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> "A stick pusher, or a pilot pushing forward on the stick is not enough for the aerodynamics of the 737 MAX in certain circumstances. The position of the engin

> "A stick pusher, or a pilot pushing forward on the stick is not enough for the aerodynamics of the 737 MAX in certain circumstances. The position of the engines means the thrust tends to push the nose up, and at low speed, the elevator controlled by the stick alone is not enough to push the nose down when nearing a stall. Instead, the trim must be used, which moves the whole horizontal stabilizer rather than just the elevator. That's not part of the procedure on most aircraft, including other 737s, so regulators would not allow pilots rated for 737s to easily transfer their rating to the new aircraft, if they were willing to certify such an aircraft at all." I believe this is incorrect. From what I understand, the 737 NGs and 737 MAXes both pitch up when thrust is increased and both may need to be trimmed back to counteract this. The reason MCAS is there is because the characteristics of the MAX are different from NG (that is, the airspeeds and angles of attack at which particular trims are required have changed), making the MCAS system regulatorily necessary, not mechanically necessary. Because either the MAX needs a system that emulates the handling of the NG, or pilots need to be trained specifically for the MAX, and the former is cheaper. In other words the MAX is not objectively mechanically worse, but rather objectively mechanically different.

Zak 8y ago
All jets with low wings and underslung engines (most modern airliners) experience a pitch-up moment from engine thrust, and trim is used to compensate. When the plane is being flown in some steady state, pilots adjust the trim until no force on the controls is required to maintain that state - they're not getting a specific setting from a table or memory. What's different is that at low speed, high thrust, and high angle of attack, the elevator of the MAX does not always have enough pitch moment to reduce the angle of attack. I'm inclined to say having an elevator that's not effective enough to recover from all the stall conditions regulators test for without help from the trim is probably a flaw. Whether there's a good technical reason the elevator couldn't be more effective (probably just bigger), a regulatory reason (some rule says it's not a 737 anymore if they change it), or a non-technical reason (e.g. more shared parts to make it cheaper), I can't guess.
- darkpuma 8y ago
  > "What's different is that at low speed, high thrust, and high angle of attack, the elevator of the MAX does not always have enough pitch moment to reduce the angle of attack." It's my understanding that for the 737 NG as well, there are stall scenarios at particular speeds, levels of thrust and angles of attack where trimming the stabilizer is necessary to recover. That the difference between the NG and MAX is what those particular values are, not whether or not that scenario exists ever.

Zak 8y ago

All jets with low wings and underslung engines (most modern airliners) experience a pitch-up moment from engine thrust, and trim is used to compensate. When the plane is being flown in some steady state, pilots adjust the trim until no force on the controls is required to maintain that state - they're not getting a specific setting from a table or memory. What's different is that at low speed, high thrust, and high angle of attack, the elevator of the MAX does not always have enough pitch moment to reduce the angle of attack. I'm inclined to say having an elevator that's not effective enough to recover from all the stall conditions regulators test for without help from the trim is probably a flaw. Whether there's a good technical reason the elevator couldn't be more effective (probably just bigger), a regulatory reason (some rule says it's not a 737 anymore if they change it), or a non-technical reason (e.g. more shared parts to make it cheaper), I can't guess.

darkpuma 8y ago
> "What's different is that at low speed, high thrust, and high angle of attack, the elevator of the MAX does not always have enough pitch moment to reduce the angle of attack." It's my understanding that for the 737 NG as well, there are stall scenarios at particular speeds, levels of thrust and angles of attack where trimming the stabilizer is necessary to recover. That the difference between the NG and MAX is what those particular values are, not whether or not that scenario exists ever.