c5load
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Can An Airliner Fly Inverted?

Mon Apr 12, 2010 2:06 am

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?
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stratosphere
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RE: Can An Airliner Fly Inverted?

Mon Apr 12, 2010 2:27 am

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
 
UAL747
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RE: Can An Airliner Fly Inverted?

Mon Apr 12, 2010 2:29 am

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
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Starlionblue
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RE: Can An Airliner Fly Inverted?

Mon Apr 12, 2010 3:49 am

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.
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chrisjw
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RE: Can An Airliner Fly Inverted?

Mon Apr 12, 2010 10:27 pm

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.
 
alaska737
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RE: Can An Airliner Fly Inverted?

Tue Apr 13, 2010 12:40 am

Debbie Rihn Harvey flew a Southwest 737 inverted, I have no idea how long, but I did see the picture.
 
tdscanuck
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RE: Can An Airliner Fly Inverted?

Tue Apr 13, 2010 5:15 am

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.
 
747400sp
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RE: Can An Airliner Fly Inverted?

Tue Apr 27, 2010 2:34 am

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.
 
roseflyer
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RE: Can An Airliner Fly Inverted?

Tue Apr 27, 2010 4:13 am

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.
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corey07850
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RE: Can An Airliner Fly Inverted?

Tue Apr 27, 2010 1:24 pm

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

 
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HAWK21M
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 4:37 am

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
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Zkpilot
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 2:33 pm

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
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474218
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 5:40 pm

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.
 
flybaurlax
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 6:43 pm

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.
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Mastropiero
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 7:00 pm

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....   
 
474218
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 7:15 pm

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.
 
Mastropiero
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 7:23 pm

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.
 
474218
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 7:37 pm

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.
 
MD11Engineer
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RE: Can An Airliner Fly Inverted?

Wed Apr 28, 2010 7:56 pm

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
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HaveBlue
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RE: Can An Airliner Fly Inverted?

Thu Apr 29, 2010 2:38 am

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.
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soon7x7
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RE: Can An Airliner Fly Inverted?

Thu Apr 29, 2010 4:12 am

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...
 
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Starlionblue
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RE: Can An Airliner Fly Inverted?

Thu Apr 29, 2010 4:46 am

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.
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CPH-R
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RE: Can An Airliner Fly Inverted?

Thu Apr 29, 2010 1:22 pm

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
 
3MilesToWRO
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RE: Can An Airliner Fly Inverted?

Thu Apr 29, 2010 3:54 pm

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".
 
tdscanuck
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RE: Can An Airliner Fly Inverted?

Thu Apr 29, 2010 4:40 pm

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.
 
Mastropiero
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RE: Can An Airliner Fly Inverted?

Sat May 01, 2010 9:03 am

Quoting 3MilesToWRO (Reply 23):
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".

Thanks, I understand it now. I got somehow confused..... this leads to another question. Assuming, for a moment, that you can indeed command enough "nose down", and increase AOA to such limits, will an airliner´s wing, with its design, provide lift? Some sort of lift, I mean?
 
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Zkpilot
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RE: Can An Airliner Fly Inverted?

Sun May 02, 2010 7:53 am

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".

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 to climb or maintain altitude. It is true that commercial aircraft tend to have less elevator control in this direction... however it comes down to airspeed and to a certain extent engine thrust.... ie if you keep your airspeed up you gain greater control effectiveness as well as lift. If you have an AoA that has the engine thrust partially aimed downwards then this would provide a certain amount of lift also.
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vikkyvik
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RE: Can An Airliner Fly Inverted?

Sun May 02, 2010 9:41 am

Quoting 3MilesToWRO (Reply 23):
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.

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.
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tdscanuck
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RE: Can An Airliner Fly Inverted?

Mon May 03, 2010 1:42 am

Quoting Mastropiero (Reply 25):
Assuming, for a moment, that you can indeed command enough "nose down", and increase AOA to such limits, will an airliner´s wing, with its design, provide lift? Some sort of lift, I mean?

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 about 6.3 per radian. Given that you don't need very high Cl at typical cruise speeds, you're easily capable of generating enough Cl with an inverted wing as long as you're not flying really slowly.

Tom.

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