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Runway Incursion at Shanghai Hongqiao Airport

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  • #16
    Originally posted by Gabriel View Post
    In an Airbus in normal law, pulling back relentlessly on the sidestick will not result in a relentless pull-up simply because HAL won't follow your commands.
    Maybe I'm arguing over semantics, but I'm not sure it's correct to say "Hal won't follow your command", because it will give you the maximum available nose-up without stalling

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    • #17
      Originally posted by Black Ram View Post
      Maybe I'm arguing over semantics, but I'm not sure it's correct to say "Hal won't follow your command", because it will give you the maximum available nose-up without stalling
      Maybe I'm arguing over details, but it won't do that either.

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      • #18
        Originally posted by Black Ram View Post
        Maybe I'm arguing over semantics, but I'm not sure it's correct to say "Hal won't follow your command", because it will give you the maximum available nose-up without stalling
        Below certain speed threshold it will give you a load factor proportional to the stick displacement. 100% stick back will be 2.5G.
        Below that threshold, it will give you a pitch rate proportional to the stick displacement. At 100% stick back it will be... I don't remember... was it 5 deg per sec?
        In both cases, the AoA will be capped first by Alpha max, so if Alpha max is achieved before 2.5G or 5 deg per sec, it will not pitch up past Alpha max.
        Alpha max is less than Alpha stall.

        I am simplifying. There are changes in the behavior as you pass through Alpha floor and Alpha proc before reaching Alpha max.

        And during the take-off run, rotation and the very first seconds of climb, the behavior is also different, as explained by Evan.

        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
        --- Defend what you say with arguments, not by imposing your credentials ---

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        • #19
          Originally posted by Evan View Post
          FBW itself is just a means of translating pilot commands into flight surface movements... It's almost funny how ignorant everyone on aviation forums are about FBW. They spout this kind of nonsense as if legions of aerospace engineers are just complete idiots. If you knew how much redundancy Airbus had to build into the A320 to get it certified, how paranoid the regulators were and how over three decades that redundancy has never been needed to it's full extent you might begin to understand how counter-productive all this scarebus chatter is.
          For the record, I have nothing against FBW. I do have some objections to Airbus' approach to FBW, i.e the "transfer function" that "translates pilot commands into flight surface movements". Do I think it's unsafe? No. But I do like Boeing's approach better.

          --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
          --- Defend what you say with arguments, not by imposing your credentials ---

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          • #20
            Originally posted by Gabriel View Post
            For the record, I have nothing against FBW. I do have some objections to Airbus' approach to FBW, i.e the "transfer function" that "translates pilot commands into flight surface movements". Do I think it's unsafe? No. But I do like Boeing's approach better.
            Boeing is also using c-star control law. What do you mean by "transfer function"?

            I probably prefer the yoke/column as a FBW traducer. The sidestick was a noble idea inspired by the space program but it really overestimated pilots not trained in a space program.

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            • #21
              Originally posted by Gabriel View Post
              Below certain speed threshold it will give you a load factor proportional to the stick displacement. 100% stick back will be 2.5G.
              Below that threshold, it will give you a pitch rate proportional to the stick displacement. At 100% stick back it will be... I don't remember... was it 5 deg per sec?
              In both cases, the AoA will be capped first by Alpha max, so if Alpha max is achieved before 2.5G or 5 deg per sec, it will not pitch up past Alpha max.
              Alpha max is less than Alpha stall.

              I am simplifying. There are changes in the behavior as you pass through Alpha floor and Alpha proc before reaching Alpha max.

              And during the take-off run, rotation and the very first seconds of climb, the behavior is also different, as explained by Evan.
              If you command a pitch/speed scenario that results in a dangerously elevated AoA (barberpole on the speed tape), you enter the alpha protect regime. At that point stick deflection commands AoA directly, not pitch rate or load factor. You can still increase pitch, but the limit is alpha max, a safe margin below stall. If you hold full aft sidestick, you will be flying safely at alpha max. If you release it, it goes back down to alpha protect. If you firewall the thrust and yank full back stick, I'm told all bets are off and you may even exceed CL max and momentarilly stall.

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              • #22
                Originally posted by Evan View Post
                Boeing is also using c-star control law. What do you mean by "transfer function"?

                I probably prefer the yoke/column as a FBW traducer. The sidestick was a noble idea inspired by the space program but it really overestimated pilots not trained in a space program.
                I don't know what is C*, but I thought Boeing was using U*.
                In any event, in Boeing the yoke deflection is related with a speed offset from the trim speed (which, for practical terms, means an AoA offset from the trim AoA as long as you are not changing the flaps or spoilers settings). If you reduce thrust and don't touch the yoke the nose will go down to keep the speed/AoA. In an Airbus, the nose will go up to keep 1G or will stay put to keep zero pitch rate.

                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                --- Defend what you say with arguments, not by imposing your credentials ---

                Comment


                • #23
                  Originally posted by Gabriel View Post
                  I don't know what is C*, but I thought Boeing was using U*.
                  In any event, in Boeing the yoke deflection is related with a speed offset from the trim speed (which, for practical terms, means an AoA offset from the trim AoA as long as you are not changing the flaps or spoilers settings). If you reduce thrust and don't touch the yoke the nose will go down to keep the speed/AoA. In an Airbus, the nose will go up to keep 1G or will stay put to keep zero pitch rate.
                  Boeing uses a variation of C* called C*U, which is basically C* control law with the addition of artificial speed stability. Both the Airbus and Boeing versions of C* translate pilot commands to flight surface movements. Boeing's just provides more traditional feedback with soft protections whereas Airbus has done away with manual trim altogether and added hard protections.

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