Oh no, not again!

[Jack Davis]

"Tom Sherman" <[email protected]> wrote in message
news:[email protected]...
> Jack Davis wrote:
>
> > Anyone but me remember when the new jet, (straight and
> > turbo) airliners
were
> > falling out of the sky from metal failure?
>
> For some reason I suspect that fatigue from
> pressurization/depressurization cycles is not a factor in
> aluminium alloy recumbent bicycles.
>
> Tom Sherman - Quad Cities (Illinois Side)
>

Actually Tom, I believe it was from high frequency vibration
not p/d cycles, but that should not be a problem on bicycles
either unless one is pedaling very rapidly.

Carry on.... jd

 

[Marc]

Jack Davis <[email protected]> wrote:

> Anyone but me remember when the new jet, (straight and
> turbo) airliners were falling out of the sky from metal
> failure?

Not "the new jet, (straight and turbo) airliners " it was
only one type, the DH Comet Mk1.

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[Dave Larrington]

Jack Davis wrote:

> Actually Tom, I believe it was from high frequency
> vibration not p/d cycles, but that should not be a problem
> on bicycles either unless one is pedaling very rapidly.

If one is referring to the failure which caused numerous
Comet aircraft to crash in the 1950's, these were fatigue
failures propagating from the corners of the windows
(which had fairly sharp corners - bad idea) and /were/ due
to p/d cycles.

--

Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
===========================================================
Editor - British Human Power Club Newsletter
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===========================================================

 

[Tom Sherman]

Dave Larrington wrote:

> If one is referring to the failure which caused numerous
> Comet aircraft to crash in the 1950's, these were fatigue
> failures propagating from the corners of the windows
> (which had fairly sharp corners - bad idea) and /were/ due
> to p/d cycles.

Only 2 or 3 of the Comet crashes were due to fatigue -
several other early crashes were due to excessive angle of
attack while attempting takeoff, and the remaining crashed
were due to pilot error.

However, fatigue failure would have eventually affected most
of all of the Comet 1 and 1A models if they had not be
retrofitted or scrapped.

Tom Sherman - Quad Cities (Illinois Side)

 

[Jack Davis]

"Tom Sherman" <[email protected]> wrote in message
news:[email protected]...
> Dave Larrington wrote:
>
> > If one is referring to the failure which caused numerous
> > Comet aircraft
to
> > crash in the 1950's, these were fatigue failures
> > propagating from the corners of the windows (which had
> > fairly sharp corners - bad idea) and /were/ due to p/d
> > cycles.
>
> Only 2 or 3 of the Comet crashes were due to fatigue -
> several other early crashes were due to excessive angle of
> attack while attempting takeoff, and the remaining crashed
> were due to pilot error.
>
> However, fatigue failure would have eventually affected
> most of all of the Comet 1 and 1A models if they had not
> be retrofitted or scrapped.
>
> Tom Sherman - Quad Cities (Illinois Side)
>

I was thinking that some of the early Vickers, (Viscounts?)
had a problem too but my brain turned to sawdust years ago
so I'll let others research that if they wish.

Aircraft builders did have experience with p/d cycles by the
time the Comet was built and other, piston powered, aircraft
had square corners which did not tear. Work hardening of the
aluminum skin from H.F. vibration combined with the
additional stress of higher altitudes and higher speeds
resulted in failures, often starting in corners, that
obviously were not expected from causes that were little
understood. Failure was occurring not only in sheet metal
but also in castings and machined aluminum parts.

Good thing those intelligent engineers figured it out
and fixed it or we might not even have an airline
industry today.

Jack

 

[Sticker Jim]

> > I work on aircraft and deal with aluminum alloys daily,
> > specifically
2024
> > and 6061. The biggest problem with aluminum is that it
> > work hardens.
Steel
> > can be loaded an almost infinite number of times just so
> > long as you
never
> > go past it's point of failure....
>
> Don't you mean fatigue limit, and not failure?
>
> Failure is an ambiguous term in this context - does it
> refer to yield, exceeding UTS, or fracture (all of which
> will occur at different strain values for most steels
> under most conditions)?

Correct, that's why I didn't specify which "failure". The
lowest "failure" point for most shapes and profiles would
usually be bending, I would guess, but steel doesn't
necessarily "fatigue" - at least the mild steel and
stainless alloys I regularly use.

 

[Sticker Jim]

"Jack Davis" <[email protected]> wrote in message
news:qD%[email protected]...
> Anyone but me remember when the new jet, (straight and
> turbo) airliners
were
> falling out of the sky from metal failure?

Yup. I remember some fledgling airliners that put their
companies in a bad light because the fuselages were
expanding and contracting so much from pressure changes that
they ended up have explosive failures in the outer skins due
to the aluminum work hardening.

 

[Mark Leuck]

"Dave Larrington" <[email protected]> wrote in message
news:[email protected]...
> Jack Davis wrote:
>
> > Actually Tom, I believe it was from high frequency
> > vibration not p/d cycles, but that should not be a
> > problem on bicycles either unless one is pedaling very
> > rapidly.
>
> If one is referring to the failure which caused numerous
> Comet aircraft to crash in the 1950's, these were fatigue
> failures propagating from the corners of the windows
> (which had fairly sharp corners - bad idea) and /were/ due
> to p/d cycles.
>
> --
>

Yup, interesting show about it on the History Channel a few
months ago

 

[Torben Scheel]

"Tim Hall" <[email protected]> wrote in message
news:[email protected]...
> On Sun, 14 Mar 2004 11:10:15 -0600, Tom Sherman
> <[email protected]> wrote:
>
> >Jack Davis wrote:
> >
> >> Anyone but me remember when the new jet, (straight and
> >> turbo) airliners
were
> >> falling out of the sky from metal failure?
> >
> >For some reason I suspect that fatigue from
> >pressurization/depressurization cycles is not a factor in
> >aluminium alloy recumbent bicycles.
> >
> Proof (again) that recumbents can't climb.
>
>
> (Runs away very fast)

No need for doing that - just a few steps up the hill, and
the recumbeteers will never catch you ;-)

T

 

[Peter Clinch]

Torben Scheel wrote:

> No need for doing that - just a few steps up the hill, and
> the recumbeteers will never catch you ;-)

Until it's time to go down the other side... But have a look
at the video clip of the Lightning R84 in action on their
web site if you want to eat your words slightly more
directly, or note that the Classique Genevoise course is
80km of an unflat variety, and the first 5 places were taken
by 'bents last year despite starting from the back...

If recumbents "can't climb" then it could reasonably be said
that uprights "can't do headwinds"...

Pete.
--
Peter Clinch University of Dundee Tel 44 1382 660111 ext.
33637 Medical Physics, Ninewells Hospital Fax 44 1382 640177
Dundee DD1 9SY Scotland UK net [email protected]
http://www.dundee.ac.uk/~pjclinch/