Does the W&B include the O2 bottle filled or not

[Parker_Woodruff]

Does anyone know if when Mooney weighs the aircraft at the factory if they include the O2 bottle filled or unfilled?  The compressed O2 adds a few pounds of weight.  Maybe someone here can calculate the difference.

I've been meaning to ask this question for quite some time but happened to remember it while sitting in front of the computer.

[smwash02]

115 cuft of O2 is 10.26lbs.

I would expect the tank to be empty since it can all be drained and all can be used.

[carusoam]

Add to SMW’s excellent response....
 

1) Fantastic technical question...

2) Expect it to be similar to a fuel tank....

3) When it is empty, it has unusable O2 in it still...

4) Further... It would require drawing a vacuum to remove all of the O2....

5) At that level of accuracy, you would have to account for the altitude you were flying at to count most of the unusable part...  similar to buoyancy in an altitude varying density column...

6) Compare this to when you do the WnB... do you account for the level of oil in the engine’s sump...?  Or do you always fill the sump to the same place prior to flight?

7) Technically, the WnB is important for each flight  weight inside the bottle can be estimated pretty closely by using the pressure inside the bottle...

8) You get extra credit for the buoyancy calculation...  

You really know your stuff if you include the un-usable O2 in the calculation, as the pressure gauge has a redline for its unusable level... (?)

 

9) Technical question part 2.... if you are flying around draining fuel from the tanks because of an emergency situation.... you may be dumping weight... but you are also dumping flammable materials....

10) If dumping flammable materials... consider off loading the O2 as well...

 

Now to find a chart of weight of O2 vs. pressure, for your tank...   and an accurate Cg for the tank’s volumetric Cg...

I have not seen O2 included in any WnB calculations...  it is a tank, like fuel and oil...  it has a Cg, and an unusable aspect to it...

 

This would be an even more interesting question for people flying a Brand B aircraft... where the balance can fall outside of the envelope as fuel gets emptied...  even a portable O2 bottle could be art of the true WnB calculation...

 

PP thoughts only, not a CFI...

Best regards,

-a-

[smwash02]

9 minutes ago, carusoam said:

3) When it is empty, it has unusable O2 in it still...

4) It would require drawing a vacuum to remove all of the O2....

Great points. I 'simplified' the answer since I wouldn't expect anyone to go to those lengths. The unusable removed would be quite small unlike the oil/fuel weights.

Edited April 22, 2021 by smwash02

[Parker_Woodruff]

1 hour ago, smwash02 said:

115 cuft of O2 is 10.26lbs.

I would expect the tank to be empty since it can all be drained and all can be used.

at what PSI?

[smwash02]

7 minutes ago, Parker_Woodruff said:

at what PSI?

"At what temperature?" would be the retort.

I've attached a snip from the service manual that shows what the pressure reading should be by temperature for a full tank.

[MIm20c]

Parker, if I get ramp checked and asked for my O2 pressure as he pulls out a calculator I’m going to be pissed

[carusoam]

Sounds like an interesting question for the Mooney factory if you want to visit their site... or the usual tech guys like @Blue on Top and @PT20J...

Best regards,

-a-

[A64Pilot]

I believe that a cu ft of a gas will be a cubic foot regardless of temperature, pressure will rise with temperature, but it’s mass won’t.

I’m sure the aircraft is weighed empty, the O2 bottle can hold 10 lbs as can the hat shelf, but both are empty.

Aircraft aren’t weighted to such exacting tolerances to begin with, the scales just aren’t perfect. Military weight cells for weighing OH-58’s had a plate on them saying the were accurate to 10 lbs or .1% whichever was greater, so you could weigh an aircraft perfectly and be 30 lbs off.

‘We would raise and lower the aircraft four times zeroing the scales each time, throw out the weight that was furthest off and average the three, about as good as you can get, but airplanes I’ve only seen weighed once.

‘It’s sort of a measure it with a micrometer, mark it with chalk and cut it with an axe kind of thing.

Meaning that the O2 bottle weight is an intelligent question as it’s back in the back isn’t it? If so then with that arm 10 lbs could be significant.

‘Great “Stump the Chump” question for check rides.

Edited April 23, 2021 by A64Pilot

[201er]

What’s heavier? A pound of air or a pound of compressed air?

[kortopates]

Just look at your equipment list in the weight and balance section to see what weight they used for your bottle. You can look up the filled and empty weight on the internet to tell - but your installed weight will include the regulator - but I am sure you can still tell.


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[PT20J]

Interesting question. I don’t think there is a specific requirement. There is nothing in FAA-H-8083-1B (Weight and Balance Handbook) about it. There is also nothing in the W&B section of the AFM about it for a M20TN. Mooney likely weighs with the bottle empty to get the lowest empty weight. One could certainly argue that the oxygen gas is part of the payload. After all, it is not required for all flights.

To be certain, I’d email support@mooney.com and ask.

Skip

[A64Pilot]

I would assume due to safety concerns that the bottle isn’t filled until very near the end of the assembly line, same with fuel.

‘Aircraft weighing is done before fuel is added, usually engine oil and unusable fuel etc are calculated not added prior to weighing

Often once an aircraft is fueled, from a fire safety standpoint, the requirement for fire extinguishing systems etc change, It may be as Oxygen is of course an accelerant that it’s treated similarly.

‘For you guys with icing fluid tanks, I assume the fluid is not included in basic aircraft weight? I’d expect O2 to be the same?

[MikeOH]

As a pragmatic, practicing, engineer...NOT a theoretical physicist, I'm going to worry about this when I believe that the weight shown on the W&B for my 50 year old airplane is accurate to 10 lbs

[Mcstealth]

TKS is weighed with a full tank.

Just poking the bear here.

[jlunseth]

A pound of compressed gas weighs a pound, but a volume of compressed gas weighs more than the same volume of gas that is not compressed.  If you want real world experience just lug some scuba tanks around.

[exM20K]

9 hours ago, Mcstealth said:

TKS is weighed with a full tank.

Just poking the bear here.

Not necessarily.  You must check the equipment list for a particular plane.  There is a line item for full fluid, but in my case, it isn’t checked.

the photo will prolly post upside down or sideways, but I’m counting on @carusoamto fix it for me!

[A64Pilot]

Usually consumables are not included in the basic weight, as they are consumed in flight, fuel for instance. Oil is included even though some may be consumed, it’s not much.

By including the line item of what it weighs full they are of course giving you that information 

[Blue on Top]

All y'all are funny and great at the same time .  

There is a difference between BEW (Basic Empty Weight) and BOW (Basic Operating Weight).  BEW includes all unusable or undrainable fluids.  BOW includes fluids and equipment in the normal operating state (engine oil at full; full O2, if planned on using; full TKS fluid, again if planned on using; charts/manuals/etc.; pilot, again if planned on using, etc.)

O2 is probably not serviced until in Production Flight Test where it is actually verified that it works.