From: "Orion105" 
To: "'Richard Schwartz'" 
Cc: 
Reply-To: "Orion105" 



Richard

Thanks for the "artworks" ahem....

No, the rotational sense I was on about was that of the secondary mirror
acting as a pendulam and "nodding", rotating around the vanes.

Ado

> -----Original Message-----
> From: Richard Schwartz
>
> If you mean twisting around the tube axis, the
> resistance to twisting comes
> from the fact that the vanes are not co-planar
> with the optical axis.   From
> the end of the tube, you want see this (may the
> e-mail have mercy on my
> ascii art):
>
>
>
> Are there any rules of thumb regarding the
> length to width ratio of
> spider vanes.  I see them made quite thin (10:1
> or higher) and quite
> thick (4:1 or so).  I guess you need width to
> stop rotation of the
> diagonal, but how much is optimum?
>
> I have seen spider vanes that taper in width
> markedly from the outside
> of the UTA to the hub.  I have even seen a
> design that goes the other
> way.  Is there any advantage in tapering?  It
> seems to me that
> resistance to twisting is proportional to the
> width of the vane and so a
> tapered vane would be only as good as its
> narrowest point.  Is this
> right?
>
> Ado
>

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