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(Popular Mechanics)   In the new movie Flight, the pilot turns his airliner upside down to save it from an uncontrolled descent. Is that really possible? Here comes the aeronautical science   (popularmechanics.com) divider line 91
    More: Interesting, aeronautical science, landing gear, flight controls, catastrophic failure, blood  
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8522 clicks; posted to Geek » on 06 Nov 2012 at 11:02 AM (2 years ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



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2012-11-06 01:52:02 PM  

Dinobot: Quasar: There was a real life flight disaster where the plane lost some flap hydraulics or controls and the pilots tried the inverted method to try to save the plane but were unable to manage it. Valiant attempt.

Yep
Alaska Airlines Flight 261
http://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261


I couldn't believe this wasn't mentioned in the article. Reading the transcript of the voice recorder from that accident gives me the chills every time.
 
2012-11-06 02:11:53 PM  

Click Click D'oh: The article talks about Barrel Rolls, which if you had read my post, you would realize are not the same as ailerons rolls, which is what is shown in the movie


I submit that the Hollywood CGI folks who did the crash sequence in the film wouldn't know the difference between the two maneuvers and what they look like. What happens on the movie screen is irrelevant to the discussion.

In any case the maneuver by definition couldn't be an aileron roll because the tailplane is locked in the nose-down position. It would be an outside barrel roll.
 
2012-11-06 02:15:43 PM  

majestic: Rent Party: UberDave: Flying an aircraft that size upside down has to be tough. It's a different situation altogether.

There is a local Seattle test pilot for Boeing that got in trouble for doing a barrel roll with a new 707 right over the city. Everyone freaks out about it, but he just said "It was well within the flight capabilities of the aircraft, and I wanted to show it off to the customer." The customer was some Saudi dude who happened to be on board, and was apparently thrilled with the move.

Video Goodness of Said Event

That event (aileron roll of a Dash 80) was mentioned in TFA. What you state is not what happened, and not even what the video you linked claims. Go vote 3 or 4 more times. We need more like you!


Oh I'm sorry, why don't you tell me what bit of pedantry was wrong and then inform us that you've got 15 hours on a rented Cessna which is why you're such a farking expert, and then go fark off.

Dude rolled a 707 over Seattle. That's a fact. Dude said it was well within the flight capabilities of 707. That is also a fact. You are a complete douchebag. Yet another fact.
 
2012-11-06 02:19:51 PM  
Ok, but what maneuver is appropriate to evade the leap of a Mega Shark?

i45.tinypic.com
 
2012-11-06 02:22:32 PM  
Probably the best real-life account of how well a large aircraft (and pilot) can manuever in extreme circumstances and survive.
http://en.wikipedia.org/wiki/Federal_Express_Flight_705 

/Rolled the plane to stop a guy who was wailing on him with a hammer.
 
2012-11-06 02:24:19 PM  

Ambitwistor: Ok, but what maneuver is appropriate to evade the leap of a Mega Shark?

[i45.tinypic.com image 285x480]


Trick question. It is impossible to evade the leap of a Mega Shark.
 
2012-11-06 02:28:40 PM  

Rent Party: majestic: Rent Party: UberDave: Flying an aircraft that size upside down has to be tough. It's a different situation altogether.

There is a local Seattle test pilot for Boeing that got in trouble for doing a barrel roll with a new 707 right over the city. Everyone freaks out about it, but he just said "It was well within the flight capabilities of the aircraft, and I wanted to show it off to the customer." The customer was some Saudi dude who happened to be on board, and was apparently thrilled with the move.

Video Goodness of Said Event

That event (aileron roll of a Dash 80) was mentioned in TFA. What you state is not what happened, and not even what the video you linked claims. Go vote 3 or 4 more times. We need more like you!

Oh I'm sorry, why don't you tell me what bit of pedantry was wrong and then inform us that you've got 15 hours on a rented Cessna which is why you're such a farking expert, and then go fark off.

Dude rolled a 707 over Seattle. That's a fact. Dude said it was well within the flight capabilities of 707. That is also a fact. You are a complete douchebag. Yet another fact.


