Airplane oxygen refills

[Ian]

I was wondering what the best valve types and cylinder sizes for oxygen were. And is getting refills for your own cylinders available in Australia or more specifically Canberra or Sydney. The market appears to be dominated by companies only doing refills on their own cylinders. The US market cylinders have CGA-540 male fittings and the Australian market has CGA-540 female fittings.

If I bought pin indexed CGA-870 valved cylinders am I going to be able to get them filled with industrial/veterinarian oxygen?

 

There's an interesting article on the supply of oxygen here https://www.avweb.com/features/pelicans-perch-13getting-high-on-welders-oxygen/

Not sure that it's true but it's food for thought.

 

I've always thought that the options that oxygen provides would be beneficial

There are a few more articles on oxygen here

https://www.kitplanes.com/homebuilt-o2/

https://www.kitplanes.com/military-oxygen/

https://www.kitplanes.com/how-to-use-your-oxygen-system/

[KRviator]

The other alternative - if you are use it routinely - is to get rid of the cylinder and use an oxygen concentrator like the Inogen G-series. Kitplanes did a writeup on their early ones in 2010 and I've been thinking about it for the RV. You can pick up a G3 for well under $2K on Gumtree.

They are mostly single-place units though, so it depends on your intended use. OVer time it'll be cheaper and less hassle than refilling cylinders - cheap as that may be - but you'll need 2 if you plan on flying high with a Coey repeatedly.

[Ian]

2 hours ago, KRviator said:

The other alternative - if you are use it routinely - is to get rid of the cylinder and use an oxygen concentrator like the Inogen G-series. Kitplanes did a writeup on their early ones in 2010 and I've been thinking about it for the RV. You can pick up a G3 for well under $2K on Gumtree.

I was never sure how the non-aviation O2 concentrators coped with altitude, for example the "Inogen One At Home" system is rated to 8000 feet". Even with an oxysaver cannula you need about 1.6L/m to maintain blood oxygen. https://www.peter2000.co.uk/aviation/oxygen2/index.html

If someone want to buy and test them that would be good 🙂

 

[facthunter]

Inhaling Pure O2 is not good for your health..  Nev

[Ian]

21 minutes ago, facthunter said:

Inhaling Pure O2 is not good for your health..  Nev

Like many things it depends on the dose, oxygen toxicity results from inhaling oxygen as higher partial pressures, so inhaling higher concentrations of oxygen at altitude is a good thing if the partial pressure is equivalent to sea level oxygen. 100% oxygen at sea level not so good, even worse if you're diving. U2 pilots have been doing it for decades however their problems recently have related to the bends due to higher operational tempos.

https://www.smithsonianmag.com/air-space-magazine/killer-at-70000-feet-117615369/

With the little blood oxygen sensors becoming readily available you can monitor your oxygen levels with little trouble. Even simple maths can become harder at altitude.

Edited March 15, 2023 by Ian

[facthunter]

Carried it In PNG but never used it at levels up to   FL 180. Bends is caused by Nitrogen bubbles  generally but at very high altitudes you would need a version of a pressurised space suit. Pretty sure CASA would have the details of a required system. An imported (from USA) Twin Comanche I owned had an oxygen system in it as it regularly operated over the Rockies in NW USA. The Motors were factory turbocharged as well. You'll run out of puff at around FL140 without it.. I had to do a course on Hypoxia and a baro chamber as part of a pressurisation endorsement. Nev

[skippydiesel]

In Australia, without a half decent mountain range, like the Alps/Rockies/Himalayas/ Andes/ PNG Central Cordillera,/etc,  I can understand why some (commercial/jets/etc) aircraft might want to fly at altitudes where O2 supplementation or pressurization might be desirable but why would your average  recreational pilot want to do so ? Sure getting over weather might be  desirable when "the moon is blue" but then you can always decide not to fly that day.

[Ian]

There's a few reasons.

• Oxygen improves awareness even at lower altitude, fly to 10000 feet and take a few maths questions, you'll be surprised at how slow you become.
• Speed, efficiency and angle of attack, your most efficient speed occurs at the optimal angle of attack so you can minimise flight time and fuel burn by going high.
• weather, sometimes the weather is just bad on the way and good at either end. A bit of altitude might be all you need.
• Some people swear by the fact that oxygen makes them feel more refreshed even after a flight below 10000.
• Tailwinds.
• 

Edited March 18, 2023 by Ian

[facthunter]

