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> That might be the case for some systems, but it isn't the case for airliners. Some planes like the U-2 are notoriously hard to fly, and spacecraft definitely

by cbanek 9y ago

> That might be the case for some systems, but it isn't the case for airliners. Some planes like the U-2 are notoriously hard to fly, and spacecraft definitely require very fast reaction speeds. > You can still have a direct wire from the controls in the cockpit to the actuators that move the control surfaces, with no computer intervention. Not likely. You'll probably still need digital electronics to check that you aren't violating range of motion stops, or overtaxing the part or pushing it past its limits. Then to move one wing or do some logical action, you're really twiddling a dozen or more wires at the same time, in just the right way. That requires a different control mechanism that basically mimics the flight computer, and it's not something that I think a human or even a pair of humans can do. Now let's say you can wire everything up, and actually control it. That's so much wire which is a maintenance nightmare (just imagine if a few of these wires broke, and you didn't figure it out until you tried it). Not to mention the extreme weight of millions of long cable runs to the front of the aircraft. > If it were, humans would not have been able to fly them before fly-by-wire controlled by computers came along. I don't think airliners would be even close to where they are today without fly-by-wire. It's a game changing technology.

pdonis 9y ago
> Some planes like the U-2 are notoriously hard to fly Yes, because of the high altitude, which makes the safe flight regime much narrower. An airliner doesn't fly that high. > spacecraft definitely require very fast reaction speeds. Yes, but a spacecraft isn't an airliner. I specifically said it isn't the case for airliners. > You'll probably still need digital electronics to check that you aren't violating range of motion stops, or overtaxing the part or pushing it past its limits. Possibly. But those electronics should be separate from the automated flight computer. Btw, by "wire" I just meant "a direct means of sending information". It doesn't have to be a mechanical wire and pulley. I'm just saying that there ought to be a way of cutting out the flight computer's automated decision making and just letting the pilot's control inputs drive the control surfaces. > to move one wing or do some logical action, you're really twiddling a dozen or more wires at the same time, in just the right way There's no "twiddling". See above. > That's so much wire No, it's the same wire that already goes from the cockpit to the control actuators. See above. > I don't think airliners would be even close to where they are today without fly-by-wire In terms of comfort, convenience, and more economical operation when everything is working properly, sure, I absolutely agree. But as far as the basics of flight are concerned, they're still the same. It shouldn't be possible for a plane that was in safe straight and level flight to suddenly go haywire without the pilots being able to stop it, just because some computer crashed.
- foldr 9y ago
  >Btw, by "wire" I just meant "a direct means of sending information". It doesn't have to be a mechanical wire and pulley. I'm just saying that there ought to be a way of cutting out the flight computer's automated decision making and just letting the pilot's control inputs drive the control surfaces. This exists already in Airbus aircraft (Direct Law).
  - pdonis 9y ago
    > This exists already in Airbus aircraft (Direct Law). I can't tell from the article whether this mode was activated in the Quantas incident or not. It sounds like it was, but the article doesn't use precise terminology. The question I would have is, what happens to Direct Law if there is a computer crash? Could what is described in the article--pilot giving control input but plane not responding because computer is overriding it--happen under Direct Law? Could it happen under Direct Law if a computer crashed?
    - foldr 9y ago
      >what happens to Direct Law if there is a computer crash? I'm not quite sure what you mean by this. Are you talking about the flight control computers? If all of the redundant flight computers crash then the plane won't be controllable, but that is incredibly unlikely. It is like asking what will happen if all of the hydraulic systems fail, or if one of the wings fall off. If one of the flight control computers crashes, then that is one way of triggering a switch from Normal Law to Alternate Law. >Could what is described in the article--pilot giving control input but plane not responding because computer is overriding it--happen under Direct Law? No. Under Direct Law the pilots inputs are directly translated to control surface deflections.
      - pdonis 9y ago
        > Are you talking about the flight control computers? One out of three of them, yes. That's what happened in the Quantas flight. Would Direct Law still work under those conditions? > If one of the flight control computers crashes, then that is one way of triggering a switch from Normal Law to Alternate Law. Should that have happened in the Quantas flight described in the article? > Under Direct Law the pilots inputs are directly translated to control surface deflections. Hm. If that's true then the obvious thing for the pilots to do would have been to go into Direct Law mode, but I don't see that mentioned in the article.
JumpCrisscross 9y ago
> spacecraft definitely require very fast reaction speeds Transatmospheric "flight" is practically impossible for a human to directly control. Even in a simulation, the changing atmospheric density's nonlinear effects on lift and drag require real-time calculus in a way we have not evolved to process. Add to that turbulence, et cetera, and the effort quickly becomes futile.
- cbanek 9y ago
  Totally agree. Really I meant reaction / processing times. Although there was one time that comes to mind (less flight and more falling): https://en.wikipedia.org/wiki/Mercury-Atlas_9 https://en.wikipedia.org/wiki/Mercury-Atlas_9

