4 ms·

I wonder what the failure modes for this would be like. Consider a Boeing 777X going along at its cruising speed and the locking mechanism for the wing tips ju

I wonder what the failure modes for this would be like. Consider a Boeing 777X going along at its cruising speed and the locking mechanism for the wing tips just disappears; primary and secondary. The wingtip is effectively unsecured. What happens?

theothermkn 8y ago
If we're going to do failure modes effects analysis, we'd need to know what the mechanism is in order to enumerate the possible failure modes (along with their likelihoods). For example, if the wing tips are actuated by a worm drive, then there is no "and the locking mechanism...just disappears;" The drive would be the locking mechanism. There are probably also suitable bistable mechanisms that lock in the open and closed positions, requiring actuation to unlock them. > What happens? In the large, I'm sure the teams of engineers at Boeing have it covered.
- theoh 8y ago
  The conventional locking mechanism that I've seen documented is like the lock on a bank vault: several pins, aligned with the hinge, which slide parallel to it, locking inboard and outboard sections in place. This locking mechanism means that the number of pins and their dimensions can be scaled to handle arbitrary loads, and there's no single point of failure.
  - VectorLock 8y ago
    Thats what it looks like just looking at the video. Some kind of pins that slide in when the hinge is fully down. So one in a billion confluence of errors makes the pins disengage in the middle of a flight. What happens?
    - theoh 8y ago
      Well, the lift on the wingtip is going to make it fold up. In the worst case, I guess it might break off, but it's a very small part of the wing, and it presumably doesn't contain fuel tanks. Chances of it damaging the inboard section have to be quite small and I wouldn't be surprised if the hinge is designed to cope with the forces involved. For comparison, see these stories of aircraft flying safely with a much larger wing area unintentionally folded: https://theaviationist.com/2014/02/19/us-navy-fighters-folded-wings/ https://theaviationist.com/2014/02/19/us-navy-fighters-folde...
      - NickNameNick 8y ago
        It might not even fold up. The wingtip probably incorporates some amount of wash-out (reduced or even negative angle of attack, as compared with the wing root) There might not be much or any upward force on it. Depending on how the actuators work, they may be strong enough to hold the wingtip in place without the locking mechanism.
        rlpb 8y ago
        If there's little or no upward force on it, they might as well not have the wingtips since they wouldn't be generating lift! (devices such as winglets excepted; I don't think that applies here)
        AceyMan 8y ago
        > [...] except for devices such as winglets You answered your own question and didn't know it. If the additional width added here has no net lift benefit but served as winglets do to reduce induced drag from the 'mixing boundary' but even more effectively – since the outward moving airmass doesn't have to accelerate (read: change direction) when it hits the base of the winglet, but instead gets to continue smoothly migrating to the tip – I can absolutely see how that would pay off in efficiency gains. Wings can be designed to have nearly arbitrary amounts of lift: reducing drag for a given amount of lift is the secret sauce, which could very well be what this design achieves. (me: FAA Licensed Dispatcher)
        theothermkn 8y ago
        Licensed to dispatch planes or not, everything you've said about fluid dynamics is wrong. You first seem to have confused "winglets" with "vortex generators." I think. The only winglike thing that messes with the viscous boundary layer is a VG. Second, winglets have nothing to do with a "mixing boundary;" They do what they do, even in completely inviscid flow, where there is no boundary layer. Third, whether an air mass has to "accelerate" has nothing to do with efficiency. For example, air is adiabatically compressed as it meets the stagnation point on a wing, or en masse as it enters a subsonic diffuser (jet intake). The former is a consequence of fluid flow in general, and the latter is by design. Both are completely isentropic and lead to no total pressure losses in the flow. Finally, it's meaningless to say that wings "can be designed to have...arbitrary amounts of lift," and plainly incorrect to say that drag is the "secret sauce." (Aeroelastic flutter? Wing mass? Control moments? Moment coefficients?) Reducing induced drag is done in exactly two ways. You either increase the span or put a winglet on so you can effectively increase the span while still being able to park the plane. Nobody thinks they can do brain surgery, but everybody is a fluid dynamicist.
- VectorLock 8y ago
  I'm sure they've covered it but I'm curious as to what exactly happens.
superfrank 8y ago
I am not in anyway an aerospace engineer, but from the bits I do know about airline safety, but that seems like a pretty obvious question to ask so I feel like this scenario has to have been considered. We just had that southwest flight land with a missing engine and a hole in the side, and back in the 80s we had that hawaiian flight land safely with the roof ripped off (https://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243 https://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243). Modern airliners are built to fly in some pretty insane conditions. I wouldn't want to be on the plane to find out, but my gut says you'd be fine.
Axsuul 8y ago
It's most likely accounted for. What happens is the plane takes on additional drag with decreased fuel efficiency. In the industry there is always a high safety factor when it comes to designing systems with human lives at risk. The same applies to something like elevators. Multiple suspension cables can snap and the power can go out and the elevator can still run.
- John_KZ 8y ago
  >What happens is the plane takes on additional drag with decreased fuel efficiency. Did you just assume that? Because I'm pretty sure that a folded wingtip in flight would result in a nearly unstoppable spiral of death.
  - mpweiher 8y ago
    Why are you so sure? I am not sure, but my educated guess would be towards the "additional drag, possibly asymmetric" scenario. Here's the story of the F-15 that was landed with an entire wing missing: https://theaviationist.com/2014/09/15/f-15-lands-with-one-wing/ https://theaviationist.com/2014/09/15/f-15-lands-with-one-wi... Parts of wings missing, engines falling off etc. happen. What wasn't survivable was the thrust reversers deploying in-flight: https://en.wikipedia.org/wiki/Lauda_Air_Flight_004 https://en.wikipedia.org/wiki/Lauda_Air_Flight_004 Oh, I stand corrected: "As evidence started to point towards the thrust reversers as the cause of the accident, simulator flights were made at Gatwick Airport which appeared to show that deployment of a thrust reverser was a survivable incident. Lauda said that the thrust reverser could not be the sole cause of the crash"
    - John_KZ 8y ago
      The aerodynamics of fighter jets are massively different from commercial airliners. The Lauda incident was "survivable" in the sense that they had a 3-second window to realize that the reverse thruster was deployed and take action. Without having any indication of what was happening, and with no training on what to do. So as you understand the statement was made purely to try and defend the manufacturer and airliner. Blaming pilots is a very economical way out. >Parts of wings missing, engines falling off etc. happen. There's only a handful of recorded engine losses (as in "ripped off the plane") of which not all were survivable. Also losing the engine is much better than damaging the wingtip. It's much closer to the body. And please substantiate on the "Part of wings missing all time" statement, like it's a casual thing that happens all the time. Do you have any cases where a large part of the wing was ripped off? Near the end? Because I'm not aware of a single one. Wing damage happens, but aerodynamically significant wing damage is rare and lethal.
namirez 8y ago
Nothing major will happen. If an aircraft loses one wingtip, the aerodynamic drag increases slightly (called the induced drag) which in turn causes a small moment about the vertical axis (yaw moment). The moment can be compensated by applying extra rudder.
SmellyGeekBoy 8y ago
The same could be said for any of the movable control surfaces, e.g. the flaps, ailerons, landing gear, rudder etc. The answer being that these things are tested to destruction and procedures and failsafes put in place when necessary. Edit: For the wingtips specifically I'd imagine not a lot of difference at all control-wise, just a loss of efficiency.

