Re: 747 wing stress test: This can't be true can it?

Date:         09 Apr 97 03:09:26 
From: (C. Marin Faure)
Organization: Northwest Nexus Inc.
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In article <airliners.1997.840@ohare.Chicago.COM>, "Hans Jakobsson"
<> wrote:

> I just received a question regarding stress tests on 747s.
> Quote:
> "Is it true that a 747's wings were pulled upwards until both
> wing tips touched. (In some sort of stress test)."
> End of quote.
> I know that they do all sorts of stress tests but this can hardly be true,
> can it? My reference archives don't mention this at all. Sure, the wings
> can withstand some stress but this is a bit too heavy, I think.

The statement you read is not correct.  The wings cannot be pulled up
until they touch.  We have film of the 747 wing-to-ultimate-load test in
our archives here at Boeing (and all the other planes, too- B-52, 727,
757, 767 (the fuselage broke before the wings on that one) and the 777.  I
believe the 747's wingtips were pulled up to about 16 feet above their
normal no-load position before they broke.  In the case of the 747, this
test showed that the wings were far stronger than they needed to be, so
the engineers were able to go back in and remove some unecessary structure
and/or reduce some metal thickness.  There was no compromise in strength,
and the plane became lighter which meant it's payload went up.  The
primary value of these wing tests is to prove that the wings are as strong
as our engineers and computers say they are, and to provide data which
will help us plan derivatives of the airplane down the road.

C. Marin Faure
  author, Flying A Floatplane