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Builders and Techies All:

As I recall from my PADI days (Put Another Dollar In), nitrox bottles
are kept seperate and are prepared differently than standard scuba
bottles. I believe that the possibility of trace oil in "regular"
compressed SCUBA air contaminating tanks destined to be filled w/ NITROX
was the concern. Something to do with flames, bursting and subsequent
explosions, and that sort of thing.  Bears investigating. If you choose to have your bottles filled with compressed air or the
like by a scuba shop and are using either SAE or DIN divers type tanks,
be aware of the "BURST DISC" on the output tank fittings.  The burst
disc does exactly that in case of overpressure. I have seen these blow
off on tanks that were kept in the trunk of a car after being left in
the sun for a couple of hours.  You should consider the interior temp of
your bird and the greenhouse effect of your canopy if you have such a
bottle in the cabin.  Be advised that a burst disc going off will be a
defining event in your life if it happens while aloft.

I am not schooled to be able to say the effect of altitude on a
pressurized cylinder.  Would the decreasing pressure in a
non-pressurized aircraft at altitude cause an increase in pressure seen
by the interior of a pressurized cyclinder?  If yes, again look closely
at the burst disc issue. A possible alternative would be to have the
tank filled to a lower pressure.  Please make sure you check this lower
pressure personally.

If you are going to utilize scuba tanks,  may I respectfully recommend
you consider using the DIN sytle of tanks and regulators as they are
designed to a higher set of standards and routinely are used by Higher
Tech divers(read: cavers, S.A.R., wreck penetration , etc). The
difference in cost is not very significant and the reliability of the
DIN style is far better.

Lastly, the proposal of filling the tanks with pure O2 gives me cause to
pause.  If the incident precipitating an emergency descent stems from a
shorted circuit/flames/smoke/and the like, I would be concerned as to
the advisability of a source of O2 to fill my cockpit.  Any leak, faulty regulator (first or second stage), or comprimised bottle would
quickly result in an oxygen enriched atmosphere.  While I am not an
engineer, nor able to compute the theoretical volumetric concentrations
and resulting ignitable mixes that may result, prudence dictates your
proceding very carefully. The tragedy and aftermath of the Apollo 1
testpad fire had the enriched cabin Oxygen level as a direct contributor
to the loss of three very good men. While the  "EXperimental" builders catagory allows innovation at a
myriad of opportunities,  we must continually evaluate the  directions
taken. While our military has taken one road,  keep in mind that their
"cost no object" approach and considerations of other military
objectives could result in a different decision as should be made by a
non-combatant.  The ability to take the path to an elegent solution may
win approval at an exhibition,  but in some cases, the very elegence of
the solution may conceal a hidden "smouldering" danger. I take this opportunity to wish all fellow participants on this forum
the happiest of holidays.  May you be surrounded by those you have
chosen to call your friends.  Build and fly safely so we can relive
these wonderful times far into the future.  Regards to all.....Jeffrey
B. Chipetine

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