theothermkn 8y ago

If we're going to do failure modes effects analysis, we'd need to know what the mechanism is in order to enumerate the possible failure modes (along with their likelihoods). For example, if the wing tips are actuated by a worm drive, then there is no "and the locking mechanism...just disappears;" The drive would be the locking mechanism. There are probably also suitable bistable mechanisms that lock in the open and closed positions, requiring actuation to unlock them. > What happens? In the large, I'm sure the teams of engineers at Boeing have it covered.

theoh 8y ago
The conventional locking mechanism that I've seen documented is like the lock on a bank vault: several pins, aligned with the hinge, which slide parallel to it, locking inboard and outboard sections in place. This locking mechanism means that the number of pins and their dimensions can be scaled to handle arbitrary loads, and there's no single point of failure.
- VectorLock 8y ago
  Thats what it looks like just looking at the video. Some kind of pins that slide in when the hinge is fully down. So one in a billion confluence of errors makes the pins disengage in the middle of a flight. What happens?
  - theoh 8y ago
    Well, the lift on the wingtip is going to make it fold up. In the worst case, I guess it might break off, but it's a very small part of the wing, and it presumably doesn't contain fuel tanks. Chances of it damaging the inboard section have to be quite small and I wouldn't be surprised if the hinge is designed to cope with the forces involved. For comparison, see these stories of aircraft flying safely with a much larger wing area unintentionally folded: https://theaviationist.com/2014/02/19/us-navy-fighters-folded-wings/ https://theaviationist.com/2014/02/19/us-navy-fighters-folde...
    - NickNameNick 8y ago
      It might not even fold up. The wingtip probably incorporates some amount of wash-out (reduced or even negative angle of attack, as compared with the wing root) There might not be much or any upward force on it. Depending on how the actuators work, they may be strong enough to hold the wingtip in place without the locking mechanism.
      - rlpb 8y ago
        If there's little or no upward force on it, they might as well not have the wingtips since they wouldn't be generating lift! (devices such as winglets excepted; I don't think that applies here)
        AceyMan 8y ago
        > [...] except for devices such as winglets You answered your own question and didn't know it. If the additional width added here has no net lift benefit but served as winglets do to reduce induced drag from the 'mixing boundary' but even more effectively – since the outward moving airmass doesn't have to accelerate (read: change direction) when it hits the base of the winglet, but instead gets to continue smoothly migrating to the tip – I can absolutely see how that would pay off in efficiency gains. Wings can be designed to have nearly arbitrary amounts of lift: reducing drag for a given amount of lift is the secret sauce, which could very well be what this design achieves. (me: FAA Licensed Dispatcher)
        theothermkn 8y ago
        Licensed to dispatch planes or not, everything you've said about fluid dynamics is wrong. You first seem to have confused "winglets" with "vortex generators." I think. The only winglike thing that messes with the viscous boundary layer is a VG. Second, winglets have nothing to do with a "mixing boundary;" They do what they do, even in completely inviscid flow, where there is no boundary layer. Third, whether an air mass has to "accelerate" has nothing to do with efficiency. For example, air is adiabatically compressed as it meets the stagnation point on a wing, or en masse as it enters a subsonic diffuser (jet intake). The former is a consequence of fluid flow in general, and the latter is by design. Both are completely isentropic and lead to no total pressure losses in the flow. Finally, it's meaningless to say that wings "can be designed to have...arbitrary amounts of lift," and plainly incorrect to say that drag is the "secret sauce." (Aeroelastic flutter? Wing mass? Control moments? Moment coefficients?) Reducing induced drag is done in exactly two ways. You either increase the span or put a winglet on so you can effectively increase the span while still being able to park the plane. Nobody thinks they can do brain surgery, but everybody is a fluid dynamicist.
VectorLock 8y ago
I'm sure they've covered it but I'm curious as to what exactly happens.

