Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: earl1937 on December 31, 2014, 05:36:48 AM
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:airplane: In light of the aircraft accidents recently in Asia, it got me to thinking about the size of airliners and where is the maximum size which we will ever see in aircraft design! I think the Boeing 767, 777 series of aircraft are about as big as they should ever get. The 777's wings "flex" a total of 54 feet, 27 feet up or down during flight and I have to wonder, what actually happens to that wing, if they should stumble into a thunderstorm of any size. I know they have to have flex, because if they didn't, things would break a lot quicker! I realize the flex contributes to a "smoother" ride for the paying customers, but at what point does that flex become a danger to the flight of the aircraft?
Then you have the 737 that just ran off the end of the runway yesterday, have the aircraft gotten to heavy to be forgiving at all? Makes you wonder! There just doesn't seem to be any margin for pilot error in these new, big and wonderful, if the weather is good, aircraft!
I know that we have all these graphs and charts on what we are suppose to do and how to safely fly the aircraft, but it still comes down to the "skill" of the pilot! That is a problem that is always going to be with us, no matter what!
Just like the 737 that ran off the end of the runway, the captain knew he was to fast and to high to get the thing down, but he was flying in a "monsoon" weather event and he didn't want to go around, I guess, but he wound up being real lucky that the aircraft didn't break up and kill a bunch of people!
Seems like airline accidents comes in "3's", now we have had two, just wonder what the third will be like?
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Sorry to be the bearer of bad news but this is the 3rd airplane accident this year with a Malaysian airline. Can't forget the one that was shot down over the Ukraine. :(
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.........and the 380 trumps the 777 in almost every aspect.
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I posted this in the aircraft and vehicle forums back in July. Not a passenger plane but...
There was a thread titled "What do you consider a beast?" I think this qualifies. It took off from Minneapolis St. Paul International today. I didn't see it but caught it on the news:
(http://upload.wikimedia.org/wikipedia/commons/0/06/Antonov_An-225_Manchester_Coleman.jpg)
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Sorry to be the bearer of bad news but this is the 3rd airplane accident this year with a Malaysian airline. Can't forget the one that was shot down over the Ukraine. :(
That one was no accident. It was a terrorist crime.
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Yes Ripley I agree, I should have made it more clear. Was just trying to say that the 3rd has already happened. That is all... :salute
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:airplane: In light of the aircraft accidents recently in Asia, it got me to thinking about the size of airliners and where is the maximum size which we will ever see in aircraft design! I think the Boeing 767, 777 series of aircraft are about as big as they should ever get. The 777's wings "flex" a total of 54 feet, 27 feet up or down during flight and I have to wonder, what actually happens to that wing, if they should stumble into a thunderstorm of any size. I know they have to have flex, because if they didn't, things would break a lot quicker! I realize the flex contributes to a "smoother" ride for the paying customers, but at what point does that flex become a danger to the flight of the aircraft?
Then you have the 737 that just ran off the end of the runway yesterday, have the aircraft gotten to heavy to be forgiving at all? Makes you wonder! There just doesn't seem to be any margin for pilot error in these new, big and wonderful, if the weather is good, aircraft!
I know that we have all these graphs and charts on what we are suppose to do and how to safely fly the aircraft, but it still comes down to the "skill" of the pilot! That is a problem that is always going to be with us, no matter what!
Just like the 737 that ran off the end of the runway, the captain knew he was to fast and to high to get the thing down, but he was flying in a "monsoon" weather event and he didn't want to go around, I guess, but he wound up being real lucky that the aircraft didn't break up and kill a bunch of people!
Seems like airline accidents comes in "3's", now we have had two, just wonder what the third will be like?
How does the wing flex on the 787 compare to the 777? I recall seeing some pictures of it in flight and being amazed at how much those wings are flexing.
Then you have gliders like this:
(http://www.sailplanedirectory.com/data/planes/images/99_4_B.jpg)
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...I realize the flex contributes to a "smoother" ride for the paying customers, but at what point does that flex become a danger to the flight of the aircraft?
Very good point - especially in light of the recent AirAsia - it seems that the flex is probably what killed the aircraft. That's two regional jets that have gone down in that area due to thunderstorms in the past 5 years. While the flex offers a smoother ride, it also causes metal fatigue and other joint issues versus a sturdier design of most 1940-1950 designed birds. I'm sure that a tired bird (like the A320 that had over 13'000 flights) tolerances were also part of the problem of the break-up.
Boeing and others in the 50's found out that allowing flex in the wingspan allows for a more comfortable ride but at what cost? Do composite materials eliminate some of that metal fatigue we often see as causes of air disasters?
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I posted this in the aircraft and vehicle forums back in July. Not a passenger plane but...
There was a thread titled "What do you consider a beast?" I think this qualifies. It took off from Minneapolis St. Paul International today. I didn't see it but caught it on the news:
<snip>
So what do you suppose the com instruction for G-BCJN was? "Hold short. Hold very, very, very short." ;)
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What killed the recent air asia plane was flying into conditions with updrafts capable of sending fist sized hailstones up for another layer.
That will break apart most any plane.
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I think the size of an aircraft is only limited by the airport infrastructure it requires. At some point the size of the aircraft will be limited by the space it occupies and the length of time it has to remain on the ground, which will no longer justify the dimensions.
However, I will take big over fast. I can't imagine sucking up the climbout or the descent required for hypersonic flight.
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Much has to do with the weight and the area.
In that, I don't mean PSI but rather pounds per a larger area such as 1000sq feet (that figure just a random figure) but you get my drift.
A large plane such as the russian one shown earlier might be within PSI of most ramps but I'll bet it's main gear footprint could buckle some ramps.
