Brenintw From Taiwan, joined Jul 2006, 1449 posts, RR: 1 Posted (6 years 7 months 1 week 6 days ago) and read 3580 times:
In a number of threads, there's been mention of a CI 744F failing a pressurization test while being prepped for delivery. How are modern aircraft pressurization tested?
Are they flown to above a certain level (10K feet?) and pressurized? Are they pressurized on the ground? If so, to what pressure are they tested? I imagine the pressure differential between the inside of a cabin and the outside at 45K feet is pretty substantial which would mean that the cabin would need to be pressurized quite heavily to test on the ground (assuming that a similar pressure differential is used for testing).
Inquiring minds want to know
Bren
I'm tired of the A vs. B sniping. Neither make planes that shed wings randomly!
Tristarsteve From Sweden, joined Nov 2005, 3693 posts, RR: 34 Reply 1, posted (6 years 7 months 1 week 5 days 21 hours ago) and read 3564 times:
They are tested on the ground. First you have to safety systems that are affected by pressure, noticeably the oxygen regulators.
Then basically you shut the doors and start the APU and run the packs and follow the instructions in the Maint Manual about how to control the system. Some aircraft will not pressurise on APU air, the B737-200 wont, the easy way then is to start an engine and run it until you get over the "hump". This is when all the doors seals start being effective at about 2psi diff. Then you can shut the engine down and the APU is sufficient.
The pax doors hang in, and with APU supply the air rushes out round the doors until there is too much flow and the doors are pushed into the frames and seal.
N231YE From , joined Dec 1969, posts, RR: Reply 4, posted (6 years 7 months 1 week 5 days 16 hours ago) and read 3506 times:
I have the video of the 777 test. Basically, Boeing wraps the airplane in plastic tarps, while it is on the ground. Then, they add pressure to the airplane via an external port, and they watch for any movement of the tarps-which signifies a leak. On the first 777 test, a faulty door seal caused the airplane to depressurize. Boeing engineers subsequently redesigned the seal, and tested it a second time, and the test was a success.
Dougloid From , joined Dec 1969, posts, RR: Reply 5, posted (6 years 7 months 1 week 5 days 15 hours ago) and read 3505 times:
We did the MD11 environmental system/pressurization tests with two huffers, one was a Ford truck with two 8V71 Detroit Diesels mounted back to back running a Roots blower, and the other was a single 12V92 twin turbo Detroit Diesel running a single roots blower....saves engine or APU hobbs time and we could barely get her to max differential altitude (40,000 feet). It was also like pressing a pair of pants-it smoothed out all the wrinkles in the skin. This test took about 10 hours to make all the points and they locked you in.
They did a preliminary test of the hull back in the plant right after they put the windows in, when the hull was about 50 per cent complete. A lot of stuff was open then that could be resealed if necessary.
The guys would go over the exterior with gloves and look around the windows and other likely places for leaks. I myself have looked for leaks with a rag or piece of cloth. They'll ruffle or move over a leaking fastener, but you'll also see streaks around the fasteners.
Dw747400 From United States of America, joined Aug 2001, 1244 posts, RR: 1 Reply 6, posted (6 years 7 months 1 week 5 days 12 hours ago) and read 3461 times:
I'm not an expert, but I believe the prototype tests most of you are reffering too are done on development aircraft only. I'd imagine a production aircraft coming off the line would be tested as Tristarsteve said.
DALMD88 From United States of America, joined Jul 2000, 2365 posts, RR: 15 Reply 7, posted (6 years 7 months 1 week 5 days 11 hours ago) and read 3443 times:
Quoting Dw747400 (Reply 6): I'm not an expert, but I believe the prototype tests most of you are reffering too are done on development aircraft only. I'd imagine a production aircraft coming off the line would be tested as Tristarsteve said
I'd bet they do a max pressure and decay check on every new airframe. It would be one of the system check outs just like at the end of any overhaul.
AeroWeanie From United States of America, joined Dec 2004, 1600 posts, RR: 52 Reply 8, posted (6 years 7 months 1 week 5 days 10 hours ago) and read 3420 times:
Such tests can be a little dangerous. When they tested the #1 DC-10, before its first flight, the forward lower cargo door blew out rather violently, at full delta pressure.
Dougloid From , joined Dec 1969, posts, RR: Reply 9, posted (6 years 7 months 1 week 5 days 9 hours ago) and read 3395 times:
Quoting AeroWeanie (Reply 8): Such tests can be a little dangerous. When they tested the #1 DC-10, before its first flight, the forward lower cargo door blew out rather violently, at full delta pressure.
