# Experimental Aircraft Oxygen Systems

### Help Support Homebuilt Aircraft & Kit Plane Forum:

#### cvairwerks

##### Well-Known Member
FYI....the military has been on selectable diluter-demand/100% systems since about 1941.....

#### Rhino

##### Well-Known Member
I flew for 14 years in the Air Force, 1983-1997, and we had pressure demand systems.

Last edited:

#### cvairwerks

##### Well-Known Member
The pressure demand regulators consist of a diluter demand section with an additional regulator circuit that then maintains the hose to mask pressure slightly above cockpit pressure. Once you get above 34,000 feet, it switches to 100% oxygen and maintains the positive pressure within the hose to mask. If you want to complicate it more, then you move to the PPBG regulators...Positive Pressure Breathing under G... These regulators function as PD units, until the aircraft starts pulling more than 1 g during maneuvers. It will then ramp up the hose to mask pressure based on a combination of breathing demand vs a g loading schedule. For a quick and dirty comparison, think fixed and variable pressure CPaP in the airplane with oxygen supplementation.

The change from high pressure bottles to LOX and then to OBOGGS has been a huge help in improving onboard O2 capability and reliability for flight crew, although some initial choices in system architecture for the F/A-22 eventually required some big changes in both system design and operational requirements.

Last edited:

#### Cardmarc

##### Well-Known Member
Best thing now is the portable o2 concentrators. No o2 refills! Mine has lasted as long as I need it to and it’s good tom18k. Aviation Consumer Mag had a great review on them not long ago.

#### Rhino

##### Well-Known Member
The pressure demand regulators we used in the Air Force (pictured above) did not maintain any mask pressure unless you switched it to emergency. You could remove your mask and no oxygen would flow, as it would in a diluter system. That's why there was a flow indicator on the front of the regulator, so you could see oxygen start to flow when you inhaled (demand). That's if you had it set to 100%. If it was on normal all you got was ambient air. Had we had a constant pressure system on our aircraft, the oxygen system never would have lasted for our entire mission durations (our helmets were always hooked up). We commonly went 14 hours with a 34 man crew, and sometimes significantly longer in special circumstances. If you switched it to emergency, it tried to explode your lungs with massive amounts of pressure. That's what we were supposed to do with a decompression above 34,000 feet, but there was no way you could exhale with that much pressure. You had to crack a leak in your mask to exhale. I can't promise things haven't changed since I retired in '98, but it appears they still use the exact same regulators on at least some aircraft.

#### cvairwerks

##### Well-Known Member
There have been some regulator changes since then. I used to have to test the CRU-93's and -98's in our F-16's. The 93's were on our LOX birds and the -98's on our OBOGGS birds. Probably been 17 years since I had to run all the in aircraft regression tests on either version. I don't think I've even touched an F-16 since about 2006 on our flight line. I'm still LOX certified, but haven't had to do a bottle charge in at least 4 years now.

#### Rhino

##### Well-Known Member
Maybe that's what it is then. I was on RC-135s, and we used the CRU-60P, which I still have.

#### HomeBuilt101

##### Well-Known Member
>Best thing now is the portable o2 concentrators. No o2 refills! Mine has lasted as long as I need it to and it’s good tom18k. Aviation Consumer Mag had a great review on them not long ago.

What device did you get?

This sounds like a good approach... for those who have done the research on these units can you please share what you learned?

#### tallank

##### Well-Known Member
Best thing now is the portable o2 concentrators. No o2 refills! Mine has lasted as long as I need it to and it’s good tom18k. Aviation Consumer Mag had a great review on them not long ago.
What unit is good to 18k?. Most specs. I see say 10k.

#### tallank

You can buy a new A-12A diluter-demand regulator good up to 32,000 feet for $1900. This one looks like the ones used in 1940's-1950's airplanes. So yeah you can do that route but it turns out to be very expensive. I looked into this because I wanted to do what Paul Dye did. But it's very pricey. Or you buy an old regulator and hope that it works, or, if it does, that it will continue working. I didn't choose to risk my life that way., I have most back issues of Kitplanes what month and year was the article posted. I vaguely remember that article. #### Saville ##### Well-Known Member I have most back issues of Kitplanes what month and year was the article posted. I vaguely remember that article. You're probably thinking of the Paul Dye article which I referenced in my post. #### mikoman ##### Member HBA Supporter I didn't come up with this, but it's the setup I use, except a smaller bottle because I'm usually solo at altitude [Was originally posted on POA by a Dr. Bruce Chien, a senior AME] Go to a welding shop or a medical supply shop and BUY outright the biggest Aluminum cylinder you can- a Super "D" or 50 cu. ft. Why? Because a fill of the smallest compared to the biggest runs the$13.00 up to $18.00. Getting the fill is the inconvenience. Buy a stepdown regulator (welding type) for ~$40 and put it on top. Buy an 8 foot piece of 80 PSI hose and the appropriate CGA 540 fittings (or have the shop do it for you) and run from the end of the stepdown regulator to another CGA 540 fitting. At this end, buy a Skyox regulator and install it. The Skyox regulator is expensive (\$200) but is a precision machined device that automatically doubles flow if two are plugged in, triples for three, etc. It doesn't leak and it's near bulletproof.

Now you have a tank strapped down in the baggage compartment, and complete control in between the PIC seats.

This way you have 1) huge O2 supply, = 30 man hours at 18,000 on cannulas e.g, more than you have fuel, and on some trips you will be able to make the return w/o a refill.

Fill it at your local welding shop. Yes, I know all about ABO, but they all come from the same 25,000 gallon tank. Even medical oxygen, too.
Thank you for the post and know how. I like the idea of the 8ft hose and end regulator at the tip . As you know experimental aircraft are not known for an expansive seating arrangement or storage area and the set up you describe works perfect. At my age early 60's I use O2 if I am at 10,000 or above. Those portable pulse ox meters are sure helpful