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Old 27th Apr 2019, 09:32
  #4426 (permalink)  
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 58
Posts: 412
Originally Posted by bill fly View Post
Specifically: Boeing designed and placed into service an airplane with an active control system that had unilateral control over the horizontal stabilizer, with enough authority to place the airplane in an unrecoverable state if just a single component failed. Further this system gave no indication to the pilots that it was operating, or when malfunctioning that it was operating in error. Additionally this system, which was created solely to increase the amount of force required to pitch up the aircraft at high AOA used the most critical part of the airframe to do this minimal task, instead of using a passive system that had no control authority

Yep. So it is. And still they are faffing around with MCAS to get it recertified.
The only honest way out of this, and it isnít cheap, is a dedicated feel augmentation within the control run. Can be a spring, or a feel unit mod, as suggested way back, but not yet more tampering with the stabiliser.
I never liked the STS on the 300 and since then B have made use of stab tinkering for other sorts of cases - tankers etc. When we did a max fuel transfer on the Victor, we had to keep both of the aircraft in trim - and we did this by trimming as required, without some background programme interfering.
I guess the most important phrase here is isnít cheap.
These days that is enough reason for not doing the honest solution.
A feel augmentation system that takes AOA as input, what could possibly go wrong? I'm sure others can give scenarios where this would be a bad idea...

I previously pointed out that any system that takes a small input such as AOA, and produces a large output (whether feel or trim), is inherently undesirable and unpredictable. MCAS creates a semblance of smoothness by applying trim over a 10 second interval. Applying such a delay into elevator feel would create all kinds of feedback lags, and the solution could be worse than the problem.

The cost issue with any non-software change is how many years that would take to design, test and certify, and what production would be done in the meantime? Boeing have painted themselves into a corner, and the only way out seems to be double or quits (to mix metaphors).
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