Musta made the guys inside a little uncomfortable LOL...especially the ones that had the burritos for lunch LOL.
I did at least two or three of the 10 hour tests on MD11s. We'd run it up to max differential and then stairstep down in 500 foot intervals while everyone in the cabin was running around spraying duct sensors with circuit chiller.
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 10 Reply 10, posted (6 years 7 months 1 week 5 days 9 hours ago) and read 3390 times:
Quoting DALMD88 (Reply 7): I'd bet they do a max pressure and decay check on every new airframe. It would be one of the system check outs just like at the end of any overhaul.
We did a pressure/decay test on every L-1011 built. Fuselage had to hold X amount of pressure and could not decay (leak down) faster than a prescribed amount (I don't remember the actual numbers). Test were always done on the production line during graveyard shift (12:00AM to 7:00AM). The test aircraft was roped off and only the test crew and inspectors were allowed in the area.
Dw747400 From United States of America, joined Aug 2001, 1244 posts, RR: 1 Reply 11, posted (6 years 7 months 1 week 4 days 3 hours ago) and read 3275 times:
Quoting DALMD88 (Reply 7):
I'd bet they do a max pressure and decay check on every new airframe. It would be one of the system check outs just like at the end of any overhaul.
Never said they didn't... just that I'd imagine it is done more along the lines of the tests described in the MX manual, not the same way as the initial test was conducted.
BAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0 Reply 12, posted (6 years 7 months 1 week 3 days 10 hours ago) and read 3195 times:
Quoting Dw747400 (Reply 11): not the same way as the initial test was conducted.
Do you mean they might do one type of test for certification, and another for their own QA?
That does sound about right - there are similar processes in the automotive and computing industries, (which are the only ones I can speak authoritatively about).
Quoting AeroWeanie (Reply 8): When they tested the #1 DC-10, before its first flight, the forward lower cargo door blew out rather violently
Dougloid From , joined Dec 1969, posts, RR: Reply 13, posted (6 years 7 months 1 week 3 days 4 hours ago) and read 3167 times:
Quoting BAe146QT (Reply 12): Quoting Dw747400 (Reply 11):
not the same way as the initial test was conducted.
Do you mean they might do one type of test for certification, and another for their own QA?
The first one's for the shop, to fix any faults when the inside of the hull's more accessible. When it passes that, then the interior stuff goes in and the test for the money, which usually is part and parcel of a pressurization system/environmental system checkout gets sold to regulatory authorities or more usually a designee.
Lehpron From United States of America, joined Jul 2001, 7028 posts, RR: 22 Reply 14, posted (6 years 7 months 5 days 7 hours ago) and read 3019 times:
High altitudes are about pressure differences, not the actual pressures. If an aircraft is flying where the air pressure is ten times less, then the pressure inside will try to expand the tube like a balloon. To test that on the ground, aircraft are filled up with air until the pressure inside is ten times high than outside. But they usually test to greater than just most likely flight conditions, they may go to 12 times like for a 772, or more depending on the design requirement or regulations.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
Kalvado From United States of America, joined Feb 2006, 471 posts, RR: 0 Reply 15, posted (6 years 7 months 5 days 5 hours ago) and read 2999 times:
Quoting Lehpron (Reply 14): If an aircraft is flying where the air pressure is ten times less, then the pressure inside will try to expand the tube like a balloon. To test that on the ground, aircraft are filled up with air until the pressure inside is ten times high than outside.
AeroWeanie From United States of America, joined Dec 2004, 1600 posts, RR: 52 Reply 17, posted (6 years 7 months 4 days 13 hours ago) and read 2951 times:
Quoting Lehpron (Reply 14): High altitudes are about pressure differences, not the actual pressures. If an aircraft is flying where the air pressure is ten times less, then the pressure inside will try to expand the tube like a balloon. To test that on the ground, aircraft are filled up with air until the pressure inside is ten times high than outside. But they usually test to greater than just most likely flight conditions, they may go to 12 times like for a 772, or more depending on the design requirement or regulations.
Not quite. Its the pressure difference that counts, like you first sentence states. When doing the test at sea level, you create the same pressure difference, not ten times.
Quoting HAWK21M (Reply 16): Isn't prototype testing of pressurised fuselage carried out underwater to reduce Impact damage.
You are getting confused with the fatigue test, where the fuselage is pressurized over and over again to see if any damage results. This is often done in a water tank.
