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Can An Airliner Fly Inverted?  
User currently offlinec5load From United States of America, joined Sep 2008, 917 posts, RR: 0
Posted (4 years 1 week 1 day 2 hours ago) and read 13506 times:

Watching "United 93" the other day (RIP), it showed the 757 cockpit going inverted, so I can only assume that to be true. Were the passengers just simply unable to recover in time or once a plane like that goes inverted, is it impossible to recover no matter how much time they have?


"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
28 replies: All unread, showing first 25:
 
User currently offlinestratosphere From United States of America, joined Sep 2007, 1647 posts, RR: 4
Reply 1, posted (4 years 1 week 1 day 2 hours ago) and read 13498 times:

Tex Johnston Boeing chief test pilot for the 707 did a barrel roll in a 707 in a demo flight over Lake Washington

http://www.youtube.com/watch?v=3IV9PZW1N9U



NWA THE TRUE EVIL EMPIRE
User currently offlineual747 From , joined Dec 1969, posts, RR:
Reply 2, posted (4 years 1 week 1 day 2 hours ago) and read 13492 times:

Anything can fly inverted for a certain amount of time, given enough propulsion.   In fact, anything can fly as long as there is enough energy propelling it forward and up.

But to answer your question:

Yes, it can, but structurally it would begin to fail, along with all of the fuel lines/hydraulic lines which rely on gravity for some functions.

UAL


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 3, posted (4 years 1 week 1 day 1 hour ago) and read 13405 times:

Recovery is certainly possible given enough altitude and assuming the aircraft does not exceed structural limits. UA93 was either too close to the ground and/or going too fast to recover, or the pax simply didn't have the skillset required.


"Simple" inverted flight (just flying along upside down) should be fine structurally, but as mentioned gravity dependent systems like fuel and possibly lubrication would mean the engines would eventually stop. Also, negative g limits are lower than positive g limits, so the risk of structural failure is higher.


Tex Johnston did a barrel roll, meaning the aircraft was in a one g condition the whole time. In essence, the aircraft did not
"know" that it was inverted.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinechrisjw From United States of America, joined Jan 2009, 123 posts, RR: 0
Reply 4, posted (4 years 1 week 6 hours ago) and read 12912 times:

I thought I read on here that the 777 went inverted during it's certification flight testing when it was doing stalls. I may be wrong though.

User currently offlinealaska737 From United States of America, joined Feb 2006, 1062 posts, RR: 5
Reply 5, posted (4 years 1 week 4 hours ago) and read 12787 times:

Debbie Rihn Harvey flew a Southwest 737 inverted, I have no idea how long, but I did see the picture.

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 6, posted (4 years 6 days 23 hours ago) and read 12640 times:

Quoting chrisjw (Reply 4):
I thought I read on here that the 777 went inverted during it's certification flight testing when it was doing stalls.

I think that was a bank past 90 degrees... technically that's inverted, but it's not exactly the same as intentionally going full upsidedown.

Tom.


User currently offline747400sp From United States of America, joined Aug 2003, 3301 posts, RR: 2
Reply 7, posted (3 years 11 months 4 weeks 2 hours ago) and read 11572 times:

I believe a Fed EX DC10 30 flew inverted when the second officer tried to kill him self and the crew. The Captain had to fly the DC10 like a fighter jet to blow the second officer plot.

User currently offlineRoseFlyer From United States of America, joined Feb 2004, 9378 posts, RR: 52
Reply 8, posted (3 years 11 months 4 weeks ago) and read 11530 times:

Quoting ual747 (Reply 2):
Anything can fly inverted for a certain amount of time, given enough propulsion. In fact, anything can fly as long as there is enough energy propelling it forward and up.

If a modern jet (with the exception of the 787) flies inverted, the hydraulic system will fail rather quickly since it is a pressurized gravity system that uses air pressure to supply hydraulic fluid. When inverted, the hydraulic pumps will cavitate and fail within minutes.

Depending on fuel quantity, fuel may fail since gravity is required.

The last system to fail will be engines and IDG/APU as they use a scavenge system for oil that does require gravity.

Military aircraft have additional scavenge pumps and different reservoir pressurization so that they will not fail when inverted. Fuel systems use a different type of fuel pump as well.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlineCorey07850 From United States of America, joined Feb 2004, 2525 posts, RR: 5
Reply 9, posted (3 years 11 months 3 weeks 6 days 15 hours ago) and read 11383 times:

Quoting stratosphere (Reply 1):
Tex Johnston Boeing chief test pilot for the 707 did a barrel roll in a 707 in a demo flight over Lake Washington

One of my favorite pictures



User currently offlineHAWK21M From India, joined Jan 2001, 31573 posts, RR: 57
Reply 10, posted (3 years 11 months 3 weeks 6 days ago) and read 11044 times:

Quoting 747400sp (Reply 7):
I believe a Fed EX DC10 30 flew inverted when the second officer tried to kill him self and the crew. The Captain had to fly the DC10 like a fighter jet to blow the second officer plot.

