Re: High Velocity using Block & Tackle

"Everett M. Greene" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> "Jonathan Barnes" <[EMAIL PROTECTED]> writes:
> > "g3_josh" <[EMAIL PROTECTED]> wrote
>
> > > First I'm just wondering if anyone out there has ever used a block and
> > > tackle system to achieve high cable acceleration?  My M.E. senior
> > > design team is proposing using a block and tackle mechanism in
> > > "reverse" to accelerate a cable from 0 to 250 mph in 2 seconds.  The
> > > proposed system uses hydraulic actuators (rams) to push apart a large
> > > structure of sheaves (pulleys).  The mechanical advantage the rams see
> > > would be on the order of 1/100th, or you could say the cable end of
> > > the block and tackle system would see a mechanical advantage of 100.
> > >
> > > Secondly I would really appreciate some input on cable selection.
> > > Synthetic, steel? We like the idea of synthetic because of its light
> > > weight characteristics, but are not sure how it might react in the
> > > machine.
>
> > What is the G force on a cable as it tries to run round a pulley at 250
MPH?
> >
> > With small pulleys the G force is huge. With large pulleys the inertia
of
> > the pulleys is huge...
> >
> > If you have 100 wraps the cumulative friction in the system will put a
huge
> > tension on the cable.
> >
> > How is this cable slowed up from 250 MPH ?
>
> All good questions.
>
> The OP might try to find some info regarding aircraft carrier
> catapults which may work on the principle he's describes.

I thought aircraft catapults where like pop guns, powered by the ship's
steam.
I don't think cables are used except to connect the aircraft to the block,
with no use of a pulley at all.


--
Jonathan

Barnes's theorem; for every foolproof device
there is a fool greater than the proof.

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