Re: Questions about the DH Comet

Date:         08 Sep 97 02:03:48 
From:         drdjp@spamless-in-seattle.accessone.com (Dave Paisley)
Organization: StP in '97
References:   1 2
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> Trond Olav Berg wrote:
> > I am curious about the first commercial jet airliner: the british Comet.
> > When was this project started?

marcmsc@geocities.com wrote:
> It was started with the Barbazon comitee in Jun 43, which proposed 5 a/c
> to be built by GB. On of which was the DH 106 alias Comet.

That's Brabazon, as in Lord Brabazon who headed the committee. (and also
the author of the horrendous Brabazon airliner fiasco.)

<snip other questions>

> > 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.

The actual cause was the lack of understanding of the fatigue effects of
pressurization cycles on the (somewhat) square window corners. That was
fixed and the airplane was about as reliable as any other jet. However, I
suspect the engine installation caused more maintenance problems than the
707 and DC-8, due to the limited access.

> > How did jets inside the wings perform, compared to the jets on the 707 etc?
>
> This design was unique. It was very nice for the eyes, meaning the a/c
> was superb to observe with this one of a kind design. However an engine
> mounted in a wing is not very safe. Think that the engine is running at
> high speed and that in the wing you have that huge amount of fuel. So if
> a blade separates, you will have a nice explosion. After the YP crash
> the shielding around the engines were reinforced, just in case of ...
> None of the Comet crashes was due to engine explosion.

Another major problem with that design is that the wing root has to be
custom designed to the engine, and that advances in engine technologies
like higher bypass fans, couldn't be installed on the Comet. The podded
engine approach was much easier to incorporate technology advances on.

You simply can't afford to redesign the primary wing structure every time
you want to put a different engine in. Added to that, once the engine
diameters had grown a bit, it would be impossible to fit them in anyway.
And beyond that, even if you could find a way to make them fit,
compensating for the enormous cutouts in the wing structure would make it
far too heavy, and the airplane too inefficient.

Like many British designs of the post war years, both military and
commercial, it was a pretty airplane, but was too small and had no growth
capability designed in.

regards,
dave