Whats this story about?.
regds
MEL.



Think of the brighter side!
User currently offlineZkpilot From New Zealand, joined Mar 2006, 4773 posts, RR: 9
Reply 11, posted (3 years 11 months 3 weeks 5 days 14 hours ago) and read 10929 times:

Quoting HAWK21M (Reply 10):
Quoting 747400sp (Reply 7):
I believe a Fed EX DC10 30 flew inverted when the second officer tried to kill him self and the crew. The Captain had to fly the DC10 like a fighter jet to blow the second officer plot.

Whats this story about?.
regds
MEL.

An engineer who had been stood down managed to jumpseat on that flight. He had weapons with him (I think hammer/axe) that he used to hit the FO then the Capt. The Capt then made some abrupt control manuevers that sent the engineer flying out of the flight deck where the FO and I think at one stage the Capt also struggled with him. They eventually managed to land the plane and have police arrest the Engineer.
The whole incident is on 'Air Crash Investigation' (Nat Geo).
Ok this link explains it better:
http://en.wikipedia.org/wiki/FedEx_Flight_705
Season 3 Episode 4



54 types. 38 countries. 24 airlines.
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 12, posted (3 years 11 months 3 weeks 5 days 11 hours ago) and read 10830 times:

When aircraft fly inverted they do so with a very high angle of attack (AOA) so the wing can create lift.

Since airlines have very little elevator movement in the down direction (aircraft nose down) I don't think you could get the AOA high enough to allow the wing to create the required lift.


User currently offlineflybaurLAX From United States of America, joined Oct 2008, 637 posts, RR: 0
Reply 13, posted (3 years 11 months 3 weeks 5 days 10 hours ago) and read 10812 times:

Quoting 474218 (Reply 12):
Since airlines have very little elevator movement in the down direction (aircraft nose down) I don't think you could get the AOA high enough to allow the wing to create the required lift.

A 737-700 will fly upside down, but it will lose altitude pretty fast, and unless you drop the gear the airspeed will increase pretty quickly.



Boilerup! Go Purdue!
User currently offlineMastropiero From Spain, joined Dec 2005, 124 posts, RR: 0
Reply 14, posted (3 years 11 months 3 weeks 5 days 9 hours ago) and read 10800 times:

Quoting flybaurLAX (Reply 13):
Since airlines have very little elevator movement in the down direction (aircraft nose down) I don't think you could get the AOA high enough to allow the wing to create the required lift.

I don´t think I agree. The only way to increase AOA, as far as I know, is elevator up. Air doesn´t care whether you´re flying through it upside down or not, it will work the same way. The only difference is that when you´re flying normal, lift goes against gravity, whereas upside down lift goes towards it, hence you would lose altitude...... I hope I got my facts right, I am a complete "aficionado", so be kind to me if I´m wrong....   


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 15, posted (3 years 11 months 3 weeks 5 days 9 hours ago) and read 10788 times:

Quoting Mastropiero (Reply 14):
I don´t think I agree. The only way to increase AOA, as far as I know, is elevator up.

If your upside down, down becomes up and up becomes down.


User currently offlineMastropiero From Spain, joined Dec 2005, 124 posts, RR: 0
Reply 16, posted (3 years 11 months 3 weeks 5 days 9 hours ago) and read 10778 times:

Quoting 474218 (Reply 15):
If your upside down, down becomes up and up becomes down.

Lol, yeah, I got the basics of that one figured out. However, in order to increase the AOA, you still need to pull back on your stick/yoke, thus commanding "elevator up".

I assume you are thinking that in order to increase the AOA you have to point the nose towards the sky?? That´s the only sense I make out of your sentence:

Quoting 474218 (Reply 12):
Since airlines have very little elevator movement in the down direction (aircraft nose down)

I repeat, air doesn´t know whether you are upside down or not. It will meet the wings in the same way, and it will behave the same way. It doesn´t matter if "up becomes down" or not.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 17, posted (3 years 11 months 3 weeks 5 days 9 hours ago) and read 10766 times:

Quoting Mastropiero (Reply 16):
Lol, yeah, I got the basics of that one figured out. However, in order to increase the AOA, you still need to pull back on your stick/yoke, thus commanding "elevator up".

I assume you are thinking that in order to increase the AOA you have to point the nose towards the sky?? That´s the only sense I make out of your sentence:

Yes you have to increase the AOA to fly inverted, point the nose to the sky and when you are inverted you increase the AOA by pushing the column/stick forward.


