Club Homepage Forums The Cessna 150-152 Fly-In Fly-In Questions CPAP in a Tent?

Following the CPAP thread with interest. Don't need one yet, but assuming that I will at some point.

Geoff's comment about CO2 driving respiration got my attention. Going to forward that to the doc I've been talking with.

Aircraft pressurization is based on the limits of the pressure vessel (fuselage) structure. They are designed for a maximum differential pressure between inside and outside (max diff). The engine(s) provide bleed air that flows continuously into the cabin. A calibrated outflow valve lets air out. It's either open or closed. A controller can call for a cabin altitude and the outflow valve holds it. If the cabin altitude desired is too low, the controller is overridden and the outflow valve keeps the cabin at max diff. If the outflow valve fails, there is a second one that takes over. It's pretty primitive - the whole thing is a calibrated leak and goes back to the commercial airliner, Boeing 307 just before we were in WWII.

Max differential pressure is about 8.4 psi. And again, that is pretty much standard throughout the industry. Whether is it Boeing, Airbus, Lockheed, McDonald Douglas, Embraer or Lear etc.

Imagine trying to blow up a balloon to one size in a constant state. With air entering the balloon at one end and then you create a hole at the other end to release just enough of the air to keep the balloon at the desired size you want.

Compressed air off one of the low stage compressors of the engine will supply the cabin with air to both give you climate control and pressurization. And it is pretty much FREE! You are just stealing just a little of the compressed air off the engine. No freon is used in jet aircraft air conditioning systems.

Carbon Dioxide is what controls breathing, not oxygen in and of itself. Interestingly, hyperventilation reduces the amount of CO2 but also changes the chemistry of the blood to tend toward alkaline. This can result in lung damage as well as damage to other organs.

Maybe we should all take a deep breath and think about this some more.

I THINK I read recently that Airbus are looking to increase cabin pressure to lower cabin altitude. So if the industry "standard" is to keep cabins at 10,000MSL - the new standard will be 8,000MSL.

I think the newer composite fuselages allow for the greater differential while maintaining fatigue life of the hulls.

DO YOU GUYS NOT READ WHAT I TYPE!?!?!

I never said anything about 10,000 ft being standard! It has to do with cabin deferential pressure at 8.4 psi. This would put your cabin at about 6,000 ft if you were at FL370. In other words, Denver Colorado field elevation. You would have to go to FL410 or FL420 to get to a cabin altitude of 8,000 ft.

Maximum cabin pressure differential differs with different types of airplanes. For example, the Cessna P210 max diff is 3.35 PSI, so if you're flying above 20,000 feet, the cabin is going to be above 10,000 feet. From what I've seen, airliners have max diff pressures of 7.5 to 9.4 PSI. Rule of thumb is that the cabin pressure is at about 8,000 feet at cruising altitudes. (Which was below the elevation of my house when I lived in Colorado.)

Not on Boeing, Lockheed, Douglas, Airbus and Bombardier. 8.4 MAX psi at altitude. I stand by my statement. I have only been teaching this for 20 years and flying these planes for 20 years...

Ron - I DID read what you said - and I said I THOUGHT I had read that Airbus were making a change.

And YES - I'm all for the fact the aircraft are applying a differential pressure as you state. But for passengers the experience is more in terms of "attitude felt" which is what I THOUGHT I was summarizing.

Dig Dig Dig Dig.....

So to summarize a number of decent looking sources.

Turns out - CONCORD was the first to offer an improved cabin experience over other pressurized airliners. Operating at 60,000ft - the cabin "felt" like 6,000ft. At a time when most airliners were aiming for 8-10,000ft after applying maximum pressure differential to their maximum cruise height. They had a serious differential of 13.6lb applied. No wonder those windows were tiny and thick. I wonder what a decompression event would have felt like at maximum altitude. Serious case of the bends I think.

Turns out I was wrong about it being Airbus. Boeing were next to make a substantive difference with the Dreamliner. Aiming for a 6,000ft experience - and from what I read - not using bleed air. Another benefit of the carbon hull being not having to scrub all the humidity out the air to dry it to help with long term corrosion issues of pressurized wet air on an aluminum hull. Passengers feel less dehydrated after a long trip as the air is moister.

And Airbus were next with the A350.

--

Peace.

So what's the opinion about using a CPAP device in a tent at Clinton?