Over Lake Washington, not Seattle. No mention of any "Saudi dude" on-board, since it was a test flight. He did not even get in trouble as he was showcasing the planes abilities to the president of Boeing. Otherwise, everything you stated is correct. Which means you were incorrect about pretty much everything.

So, double douche-bag to you!
 
2012-11-06 02:45:26 PM  

Eirik: Wasn't there another near-crash a few decades ago that started with the plane doing a roll and then diving straight down? IIRC, it was something like a 727, the pilots saved the plane and landed safly, but then erased the flight data recorder because he felt it wasn't a crash. Speculation was that the flight crew was doing something to test the limits of the plane and did something stupid. Anyone reconzie that?


http://en.wikipedia.org/wiki/TWA_Flight_841_(1979)

The 727 crew was playing with non-approved flap settings at cruise by pulling the circuit breakers at certain flap positions not normally selectable. Rolled twice, but landed safely with substantial airframe damage.

http://en.wikipedia.org/wiki/China_Airlines_Flight_006

747 engine flamed out and the crew didn't follow proper procedures and ended up rolling it and pulling 5G in the recovery. Landed with huge chunks of the elevator missing and other damage.
 
2012-11-06 02:47:25 PM  

Cthulhu_is_my_homeboy:
I submit that the Hollywood CGI folks who did the crash sequence in the film wouldn't know the difference between the two maneuvers and what they look like.


Bullshirt. Per capita there are more airplane nerds in a typical vfx facility than there are at most major airports.
However, if the client asks for an aileron roll, you give him a god damned aileron roll.
 
2012-11-06 02:49:34 PM  

fluffy2097: what?

No.

You pull back on the stick to leave a dive.


If your control surfaces were jammed in a "stick forward" orientation, inverting would be your only logical option.
 
2012-11-06 02:53:29 PM  

SacriliciousBeerSwiller: fluffy2097: what?

No.

You pull back on the stick to leave a dive.

If your control surfaces were jammed in a "stick forward" orientation, inverting would be your only logical option.


That, or removing the ham sandwich jammed in the ejector seat lever.
 
2012-11-06 03:00:14 PM  

Cthulhu_is_my_homeboy: In any case the maneuver by definition couldn't be an aileron roll because the tailplane is locked in the nose-down position. It would be an outside barrel roll.


I kind of assumed they forgot all about that after using it as a convenient excuse to start the crash sequence. Negative Gs and airliners are not friends.
 
2012-11-06 03:18:26 PM  
Can we see them try this on MythBusters?
 
2012-11-06 03:51:15 PM  
I'm glad the expert mentioned the absurdity of gliding a commercial jet to a safe landing on the Hudson. If it were in a movie and not real life I'm sure there'd be a bunch of fark experts posting how impossible that would be also.
 
2012-11-06 04:01:23 PM  

Click Click D'oh: I kind of assumed they forgot all about that after using it as a convenient excuse to start the crash sequence. Negative Gs and airliners are not friends.


If you're gonna be pedantic, you have to commit.

Anyway, whether or not it's possible to *save* an airliner with a jammed stabilizer by rolling it inverted is entirely open for debate, but there's no question that it's possible to do so and has been tried. Flight's writers pretty clearly based the entire accident sequence off Alaska Airlines 261, the major difference being that the last-ditch attempt to stop the dive by inverting it works in the movie, and for some reason they're able to roll back over again and crash land in a field. Alaska 261, by contrast, made a big, high-speed splash into the Pacific.

I was willing to suspend disbelief in the method of recovery, as the movie as a whole is a far more realistic take on the industry than most people who see it will likely believe.
 
2012-11-06 04:11:22 PM  

davidphogan: I'm glad the expert mentioned the absurdity of gliding a commercial jet to a safe landing on the Hudson. If it were in a movie and not real life I'm sure there'd be a bunch of fark experts posting how impossible that would be also.


Airliners have been ditched successfully and moderately successfully before.

