Thoughts on Seattle Times article published Sunday morning Seattle time 2 f3 D. Z6 z% }" v# W& V" s- b$ s3 B, \, U6 L; m
This article is generally well written and seems quite accurate. One point of clarification is that early on in the 737MAX development it was thought that MCAS would only be needed at particularly high Mach numbers. For those conditions the prediction was that the original 0.6 degrees of MCAS stabilizer authority would be sufficient. That proved to be pretty close to the case during flight testing and the final MCAS increment size for cruise and higher Mach numbers is very close to 0.6 deg. Later on it was determined that MCAS would also be needed at lower Mach numbers. With that extension of MCAS came the MCAS authority vs. Mach number schedule that is in the current design. The high Mach end of that schedule is approximately 0.6 degrees. Only with Mach Number less than 0.4 is the MCAS authority 2.5 degrees. The larger authority at lower Mach numbers is needed as the effectiveness of the horizontal stabilizer is less at lower speed. It is quite common that flight control functions are given higher authority at lower airspeed and less authority at airspeed increases.
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# K& l# r. U( C5 L1. 这个解释了scope creep的一部分原因 0 x& q& S. W3 J7 y+ t/ M6 w2. 解释了包子那本看起来自相矛盾的波音手册是怎么来的：一部分是改变以前的文字，一部分是更改以后的说明 & I( [! [6 {2 d( I, s3 C& f, Z3. Now if part of the fix is to limit stab trim, what about low mach scenario where that degree of trim was considered necessary?
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那段关于jackscrew的跟你说的一样. 你说认证过程出了问题, 果然!!! / y- ~( [! i R1 ?# M# g9 e& v, L+ }* m( a
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这是个两难的问题，碰上故意要坠机或者昏了头的飞行员怎么办？不是没有出现过。, G! y. Y: R4 n0 ]+ H
即使正常飞行员在空中产生错觉也常有的事，尤其是云中或漆黑的夜晚，有时会把天地搞反了。记得以前看到过要求飞行员要相信仪表，说明仪表出错的几率要大大低于飞行员的错觉。! l; t3 i: h1 {: y$ j/ k/ T
现在飞机上各种传感器应该是相当成熟的东西了，迎角传感器应该是飞机投入实用时就有了，如果是迎角传感器出了问题应该是相当低级的错误，比如安装不牢固，这种错误只要维护人员细心就很容易查出来。如果不容易查出来就是设计或制造的问题了，比如迎角超过某个值容易被卡住，导线接头接触不好，这在地面几乎没法查。
' t/ d9 k/ q8 X1 N3 K) a r; k _2 `% G! R8 s. C- E B上面那个Boeing insider的帖子只说后来决定低速时也要MCAS，没说为什么。昨晚WSJ关于司法部调查波音的新闻里有这么一段： ( ~5 N3 ?5 T0 O8 U ; V5 R& y3 X6 [0 t, C
But as the engineering effort and flight tests progressed, according to industry and FAA officials familiar with the process, the Boeing team saw the same feature as a potentially important safety net for a different hazard highlighted in previous crashes: lower-altitude stalls in which startled pilots mistakenly pulled back on the controls and sometimes crashed aircraft. FAA officials also recognized the potential benefits and approved the system as part of the overall MAX approval.
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如果属实，纯属有些人聪明过头。这也解释了为什么fix要restrict authority, 突然间又不担心低速了
雷达卡
楼主
显身卡
发表于 2019-3-18 00:37:44
既然波音可以自己替自己安全检查，那要FAA干什么呢