Dougloid From , joined Dec 1969, posts, RR: Reply 18, posted (6 years 7 months 4 days 7 hours ago) and read 2936 times:
Quoting Lehpron (Reply 14): High altitudes are about pressure differences, not the actual pressures. If an aircraft is flying where the air pressure is ten times less, then the pressure inside will try to expand the tube like a balloon. To test that on the ground, aircraft are filled up with air until the pressure inside is ten times high than outside. But they usually test to greater than just most likely flight conditions, they may go to 12 times like for a 772, or more depending on the design requirement or regulations.
Never happens. You're talking 150 to 170 psi. Everyone inside would die from the bends LOL
We tested MD11s to max cabin differential pressure which is equivalent to 41,000 feet altitude. which is about a 10 psi differential
BAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0 Reply 19, posted (6 years 7 months 4 days 7 hours ago) and read 2932 times:
Quoting AeroWeanie (Reply 17): You are getting confused with the fatigue test, where the fuselage is pressurized over and over again to see if any damage results. This is often done in a water tank.
Unless I am mistaken, this was first done for the Comet-I to try and work out why they kept ending up like they had run through the Chicago Bears' defensive line.
BAe built a whacking great big water tank that enclosed everything but the wings, (they poked through gasketed holes?) and ran one up and down until the fuselage cracked. At which point they said, Aha! Let's ditch the enormous square picture windows.
AeroWeanie From United States of America, joined Dec 2004, 1600 posts, RR: 52 Reply 21, posted (6 years 7 months 4 days 2 hours ago) and read 2912 times:
Quoting BAe146QT (Reply 19): Unless I am mistaken, this was first done for the Comet-I to try and work out why they kept ending up like they had run through the Chicago Bears' defensive line.
BAe built a whacking great big water tank that enclosed everything but the wings, (they poked through gasketed holes?) and ran one up and down until the fuselage cracked. At which point they said, Aha! Let's ditch the enormous square picture windows.
Correct, except BAe wasn't yet a glimmer in anybody's eye. It was Dehavilland that built the airplane and the tank test was done at Farnborough, by the RAE. They used the airframe of G-ALYU.
Lehpron From United States of America, joined Jul 2001, 7028 posts, RR: 22 Reply 23, posted (6 years 7 months 3 days 7 hours ago) and read 2870 times:
Quoting AeroWeanie (Reply 17): Not quite. Its the pressure difference that counts, like you first sentence states. When doing the test at sea level, you create the same pressure difference, not ten times.
Quoting Dougloid (Reply 18): Never happens. You're talking 150 to 170 psi. Everyone inside would die from the bends LOL
We tested MD11s to max cabin differential pressure which is equivalent to 41,000 feet altitude. which is about a 10 psi differential
So they pump air out of the inside then, evacuating it? I hear there are a few people inside during the test.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
Kalvado From United States of America, joined Feb 2006, 471 posts, RR: 0 Reply 24, posted (6 years 7 months 3 days 5 hours ago) and read 2860 times:
Quoting Lehpron (Reply 23): So they pump air out of the inside then, evacuating it?
Like any tube, plane body withstands load from inside much better than from outside. A simple experiment: get a paper bag, make it approximately circular, and try to break from inside applying pressure uniformly... for comparason, just try to crumple same bag from outside (you don't want to crumple the plane, right?)
Now, once you're applying pressure from inside:
Units of pressure are PSI - pounds per sq. inch. When you apply differential pressure of 1 PSI from inside, each square inch of the body is subjected to 1 lb of force. It doesn't matter if you're in DEN or JFK - 1 PSI pressure differential means exactly the same.
As it was mentioned before, 10 PSI is a reasonable real-life pressure differential, and that's what the plane is designed for - 10 pounds per sq. inch of body from inside. It doesn't matter if that's 14.5 PSI outside /24.5 inside on the ground, or 3 PSI outside/13 inside at FL300 - the force on the body is the same, 10 LB per sq. inch.
25 Dougloid: Pressurized on the ground to max differential by the use of two huffers-one was a Ford truck with two 8V71 Detroit Diesel's back to back driving a mo
26 Kalvado: I see what you're saying, thank you for correction.. And I bet every 0.1 PSI costs hundreds pounds of weight.... On the other hand, using 10 is just
27 TheJoe: Well, I can tell you a little about how they do a pressure run after a heavy maintenance check... All the work done on the aircraft is recorded. For e
28 Dougloid: What are you getting at? How does pressure differential affect weight?
29 Dougloid: Absolutely correct. A man on the outside with a cloth will do as well, too. That is why folks who work with the stuff take the time to understand the
30 Kalvado: _Maximum_ differential - just strength of the body... which translates into extra mills of metal..
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