Successful:
Pan Am Boeing 337: http://en.wikipedia.org/wiki/Pan_Am_Flight_6
Japan Air Lines Douglas DC-8: http://en.wikipedia.org/wiki/Japan_Airlines_Flight_2

Moderately successful:
Ethiopian Airlines Boeing 767: http://en.wikipedia.org/wiki/Ethiopian_Airlines_Flight_961

As for gliding an airliner, the Canadians have perfected that.
Air Canada Boeing 767 (aka Gilmi Glider): http://en.wikipedia.org/wiki/Air_Canada_Flight_143
Air Transat Airbus A330: http://en.wikipedia.org/wiki/Air_Transat_Flight_236
 
2012-11-06 04:23:24 PM  

serial_crusher: Why was it going down in the first place? Did somebody deflate the autopilot again?


Maybe he was busy:

farm2.static.flickr.com
 
2012-11-06 04:47:31 PM  

majestic: Rent Party: majestic: Rent Party: UberDave: Flying an aircraft that size upside down has to be tough. It's a different situation altogether.

There is a local Seattle test pilot for Boeing that got in trouble for doing a barrel roll with a new 707 right over the city. Everyone freaks out about it, but he just said "It was well within the flight capabilities of the aircraft, and I wanted to show it off to the customer." The customer was some Saudi dude who happened to be on board, and was apparently thrilled with the move.

Video Goodness of Said Event

That event (aileron roll of a Dash 80) was mentioned in TFA. What you state is not what happened, and not even what the video you linked claims. Go vote 3 or 4 more times. We need more like you!

Oh I'm sorry, why don't you tell me what bit of pedantry was wrong and then inform us that you've got 15 hours on a rented Cessna which is why you're such a farking expert, and then go fark off.

Dude rolled a 707 over Seattle. That's a fact. Dude said it was well within the flight capabilities of 707. That is also a fact. You are a complete douchebag. Yet another fact.

Over Lake Washington, not Seattle. No mention of any "Saudi dude" on-board, since it was a test flight. He did not even get in trouble as he was showcasing the planes abilities to the president of Boeing. Otherwise, everything you stated is correct. Which means you were incorrect about pretty much everything.

So, double douche-bag to you!


You must not be from around here. Lake Washington borders the entire eastern side of Seattle. Every inch of the city's eastern border is Lake Washington. So you're not only wrong, you're a douchebag pedant.

He got his ass chewed by the farking President of Boeing over it. So you're wrong again, and a douchebag pedant.

In other words, you're a douchebag pedant, just like I said. So do please fark off.
 
2012-11-06 04:54:48 PM  

Charlie Freak: UberDave: Flying an aircraft that size upside down has to be tough. It's a different situation altogether.

It's a different situation...

Flying inverted is flying inverted, the difference in an airliner is that if your solution goes to shiat, because of inertia, it doesn't respond as quickly to control inputs if and when you need to fix things. This of course does not take into account things like passenger comfort or other features of aerobatic aircraft, like symmetrical wings and inverted-capable fuel and oil systems.

Other than that, spatial-awareness-wise, it's not much different than flying a Cessna inverted.



Glad to see this was covered. Now I'm off to YouTube to watch Bob Hoover pour ice tea while rolling a Shrike Commander.
 
2012-11-06 05:09:44 PM  

clear_prop: As for gliding an airliner, the Canadians have perfected that.
Air Canada Boeing 767 (aka Gilmi Glider): http://en.wikipedia.org/wiki/Air_Canada_Flight_143
Air Transat Airbus A330: http://en.wikipedia.org/wiki/Air_Transat_Flight_236


We have a gift (for running out of gas).
 
2012-11-06 05:26:58 PM  
Boeing tests its planes to roll, my great uncle was one of the first commercial pilots to fly the 747, he and a bunch of other PanAM captains went out to were they were testing the 747. They wanted to see if the commercial pilots (many of whom were veteran military aviators) could put the plane through the same paces as the test crew. One of the things they had them do was take the 747 into a roll.

So these planes can roll, but a low altitude roll like that... I dunno. I would think passengers would slip right out of the those shiatty little seatbelts.
 
2012-11-06 05:38:08 PM  
Well yeah, if youre crashing and you roll over youll start going up. Basic physics.
 
2012-11-06 05:39:45 PM  
All they need to do is ask Greg Feith. He's the Stanton T. Friedman of airplane shows.
 
