an angle does not bring the velocity to zero.
Also 100% of the velocity does not apply. The amount depends on the angle.

The amount of G forces the body can take depends on how they are applied to
the body. Also the surface area of the body accepting the forces matters.
This is why racing belts are so wide. Smaller belts could easily restrain
the body identically, but the pressure applied to the body would be greater
at an equivalent G force.

Norman

"btgoss" wrote ...

You're absolutely right, and I agree with you that improving car
construction in the area of crush zones would be the simplest, least
expensive, and most rewarding place to start improving safety.

When you say Martinsville is not a high speed track, everything's relative.
From what I understand, the severity of a barrier impact can be expressed
with a physics formula:

IS = .5m(V sin J)

where IS = impact severity, m = mass, V = velocity, and J = trajectory angle
(the angle between the line of the car's motion and the barrier face).  The
heavier the car, the worse the impact.  The faster the car's going, the
worse the impact.  And the more "head-on" the car hits the barrier, the
worse the impact.  While Martinsville doesn't see anywhere near the top
speed of some other tracks, it shares something with Loudon in that the
turns are sharp and the wall at the end of the straight is at a very high
angle to the straight.  So even though the speed might be lower, the
trajectory angle is probably higher and that can still make for some ***
impacts.

I was just trying to make the point, and not very well, that speed has
little to do with this type of impact. The stiffness of the car, and the
dramatic stopping of the car is what causes the huge forces to be generated.
I used the Martinsville accident to try and show that it has happened at
much slower speeds than acheived at C***te or Louden.

btgoss

It actually came from the Earnhardt accident investigation report, and is purportedly something that's used in highway barrier design studies.

Since we're considering the wall as immovable, the wall is applying exactly as much energy back through the car as the car is applying to the wall.  If the mass of the car is greater, that translates into more energy transmitted back through the car.  

agreed.  As I remember it, Earnhardt's car was travelling about 35mph perpendicular to the wall and decellerated to -10mph.  The crash impulse was 80 ms.  I think that translated into a peak decel of about 60G.

That's why the formula adjusts the velocity by the sine of the trajectory angle, the smaller the angle the less severe the impact.

Eldred
--
Dale Earnhardt, Sr. R.I.P. 1951-2001
Homepage - http://www.umich.edu/~epickett
F1 hcp. +16.36...Monster +360.54...

Never argue with an idiot.  He brings you down to his level, then beats you
with experience...
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My point is that if you have a 1000lb car and a 10000lb car and both have
the same initial speed and both decelerate to zero(or whatever) in the same
amount of time, then the *driver* feels an identical "crash" force. Now the
total energy of the collision is higher in the heavier vehicle.

KE = .5 x mass x velocity x velocity

So a heavier vehicle will put a bigger wallop on whatever it hits since it
has higher energy.

Yes they need to take into account impact energy with highway barriers since
they want to absorb the impact of a car without allowing the car to pass
through the barrier. The same is true of race track walls. They do not want
them to fracture and shrapnel the crowd.

The impact the driver feels are acceleration forces. The impact energy of a
collision says nothing about the acceleration forces.

Norman

"Norman Black" wrote ...

It actually came from the Earnhardt accident investigation report, and is
purportedly something that's used in highway barrier design studies.

Since we're considering the wall as immovable, the wall is applying exactly
as much energy back through the car as the car is applying to the wall.  If
the mass of the car is greater, that translates into more energy transmitted
back through the car.

force.

agreed.  As I remember it, Earnhardt's car was travelling about 35mph
perpendicular to the wall and decellerated to -10mph.  The crash impulse was
80 ms.  I think that translated into a peak decel of about 60G.

That's why the formula adjusts the velocity by the sine of the trajectory
angle, the smaller the angle the less severe the impact.

Indeed, the most straightforward way being to install/design appropriate
"crumple zones" in the chassis construction.  This acts as a one time only,
non returning spring, but does the job.
NASCAR won't mandate it though.

cheers
John

-John

mandate (mndt)
n.
An authoritative command or instruction.

As long as a governing body does not MANDATE safety requirements, teams will
do whatever they feel is appropriate, within (or demonstrably within) the
technical regulations of the racing formula.

The fact that no discussion has taken place is a clear indication that
NASCAR does not care to assess the situation further than on a case by case
basis.

In order to enforce an uncompetetive construction method onto the teams,
such a requirement must be MANDATED by the governing body.

I'm not talking about what NASCAR did or did not do, I'm talking about what
they will not do now.  If the teams have compromised the safety of their
cars too greatly for a competetive advantage, then NASCAR should step in, so
that all teams can build safer cars without losing any advantage, or
equality with other teams.

cheers
John

-John

Eldred
--
Dale Earnhardt, Sr. R.I.P. 1951-2001
Homepage - http://www.umich.edu/~epickett
F1 hcp. +16.36...Monster +360.54...

Never argue with an idiot.  He brings you down to his level, then beats you
with experience...
Remove SPAM-OFF to reply.