Without supercharging most pistons will struggle above about FL 120. Some of the worst weather conditions  (icing and turbulence) are around FL 180. The average/standard adiabatic lapse rate is 2 degrees/1000'. On very hot days with high surface temps in the desert/inland, the turbulence at the lower levels(caused by convection) will go higher as the day progresses and be abv FL120 by mid afternoon. At such times you might get an advantage to keep above it but you will be in it at climb and descent and would be better just flying earlier in the day.. Use the adiabatic rate to calculate the freezing level.  It's spelled out on the forecast. Above that any precipitation will cause airframe icing which can be rapid and really raises your weight and increases the stall speed and increases drag often making it impossible to hold a safe height. Light aircraft do not have adequate de icing systems at all except from carb heat. Prop ice can make it impossible to read the instruments due to the vibration. You have to find warmer air and quickly or be sure of being able to stay clear of cloud or any chance of supercooled rain drops falling... Nev

[Ian]

The graph shows a defiant which is NA and while the rate of climb is slowing it remain adequate up to FL180.

On 18/03/2023 at 6:47 PM, facthunter said:

Light aircraft do not have adequate de icing systems at all except from carb heat. Prop ice can make it impossible to read the instruments due to the vibration. You have to find warmer air and quickly or be sure of being able to stay clear of cloud or any chance of supercooled rain drops falling... Nev

Agree completely on the risks associated with icing, weather and the lack of effective mitigations on GA aircraft.

 

It's somewhat ironic that on planes where rejecting heat is often an issue that the cold is a problem in other areas.

[skippydiesel]

As I understand it; In Australia, recreational pilots are overwhelmingly VFR and are limited to 10,000ft ceiling.  Contemplating flight above his level or in marginal weather, is either a fun academic debate or a declaration of intent to join the IFR crowd.

 

I am sure the challenge of obtaining an IFR rating is a worthy one, however it comes at significant cost (in training, maintaining & operating IFR rated aircraft). 

 

In my mind there are three reasons why very few Australian recreational pilots go for the IFR rating;

• The financial hurdle is a big one, as is the continued maintenance of the rating - if you are not being payed to fly IFR, whats the point?
• Australia is usually  blessed by great (VFR) flying weather - how often will a rec pilot actually need (as apposed to want) to file IFR?
• Recreational pilots can always decide to fly another day - no pressure to fly in marginal weather

 

 

[Ian]

49 minutes ago, skippydiesel said:

As I understand it; In Australia, recreational pilots are overwhelmingly VFR and are limited to 10,000ft ceiling.  Contemplating flight above his level or in marginal weather, is either a fun academic debate or a declaration of intent to join the IFR crowd.

There's no requirement for IFR, IFR is required for class A airspace which is

• Above FL245 outside radar coverage
• Above FL180 within radar coverage

So the opportunity to expand your horizons is simply limited by oxygen and your aircraft.

 

The chart below is an example of a really good resource provided to the flying community.

https://www.casa.gov.au/australian-airspace-structure

 

[onetrack]

I would've thought that adding extra weight in the form of oxygen equipment to an ultralight (RA-Aus registered) aircraft - which is already seriously limited in its payload capacity - would have been something to avoid.

[facthunter]

There's nothing more boring than sitting at high Levels and moving as if you're stopped. You just won't get UP there either without supercharging and the OAT will require cabin heating.   Nev

[Ian]

One think that people don't appear to understand well is how altitude impacts efficiency.

You will burn the same amount of fuel regardless of your altitude if you are flying at your best L/D ratio ie best glide ratio.

Your most efficient flying speed is your best glide speed which is generally a bit slow so people fly much faster and burn lots more fuel. This best glide speed is your optimal  angle of attack at which drag is lowest.

However you best glide speed increases as your altitude increases, effectively your drag remains constant so the higher you go the shorter your trip time. However your fuel burn remains constant (ignoring climb and descent phases)

Energy = Force X Distance  (drag is constant and Distance is constant so energy remains the same)

 

There are a couple of flies in the ointment through, engines lose power as altitude increases limiting your maximum altitude and secondly your flutter speed Vne remains at altitude even though the air is thinner.

 

The other fly in the ointment is where to buy oxygen at a price at low cost. Unfortunately there doesn't appear to be many options.

[facthunter]

Ground NM's per Litre is what counts and that takes headwinds etc into consideration.  Pistons don't usually get a lot of advantage going high. Jets do and avoid low levels. Your plane will have a service ceiling and an absolute ceiling. You can't ignore the OAT when it's well below zero. You'll freeze. also if you have a fire or an emergency you take a long time to safely get down. You don't see much either.   Nev

[Ian]

12 minutes ago, facthunter said:

There's nothing more boring than sitting at high Levels and moving as if you're stopped. You just won't get UP there either without supercharging and the OAT will require cabin heating.   Nev

I agree that it might be a little monotonous, however the image posted earlier is a NA plane climbing to 17500 pretty easily and if you're going from point A to B you might be willing to accept the monotony.

