Re: Questions about the DH Comet

Date:         03 Oct 97 01:18:33 
From:         Dennis Howard <dennis@lythal.demon.co.uk>
Organization: dennis the menace
References:   1 2 3
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In article <airliners.1997.2326@ohare.Chicago.COM>, Graham Glen <Graham@irving.demon.co.uk> writes
>Getting back to the fatigue failures, could anybody confirm what I think
>I read some years ago that as part of the redesign undertaken after the
>failures the alloy used for the skin was changed to one with a higher
>copper content, making it more malleable and less prone to cracking?

The problem was the high stress concentration generated at the cut outs
in the fuselage shell due to the cut-out shape. The fatigue life of the
structure in the area of these stress concentrations where riveting was
present was considerably reduced and any badly riveted holes
(interference fit not tight or burrs on the holes) could have further
exacerbated this. Mansfield at the R.A.E.(I think) had done research
work on neutral holes (i.e.cut-outs) in pressurised cylinders and this
work was an influence on the fuselage redesign work.
  As for material, I don't think the crack prone high strength zinc
based alloys were in much use then and the fuselage was probably made
from a DTD546 type Cu. based alloy which is fairly forgiving.

Dennis.
--
Dennis Howard