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Recommend O2 cylinder size for RV7/9

Av8safe

Well Known Member
I am likely going with the Mountain High O2D2 EDS system and am looking for recommendations on cylinder size for the RV7. Wanting to find the sweet spot that balances duration and cylinder size/weight in the baggage area.
 
I've got a MH O2D2 portable system with the AL-180 bottle. This gives me 4.9 hours duration for one person at 15,000 according to the MH charts.

My rationale for picking a relatively small bottle is as follows:

1. The time I spend at O2 levels is a small portion of my flight time for any given flight.

2. I have easy (my hangar) access to refills.

3. I have limited room and didn't want anything permanently installed.

4. I'd like to easily be able to take it along if I fly someone else's airplane.

Of the reasons I listed, I think having easy access to refills might be pivotal. If I had to take the bottle in for refills, I may opt for more capacity to minimize the inconvenience.

Also, if I had an ongoing need in terms of a frequent trip that required X hours of oxygen and if I knew that typical loading for that recurring flight left plenty of room for a bigger bottle, I might opt for the bigger bottle.

I suppose with most things, a realistic picture of your intended mission is critical for planning purposes.

FWIW
 
I have the AL-248 and have it mounted forward of the seats on the high pressure fuel pump cover with MH supplied clamps. The controller is velcroed just forward of the fuel selector. Everything is in view and easy to access in flight and quickly removed for refills or when not on a trip. On coast-to-coast trips (three, so far), I have begun with a full bottle and refilled once, on the other coast, or in Montana, on the way home - with two people using the O2. Out west generally cruise at 12,500' to 16,500'. Highly recommend the MH O2D2 system!

Merrill
 
If you don't have easy O2 refill access, get a larger bottle. Refills are often flat-price regardless of size. The bottle should be removable, since walk-in bottles cost less to refill than if they have to bring the rig to the plane.

Dave
 
This depends on your trips. Are you going only to places where you can get easy, cheap fills? If so, get a bottle sized for that. Are you going for example to Mexico where a fill might be more complicated and need 2 people at 15k’ for 6 hours? Get a bigger bottle.

There not a “this is the answer” option, it’s about what you want to do with it :)
 
in-hangar O2 refill system?

I've got a MH O2D2 portable system . . .

. . . 2. I have easy (my hangar) access to refills.

. . . having easy access to refills might be pivotal. If I had to take the bottle in for refills, I may opt for more capacity to minimize the inconvenience.

What is your in-hangar O2 refill equipment? Is it something that's available to us po-folk?
 
What is your in-hangar O2 refill equipment? Is it something that's available to us po-folk?

2 large welding O2 bottles, a cascade hose, a whip with a valve and you're done. Priceless for the long distance travelers. Useless for remaining in the pattern.
 
On in-hangar refills, check that your insurance company will cover you if there's ever an accident. It's one of those special clauses we never think about until we need them...

I have a local scuba shop that will refill a small o2 cylinder for $8 (our aviation cylinders are basically the size of a small medical o2 cylinder or scuba rebreather cylinder.) I considered a cascade system to refill but the math showed it paying itself off in something like 7,000 years :)
 
Requirements

To clarify, I am seeking thoughts on the size cylinder for the aircraft. The primary use case is for two people for longer trips, where we will also be taking 50-60 lbs of baggage. This leaves me with enough useful weight for a cylinder in the back or potentially the forward mounting locations mentioned. As for refills at my home base, I have easy options. Thanks for the input!
 
Forward mounting option

I have the AL-248 and have it mounted forward of the seats on the high pressure fuel pump cover with MH supplied clamps. The controller is velcroed just forward of the fuel selector. Everything is in view and easy to access in flight and quickly removed for refills or when not on a trip.

Merrill

Photo’s? I like this option for the reasons you stated and also helps my cg.
 
ok, cylinder sizes... I have 3 and may be picking up some more. Cylinders are cheap:

  • M4 - This one is usually in the plane all the time. It's small and light and it's there if I'm every flying and decide to go higher. Or if it's night time and I feel like putting on o2.
  • M9 - This one is around for the usual continental-US trip. It's big enough that the two of us should have sufficient o2 for almost anything, and it's easy enough to get a fill in a pinch in CONUS.
  • D - This is the international cylinder. Gets us 6hrs each at 15k which is usually enough for almost anything. We used 2/3 of it flying over the Mexican plains at 13-14k last month