2012-11-06 05:42:24 PM  

Donau: Boeing tests its planes to roll, my great uncle was one of the first commercial pilots to fly the 747, he and a bunch of other PanAM captains went out to were they were testing the 747. They wanted to see if the commercial pilots (many of whom were veteran military aviators) could put the plane through the same paces as the test crew. One of the things they had them do was take the 747 into a roll.

So these planes can roll, but a low altitude roll like that... I dunno. I would think passengers would slip right out of the those shiatty little seatbelts.


Barrel roll vs aileron roll. Barrel roll is 1G, plane doesn't even know it is upside down. Go find the YouTube video of Bob Hoover pouring tea. Aileron roll is negative G, and not recommended for airliners.
 
2012-11-06 05:48:45 PM  
clear_prop:Barrel roll vs aileron roll. Barrel roll is 1G, plane doesn't even know it is upside down. Go find the YouTube video of Bob Hoover pouring tea. Aileron roll is negative G, and not recommended for airliners.




An inside (top of the plane points to the center of the barrell) barrel roll would allow for the above. It sounds like the movie is showing an outside (top of th plane points away from the center of the barrell) barrel roll.
 
2012-11-06 05:56:42 PM  
In the new movie Flight, the pilot turns his airliner upside down to save it from an uncontrolled descent. Is that really possible?

Let's ask Peppy Hare!
 
2012-11-06 06:25:35 PM  

Jim DiGriz: clear_prop:Barrel roll vs aileron roll. Barrel roll is 1G, plane doesn't even know it is upside down. Go find the YouTube video of Bob Hoover pouring tea. Aileron roll is negative G, and not recommended for airliners.


An inside (top of the plane points to the center of the barrell) barrel roll would allow for the above. It sounds like the movie is showing an outside (top of th plane points away from the center of the barrell) barrel roll.


Haven't seen the movie, but from the previews it looks like an aileron roll. With the elevator stuck at full nose down, you can't do a barrel roll since it involves pulling up and banking.
 
2012-11-06 07:01:27 PM  

costermonger: Anyway, whether or not it's possible to *save* an airliner with a jammed stabilizer by rolling it inverted is entirely open for debate,


No, it's not. Even if you did manage to defy physics and fly the plane upside down using only angle of attack to keep it in the air (and somehow the suck elevators don't make you do outside loops until you stall and crash), there is still no airliner in service with landing gear on the crown of the fuselage so the whole crash and burn ending is still in play. As I have yet to find the switch to momentarily suspend physics in the event of an emergency, that really isn't an issue because the crash and burn will come right when it's expected.

We aren't talking about fighter jets or acrobatic aircraft. Airliners don't do the upside down thing very well.


costermonger: but there's no question that it's possible to do so and has been tried.


It's been tried, but that doesn't make it possible.


costermonger: Flight's writers pretty clearly based the entire accident sequence off Alaska Airlines 261...


In which everyone died.

costermonger: the major difference being that the last-ditch attempt to stop the dive by inverting it works in the movie, and for some reason they're able to roll back over again and crash land in a field. Alaska 261, by contrast, made a big, high-speed splash into the Pacific.


So yeah, it doesn't work in the real world after all.
 
2012-11-06 07:27:14 PM  
oh yea?

WELL, what if you put a 737 on a giant treadmill moving at 200 or whatever mph? Could the plane take off?

*runs away
 
2012-11-06 07:37:07 PM  
the problem with the movie is that the plane doesn't have hydraulics to begin with that would fail
 
2012-11-06 07:43:28 PM  

Rent Party: majestic: Rent Party: majestic: Rent Party: UberDave: Flying an aircraft that size upside down has to be tough. It's a different situation altogether.

There is a local Seattle test pilot for Boeing that got in trouble for doing a barrel roll with a new 707 right over the city. Everyone freaks out about it, but he just said "It was well within the flight capabilities of the aircraft, and I wanted to show it off to the customer." The customer was some Saudi dude who happened to be on board, and was apparently thrilled with the move.

Video Goodness of Said Event

That event (aileron roll of a Dash 80) was mentioned in TFA. What you state is not what happened, and not even what the video you linked claims. Go vote 3 or 4 more times. We need more like you!

Oh I'm sorry, why don't you tell me what bit of pedantry was wrong and then inform us that you've got 15 hours on a rented Cessna which is why you're such a farking expert, and then go fark off.

