[Canberrauav] catapult design

Chris Gough christopher.d.gough at gmail.com
Fri Nov 9 06:24:48 EST 2012

> 34 Kg for a 1.7 metre rail (the plane takes up the last 300mm of the rail)

7G ! close to the 8G limit on the accelerometers, 40% more than the EDF jet pilots use/recommend. Probably to much force.

> 29 Kg for 2m

<6G. Maybe ok I guess.

> 21 Kg for 2.7m

> 19 Kg for 3m, or 14 Kg if we opt for 13m/s launch speed.
> Is 19/14 Kg manageable? That is alot of tension. Someone check my figures
> please!

I pick up / put down my 22KG daughter all day. 25 Kg (5G) is no problem, probably close to the limit of comfort for a lot of people.

A bit less than 3M @ 5G sounds good.

> A longer slide than this means folding or joining lengths of slide. Some
> effort will be required to make the shuttle holding the aircraft negotiate
> the join in the slide.

Agreed, best to avoid a joint in the rails.

> I measured 3m from the dashboard of my car to the rear door.
> I just did an experiment with some 8mm shock cord - it takes 4.8 Kg to
> double its length, and it will not stretch much farther than that.

The beauty of "surgical tube" bungee is it triples it's length. This means we can use more purchase and have room for joiners etc, while staying in the confines of our rail length.

Chris Gough.

> Another hither to useless fact in my notebook for a previously explored
> project says rectangular section plastic downpipe comes in 3 metre lengths.
> 100mm x 50mm or 100mm x 65. Plastic pipe is light and easy to work with, and
> is much more car friendly than a metal structure.
> The yachting fraternity sell suitable multiple pulley sheaves, and sheaves
> suitable for mounting on the side of a mast so an internal halyard can be
> used to hoist the sail.
> Jack.
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