I'm tempted to replace the M9 & D with a pair of CFFC or KF ones. I'm watching the auction sites to see if anything comes up.
 
ok, cylinder sizes... I have 3 and may be picking up some more. Cylinders are cheap:

  • M4 - This one is usually in the plane all the time. It's small and light and it's there if I'm every flying and decide to go higher. Or if it's night time and I feel like putting on o2.
  • M9 - This one is around for the usual continental-US trip. It's big enough that the two of us should have sufficient o2 for almost anything, and it's easy enough to get a fill in a pinch in CONUS.
  • D - This is the international cylinder. Gets us 6hrs each at 15k which is usually enough for almost anything. We used 2/3 of it flying over the Mexican plains at 13-14k last month
I'm tempted to replace the M9 & D with a pair of CFFC or KF ones. I'm watching the auction sites to see if anything comes up.


Interesting...are you using a demand-type regulator? Or a plain old $25 CGA870?

That AL-180 cylinder that MH sells is basically an M6. They're all over the web for about $50-$70.
 
Forward Mounting Option

Hi Mitch,

Could not find any old pics of my O2 installation and since I'm doing the Condition Inspection, everything is a little apart. So, I mocked up the installation. I did put doublers under the cover for the bolts/nuts.

Merrill
 

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I don't know about the -8; on the -10 the long, narrow E size fits nicely between the seats, on top of the center tunnel.
 
Elegant solution

Hi Mitch,

Could not find any old pics of my O2 installation and since I'm doing the Condition Inspection, everything is a little apart. So, I mocked up the installation. I did put doublers under the cover for the bolts/nuts.

Merrill

Merrill,

Thanks so much for the photos and added details. That is a very elegant solution and I think I will be applying your modification.
 
The regulators seem to be the expensive part. I can't see a reason to use other than a $25 regulator from Amazon on a $50 M6 aluminum tank. Two liters per minute through a $2 nasal cannula, and refill for $5 at your local welding shop.

Am I missing something other than some kind of panel-mounted doodad with flashing lights? Mojo Mike spent $3000 on his O2 setup. That seems crazy to me.
 
What is your in-hangar O2 refill equipment? Is it something that's available to us po-folk?

A friend gave me his 3-bottle cascading system as Scott described. After that, because I'm single and I don't answer to anyone about how I spend my money, I bought a Hydraulics International Gas Booster (p/n 3G-SS-20).

This is an air compressor driven pump that takes oxygen from my big bottles and packs it into my little oxygen bottle at 20 times whatever my air compressor pressure is set at. If I use 100psi to drive the gas booster, I get 2000psi in my aircraft O2 bottle. I can then use each big welding gas bottle down to around 300psi which means a BUNCH of fills from each bottle.

From a purely financial standpoint the cost of entry is not justifiable. That's pretty much the story of my life. :) I'm a tool and gadget junky so I have many things that fit this description... and I'm OK with that! If we were all 100% practical, we'd also be driving a white 4 cylinder Honda Civic and we wouldn't own airplanes.
 
The regulators seem to be the expensive part. I can't see a reason to use other than a $25 regulator from Amazon on a $50 M6 aluminum tank. Two liters per minute through a $2 nasal cannula, and refill for $5 at your local welding shop.

Am I missing something other than some kind of panel-mounted doodad with flashing lights? Mojo Mike spent $3000 on his O2 setup. That seems crazy to me.

You are not missing anything. 2L/min is a lot. We wear pulse-ox finger sensors and adjust the flow accordingly. 1L/min is usually enough. Sometimes 1.5, so get a mini pediatric regulator that gives you the finer adjustment down low. I think mine does .25, .5, .75, 1, 1.5, 2, 2.5, 3, 4, 5.
 
I run the MH with a 14cu ft tank 'D' AL415 mounted on the baggage sidewall behind the CP seat. Fit perfect and I can reach over and turn it on/off while flying.
 
You are not missing anything. 2L/min is a lot. We wear pulse-ox finger sensors and adjust the flow accordingly. 1L/min is usually enough. Sometimes 1.5, so get a mini pediatric regulator that gives you the finer adjustment down low. I think mine does .25, .5, .75, 1, 1.5, 2, 2.5, 3, 4, 5.

Pediatric regulator! Great tip, thanks.
 
My RV-9A has a baggage shelf (an easy enough project) and the oxygen bottle lives atop the shelf with appropriate attachments so that it won't roll. The key is to be able to reach and turn the valve on and off in flight.

