Re: over-automation with glass cockpits

From:         James Horan <JHoran@postoffice.worldnet.att.net>
Organization: Horan Document Laboratory
Date:         08 Aug 96 12:11:48 
References:   1 2
Followups:    1
Next article
View raw article
  or MIME structure

MikeM727 wrote:
> >The Airbus has a safety feature that only allows a pilot to pull the
> >maximum g-limit of the airplane- no more. Why would you want to
> >overstress the airframe?
>
> What if a situation arises where the only way out requires overstressing
> the airplane?  This could be recovery from unusual attitudes, or evasive
> action to avoid traffic or terrain.  There have been accidents where the
> the airframe was overstressed in order to recover.  For certification, the
> airframe must withstand 150% of published G-limits without failure.
> Someday that extra 50% percent may be needed.  From what I've read, Airbus
> FBW doesn't give you that option, even in direct law.  I don't know about
> Boeing's FBW.

I would certainly guess that there is a more that 50% extra in a lot of
areas. I recall one old job shop engineer that I worked with who was
looking at some wreckage from a B-1. He said that he thought that anything
that was left together after a crash was overdesigned because planes are
made to fly not crash. Time and time again aircraft are subjected to much
higher loads than any designer anticipated and they held up. I recall a
B-52G back in the mid-80's when I was at Boeing Wichita that had a vertical
fin blown off by a gust that was approximately 5 times the Mil-Spec load.
It probably failed at around 3x.

Also remember there are two sets of loads yield and ultimate. You may bend
the aircraft but not break it. I would much rather land on a bent aircraft
that is no longer airworthy then crash on an airplane that would be
otherwise flight worthy but for the fact that it smacked into the ground.

James P. Horan, Esq.
Staten Island, NY