superfrank 8y ago

I am not in anyway an aerospace engineer, but from the bits I do know about airline safety, but that seems like a pretty obvious question to ask so I feel like this scenario has to have been considered. We just had that southwest flight land with a missing engine and a hole in the side, and back in the 80s we had that hawaiian flight land safely with the roof ripped off (https://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243 https://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243). Modern airliners are built to fly in some pretty insane conditions. I wouldn't want to be on the plane to find out, but my gut says you'd be fine.

Axsuul 8y ago

It's most likely accounted for. What happens is the plane takes on additional drag with decreased fuel efficiency. In the industry there is always a high safety factor when it comes to designing systems with human lives at risk. The same applies to something like elevators. Multiple suspension cables can snap and the power can go out and the elevator can still run.

John_KZ 8y ago
>What happens is the plane takes on additional drag with decreased fuel efficiency. Did you just assume that? Because I'm pretty sure that a folded wingtip in flight would result in a nearly unstoppable spiral of death.
- mpweiher 8y ago
  Why are you so sure? I am not sure, but my educated guess would be towards the "additional drag, possibly asymmetric" scenario. Here's the story of the F-15 that was landed with an entire wing missing: https://theaviationist.com/2014/09/15/f-15-lands-with-one-wing/ https://theaviationist.com/2014/09/15/f-15-lands-with-one-wi... Parts of wings missing, engines falling off etc. happen. What wasn't survivable was the thrust reversers deploying in-flight: https://en.wikipedia.org/wiki/Lauda_Air_Flight_004 https://en.wikipedia.org/wiki/Lauda_Air_Flight_004 Oh, I stand corrected: "As evidence started to point towards the thrust reversers as the cause of the accident, simulator flights were made at Gatwick Airport which appeared to show that deployment of a thrust reverser was a survivable incident. Lauda said that the thrust reverser could not be the sole cause of the crash"
  - John_KZ 8y ago
    The aerodynamics of fighter jets are massively different from commercial airliners. The Lauda incident was "survivable" in the sense that they had a 3-second window to realize that the reverse thruster was deployed and take action. Without having any indication of what was happening, and with no training on what to do. So as you understand the statement was made purely to try and defend the manufacturer and airliner. Blaming pilots is a very economical way out. >Parts of wings missing, engines falling off etc. happen. There's only a handful of recorded engine losses (as in "ripped off the plane") of which not all were survivable. Also losing the engine is much better than damaging the wingtip. It's much closer to the body. And please substantiate on the "Part of wings missing all time" statement, like it's a casual thing that happens all the time. Do you have any cases where a large part of the wing was ripped off? Near the end? Because I'm not aware of a single one. Wing damage happens, but aerodynamically significant wing damage is rare and lethal.

namirez 8y ago

Nothing major will happen. If an aircraft loses one wingtip, the aerodynamic drag increases slightly (called the induced drag) which in turn causes a small moment about the vertical axis (yaw moment). The moment can be compensated by applying extra rudder.

SmellyGeekBoy 8y ago

The same could be said for any of the movable control surfaces, e.g. the flaps, ailerons, landing gear, rudder etc. The answer being that these things are tested to destruction and procedures and failsafes put in place when necessary. Edit: For the wingtips specifically I'd imagine not a lot of difference at all control-wise, just a loss of efficiency.