Bursting speed of rotating disc (27/02/13)

...and its relation to rotary spark gaps.

I wanted to calculate how fast a rotating disc (as used in a rotary spark gap) could run before breaking. I found a good set of lecture notes through the Wayback machine here (or locally here) and I've condensed the relevant material into a short PDF, available here. The rather interesting conclusion is that the maximum firing rate depends solely on the properties of the disc material and the separation between the holes, not on the diamteter or rotational speed.

The lecure notes use imperial units and have a stupid unit for density - lb-sec^2/in^4. This is actually density - here is a good list of unit conversion tables. However, if you ignore all that and do everything in SI units, it works out correctly.