On Mon, 02 Nov 2009 17:25:56 -0800, Craig wrote:

On Nov 2, 4:37Â*pm, Martin Gregorie
wrote:
On Mon, 02 Nov 2009 15:47:40 -0800, Mike the Strike wrote:
So how does rubber (or modern synthetic varieties thereof) compare on
an energy storage per mass basis with lithium/ion batteries? Â*We use
them for bungee launches - how about powering a sustainer?

Good quality rubber strip stores around 3000 Â*ft/lb per pound of
rubber. Sad to say, I've completely forgotten how to convert that to
something we could compare with a battery, say to kW/kg.

I have this vision of a large coil of rubber between my legs powering
a slow-turning single-bladed prop!

That sounds potentially as dangerous to valued objects as snapping the
drive shaft of a P.39 Airacobra.

--
martin@ Â* | Martin Gregorie
gregorie. | Essex, UK
org Â* Â* Â* |

If I've calculated correctly (and I may not have) 3000 ft-lb/lb of
rubber = 8,965 joules/kg of rubber. So a 100 kg rubber band would store
896.5 kilo joules of energy which expended over 60 seconds provides a
stunning power output of (drum roll please) 15 kw. It would be damn
exciting on a FF model, but probably not practical as a sustainer.

So that's 0.25 kWh by my reckoning. By contrast the LAK FES installation
carries two 3.6 kWh batteries.

I make that rubber 0, electric 1


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |