Energy storage capacity of rubber bands for vehicle propulsion

[simon whitelock]

I am looking for a simple number which is the potential energy that can be stored in rubber. ( Joules per gram or something similar ) I know there are a number of forms of rubber and I keep reading numerous articles on how to calculate the energy content of a rubber band.
Can anyone just tell me the number for typical rubber available commercially ??
I am building a rubber band "vehicle" and I am starting off with a test bed of one band approx 3m long made up of say 50 strands which will run as a model airplane would but driving the rear wheel. I can pretty much work out frictional losses through the drive system and what horsepower I need to get up to certain speeds but before I run the test vehicle on the road I would be interested to compare the theoretical number against that actually achieved.
There must also be a optimum diameter for the band itself expressed as a ratio to the length which I am trying to find out from the modelling world but if anyone has that number I would be grateful to hear it.

Thanks
Simon

 

[DuckAmuck]

You can just measure it.
If you know the force F (weight), and the change in length x, you can compute the Hooke's constant k.
F = -kx

From there you can compute energy: E = 0.5*kx^2

Energy per mass is just E/m. If you want a maximum, hang more and more weight from a rubber band, until it breaks.
Hope this helps.

 

[Chestermiller]

Rubber typically doesn't follow Hooke's law. The observed rheological behavior of rubber is highly non-linear. You need to read some papers on the theory of rubber elasticity. Google Mooney-Rivlin equation.

Chet

 

[DuckAmuck]

It might not be linear, but you might be able to approximate. Plot weight vs stretch distance.

 

[CWatters]

Don't use rubber bands. Google FAI competition rubber as used for model aircraft. Ditto lubricant. As i recall rubber improves as it is "run in".