Some of the better posters on RB have been discussing the idea (apparently from an article posted there late last Saturday or Sunday) that the Strat will have a double layer of Kevlar with nitrogen in between. I couldn't think of why we'd want the extra weight of a second shell in order to have an extra layer of gas that provides no lift so I bounced the idea against a couple of engineers while at work yesterday. Their thoughts:
* Two reasons race car drivers (and some classy tire shops) fill their tires with nitrogen: (1) it's known as a non-leaker (2) it doesn't expand or contract very much in response to temperature changes. Having a buffer layer of nitrogen in between the helium and the cold temperatures of the stratosphere could help maintain constant shape of the exterior while buffering any temperature changes of the helium (which temperature changes would otherwise affect volume of the helium).
* Could be that if there's a surplus of electricity available and if it's worth the weight of a compressor and two tanks, nitrogen could withdrawn from one end of the Strat and compressed into tank #1 while tank #2 releases enough to make up the difference. Again, a temperature buffering mechanism.
* Most interesting idea: tetrahedronal nitrogen atom is a lot bigger than helium atom and N2 molecule is twice that big. This alone would tend to reduce amount of helium leaking through layer #1 and having even the slightest overpressure (nitrogen pressing gently against the inner layer of Kevlar) would reduce helium leakage even more. Then, whatever amount of helium did manage to leak through layer #1 would still have to wander around the nitrogen buffer layer before it ever found layer #2 and had a chance to actually escape.
Could be that our proprietary approach to "lift gas management" takes advantage of some of the above. Note: just guesses here, but from a couple of pretty savvy guys.
Caradoc
PS: With Sebass and me both having day jobs, please don't decide the board has gone to Hades if trash accumulates during daylight hours. After all, janitors do their work during the evening.
