RE: stiffening spiders

[Chris.Prael@domain.elided (Chris Prael)]

Right.  It is a fairly clever attempt to get around the leverage
problem, which is what this is all about.  

Because the Spider has full height doors, the verticle depth of the 
structure through the cockpit area is very thin.  The fact that it is
thin means that it flexes in both bending and twisting very easily. 

The stiffener adds material to this thin structure, but it adds little
to no depth.  So, its effect on bending and torsional stiffness is
pretty small.  

It would be interesting to calculate all this, but I don't have the 
software to do it.  I would guess that the stiffener increases the
torsional and bending stiffness by about 25%, possibly as much as 50%.
That is not a significant improvement, in my opinion.

By comparison, a well designed roll cage should increase torsional and
bending stiffness by 400% to 800%.  And that roll cage will weigh about
the same as the stiffener.  (If memory serves, the torsional stiffness
of the Sprint is about 4 times that of the Spider.)  This is a
significant improvement, in my opinion.

chrisp

From: Alan Lambert <gerard@domain.elided>

> I don't think so. If the chassis tries to twist, then the front plate 
> tries to rotate, which is resisted by the box beam. 
>                                      ______
>                                <<<  /      |  ^
>                                    /    o  |  ^
>                                   /        |
> ---------------------------------/  o     o|
> -------------------------------------------|  >>>
>       beam                         plate
> 
> 
> On Wed, 30 Jun 1999, Chris Prael wrote:
> 
> > Thanks, Alan.  That makes me much less ignorant.  
> > 
> > ...
> > 
> > I still think that the rest of the structure is more ballast than
> > improvement.  Though it might compensate for the inevitable sagging of
> > the floor pan with age.

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