Dude rolled a 707 over Seattle. That's a fact. Dude said it was well within the flight capabilities of 707. That is also a fact. You are a complete douchebag. Yet another fact.

Over Lake Washington, not Seattle. No mention of any "Saudi dude" on-board, since it was a test flight. He did not even get in trouble as he was showcasing the planes abilities to the president of Boeing. Otherwise, everything you stated is correct. Which means you were incorrect about pretty much everything.

So, double douche-bag to you!

You must not be from around here. Lake Washington borders the entire eastern side of Seattle. Every inch of the city's eastern border is Lake Washington. So you're not only wrong, you're a douchebag pedant.

He got his ass chewed by the farking President of Boeing over it. So you're wrong again, and a douchebag pedant.

In other words, you're a douchebag pedant, just like I said. So do please fark off.


So we found your favorite word. We'll try to work it in from now on like on PWH's show so you can get some special cereal.

Ass-chewed test pilot retired with full benefits thanks to his daring and extreme pilot skills with "some Saudi dude who happened to be on board".

Pedant yourself in the arse, captain Unger.

/Atlantic Ocean runs right next to NYC.
 
2012-11-07 04:31:54 AM  

Click Click D'oh: No...It's not possible to do what is shown in the movie.

Yes, you can barrel roll and airliner, but it is not a barrel roll shown in the movie. It's an aileron roll. The difference is that in a barrel roll, a constant gravity is maintained, meaning things don't go flying about the cabin even when inverted. A barrel roll doesn't maintain a constant gravity, thus stuff flies about the cabin... as seen in the movie. The barrel roll actually gains altitude, the aileron roll losses altitude. Wings, when not stalled, always produce lift. If you turn them sideways, they produce lift sideways. If you turn them upside down, they produce lift towards the ground. So, rolling a plane upside down would actually make it fall faster unless the nose was pitched radically upwards using the angle of attack alone to produce lift. Commercial airliners do not have enough thrust to overcome gravity, and wing lift with angle of attack alone.

Denzel Washington would have killed his passengers faster, no save them.

Let's not even think about the weird outside aileron roll that would have resulted from trying to perform an aileron roll with the controls in full nose down deflection. 

I want to throw things at the TV ever time I see that crap.


Don't disconnect wing lift from AOA. A wing produces lift against whatever direction the air attacks them from. So an inverted wing can fly upwards or downwards depending on AOA.
 
2012-11-07 06:39:11 AM  
he even kept his sense of humor. After air traffic control cleared Flight 232 for an emergency landing at Sioux City, he quipped: "Roger. You want to be particular and make it a runway, huh?") His DC-10 cartwheeled off the runway into a cornfield, but 185 of the 296 passengers and crew on board survived.

Well. I suppose it's important to have a sense of humor just before killing over 100 people.
 
2012-11-07 08:37:20 AM  
so, i asked my Dad about it... He flew passenger jets for National Airlines then PanAm after flying Phantoms in Vietnam. Now retired... cheers

Well now----Having no clue what the movie is about--I will say that I did see an add on TV with a DC-9, or MD-88 flying up side down-- That said , the airplane was not made to sustain negative g's ergo the inverted flight is BS due to the fact that the fuel boost pumps in the wings only work with fuel around them and neg. g's puts the fuel on the top of the wing ergo no fuel to operate the engines. With full nose down component to roll inverted and sustain severe neg. g's to climb is a stretch. As to aileron roll vs. barrel roll--- same maneuver except that a barrel roll is around a spot on the horizon and an aileron roll is a yank and bank , no class maneuver.
99% of all pilots have had a drink or three and the best "sticks"I have ever known drank a lot, and I was not a half bad pilot.
 
2012-11-07 10:52:42 AM  

Rent Party: Lake Washington borders the entire eastern side of Seattle. Every inch of the city's eastern border is Lake Washington.

He got his ass chewed by the farking President of Boeing over it.


Over water != over land. And being asked what he was doing up there ("selling airplanes") is getting his "ass chewed"? But whatever - the real question is why you felt the need to make up a story about a Saudi Arabian "dude".
 
