On 5/7/2013 11:07 PM, J. Clarke wrote:
In article ,
says...

On Sat, 16 Mar 2013 02:27:15 +0100, Wolfgang Weisselberg
wrote:
: RichA wrote:
:
: Weakness, focus problems (very likely due to plastic's inherent
: incapability to be machined as accurately as metal,
:
: Please provide proof
:
: it's tendency to
: change shape/size radically with temperature changes.
:
: Quite unlike metal, which *never* expands or contracts.
:
: Please look up the de Havilland DH 106 Comet 1.
: Fun when the planes disintegrate in the air after 20k hours
: due to *metal* fatigue.

Likewise the Lockheed Electra. So much vibration was transmitted into the body
of the plane that at least one airline provided soft cushions for the
passengers' feet. IIRC, they still used them, even after they were required to
reduce the plane's maximum speed by about 100 knots. But after the speed
reduction the planes at least stopped falling apart in the air.

The speed reduction was temporary until the cause of the problem could
be determined. It was determined, it was fixed, and the Electra
airframe continued in production for another 50 years. The vibration
problem was also fixed--the two were not related.

I believe that Lockheed was well aware of the risk, some safety
engineers had warned management, but the warnings were ignored in the
interest of timely delivery.


--
PeterN