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In Flight, to prevent the plane from diving, the pilot puts it upside down before flipping it back over just before landing. This is supposed to be loosely based on flight 261 from Alaska Airlines which unfortunately crashed without survivor after attempting a similar desperate manoeuvre. Let's just focus on the inverted flight part. Can a commercial airliner (50+ passengers) fly inverted for more than a few seconds before aerodynamics and/or propulsion problems arise? What are these specific problems?

Jamiec
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FrenchKheldar
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    In 1955 a Boeing test pilot did a __barrel roll with [Boeing 707](http://en.wikipedia.org/wiki/Boeing_707)__ ([watch video](http://www.aviation-history.com/video/707roll.htm)). – Oliver_C Nov 10 '12 at 19:51
  • I'm looking for evidence of steady inverted flight though, but thanks for the link. – FrenchKheldar Nov 10 '12 at 20:35
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    One obvious problem is fuel pick-up. It seems unlikely that passenger jets are fitted with the flop-tubes or header-tanks that are designed for acrobatic aircraft to allow inverted flight – RedGrittyBrick Nov 10 '12 at 22:36
  • Lift, I had thought, is provided by differential curvature of wings and Bernoulli's law. Bernoulli's law provides that in a gas, pressure is lowest on surfaces with higher velocity and highest on surfaces with low velocity. Lift occurs because the geometric design of the aircraft wing causes air to flow faster over the top of the wing than the bottom, causing the Bernoulli pressure differential to be opposite the direction of gravity. If inverted, the force created by Bernoulli's law still exists, but pushes the aircraft towards the ground, assisting gravity instead of counteracting it. – Paul Nov 10 '12 at 23:51
  • Note: *Spoilers* are inverted wings placed on race cars to provide an aerodynamic downforce. This downforce helps tires get traction to make tight turns at high speed. – Paul Nov 10 '12 at 23:59
  • Paul: I think it is possible to change the angle of attack of your wings while inverted to still generate lift. Of course, acrobatics planes probably have more symmetric wing cross section, but I'm not sure you cannot from a pure aerodynamic standpoint, fly inverted. Hence my question :) – FrenchKheldar Nov 11 '12 at 00:13
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    @Paul: RedGrittyBrick has it right. Normal aircraft are stressed for +/- N G, because those are the stresses they can encounter in turbulence. Inverted flight is nothing but -1G. However, they are not designed to do it for long, as aerobatic planes are. – Mike Dunlavey Nov 11 '12 at 00:26
  • @Mike I guess I don't understand how inverted "flight" is consistent with Bernoulli's law and the wing geometry. Where does the lift come from in inverted flight? – Paul Nov 11 '12 at 00:32
  • http://en.wikipedia.org/wiki/Lift_(force) – Paul Nov 11 '12 at 00:34
  • @Paul: Aerobatic planes have symmetric airfoils. They can lift either way, as a function of angle of attack. A non-aerobatic plane is the same way, except the curvature of the wing is an optimization because it's almost always flown upright. That curvature is not essential for lift. What determines lift is the overall deflection of the airstream, and that is controlled by the angle of the wing w.r.t the relative wind (angle of attack). – Mike Dunlavey Nov 11 '12 at 00:36
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    You know the plane crashes in the movie too right? – Chad Nov 11 '12 at 02:36
  • @Paul in practice, the shape of the wings determines a couple of very important things: 1) if the airplane can fly straight or only at an angle and 2) the various stresses within it. A 747 may be able to fly inverted in theory but break down in practice :-) – Sklivvz Nov 11 '12 at 10:56
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    **Related**: http://physics.stackexchange.com/a/295/66 – Sklivvz Nov 11 '12 at 10:57
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    @FrenchKheldar - Does Denzel Washington actually fly upside down in the movie? In the [trailer](http://www.youtube.com/watch?v=xnVNNR6CEOE#t=00m49s) he says: ___"We're gonna roll it."___ – Oliver_C Nov 11 '12 at 11:24
  • Oliver_C: Actually, I haven't seen the movie either but in the trailer, you can see the plane flying inverted without roll at pretty low speed which speed pretty unbelievable to me. Chad: I know it "crashes" but supposedly it was a somewhat controller crash landing instead of diving into the ground... – FrenchKheldar Nov 11 '12 at 16:52
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    @Sklivvz: [*Here's what I consider a very good analysis of the subject.*](http://www.av8n.com/how/htm/airfoils.html#sec-inverted-camber) If a 747 cannot fly inverted for a length of time, it is because of reasons like where the fuel and oil tank drains are, not for aerodynamic reasons. Every plane has a (fairly low) speed called Va, where maximum control deflections will not break it. Available lift, *up or down*, varies as the square of speed and, for safety, planes have to be strong enough to withstand multiple Gs in either direction. Up/downdrafts can easily create such stresses. – Mike Dunlavey Nov 11 '12 at 19:28

