3 ms·

I don't know, I feel like designing a system to prevent a pilot from lifting nose too high up seems to make more sense than a system that actively pushes the no

by kovac 7y ago

I don't know, I feel like designing a system to prevent a pilot from lifting nose too high up seems to make more sense than a system that actively pushes the nose down after it being lifted. If nothing else, passengers would feel a bit of a discomfort of a sudden nose down movement. Not sure if I missed something in the current design.

WalterBright 7y ago
> I feel like designing a system to prevent a pilot from lifting nose too high up seems to make more sense than a system that actively pushes the nose down after it being lifted Lifting the nose too high can induce a stall, which is very dangerous at low altitude.
- hef19898 7y ago
  Yep. Also pitching the nose to far down to prevent a stall.
numpad0 7y ago
No it's not about comfort. MAX engine shroud is too far forward to the point it act as canards creating pitch up force at high AoA, in a self reinforcing manner into a belly up into irrecoverable stall. MCAS prevents this by quickly pushing nose down back into airstream. I believe there were discussions earlier on that the FAA requires all civilian airliners to have positive static stability, aka CoL comfortably behind CG so air resistance straightens the attitude without inputs. The opposite of positive static stability is Fly By Wire based 4th-gen onwards jet fighters like F-16, that has CoL only barely aft of CG, that replace aerodynamic stability with electronic PID controllers multiplexed with manual axis inputs for each axes. Those planes could go into a spin over some axis that make sense if at any moment FBW loses control. The fact that MAX needed MCAS, an FBW-like system, to meet FAA standards is itself wrong, and implementation to make it a ghetto nonredundant trim system rather than full FBW is also wrong.
- WalterBright 7y ago
  > into irrecoverable stall My understanding is it wasn't enough to push it into a stall, the MCAS would just moderate the pitch up slightly so it behaved like the 737. > to meet FAA standards is itself wrong The FAA mandates that all jet airliners since the 707 have a yaw damper to correct for "dutch roll" instability. Augmented controls are normal on jets.
- rbanffy 7y ago
  > The opposite of positive static stability is Fly By Wire based 4th-gen onwards jet fighters like F-16 The risks introduced by fighter jet lack of static stability are mitigated by the installation of ejection seats. That's a tough sell for passenger aircraft.
  - foldr 7y ago
    The 737 MAX is statically stable. There are quite a lot of uninformed comments floating around that compare the plane to fighter jets like the F-16, but these are pure nonsense. An F-16 would tear itself to pieces in seconds if the flight control software malfunctioned.
    - bkor 7y ago
      It seems more to be that people use the word "stable" while maybe another word should've been used. The main criticism during the "stable" criticisms is that something like MCAS was added. The design of the plane should've been in such a way that MCAS wouldn't be needed. So instead of adding MCAS, the problem leading to MCAS should've been solved with a (huge) redesign. Note: Purely responding to the "stable" word. If people compare it to stuff like an F-16, then yeah.. they don't know / nonsense.
- foldr 7y ago
  >MCAS, an FBW-like system As WalterBright says, there is nothing 'FBW' about stability augmentation systems. In various forms these have been installed on all commercial jets for decades. 'Fly by Wire' simply means that there is no mechanical/hydraulic linkage between the stick and the control surfaces. The 737 MAX is not an FBW aircraft by any stretch of the imagination.

by kovac 7y ago

WalterBright 7y ago

> I feel like designing a system to prevent a pilot from lifting nose too high up seems to make more sense than a system that actively pushes the nose down after it being lifted Lifting the nose too high can induce a stall, which is very dangerous at low altitude.

hef19898 7y ago
Yep. Also pitching the nose to far down to prevent a stall.

numpad0 7y ago

No it's not about comfort. MAX engine shroud is too far forward to the point it act as canards creating pitch up force at high AoA, in a self reinforcing manner into a belly up into irrecoverable stall. MCAS prevents this by quickly pushing nose down back into airstream. I believe there were discussions earlier on that the FAA requires all civilian airliners to have positive static stability, aka CoL comfortably behind CG so air resistance straightens the attitude without inputs. The opposite of positive static stability is Fly By Wire based 4th-gen onwards jet fighters like F-16, that has CoL only barely aft of CG, that replace aerodynamic stability with electronic PID controllers multiplexed with manual axis inputs for each axes. Those planes could go into a spin over some axis that make sense if at any moment FBW loses control. The fact that MAX needed MCAS, an FBW-like system, to meet FAA standards is itself wrong, and implementation to make it a ghetto nonredundant trim system rather than full FBW is also wrong.

WalterBright 7y ago
> into irrecoverable stall My understanding is it wasn't enough to push it into a stall, the MCAS would just moderate the pitch up slightly so it behaved like the 737. > to meet FAA standards is itself wrong The FAA mandates that all jet airliners since the 707 have a yaw damper to correct for "dutch roll" instability. Augmented controls are normal on jets.
rbanffy 7y ago
> The opposite of positive static stability is Fly By Wire based 4th-gen onwards jet fighters like F-16 The risks introduced by fighter jet lack of static stability are mitigated by the installation of ejection seats. That's a tough sell for passenger aircraft.
- foldr 7y ago
  The 737 MAX is statically stable. There are quite a lot of uninformed comments floating around that compare the plane to fighter jets like the F-16, but these are pure nonsense. An F-16 would tear itself to pieces in seconds if the flight control software malfunctioned.
  - bkor 7y ago
    It seems more to be that people use the word "stable" while maybe another word should've been used. The main criticism during the "stable" criticisms is that something like MCAS was added. The design of the plane should've been in such a way that MCAS wouldn't be needed. So instead of adding MCAS, the problem leading to MCAS should've been solved with a (huge) redesign. Note: Purely responding to the "stable" word. If people compare it to stuff like an F-16, then yeah.. they don't know / nonsense.
foldr 7y ago
>MCAS, an FBW-like system As WalterBright says, there is nothing 'FBW' about stability augmentation systems. In various forms these have been installed on all commercial jets for decades. 'Fly by Wire' simply means that there is no mechanical/hydraulic linkage between the stick and the control surfaces. The 737 MAX is not an FBW aircraft by any stretch of the imagination.