User currently offlineMD11Engineer From Germany, joined Oct 2003, 13797 posts, RR: 63
Reply 18, posted (3 years 11 months 3 weeks 5 days 8 hours ago) and read 10758 times:

Quoting RoseFlyer (Reply 8):
If a modern jet (with the exception of the 787) flies inverted, the hydraulic system will fail rather quickly since it is a pressurized gravity system that uses air pressure to supply hydraulic fluid. When inverted, the hydraulic pumps will cavitate and fail within minutes.

Possibly not on Douglas aircraft, since they use a hydraulic reservoir design pressurized by hydraulic pressure itself through a bootstrap piston system. There is no (or should be no) air in the reservoir. On Boeings and Airbi I concur.

Jan


User currently offlineHaveBlue From United States of America, joined Jan 2004, 2090 posts, RR: 1
Reply 19, posted (3 years 11 months 3 weeks 5 days 2 hours ago) and read 10653 times:

Quoting c5load (Thread starter):
Were the passengers just simply unable to recover in time or once a plane like that goes inverted, is it impossible to recover no matter how much time they have?

The way I remember it is that when the terrorists realized the passengers were about to breach the door the lead terrorists said to put it down. They knew they were about to get overrun and decided to suicide it into the ground instead of fighting with and possibly losing against the passengers. That's the way I remember it but I may be wrong.

So anotherwords in my version the terrorists intentionally flew it into the ground as they were aware the passengers had overtaken the bad guys in the back and were trying like hell to get into the cockpit.



Here Here for Severe Clear!
User currently offlinesoon7x7 From , joined Dec 1969, posts, RR:
Reply 20, posted (3 years 11 months 3 weeks 5 days ago) and read 10619 times:

I can't see an intentional sustained inverted flight possible as the fuel scavenge pumps are located at the bottom of the tanks which would now be on the top...fuel starvation would result...in addition the angle of attack would be so radical, the wing design (critical wings) could not sustain it...I would also be concerned about angle of attack where the engine nacelles are concerned...it might cause compressor stalls...

Flight 93 was an inverted dive as many aircraft out of control have a tendancy to roll onto their backs...

Test Johnstons roll is about as close as I imagine you could get...even a 747 could execute that maneuver but sustained?...I don't think so...


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 21, posted (3 years 11 months 3 weeks 5 days ago) and read 10605 times:

Tex Johnston performed a barrel roll. This means that the aircraft is experiencing more or less 1 g towards the "floor" all the way through, even when upside down. So fuel pumps and lubrication work as normal.

As soon 7x7 says this is not the same as sustained inverted flight.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineCPH-R From Denmark, joined May 2001, 5910 posts, RR: 3
Reply 22, posted (3 years 11 months 3 weeks 4 days 15 hours ago) and read 10539 times:

The hhead of QI did a barrel roll with an empty ATR over SGD a couple of years ago. A spotter caught it on camera and all hell broke lose, courtesy of the tabloids: http://jp.dk/uknews/article1699863.ece

User currently offline3MilesToWRO From Poland, joined Mar 2006, 275 posts, RR: 0
Reply 23, posted (3 years 11 months 3 weeks 4 days 13 hours ago) and read 10496 times:

Quoting Mastropiero (Reply 16):

Lol, yeah, I got the basics of that one figured out. However, in order to increase the AOA, you still need to pull back on your stick/yoke, thus commanding "elevator up".

No. As long as we talk about stable flight upside down you all the time must have leading edge higher than trailing edge. And "higher" is related to Earth surface, not to aircraft floor. Which means that flying inverted you must reverse the trim. The tail must pull down to Earth, so in inverted flight it must be commanded what normally would be named "nose down".


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 24, posted (3 years 11 months 3 weeks 4 days 12 hours ago) and read 10475 times:

Quoting MD11Engineer (Reply 18):
Possibly not on Douglas aircraft, since they use a hydraulic reservoir design pressurized by hydraulic pressure itself through a bootstrap piston system. There is no (or should be no) air in the reservoir. On Boeings and Airbi I concur.

Boeing has switched to bootstrap hydraulics for 787.

Tom.


25 Mastropiero : Thanks, I understand it now. I got somehow confused..... this leads to another question. Assuming, for a moment, that you can indeed command enough "
26 Zkpilot : negative.... your subsequent comment is more like it. You have to push forward (what would normally be down) when inverted to have a higher AoA...ie
27 Post contains images vikkyvik : Not to nitpick ( ), but when you're talking about AOA, then you're talking about an angle relative to the freestream flow, not the Earth.
28 tdscanuck : Yes. The slope of the Cl vs. AoA curve is almost completely independent of the exact airfoil (assuming a clean wing here)...it's always going to be a
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