Presurization - Whats it take ?

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Volzalum

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Come again? A cheap balloon, one you blow up with your own lungs, will have less than 0.5 PSI.
The pressure inside the balloon is roughly 14.7 psi. The pressure differential between the inside of the balloon and the outside (at STP) will be less than 0.5 psi.
 

ScaleBirdsScott

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Seems if someone wanted to start simple, why not copy the Skymaster using Twin Boom structure with a dead simple pressure-vessel cabin more-or-less suspended from the middle of the wing? Of course just stick to hanging one engine off the front spherical bulkhead of the vessel. And the "door" problem could be solved by just having the whole aft end of the thing pop and rock off like the door of an autoclave, thus your sealing is a simple (large) O-ring. But, it rocks up between the twin booms so that you have nice easy access. Then of course limit your windscreen to being in the "nose" spherical bulkhead of the cylinder and windows can be positioned logically along the cylinder wall as little portholes. Very standard stuff and relatively easy to solve the structure I think.

Limit hull penetrations to a few key points this way as well. All structure can mount to lugs on the outside of the vessel. Gear, engine, wing, etc would not impinge on the simplified cylindrical pressure boundary, while still being structurally tied.

Yes you'd be in what amounts to a flying submarine but for simplifying structural systems and construction it might be a valid compromise.
 
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cvairwerks

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We run a pressurized cockpit on our fighters. Takes quite a bit of structural engineering on the design side as well as understanding the principles of pressure vessel design. Everything that penetrates the vessel comes into play with the design, down to the control cables that penetrate the bulkheads. The design guys even have to account for pressure leaks thru the electrical connectors.

Once the canopy is installed and fully fitted, it can take a day or more to find and seal leaks within the structure, so as to make the allowable leakage specifications. We even have to go as far as using ultrasonic test equipment to chase leaks. All this for a vessel that has to maintain a differential of about 6-8 psig, and withstand the pressure cycling for that differential, for at least 100,000 cycles........ Not exactly a trivial task. BTW, you can buy a decent C-172 for what the cabin pressure control valve costs!
 

wsimpso1

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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.
So there is a heat exchanger, the AC evaporator, and it is not an added component. This is requiring the entire AC system where that was not a given in the original post. But if no AC, you do need to adjust the temperature of the pressurization air...
 

Dan Thomas

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The pressure inside the balloon is roughly 14.7 psi. The pressure differential between the inside of the balloon and the outside (at STP) will be less than 0.5 psi.
And the differential is what matters. By your reasoning I could say that my Jodel had 14.7 PSI in it.
 

Dan Thomas

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So there is a heat exchanger, the AC evaporator, and it is not an added component. This is requiring the entire AC system where that was not a given in the original post. But if no AC, you do need to adjust the temperature of the pressurization air...
The 210's system ran the cabin air from the turbo, through the sonic valve (which generates a sonic pressure wave to act as an increasing restriction to the air as its velocity increases, and the pressure drop of the air cools it some), through the heat exhanger (a little radiator) and into the cabin. The exchanger was in a box with a valving mechanism to duct either heated air from around the exhaust system (just like the usual cabin heat system) through it, or cold air from an air inlet in the front of the cowl. The airplane I worked on also had an aftermarket airconditioning system, with the usual compressor and evaporator and condenser exchangers. It was used mostly on the ground. It's weight was not insignificant.
 

rv6ejguy

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The air from the turbo compressor could be anywhere from 150 to 300F, depending on compressor efficiency,OAT and pressure ratio. Having a simple cabin heat exchanger would reduce this down to livable levels and reduce the load on the a/c if fitted for little weight penalty.
 

Twodeaddogs

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The Me109 G5 was pressurised; they modified a G2 airframe by sealing the bulkheads, adding a compressor to the engine, adding inner tube to the canopy to inflate and seal it, added a cavity for dehumidifier tablets in the windscreen and added boots or blobs of sealant to any control rod,cable or wiring bundle that passed through the bulkheads. It was designed so that the aircraft could either be configured as a high altitude reconnaisance aircraft or be tasked to shoot down the enemy's recce aircraft.
 

BBerson

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I don't think any solo homebuilder has ever built a pressurized Homebuilt? Lancair was a major kit company that evolved over decades. Lancair IVP production has ended, I think. So that leaves only Raptor ;) .
But Raptor isn't a solo effort either.
 

