Presurization - Whats it take ?

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pictsidhe

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The year before last I had my first Sailplane ride. It was great other than I had a headache for several hours after the flight. This may have been for a couple different reasons or a combination or the two. This matter got me thinking along the lines of pressuring aircraft because I didn't want my ambitions to fly planes dashed. The matter may be a non-issue for me but regardless I think I may have thought of a pretty revolutionary way of pressuring a craft with very little weight and perhaps the best part is it would allow for aircraft shape non-conforming to pressurize standards (non-circular) cross-sections. Probably not actually revolutionary but it would simply be to build a pressure vessel separate from the airframe to house pilot/passengers. Would allow for more flexibility in design of aircraft hull shape as well as and perhaps most importantly un-coupling of other components such as wings or control surfaces and the need for robustness of design/materials in what would be these areas.
I believe BoKus high altitude sailplane was designed like that.
 

pictsidhe

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I'm good with that .... lol

Heck no. I was just curious after watching a recent project on YouTube and started trying to do some real research on the subject only to find little to nothing on the internet about how light GA air frames and successful home builts actually accomplished it and what is involved in structures and systems.

It seems to me the systems part is fairly easy following the IV-P path of using off the shelf components from a P-Baron or Malibu, et. al. But couldn't find anything on what to expect around door frames, window sealing methods, door latching, areas of known fuselage weakness, windshield and window thickness, control pushrod and cable sealing, pressure vessel pass through best practices, ect. ect. ect.... There's just nothing out there that I could find beyond a couple of artcls about the IV-P and they were scant on details.
You'll need to do the structure yourself. The forces you'll need to contain are so large you'll have to optimise everything.
 

Dan Thomas

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The year before last I had my first Sailplane ride. It was great other than I had a headache for several hours after the flight. This may have been for a couple different reasons or a combination or the two. This matter got me thinking along the lines of pressuring aircraft because I didn't want my ambitions to fly planes dashed. The matter may be a non-issue for me but regardless I think I may have thought of a pretty revolutionary way of pressuring a craft with very little weight and perhaps the best part is it would allow for aircraft shape non-conforming to pressurize standards (non-circular) cross-sections. Probably not actually revolutionary but it would simply be to build a pressure vessel separate from the airframe to house pilot/passengers. Would allow for more flexibility in design of aircraft hull shape as well as and perhaps most importantly un-coupling of other components such as wings or control surfaces and the need for robustness of design/materials in what would be these areas.
The pressurized airplane's wings are no different from the non-pressurized, other than being a bit stronger, maybe, to carry the heavier airplane. It's the fuselage that's different, specifically that section that houses the occupants, and a separate pressure vessel inside a fuselage would result in redundant structure. That would add weight, cost and complexity, which is why even airliners don't do that.

As mentioned earlier, start figuring how much force is applied to the inside of a cockpit when you have 3 or 4 PSI in it. That's three or four pounds against every square inch of it. Tons and tons, and if it isn't strong enough to take it the airplane just explodes and ruins your day.
 

rbarnes

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All this to avoid wearing a mask (or just a nasal cannula)?
Of course not, I understand why very few do it.... but you can't find anything definitive on the subject beyond "It's not worth it" .... "It's too hard".... "Dont waste your time".

What are the real structural reinforcements needed ?
How would you go about figuring out where you would put them ?
How would you design the door latching system ?
How would you design the window sealing system to allow for hull expansion ?
Same for the door ?

It's not like I have an RV-10 in the garage I'm dreaming of pressurizing. I'm just looking for some real world answers beyond.... "It's too hard to bother with"
In the magical fairy land of unlimited funds and resources how would you go about doing it ?
 

pictsidhe

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What are the real structural reinforcements needed ?
How would you go about figuring out where you would put them ?
How would you design the door latching system ?
How would you design the window sealing system to allow for hull expansion ?
Same for the door ?


In the magical fairy land of unlimited funds and resources how would you go about doing it ?
In the magic fairy land, same as people do in this one. As has been said, you need to analyse the problem before any solutions could be proposed. Without knowing the forces, no suitable structure can be designed. What is needed is totally dependent on the specific design. That's shape and size. Yes, you should be able to copy the general operation of someone's door latch etc. But you will still need to redesign it for your fuselage. Unless you are using the whole door and frame from a donor plane. Even that will not work if your fuselage is much different in size or shape.
 

Vigilant1

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In general:
Small openings
Make the pressure vessel simple and as small as practical
Composite construction could be very attractive due to strength/weight, ease of making compound curves, airtight.

There were a couple of other threads a few years ago on this (search for thread titles with "pressurized", etc). There weren't detailed formulii, structural calcs, etc.
Building a partial pressure suit might be simpler and more reliable.
 

wsimpso1

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The systems for a turbocharged airplane are remarkably simple, especially if you already have adequate air conditioning. No need for fancy regulators on the supply side, just a sonic nozzle and the outflow valve does the cabin pressure regulation. Most parts probably off the shelf.
The structure and leakage control is the hard part.
No heat exchanger?
 

