When fighting headwinds, it would take a difference of greater than 15 knots to compel me to fly at 8,000 rather than 18,000. Tailwinds are when flying high really pays off, as they typically increase with altitude. A few months ago, a 50 kt tailwind at FL180 netted me an 18% savings in time and dollars over the 30 kt tailwind at 8,000.
My only option to resupply my built in oxygen tank on airport locally was a $90 charge to "fill" with no guarantee they could top it off to 1850 psi for what ends up costing me less than $8 for the same amount purchased in bulk from the local gas supplier (assuming a full fill from 500 psi when doing it myself). I estimate that ~9 aircraft refills (only 3 runs to the gas store to swap cylinders) will be the breakeven point to cover my equipment costs, but that is not the primary appeal. The instant availability to fill up in my own hangar at my convenience rather than taxiing across the field and waiting at their convenience made the decision easy.
I purchased a 3 cylinder cascade manifold, the FBO-3 from http://www.aviationoxygen.com/aviation- ... stems.html
A more sophisticated system that you can specify part by part, at a commensurately higher price is available from Mountain High: http://www.mhoxygen.com/index.php/groun ... ansfillers
I cannot recommend strongly enough that you purchase an “Oxygen Cleaned” transfill manifold from a reputable dealer assembling it for the sole purpose of Oxygen use, as the consequences of even a small amount of petroleum lubricant or any other compound that reacts explosively in a pure oxygen environment anywhere in the system could be catastrophic.
In addition to the 3-tank transfill manifold, I bought three 125 cu ft cylinders, and built a cart to haul them to the fill port in the nose. I would have preferred to purchase a 3-tank cart ready made, but the cheapest I could find was $3,500. I built mine for a little more than $210, modifying an inexpensive 2 tank cart:
- https://www.amazon.com/gp/product/B004G ... UTF8&psc=1
https://www.amazon.com/gp/product/B001X ... UTF8&psc=1
I spent a week or so nosing through every bit of oxygen tank handling safety information I could get my hands on, then cobbled the bits together:
Be smart and aware, and the fill process is easy and safe:
1. Ensure that there are no petroleum lubricants or any other compound that reacts explosively in a pure oxygen environment anywhere on your hands, person, or near the fill site. It would be wise to use wrenches cleaned with 409, then alcohol, that are dedicated for this purpose only.
2. Check that the bleed valve is closed.
3. Uncover the fill port in the nose and attach the PB3 fill connector using a 7/16 wrench to steady the tank fitting, while using another 7/16 wrench to tighten the fill adaptor slightly tighter than hand tight.
4. Identify the lowest pressure tank of the three, and open the tank valve very slowly. Feel for heat, and back off the flow if heat starts to build.
5. As the pressure between the lowest pressure tank and the aircraft tank equalizes, note the pressure, write it down on a piece of tape stuck to the tank, and then close the valve.
6. Identify the next lowest pressure tank of the three, and open the valve very slowly. Again, feel for heat, and back off the flow if it starts to heat up.
7. If this tank is capable of filling to 1850 psi, close the valve as it reaches that pressure and write “>1850” on a piece of tape stuck to the tank. If not, as the pressure between this tank and the aircraft tank equalizes, note the pressure, write it on the tank, then close the valve.
8. Use the highest-pressure tank to top off the fill.
9. Close all tank valves, open the bleed valve to depressurize the manifold, then disconnect the fill adapter from the aircraft fill port. Close the bleed valve and cover the adapter and fill port.
10. Once the highest pressure tank cannot fill to 1850, it is time to replace the lowest pressure tank with a freshly filled cylinder, to now be used as the highest pressure tank, dropping the other two down in fill sequence.