2012-11-07 02:43:46 PM  

Click Click D'oh: No, it's not. Even if you did manage to defy physics and fly the plane upside down using only angle of attack to keep it in the air (and somehow the suck elevators don't make you do outside loops until you stall and crash), there is still no airliner in service with landing gear on the crown of the fuselage so the whole crash and burn ending is still in play. As I have yet to find the switch to momentarily suspend physics in the event of an emergency, that really isn't an issue because the crash and burn will come right when it's expected.We aren't talking about fighter jets or acrobatic aircraft. Airliners don't do the upside down thing very well.


There's no defying of physics occurring there. Every wing is capable of inverted flight - the only question is the degree of efficiency and how much AoA you need to approximate the non-inverted performance of the wing. Whether the aircraft it's attached to can actually roll inverted is also a given - they all can, barring some kind of artificial restrictions on flight envelope like Airbus's fly-by-wire system. So the only real question is whether or not the aircraft the wing is attached to can actually sustain inverted flight. Does it have enough down elevator to maintain sufficient AoA to generate the required lift? Can it's engines operate inverted? Is some other system going to fail as a result of being inverted before any of that matters?

The movie makes the assumption (and nobody here is qualified to say definitively one way or another - it's not tested, listed or easily calculable) that the MD-80 - in a full nose-down trim event, has sufficient elevator authority to generate the required angle of attack to keep the plane in the air while inverted. They also make the assumption that the engines wouldn't survive this (which is a lot easier to guess at than flight control authority - they probably can't last upside down for very long at all), which kind of makes the last question a moot point.

Click Click D'oh: It's been tried, but that doesn't make it possible.


It's physically possible to roll any airplane inverted. Whether it's a sustainable or even recoverable situation once you're there, that depends on the aircraft.

Click Click D'oh: So yeah, it doesn't work in the real world after all.


Never said it could save the aircraft. People who think the crash scene in the movie is totally ridiculous are almost always focusing on the wrong part. There's no underlying physical law that prevents the sequence from happening more or less as advertised from the start of the dive until they're upside down. What doesn't jive is the part of the sequence where they roll the aircraft back over and appear to have solved their nose-down input problem.
 
2012-11-07 02:58:57 PM  

costermonger: What doesn't jive jibe is the part of the sequence where they roll the aircraft back over and appear to have solved their nose-down input problem.


/sorry, pet peebe
 
2012-11-07 04:30:18 PM  

Thunderboy: costermonger: What doesn't jive jibe is the part of the sequence where they roll the aircraft back over and appear to have solved their nose-down input problem.

/sorry, pet peebe


25.media.tumblr.com
 
2012-11-07 04:51:00 PM  

costermonger: There's no defying of physics occurring there. Every wing is capable of inverted flight - the only question is the degree of efficiency and how much AoA you need to approximate the non-inverted performance of the wing.


Hence, the denial of physics part. Since in order to generate lift using AoA alone, you induce drag that the aircraft could not produce enough thrust to maintain forward speed, would slow down rapidly and the then the whole crashing bit. As said previously, fighter jets and acrobatic airplanes can sustain inverted flight. Passenger jets can not... at least without physics looking the other way or the sudden addition of a couple extra engines.

costermonger: So the only real question is whether or not the aircraft the wing is attached to can actually sustain inverted flight.


So wait, you just said my statements were all wrong but then came to the same conclusion anyways?.... Seriously? Are you even reading before responding? I've been saying all along that an Airliner can not perform this maneuver. Note specific exemptions for fighter aircraft and acrobatic aircraft which can. I've been saying all along that a specific type of aircraft, with specific handling characteristics can not perform as shown on the movie, even though other classes of aircraft can. A rather silly thing to point out since the movie isn't about blue and gold painted F/A-18s. It's about an airliner. Hence, all my statements regarding the acrobatic maneuver in the movie are about the plane in the movie, and airliner.

costermonger: The movie makes the assumption (and nobody here is qualified to say definitively one way or another - it's not tested, listed or easily calculable) that the MD-80 - in a full nose-down trim event, has sufficient elevator authority to generate the required angle of attack to keep the plane in the air while inverted.