I usually an solo when I fly with oxygen, so I put the bottle on the right side of the airplane and don't have to worry about it smacking me up side the head in case of forced landing. I do not clamp it down. If I was flying with two on board, I'd probably remove the shelf and put the oxygen bottle in the baggage compartment.

The advantage of pulsed oxygen delivery is that you can fly more hours between fill ups. Sometimes it's hard to get oxygen if you run out, out in the sticks.

As for cheap oxygen regulators... how do those compare with aviation regulators in terms of pressure (altitude) compensation, reliability in the aviation environment, etc? Seems like the wrong place to save a few bucks...
 
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As for cheap oxygen regulators... how do those compare with aviation regulators in terms of pressure compensation, reliability in the aviation environment, etc? Seems like the wrong place to save a few bucks...

Those regulators provide flow regulation, not pressure. Pressure regulation might be convenient, but is mostly unnecessary and less reliable. Flow will change with altitude and does require that, when changing altitudes, you'll want to check the flow rate every so often. Also, as noted above, it's smart to keep a close eye on your O2 saturation (true no matter what kind of O2 setup you have).

The advantage of pressure regulation is convenience. Expensive regulators will provide that, as well as pulsed O2 delivery, and some will have a demand function. Those things provide more efficient use of the O2 you have on board and therefore less expense relative to how often a fill is necessary.

In the budget O2 topic, probably a more relevant discussion is what kind of oxygen to use. Almost all bulk oxygen is USP oxygen, including welding oxygen. The difference is that some uses indicate tank evacuation during fill to remove potential contaminating particles, and aviation oxygen which has a dehydrating step to reduce the potential for regulator freeze-up at really high delivery flow rates. That's not going to be an issue in the 1 - 4 liter/min range.
 
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As for cheap oxygen regulators... how do those compare with aviation regulators in terms of pressure compensation, reliability in the aviation environment, etc? Seems like the wrong place to save a few bucks...

The technology behind them is the same. These are medical devises that people rely on to save lives every day. Using your logic, flying a plane someone built in a garage is not a good area to save a few bucks.
 
Ox tank

I have this system and have been extremely happy with it. I got the AL-180 bottle and that much O2 lasts a shockingly long time with the pulse demand thing going. Probably sufficient for most users. I get it refilled at a scuba shop.

I carry my tank in the case provided, strapped to the "center console"/flap motor housing.

I am likely going with the Mountain High O2D2 EDS system and am looking for recommendations on cylinder size for the RV7. Wanting to find the sweet spot that balances duration and cylinder size/weight in the baggage area.
 
I run the MH with a 14cu ft tank 'D' AL415 mounted on the baggage sidewall behind the CP seat. Fit perfect and I can reach over and turn it on/off while flying.

Walt - Can you post a picture of your tank mounting? I have the same MH setup & so far have just strapped the tank in the provided carrying bag into the otherwise empty copilot seat. Hoping to get my wife to fly across the country with me soon, and she will need that seat!

Also, if you use the O2D2 unit, where & how do you mount it?

Thanks,
David
 
Walt - Can you post a picture of your tank mounting? I have the same MH setup & so far have just strapped the tank in the provided carrying bag into the otherwise empty copilot seat. Hoping to get my wife to fly across the country with me soon, and she will need that seat!

Also, if you use the O2D2 unit, where & how do you mount it?

Thanks,
David

I'll grab a pic of the tank tomorrow, you can see the 02D2 mounted below the eng quadrant in this pic. Perfect location as I can plug in and operate easily while flying and all the hoses are out of the way.

i-GQ5p7m5-M.jpg


2021032014015277-6601226943706036358-IMG_1389_HEIC-XL.jpg
 
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Walt - thanks for posting the pictures.

The location under the control quadrant is perfect. My fire extinguisher occupies that spot today, I may have to find a new home for it.

I can see how the top tank bracket is attached to what appears to be a new panel forming a nice storage pocket. Is the bottom bracket mounted the same way? Is that panel riveted or screwed into place?
 
Walt - thanks for posting the pictures.

The location under the control quadrant is perfect. My fire extinguisher occupies that spot today, I may have to find a new home for it.

I can see how the top tank bracket is attached to what appears to be a new panel forming a nice storage pocket. Is the bottom bracket mounted the same way? Is that panel riveted or screwed into place?

Brackets are screwed onto the riveted panels, and the top side pocket was an added benefit of installing the panel which was mainly to support the tank installation.
 
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