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Absolutely. As a matter of fact, one of the first commercially successful aircraft (the Boeing 707) did a barrel roll during a demonstration flight. In case you don't believe my claim, here is a video to back up my claim:

Boeing 707 Barrel Roll - Pilot Tex Johnston Performs Roll In Dash-80 Prototype Aircraft In 1955.

In 1994, FedEx Flight 705 (A DC-10), was put into a barrel roll during a rather insane hijacking attempt.

Captain Sanders joined the fray as Jim Tucker struggled to control the airplane. By now, Tucker’s right arm was nearly useless as the grave injuries to his skull brought on paralysis. He knew that his wounded crewmates could not last long against Calloway, so he assisted the only way he could. He pulled the control yoke all the way back to his chest, and rolled it to the left.

The DC-10 was executing a barrel-roll at nearly 400 miles per hour—something the aircraft had never been designed to do. Peterson and Sanders were shouting “Get him! Get him!” to each other, as the three struggling men were tossed about the galley area, alternately weightless and pressed upon by three times their weight in G forces. By now, the aircraft was inverted at 19,700 feet, and the alarmed air traffic controllers in Memphis were desperately calling for Flight 705.

(EDITORIAL NOTE: I take exception to the part where the NatGeo writers state "something the aircraft had never been designed to do" because a perfect barrel roll is a constant 1G maneuver (generally with anything between .5G to 3G, well within most aircraft design parameters), and doesn't stress the aircraft in any way, although this particular execution was probably not per any aerobatics manual due to the actual fight going on.)

Basic aerodynamics doesn't really care what the orientation of the aircraft is as long as you are able to balance the forces. The basic forces you have to deal with are weight, lift, thrust and drag. In an inverted position, you may think that the combination of lift and weight would be detrimental to flight, however you can tilt the angle of attack of the wing so that even in an inverted position you can get the lift to be opposite of the "top" surface of the wing. Otherwise an aircraft would have a hard time descending.

The Smithsonian Air & Space museum has a nice web page that explains how inverted flight works. Aircraft are basically the same on a meta level. The thing to keep in mind, that many subsystems of the aircraft may not operate well for extended inverted flight. However, (and keep in mind I have not seen the movie in question) most systems will maintain operation for at least some time due to residual fluids and such in the oil and fuel systems. Depending on the aircraft make and model, the fuel and oil lines should provide at least 30 seconds to a minute of uninterrupted operation.

For aircraft that do fly inverted, you can check out any airshow and see all manner of aircraft fly inverted for extended periods of time. Jets and propeller aircraft have well understood physics. You can learn more about aerodynamics at this page if that helps. If you look at this image:

Angle of attack and lift

All you have to do is get the angle of attack to be negative for the right-side up wing (thus if the wing is upside down, it's creating a net up force against gravity). So again, it's quite possible and doesn't violate any flight dynamics.

