Re: TWA 800 wingtip separation

Date:         17 Dec 97 03:41:25 
From: (Geoffrey Sommer)
Organization: RAND
References:   1
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In article <airliners.1997.2950@ohare.Chicago.COM>,*intel*.com (Wayne Dohnal) wrote:

> During the Monday night TWA 800 NTSB hearings, the "sequencing team"
> reported that both wingtips separated from the inner portions of the
> wings fairly early in the breakup sequence.  The man giving the report
> tried to explain the logic of this, and the panelists shook their heads
> like they understood what he was saying, but I still can't understand!
> Can anyone explain how it make any sense for the wingtips to separate
> when they weren't anywhere close to the explosion or structural breakup
> area?  After watching the load test and breakup of the 777 wing on TV,
> I concluded that there was no possible way for a wing to break up in
> flight.  (I realize these are different aircraft, but I'm assuming
> Boeing would have similar wing strength across the product lines).

I haven't been following the hearings, but this makes sense.  Loss of nose
section causes massive center of gravity shift aft; this results in severe
nose-up pitching moment.  Since aircraft is flying faster than Va
(maneuvering speed) this moment results in an aerodynamic force that is
reacted through the wings, which fail in span-wise bending.

Many years ago, an XP6M jet seaplane suffered a similar catastrophic
pitch-up, as a result of a tail control surface design flaw.  As I recall,
part of one wing-tip was found embedded in the other wing-tip.  The wings
bent up until they touched above the fuselage!

   Geoffrey Sommer