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I ran across this recently. Wing testing to catastrophic failure of a 777.
http://m.youtube.com/watch?feature=youtu.be&v=rak2HldVp9M
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I ran across this recently. Wing testing to catastrophic failure of a 777.
http://m.youtube.com/watch?feature=youtu.be&v=rak2HldVp9M
:airplane: Very good! It just points out what I am trying to point out and someone else addressed this also, at what point does wing "flex" become a danger to flight? While I know the aircraft in the 40's-50's were more of a ridged design, you didn't hear of any of them breaking up in flight! Personally, I rather endure a few bumps as a wing failure!
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A flexible structure is safer than a rigid one, not the other way around.
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A flexible structure is safer than a rigid one, not the other way around.
You cant generalize it that easily. Depending on the type of material (metal), some have endurance limits while others do not. Some metals will even crack and fail regardless of how low the stress and vibrations, while others have to reach a certain 'endurance limit' (stress X cycles) before they will even began to start initiating fatigue cracks.
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I though it was safe to assume aircraft designers use suitable materials...
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Almost the entire inventory of U.S. F-16s and B-1bs have cracks. The material of construction is the limiting factor. Aluminum cracks, steel is heavy, carbon fiber delaminates, etc. There is no 'super material' out there.
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:airplane:
A flexible structure is safer than a rigid one, not the other way around.
:airplane: Not sure if you thought though your post, but with flex, comes a lot of problems and that is what i am trying to point out! At what point, or in other words, how many times can a metal object "flex" before fatigue cause the metal to fail?
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All metal wings flex. It's just a matter of how much. Even back in WWII. How many people here are aeronautical egineers anyway? I sure am not...
Here's a venerable old 747. Plently of wing flexing. This is a non-issue.
https://www.youtube.com/watch?v=WFEs-DatuHs
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All metal wings flex. It's just a matter of how much. Even back in WWII. How many people here are aeronautical egineers anyway? I sure am not...
Here's a venerable old 747. Plently of wing flexing. This is a non-issue.
https://www.youtube.com/watch?v=WFEs-DatuHs
On the ground you can't see the wingtiip of the B-24 from the pilot seat. Once in the air the wing flexes a small amount and you can see the wingtip.
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Yes, it is nigh impossible to construct a metal structure that doesn't flex under load. Skyscrapers flex in windy conditions. Even the Eiffel Tower bends and twists in wind and from sun heating.
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Yes, it is nigh impossible to construct a metal structure that doesn't flex under load. Skyscrapers flex in windy conditions. Even the Eiffel Tower bends and twists in wind and from sun heating.
Yep. You could really feel it in the old World Trade Center buildings.
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All metal wings flex. It's just a matter of how much. Even back in WWII. How many people here are aeronautical egineers anyway? I sure am not...
Here's a venerable old 747. Plently of wing flexing. This is a non-issue.
https://www.youtube.com/watch?v=WFEs-DatuHs
I was reading one of the comments, is it true that when the wing flex limit is reached, the outer engines are designed to break off?
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I have no idea. Sorry.
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A flexible structure is safer than a rigid one, not the other way around.
:airplane: "Ah, finally a response from an "aircraft engineer"!
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That's my point. Why are we even discussing it? I'm pretty sure the guys who actually are aeronautical engineers know what they're doing when they design these aircraft. By comparison we're like 8 year olds arguing over how best to screw a hooker in Bangkok...
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why bring up wing flex anyway.. are wings falling off planes?
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Very good point - especially in light of the recent AirAsia - it seems that the flex is probably what killed the aircraft. .........I'm sure that a tired bird (like the A320 that had over 13'000 flights) tolerances were also part of the problem of the break-up.
Far, far to early to assume the above.
Just saying
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Far, far to early to assume the above.
Agreed. Latest I heard suggested that ice was the culprit.
- oldman
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Wing flex is simply the cumulative deformation of the material. All materials deform under the stress induced by a load - it is called strain. If you have the same load then a thick section will have less stress and therefore less strain/deformation/flex but more weight.
The idea of not flexing or they will break is 99% of the time wrong. Flexing is only a good thing if it reduces the load in a desirable fashion, or if the parts it is attached to are going to move relative to each other no matter what (enforced displacement). So a skyscraper flexing in the wind doesn't relieve any load it is just the material straining under the stress. Again more material would cause less stress and therefore strain/deformation/flex but material isn't free or weightless. In an aircraft the wing center section is under considerable stress. It deforms. The fuselage is pressurized. It deforms. if you try to rivet a stiff piece of metal between the wing center and the fuselage it is going to break, because of those enforced displacements. So those parts are purposely made flexible (The wing attachment to the fuselage are point connections usually).
So flex is just the nature of the beast. The problem with flex isn't with strength of the wing. Wing flexing changes the aerodynamics of the wing and must be very carefully accounted for. Additionally there is the problem of the wing can act like a huge flat spring vibrating up and down and twisting. If the aerodynamic effects act at a frequency that enforces that vibration it can get ugly very fast.
As far as cracking goes, cracks grow differently in thin metals then thick metals. Thin ductile metals will usually give you plenty of time to inspect and find a growing crack. Thick ductile metals tend to grow cracks rapidly once they reach a certain size. That is why landing gear, helicopter rotor parts, etc are often life limited and have to be replaced a certain number of hours or flights.
In the old days aircraft parts might be sized based on a dozen conditions with huge multipliers added to ensure the parts were adequate. Now hundreds of combinations of conditions are considered and the parts can be ensured to be adequate with much smaller multipliers. This leads to lighter weight and often actually overall stronger structures.
So a few paragraph summary of years of study.
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Thanks :salute