The longez service ceiling is 27000 feet which is also a naturally aspirated plane https://en.wikipedia.org/wiki/Rutan_Long-EZ

Cabin heat or being impervious to the cold might be a good idea. 

 

Zooming along at low levels is a lot of fun however there are risks associated with not having altitude. Altitude also gives you more options especially if you're flying over unforgiving terrain, your options increase at the square of your altitude,  Low = Increased risk.

 

[facthunter]

At the level you quote the engine would be delivering about 30% of its max sea level power.. Nev

[Ian]

6 minutes ago, facthunter said:

Ground NM's per Litre is what counts and that takes headwinds etc into consideration. 

Headwinds and tailwinds are a factor however that's a bit of a red herring. By being able to use altitude you can fly high to get/avoid a tailwind/headwind. I'm not saying always fly high, however having more options provides advantages.

Pistons get just as much of an advantage in trip time as a jet (up to a point), aerodynamics and physics don't change. However the limitations are Vne so the airframe designer simply hasn't made the airframe safe at speed and you also start running into the limitations of propellers and compressibility drag. You can keep stacking on compressors or use higher compression pistons to compensate.

The key point is that a given airframe + load will use a set minimum amount of fuel per NM and this is dependant upon the minimum L/D. By going high you can reduce your trip time using the same amount of fuel.

The attached article provides more concisely argued stance.

 

To reduce your fuel consumption below this point requires you to change the physics of your plane. Ground effect is one way to do this and this was used by WW2 pilots getting home with low fuel.

 

ps Jets are a bit different because turbines can't throttle like piston engines, their efficiency falls off a cliff. So they need to run near full power and hence they need to fly as high as they can to maintain the best angle of attack.

Piston Airplane Cruise Performance.pdf

[facthunter]

Ground NM's/ unit of fuel are EVERYTHING in operating long distance aircraft. Everything's to save fuel and time in that order but saving time saves fuel. also and airframe engine time. When holding all planes operate at much less than full power. There's a speed limit in holding patterns and the idea is to be able to hold for as long as you can rather than divert. to some other place no one wants to be at.  This is day by day management by line pilots and part of the job.  IF you can't do it you will be gliding silently at some stage. and get a DCM. Don't Come Monday.  Nev

[skippydiesel]

29 minutes ago, Ian said:

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Hi Ian,

 

Not being "the sharpest tool in the shed" , I ask the following:

 

I fly a Sonex/Rotax 912ULS - how can I find the most efficient touring altitude for my aircraft (accepting this will change with temperature). Efficiency, in this case, takes into account such human weaknesses as bladder capacity,  the need to get to a destination (that has a comfy bed/food & drink) within  my lifetime?

 

I have always accepted 6-7000ft as being the nominal efficient cruise altitude for the Rotax 912 ULS - would you agree?

[Ian]

36 minutes ago, facthunter said:

At the level you quote the engine would be delivering about 30% of its max sea level power.. Nev

Yes I understand physics, however I was simple responding to the comment that

1 hour ago, facthunter said:

You just won't get UP there either without supercharging

Which wasn't quite correct, yes you'll have less power however some piston naturally aspirated planes have high ceilings and do get up there.

[facthunter]

A bit of margin for turbulence is wise too. Turbulence will knock off airspeed as it makes more drag and if you have a reduced margin say less than 1.3 V/s you might get a control problem.. You don't want to be too slow (or too fast). A lot of Jets cruise very close to stall speed both low speed and MMO Mach limit.  UPSETS are more likely when you do this and you certainly can't manoeuvre fast. Nev

[facthunter]

 A FRACTION of the POWER is not JUST a reduction. Historically high flying pistons are always supercharged and mechanically driven ones have multiple speed for the higher levels, Turbos were on the Liberator. 2 speed gearboxes on the DC6b and others like them. I've flown DC4 s over the Hill in PNG without high blower and they should have never been allowed to do that as they struggle with FOUR motors running, let alone make it if you lost ONE.. Nev

[Ian]

1 hour ago, skippydiesel said:

Hi Ian,

 

Not being "the sharpest tool in the shed" , I ask the following:

The article attached previously has a couple of "rules of thumb" which provide information on getting the most from your plane. Simply put it's angle of attack which largely dictates efficiency, going slow at low level or faster at altitude. Big wings and lightweight implies a higher optimal cruise ceiling.

As you go higher the maximum power available to maintain the optimal angle of attack will be the limiting factor. This is what facthunter has been alluding to however hopefully he finds the article a good read. 

The other point is that you can push slightly faster without much of a fuel flow increase and hence a less full blader.  Again as facthunter stated in the real world headwinds/tailwinds impact this however there's also a rule of thumb for calculating optimal speeds.

Edited March 20, 2023 by Ian