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RE: airborne vehicles

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> I’m working on the design of an off-road vehicle
> river crossing (bridge) and am looking for
> information regarding speeds and inclinations when
> ATV and 4WD vehicles would go airborne.  I don’t
> want the roadway profile too steep on the bridge
> approach since it becomes flat across the bridge
> and I’m concerned with the vehicle going airborne
> at the transition. I need this to be as safe as
> one might expect in this type of sport.    Are
> there any charts or an equation relating the two
> (I’m sure weight comes into play also).  Any help
> I can get would be greatly appreciated.

First, this would make the bridge boring.  Believe me, the ATV drivers WANT
to go airborne.  They usually go out of their way to accomplish this.  I
spent a portion of my youth flying through the air on 3-wheelers and dirt

But, I can understand you wanting to avoid killing some idiot and removing
their idiot DNA from the gene pool (and to avoid getting sued).

The safest and most reliable way would be to follow AASHTO guidelines as
stated by others.  

If you can't feasibly do this then you need to pull out your physics book,
also suggested by others.  Keep in mind that this isn't one of the nice
simple physics problems found in texts.  A 4-wheeler isn't a solid mass -
it's composed of 4/5 separate masses connected by springs (front and rear
axles, body, and rider/passenger).  The rider and passenger will be
partially supporting their weight by pushing against the foot pedals.  When
the ATV drops over the edge inertia (aided by leg pressure) will lift them
off the seat.  Add to this the fact that the rotation of the vehicle as it
goes over the edge will give an extra upward "push" to the passenger.

My main addition to this thread is that you stay WAY away from the
"airborne" point.  Based on personally history, if an ATV driver goes over
your bridge and inertia lifts him off the seat, he'll say "cool", turn
around, and drive over it again at double the original speed.  Either keep
the bridge mostly flat, or use some method (speed bump, horizontal direction
change, etc.) to keep the speed down.


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