Re: Questions about the DH Comet

Date:         29 Aug 97 08:10:43 
From:         piersdorff.michael@ic.gc.ca (michael piersdorff)
Organization: The Communications Research Centre
References:   1 2
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Marc Schaeffer <marcmsc@geocities.com> wrote:

>Trond Olav Berg wrote:

>> Was it a safe plane?

>No, there were 20 crashes with Comets. De Havilland underestimated the
>forces and stress at high altitude and speed. However there were no
>references at that time so the constructor can't (fully) be blamed. Also
>calculators and computers were not existing .. After solving the
>structural problems the Comet4 was pretty safe, meaning that most
>incidents could not directly be blamed on design defects.

My understanding of the problem was that most of the in-flight
breakups were explosive decompressions of the fuselage resulting from
fatigue failure.  Successive pressurisation/depressurisation cycles
(takeoff and landing, respectively) in combination with flight loads
caused cracks at the corners of the square windows used in the early
models.  Any strength of materials textbook will show that a
square-ish corner is a tremendous stress raiser in a tension stress
situation, as a pressurised fuselage most certainly is.  The solution,
of course, was to go to the more or less oval windows one sees today.

The second jetliner to fly was the AVRO Canada C-102 Jetliner.  It was
ready to have been first, but Empire still counted for something in
those days, and it would not do for one of The Colonies to beat
Britain in the honours for first flight.  The C-102's first flight was
therefore delayed until the Comet had groaned off the ground.

Only one C-102 was built, despite strong interest from Canadian and US
commercial airlines, because the then-Liberal Canadian government
wanted to concentrate AVRO's efforts on production of the CF-100
fighter, and the design of its successor (the CF-105).  It was the
time of the Korean war, remember, and our high powered thinkers were
more concerned about National Security (the Red Menace) than they were
concerned about commercial gain for the shareholders of A.V.Roe.  In
1959 their successors (Diefenbaker's Conservatives) abandoned National
Security, too, and delivered the coup de grace to the already weakened
AVRO by killing the Arrow.