Re: Explosive bolts question
- From: "Reunite Gondwanaland (Mary Shafer)" <reunite.gondwana@xxxxxxxxx>
- Date: Sun, 08 Oct 2006 22:40:11 -0700
On Sat, 9 Sep 2006 17:58:46 -0700, "Joe Delphi"
<delphi561@xxxxxxxxxxxxxx> wrote:
Many hardware items are frangible (designed to break in certain
conditions) - for example, the approach lights at the end of most airport
runways are mounted on frangible stanchions so that if an airliner is coming
in too low and hits one with its landing gear, it will break the stanchion
and not the airliner. Same for many of the sign posts and street lights
next to highways.
It's supposed to be all the posts and lights and stuff by the side of
the road now. The USAF went around and re-did all their signs with
little chunks of box beam slightly bigger than the posts themselves as
sleeves. They cut the posts at ground level, secured the above-ground
portion to the sleeve with a single bolt that would fail on impact,
and dropped the other end of the sleeve over the embedded portion of
the post.
They then discovered that with enough stop-sign flutter from high
winds the frangible fitting would "frange", so they had to stiffen the
posts to reduce the flutter. They could do so safely though, because
they no longer had to use flimsy posts, which they had used to reduce
risk of damage and injury in case of an impact. The old posts had
been sort of semi-frangible.
Mary "Seems sort of counter-intuitive"
--
Mary Shafer Retired aerospace research engineer
We didn't just do weird stuff at Dryden, we wrote reports about it.
reunite.gondwana@xxxxxxxxx or miliff@xxxxxxxx
.
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