Elevator authority, although an interesting question, is simply a red herring on your part. There is plenty of authority to say that an MD-80 can not maintain flight on AoA alone independent of (and in fact directly opposed to) wing generated lift. It's a rather straight forward calculation of thrust capability, and wing area. The MD-80 doesn't have enough thrust to overcome the drag that would be required by the necessary AoA to fly an MD-80 without wing lift. It would rapidly lose speed, thus losing AoA generated lift, and plow into the ground inverted. No passenger airliner has enough thrust to fly on AoA alone.

costermonger: Never said it could save the aircraft. People who think the crash scene in the movie is totally ridiculous are almost always focusing on the wrong part


So wait, you're saying that what's portrayed in the movie isn't completely ridiculous because the first half is plausible... and just ignore that the second part is completely asinine?

You work for Mythbusters don't you?
 
2012-11-07 06:34:03 PM  

Click Click D'oh: Since in order to generate lift using AoA alone, you induce drag that the aircraft could not produce enough thrust to maintain forward speed, would slow down rapidly and the then the whole crashing bit

Click Click D'oh: Elevator authority, although an interesting question, is simply a red herring on your part. There is plenty of authority to say that an MD-80 can not maintain flight on AoA alone independent of (and in fact directly opposed to) wing generated lift.


I get it now. Somebody somewhere along the line taught you that lift generated by the wing is somehow different than lift generated by angle of attack.

That's wrong. There's no such distinction as "wing lift" and "AoA lift", and the things you're confusing them for don't oppose one another when inverted.

Here's why:

img20.imageshack.us

This chart shows a symmetrical wing* and the right side is called a coefficient of lift graph. Starting at zero, any increase in angle of attack is met with an increase in lift. This works both ways from zero, since this wing generates a CL (lift constant) of zero when it has zero degrees angle of attack. In the terms you're using, this wing generates absolutely zero lift without angle of attack. At 10° it produces a lift coefficient of 1.2 or so, which gets put into an equation factoring things like wing area, speed and air density into the equation and pumps out a lift value.

Notice, that when the angle of attack moves to -10°, it produces the inverse of it's 10°.. Which means that this wing would produce exactly the same amount of lift whether it's upright or inverted.

Now, this example is for a symmetrical wing, which never produces lift without an angle of attack - aka, no "wing lift" in your terms, I believe.

Here's an example of the AoA/Lift relationship for a non-symmetrical wing (specifically, this is from a business jet - it would be similar enough to a DC-9/MD-80, for which I couldn't easily find a graph):

img41.imageshack.us

So the way that you can tell this wing will produce lift at an AoA of zero is that it's CL curve crosses the 0° line with a positive CL - specifically, a CL of about 0.1. This would be more or less realistic for a jet aircraft designed for high speed transportation. That said, in order for this wing to produce anything approaching the required lift to get the aircraft it's attached to off the ground, it will need to include AoA. This wing generates "wing lift", but it amounts to a very small portion of the total lift this wing would be required to produce in actual use. There isn't an aircraft/wing combination cruising around anywhere in the world that doesn't have a positive angle of attack when just flying along. The slower you go, the greater than angle will be. Always.

Note that it is still capable of flying along inverted and generating lift. It requires a slightly higher angle of attack to generate the same CL (what CL is required is determined by the other factors I mentioned above - wing area, speed, air density - but if it needs to generate a CL of 0.5 to fly at 200kts at 10,000 feet, it can do that right side up with an AoA of 3°, or inverted with an AoA of 6°. The wing doesn't care. Reduce the CL required (by having a bigger wing, or flying faster, or being lower where the air is more dense) and you get even smaller AoA values for everything, making inverted flight even easier - from the wing's perspective.

Drag has broadly the same relationship with AoA as lift does, so you're right that the drag would be higher while inverted with a transport category aircraft, but you're wrong when you make the assumption that a plane "can not maintain flight on AoA alone".

tl;dr version: wings don't work the way you think they do.
 
2012-11-07 06:38:57 PM  

Click Click D'oh: So wait, you're saying that what's portrayed in the movie isn't completely ridiculous because the first half is plausible... and just ignore that the second part is completely asinine?You work for Mythbusters don't you?


Where'd I say the first bit?
 
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