by cbanek 9y ago

pdonis 9y ago

> Some planes like the U-2 are notoriously hard to fly Yes, because of the high altitude, which makes the safe flight regime much narrower. An airliner doesn't fly that high. > spacecraft definitely require very fast reaction speeds. Yes, but a spacecraft isn't an airliner. I specifically said it isn't the case for airliners. > You'll probably still need digital electronics to check that you aren't violating range of motion stops, or overtaxing the part or pushing it past its limits. Possibly. But those electronics should be separate from the automated flight computer. Btw, by "wire" I just meant "a direct means of sending information". It doesn't have to be a mechanical wire and pulley. I'm just saying that there ought to be a way of cutting out the flight computer's automated decision making and just letting the pilot's control inputs drive the control surfaces. > to move one wing or do some logical action, you're really twiddling a dozen or more wires at the same time, in just the right way There's no "twiddling". See above. > That's so much wire No, it's the same wire that already goes from the cockpit to the control actuators. See above. > I don't think airliners would be even close to where they are today without fly-by-wire In terms of comfort, convenience, and more economical operation when everything is working properly, sure, I absolutely agree. But as far as the basics of flight are concerned, they're still the same. It shouldn't be possible for a plane that was in safe straight and level flight to suddenly go haywire without the pilots being able to stop it, just because some computer crashed.

foldr 9y ago
>Btw, by "wire" I just meant "a direct means of sending information". It doesn't have to be a mechanical wire and pulley. I'm just saying that there ought to be a way of cutting out the flight computer's automated decision making and just letting the pilot's control inputs drive the control surfaces. This exists already in Airbus aircraft (Direct Law).
- pdonis 9y ago
  > This exists already in Airbus aircraft (Direct Law). I can't tell from the article whether this mode was activated in the Quantas incident or not. It sounds like it was, but the article doesn't use precise terminology. The question I would have is, what happens to Direct Law if there is a computer crash? Could what is described in the article--pilot giving control input but plane not responding because computer is overriding it--happen under Direct Law? Could it happen under Direct Law if a computer crashed?
  - foldr 9y ago
    >what happens to Direct Law if there is a computer crash? I'm not quite sure what you mean by this. Are you talking about the flight control computers? If all of the redundant flight computers crash then the plane won't be controllable, but that is incredibly unlikely. It is like asking what will happen if all of the hydraulic systems fail, or if one of the wings fall off. If one of the flight control computers crashes, then that is one way of triggering a switch from Normal Law to Alternate Law. >Could what is described in the article--pilot giving control input but plane not responding because computer is overriding it--happen under Direct Law? No. Under Direct Law the pilots inputs are directly translated to control surface deflections.
    - pdonis 9y ago
      > Are you talking about the flight control computers? One out of three of them, yes. That's what happened in the Quantas flight. Would Direct Law still work under those conditions? > If one of the flight control computers crashes, then that is one way of triggering a switch from Normal Law to Alternate Law. Should that have happened in the Quantas flight described in the article? > Under Direct Law the pilots inputs are directly translated to control surface deflections. Hm. If that's true then the obvious thing for the pilots to do would have been to go into Direct Law mode, but I don't see that mentioned in the article.

JumpCrisscross 9y ago

> spacecraft definitely require very fast reaction speeds Transatmospheric "flight" is practically impossible for a human to directly control. Even in a simulation, the changing atmospheric density's nonlinear effects on lift and drag require real-time calculus in a way we have not evolved to process. Add to that turbulence, et cetera, and the effort quickly becomes futile.

cbanek 9y ago
Totally agree. Really I meant reaction / processing times. Although there was one time that comes to mind (less flight and more falling): https://en.wikipedia.org/wiki/Mercury-Atlas_9 https://en.wikipedia.org/wiki/Mercury-Atlas_9