Volzalum

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In the brainstorming arena, could you create the second barrier similar to a balloon? Cheap party balloons start at about 14 psi. So could you create a strong enough/light enough membrane with lightweight bands (kevlar or carbon fiber) to keep the shape of the membrane regardless of pressure without transferring the pressure loads to the outer shell?
 

rbarnes

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In the brainstorming arena, could you create the second barrier similar to a balloon? Cheap party balloons start at about 14 psi. So could you create a strong enough/light enough membrane with lightweight bands (kevlar or carbon fiber) to keep the shape of the membrane regardless of pressure without transferring the pressure loads to the outer shell?
That's an interesting idea using something like a spray on polyurea coating on the inside of a composite structure.

 

Tiger Tim

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I’m no engineer, but:

What are the real structural reinforcements needed ?
Pressure differential will prefer your pressure vessel is a sphere, if it isn’t a sphere then you’ll need to beef it up to resist that. Jetliners have cylindrical fuselages and dome-shaped pressure bulkheads at either end. Smaller aircraft have flat pressure bulkheads with reinforcing ribs across them which ought to be a bit heavier but easier to make and take up less space.

How would you design the door latching system ?
I’ve seen cases where multiple large pins are used around the perimeter (non-structural door hinges), beefy structural hinges with latches opposite, Fairchild Metros have a row of giant glorified Clecos across the lower edge of the cargo door, or you could go with a plug-type door that opens inward (though that one costs internal volume to open and close).

How would you design the window sealing system to allow for hull expansion ?
Same for the door ?
Windows usually install from the inside so any pressure just pushes them tighter into their frame. Doors can open inwards which makes for an easy-ish seal, or they often have an inflatable seal around their perimeter.
 

rv6ejguy

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Of course not, I understand why very few do it.... but you can't find anything definitive on the subject beyond "It's not worth it" .... "It's too hard".... "Dont waste your time".

What are the real structural reinforcements needed ?
How would you go about figuring out where you would put them ?
How would you design the door latching system ?
How would you design the window sealing system to allow for hull expansion ?
Same for the door ?

It's not like I have an RV-10 in the garage I'm dreaming of pressurizing. I'm just looking for some real world answers beyond.... "It's too hard to bother with"
In the magical fairy land of unlimited funds and resources how would you go about doing it ?
I'd copy the Lancair IV-P layout, door, windows etc.. They did it for only 200 pounds extra which I think is pretty reasonable and it seems reliable.
 

Dan Thomas

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Of course not, I understand why very few do it.... but you can't find anything definitive on the subject beyond "It's not worth it" .... "It's too hard".... "Dont waste your time".
There are VERY few pressurized light singles. Not even a lot of pressurized piston twins. And why would that be?

-Cost
-Weight
-Increased complexity (which causes some of that increased weight and cost)
-Increased maintenance time and costs

Add the fact that pressurization permits much higher cruising altitudes, so besides the IFR ticket, you's also need de-ice or anti-ice equipment or be stuck with flying high only on the clearest days.

So we end up with an airplane that needs more power, that costs a lot more to buy or build, and that costs more to maintain and insure. In aviation, the costs of buying and owning and/or flying even a basic two- or four-seater is plenty high already. More expensive stuff just doesn't sell well in any volumes. Homebuilders often build rather than buy because they can do it for less, as long as they stay within reason.
We're often asked the same "why?" questions about the lack of available diesel engines or FADEC or engines with electronic ignition or EFI. Why are brand-new airplanes still coming with magnetos and mechanical fuel injection? Some still come with carburetors! Well, you can buy a brand-new 230 horsepower SMA diesel engine, certified, with FADEC, for around $80K, I think. Lycoming builds the iE2, and it has EI and EFI, and I don't know what it costs except that new airplanes aren't coming with it installed, which says something.

Money. Always money. What causes lift and thrust? Money.
 

Jerry Lytle

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Does anyone remember when Moony beat every one to the market with the first pressurised light plane? The Mooney Mustang, certified in 1966. Long time passing.
 

wrmiles

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No heat exchanger?
Pressurized piston aircraft I am familiar with (but been retired for 18 years) don't use a heat exchanger. Pressure ratio is low enough that air conditioning is enough. P210 did use a crude exhaust to bleed air heat exchanger for heating. Twins used combustion heater. Turbines use a heat exchanger with A/C or an ACM.
 

BoKu

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I believe BoKus high altitude sailplane was designed like that.
Kind of that but inside out. There was to be a structural cockpit that supported the crew, controls, instruments, etc, and then a separate pressure shell that slid aft over all that stuff and attached to the aft pressure bulkhead with a bayonet mechanism. The cross-sections were indeed all circular, though longitudinally it had some camber to improve forward visibility. Since the pressure shell reacted only pressurization forces, it could be (relatively) light.

The trouble with having separate pressure and structural systems is that it violates the principle of having every part do multiple jobs. That doesn't mean it's bad or that you can't do it, it just means that there are probably lighter ways of accomplishing the same thing, so it should be used with caution. In the case of that sailplane, I wanted to minimize the seal perimeter and simplify the transparency installation to the degree practical.
 
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