"David Megginson" wrote:

Thanks for all the info. Any recommendations on manufacturers? How
long does a tank last when you have four people breathing from it
instead of just the pilot?

Mine is Nelson (aka Precise Flight). I didn't choose it, but I'm very happy
with it. The previous owner of my plane threw it in as part of the deal.

When you've got four people in the airplane, it's less likely that you'll be
able to drag your gross weight up to where your passengers need O2. My
regulator has a manifold for four cannulas, but I've never used more than
two simultaneously.

Here is a link to some mfg data. My experience is reasonably consistent
with their claims.

http://www.preciseflight.com/durationstable.html

My tank is the 22 cu ft model. Installation is on the back of the copilot's
seat. A harness attaches to the seat back, and the tank straps to the
harness. In a C182, there's plenty of room for the rear seat passenger's
knees once the copilot seat is brought forward to its normal position. If
you fly something with less rear seat leg room, it might get crowded.