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Old 11th Dec 2018, 17:22
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FCeng84
 
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Gums - glad to share the level of system understanding that I can. STS and MCAS are both functions implemented within the autopilot and thus use the same path to the stabilizer that the autopilot uses for autotrim when it is engaged and controlling the elevator. In the logic MCAS has priority over STS which to me makes perfect sense as MCAS is there to address less than desirable Cm-alpha characteristics while STS is there to address less than desirable pitching moment vs. speed (would that be Cm-vcas or Cm-u?) characteristics. STS is more of a phugoid thing while MCAS is more related to short period. In my opinion, short period stability characteristics are more important than phugoid stability characteristics. Things can get out of sorts much quicker when related to short period than phugoid.
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