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Larian LeQuella
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    Do you have a better video of the Airbus 380? The second half of the video is a [rickroll](http://en.wikipedia.org/wiki/Rickrolling) and to be honest I couldn't actually tell if the aircraft rolled or not in the video. – rjzii Nov 13 '12 at 01:56
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    @RobZ My Bad!!! I didn't watch the whole thing to be honest. I have no reason to believe that it was faked since it's an easy constant 1G maneuver. :) I'll see if I can find another one (Thanks Oddthinking for editing it out). – Larian LeQuella Nov 13 '12 at 02:36
  • Wouldn't the avionics in modern airliner prevent such a maneuver? IIRC, at least in case of Airbus, the computer is quite aggressive in taking over the control once it believes that pilot is doing something dangerous. – vartec Nov 13 '12 at 13:45
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    @vartec it depends. Yes, the Airbus airframes have a lot of electronic flight controls that would attempt to prevent an inadvertent entry into maneuvers of this type, however, if the pilot executed them properly, the computer wouldn't be able to truly prevent it until it was too late and it would be safer to complete the maneuver. – Larian LeQuella Nov 14 '12 at 04:33
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    + Great answer. Of course, as you point out, a barrel roll is in no way the same thing as extended inverted flight. In a barrel roll you can hold an open cup of coffee upright the whole time. – Mike Dunlavey Nov 14 '12 at 20:22
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    @MikeDunlavey Well, it _is_ inverted form the point of view of someone standing on the ground. :) I haven't seen the movie, so I have no idea the flight parameters they are attempting to portray. Just because an aircraft appears inverted though doesn't mean that it "feels" inverted is the takeaway there. – Larian LeQuella Nov 15 '12 at 01:46
  • It makes sense to me, if something's pushing the stick forward, I *need* to be inverted, just so I'm nosing into the sky, not the ground. In the flight simulator I've tried it a lot, but the real trick is turning and navigating. All my reflexes and sense of direction are exactly backwards. – Mike Dunlavey Nov 15 '12 at 03:33
  • While i agree that flying inverted is possible in principle from an aerodynamic point of view for a wide range of aircraft, it is still unclear (and doesn't come as obvious from your arguments) whether in practice it is possible for a large passenger aircraft. As you said, in order to fly level, the aircraft would have to maintain a high angle of attack of the (inverted) wing and thus the aircraft itself. Flying in this position would mean a significantly higher drag. So the question is then if the engines can provide sufficient thrust in order to maintain sufficient forward velocity. – Scrontch Mar 26 '14 at 13:35
  • a barrel roll is in no way an answer to `Can a commercial airliner (50+ passengers) fly inverted for more than a few seconds before aerodynamics and/or propulsion problems arise?` – Federico Apr 24 '16 at 16:38
  • @Federico Why do you state that? A properly executed barrel roll takes quite a bit of time to perform. And the aircraft would be inverted for a portion of that time, being much greater than just a couple of seconds. – Larian LeQuella Apr 25 '16 at 02:19
  • Because it is a positive g manoeuver, not what laymen have in mind when asking about flying inverted (and considering what prompted the question) – Federico Apr 25 '16 at 05:22
  • @federico most laypeople have no idea what any aviation terms mean... That's part of the education one can get on this site. When I get home, let me look into the dynamics of an aileron roll if you think that will satisfy your criteria that goes beyond the question itself. – Larian LeQuella Apr 25 '16 at 12:12
  • we can discuss it in chat, if you want, to avoid bloating the discussion here. – Federico Apr 25 '16 at 12:17
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Yes, you can fly an airplane upside down, as long as the airplane frame supports the unexpected loads and the fuel, engine oil and battery acid stay where they are supposed to.

Contrary to popular belief, a plane flies not because the air above the wings moves faster than the air below, but because of circulation. This means that there is no reason why a plane couldn't fly upside down, as airshow pilots routinely do.

The links point to a very good book by John Decker on how to fly airplanes. It explains quite thoroughly why airplanes behave as they do.

LmnICE
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    + Right. Also, a barrel-roll is not even a negative-G maneuver. You can pour coffee into a cup during the whole thing. – Mike Dunlavey Mar 21 '14 at 12:50