BoKu

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I don't think any solo homebuilder has ever built a pressurized Homebuilt? Lancair was a major kit company that evolved over decades. Lancair IVP production has ended, I think. So that leaves only Raptor ;) .
But Raptor isn't a solo effort either.
Bob Lamson, Alcor
 

Heliano

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Designing a pressurized fuselage is feasible. However my suggestion is: if the designer has little or no experience evaluating fatigue and crack propagation (fault tolerant pressure vessel), move away from aluminum. Aluminum is light, it can easily be bent, folded, stretched and riveted but it is a nightmare when it comes to crack propagation. Go for a composite vessel, pressure test it through may be some hundred cycles and you are good to go. Main manufacturers are doing this: 787 (carbon), A380 (glare), A350 (carbon), etc. but remember that pressurization stresses happen simultaneously with gust, maneuver stresses. Another suggestion: programmable outflow valves are immensely complex. Use simpler, redundant mechanical fixed-differential relief valves instead. You will also need a negative-pressure relief.
 

dcarr

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I think Heliano is onto something...

Designing a pressurized fuselage is feasible. However my suggestion is: if the designer has little or no experience evaluating fatigue and crack propagation (fault tolerant pressure vessel), move away from aluminum. Aluminum is light, it can easily be bent, folded, stretched and riveted but it is a nightmare when it comes to crack propagation. Go for a composite vessel, pressure test it through may be some hundred cycles and you are good to go. Main manufacturers are doing this: 787 (carbon), A380 (glare), A350 (carbon), etc. but remember that pressurization stresses happen simultaneously with gust, maneuver stresses. Another suggestion: programmable outflow valves are immensely complex. Use simpler, redundant mechanical fixed-differential relief valves instead. You will also need a negative-pressure relief.
Aloha-Airlines-Flight-24.jpg
 

Marc Zeitlin

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I don't think any solo homebuilder has ever built a pressurized Homebuilt?
Depends on what you mean by "homebuilder", or "solo". Burt Rutan's Catbird and Boomerang were designed for pressurization, although they've never been tested or flown pressurized. But they both were Burt's private aircraft - not kits, and only one of each was built. Clearly, they were not SUCCESSFUL pressurized aircraft, as they were never pressurized, but I don't think that was the question :).
 

BBerson

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Clearly, they were not SUCCESSFUL pressurized aircraft, as they were never pressurized, but I don't think that was the question
Well, that's odd never testing the pressurization. I guess if he built them with no intention of selling the design they were "Homebuilt". Apparently not much demand for pressurized anyway.
 

wsimpso1

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White Knight One and Space Ship One were double hulled and pressurized, but that was part of a serious outfit.
 

wktaylor

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Some light reading on pressurized aircraft systems and design... NOT a trivial subject...

Cessna Training ~ Single Engine/Light Twin Pressurization ~ Student Workbook

Aircraft Pressurization - An Environmental Control System, AEM 617, Andrew Treadway

Control of Cabin Pressure - Aircraft Pressurization Systems

AC 25-20 PRESSURIZATION, VENTILATION AND OXYGEN SYSTEMS ASSESSMENT FOR SUBSONIC FLIGHT INCLUDING HIGH ALTITUDE OPERATION

What happens due to gross-over-pressurization during a ground-run test... just after Depot maintenance, prior to delivery...1999... the energy of pressurized/contained-air [gas] has-to-be-seen to be believed...
KC-135R OverPressurization~Fuselage Failure2x.jpg

KC-135R OverPressurization~Fuselage Failure1.jpg
KC-135R OverPressurization~Fuselage Failure3.jpg
KC-135R OverPressurization~Fuselage Failure4.jpg
 

pictsidhe

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Some light reading on pressurized aircraft systems and design... NOT a trivial subject...

Cessna Training ~ Single Engine/Light Twin Pressurization ~ Student Workbook

Aircraft Pressurization - An Environmental Control System, AEM 617, Andrew Treadway

Control of Cabin Pressure - Aircraft Pressurization Systems

AC 25-20 PRESSURIZATION, VENTILATION AND OXYGEN SYSTEMS ASSESSMENT FOR SUBSONIC FLIGHT INCLUDING HIGH ALTITUDE OPERATION

What happens due to gross-over-pressurization during a ground-run test... just after Depot maintenance, prior to delivery...1999... the energy of pressurized/contained-air [gas] has-to-be-seen to be believed...
View attachment 102857

View attachment 102854
View attachment 102855
View attachment 102856
That'll buff out.
 

cvairwerks

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What's even more chilling about that incident, is that the guy running the test was using an unapproved, homemade pressure gauge that had never been calibrated and had the capability of going multiple times around the scale with no indication of being past a single revolution. If I remember correctly, there was indications that at least one safety had either been bypassed or wired to never trip.

BTW...there is a photo in the report that shows where one of the over wing hatches landed, several hundred feet behind the aircraft, in part of the blast fence.

In our tests, if we hit the differential limit and the cabin safety doesn't go, we have to do an emergency dump, isolate the aircraft and call engineering.
 
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