3 ms·

> insufficiently stable to meet certification requirements Sounds like unstable to me. "I am not fat, I am just insufficiently thin".

na85 7y ago
It's stable. In aerodynamics, stability has a specific meaning and it's possible for two things to be stable, and for one of those things to be less stable than the other. Picture a pendulum that is hinged on a greased axle vs one that is hinged on a high-friction axle. Both will reach equilibrium eventually (they're stable) but one will do it faster/with fewer oscillations. The 737 MAX is longitudinally stable, but it doesn't meet certain nuanced requirements of the Airworthiness regs.
- tim333 7y ago
  Seems so. More info here: https://www.quora.com/Is-the-Boeing-737-MAX-aerodynamically-unstable-I-have-read-that-the-new-heavier-and-higher-mounted-engines-have-changed-its-center-of-gravity/answer/Alan-Dicey https://www.quora.com/Is-the-Boeing-737-MAX-aerodynamically-... > what happens is that the stick force lessens as angle of attack increases at high AoA and low airspeed, whereas in order to be compliant with certification it has to gradually increase with increasing AoA, just like a 737–100.
- petilon 7y ago
  There is so much doublespeak here. If it is less stable than required for airworthiness then it is not airworthy. Can we agree on that?
  - na85 7y ago
    Sure, but that doesn't mean it's unstable.
    - petilon 7y ago
      If it is not stable enough then it is unstable. Where do you draw the bar on stability, if not airworthiness?
      - na85 7y ago
        >If it is not stable enough then it is unstable. Nope, sorry, that's not what stability and instability mean. Stability means it will return to equilibrium if disturbed, but the issue with the MAX is that it requires a positive force gradient per the Part 25 Airworthiness Regulations, which the MAX does not exhibit in a specific part of the envelope. Stability is not a binary condition. The MAX is longitudinally stable in every part of the flight envelope. "Not airworthy" does not equate to "unstable". Those two terms are orthogonal.

na85 7y ago

It's stable. In aerodynamics, stability has a specific meaning and it's possible for two things to be stable, and for one of those things to be less stable than the other. Picture a pendulum that is hinged on a greased axle vs one that is hinged on a high-friction axle. Both will reach equilibrium eventually (they're stable) but one will do it faster/with fewer oscillations. The 737 MAX is longitudinally stable, but it doesn't meet certain nuanced requirements of the Airworthiness regs.

tim333 7y ago
Seems so. More info here: https://www.quora.com/Is-the-Boeing-737-MAX-aerodynamically-unstable-I-have-read-that-the-new-heavier-and-higher-mounted-engines-have-changed-its-center-of-gravity/answer/Alan-Dicey https://www.quora.com/Is-the-Boeing-737-MAX-aerodynamically-... > what happens is that the stick force lessens as angle of attack increases at high AoA and low airspeed, whereas in order to be compliant with certification it has to gradually increase with increasing AoA, just like a 737–100.
petilon 7y ago
There is so much doublespeak here. If it is less stable than required for airworthiness then it is not airworthy. Can we agree on that?
- na85 7y ago
  Sure, but that doesn't mean it's unstable.
  - petilon 7y ago
    If it is not stable enough then it is unstable. Where do you draw the bar on stability, if not airworthiness?
    - na85 7y ago
      >If it is not stable enough then it is unstable. Nope, sorry, that's not what stability and instability mean. Stability means it will return to equilibrium if disturbed, but the issue with the MAX is that it requires a positive force gradient per the Part 25 Airworthiness Regulations, which the MAX does not exhibit in a specific part of the envelope. Stability is not a binary condition. The MAX is longitudinally stable in every part of the flight envelope. "Not airworthy" does not equate to "unstable". Those two terms are orthogonal.