3 ms·

This is a good source: https://www.satcom.guru/2019/03/regulations-around-augmentation-systems.html https://www.satcom.guru/2019/03/regulations-around-augmentat

This is a good source: https://www.satcom.guru/2019/03/regulations-around-augmentation-systems.html https://www.satcom.guru/2019/03/regulations-around-augmentat... FAR 25 has a number of specific requirements around pitch stability, specifically, FAR 25.255(b)(1) and FAR 25.203(a), and some others. FAR 25.203(a) says "No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall" My understanding is that on the MAX, without MCAS, once you've pitched up beyond some AoA beyond 12 degrees or so, you can let go of the yoke, and the plane will continue to pitch up further until it stalls. That does not comply with the regs, and so you have MCAS which dials in some nose down trim in this situation to counteract the aircraft's natural tendency to pitch up further.

mannykannot 8y ago
If the chart presented in the article below [1] is fairly accurate and not merely representational, I think that the 737 MAX, without MCAS, does not actually become statically unstable in pitch at least until after the stall, but the response was still unacceptable, and the reason MCAS was needed for certification. There is a complication here in that the stick forces are generated by an elevator Feel and Centering Unit, which is fed by a dedicated pitot tube and the stabilizer position. Pitch instability after the stall was part of the rear-engined jet deep stall problem, and the reason for stick pushers [2]. [1] https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stability-part-10-wrap-up/ https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stabil... [2] https://leehamnews.com/2018/12/07/bjorns-corner-pitch-stability-part-3/ https://leehamnews.com/2018/12/07/bjorns-corner-pitch-stabil... Figure 3.
deleted 8y ago
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3 ms·

This is a good source: https://www.satcom.guru/2019/03/regulations-around-augmentation-systems.html https://www.satcom.guru/2019/03/regulations-around-augmentat

by cameldrv 8y ago

mannykannot 8y ago
If the chart presented in the article below [1] is fairly accurate and not merely representational, I think that the 737 MAX, without MCAS, does not actually become statically unstable in pitch at least until after the stall, but the response was still unacceptable, and the reason MCAS was needed for certification. There is a complication here in that the stick forces are generated by an elevator Feel and Centering Unit, which is fed by a dedicated pitot tube and the stabilizer position. Pitch instability after the stall was part of the rear-engined jet deep stall problem, and the reason for stick pushers [2]. [1] https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stability-part-10-wrap-up/ https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stabil... [2] https://leehamnews.com/2018/12/07/bjorns-corner-pitch-stability-part-3/ https://leehamnews.com/2018/12/07/bjorns-corner-pitch-stabil... Figure 3.
deleted 8y ago
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