Boeing's "Battle over blame": reduce power or not?

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photofly
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Re: Boeing's "Battle over blame": reduce power or not?

Post by photofly » Sat Jun 22, 2019 10:56 am

digits_ wrote:
Sat Jun 22, 2019 10:32 am
If we can assume the plane started the uncorrected/uncontrolled descent because the pilots were unable to raise the nose while they were still under Vne, it makes me wonder if airplanes can be certified if there are situations in which the control forces on the yoke with full opposite trim exceed a certain force? Are there any requirements that way? Obviously it will be very uncomfortable to fly with a plane fully trimmed in the opposite direction, but does the regulator require it to be possible?
From the way I read FAR25.255, it's only a requirement to be able to generate 1.5G, with 125lbs of pull, given as much incorrect trim as can be generated in three seconds of trim operation. Not full trim. Obviously 1.5G will enable you to pull out of the dive if you happen to be in one:
25.255(f)In the out-of-trim condition specified in paragraph (a) [3 seconds of trim etc.] of this section, it must be possible from an overspeed condition at VDF/MDF to produce at least 1.5 g for recovery by applying not more than 125 pounds of longitudinal control force using either the primary longitudinal control alone or the primary longitudinal control and the longitudinal trim system.
That section goes on to say that if you can't recover with the elevator alone, and you need to trim, the trim has to be moveable etc. etc.

Obviously a cursory reading of one regulation doesn't substitute for a full analysis of what the certfication requirements are, but I don't see anything that says a manual recovery from full nose-down trim has to be achievable.
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Kirk: This is a dangerous mission. Likely, one of us will die. The landing party will be me, Spock, McCoy, and Ensign Ricky.
Ensign Ricky: Aw, crap.

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Re: Boeing's "Battle over blame": reduce power or not?

Post by Ki-ll » Tue Jun 25, 2019 6:29 am

digits_ wrote:
Sat Jun 22, 2019 10:32 am
If we can assume the plane started the uncorrected/uncontrolled descent because the pilots were unable to raise the nose while they were still under Vne, it makes me wonder if airplanes can be certified if there are situations in which the control forces on the yoke with full opposite trim exceed a certain force? Are there any requirements that way? Obviously it will be very uncomfortable to fly with a plane fully trimmed in the opposite direction, but does the regulator require it to be possible?
Do you have a copy of “Handling the Big Jets”?
Similar case is described there. From what I remember it was a case of a stalled stabilizer drive due to aerodynamic forces and the certification outcome was reduction of nose down travel limit.
P.S. Attaching the reference.
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photofly
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Re: Boeing's "Battle over blame": reduce power or not?

Post by photofly » Tue Jun 25, 2019 6:44 am

Good call... I just finished scanning the pages but you beat me to it!
---------- ADS -----------
  
Kirk: This is a dangerous mission. Likely, one of us will die. The landing party will be me, Spock, McCoy, and Ensign Ricky.
Ensign Ricky: Aw, crap.

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