Re: thoughts on the A330

From:         cleyman@cix.compulink.co.uk ("Clive Leyman")
Organization: Pucklechurch Consultants
Date:         07 Sep 95 02:49:26 
References:   1
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In article <airliners.1995.1285@ohare.Chicago.COM>, fmcdave@aol.com wrote:

>This is not a direct comment on his posting, but might be an interesting
>sidebar for some........They were somewhat concerned because of the speed
>at which they were going to have to fly the airplanes. according to them
>the A330 and A340 are speed limited due to a buffet problem.
>Basically they told me that the wing had been a common design between the
>A330/A340 and not tuned for the placement of either two or four engines.
>The speed limit they were quoting was .78M!

Rick Hughes' message #2965 says most of it, and it was a nice change to
read some true "facts" about Airbus aircraft rather that the supposition
we normally get.

I can add a few things though - the A330 and A340 are designed to cruise
at 0.84M, rather than 0.86M, which is why the sweep is less than say a
747. But this is partly the reason why their Lift/Drag ratio is in excess
of 20, and the overall aerodynamic efficiency parameter Mach No × (L/D)
gives a VERY competitive fuel burn/seat.

We did design the wing to have identical aerodynamics on both aircraft,
and apart from the local areas around the engine/wing attachments, the
structure is also identical. It is not really a question of 'tuning' the
wing for either two or four engines - the design concept is that by
cashing in on the bending relief of the outer engines, the four-engined
aircraft can carry considerably greater TOW for the same structure, and
in fact the 'tuning' is in the careful choice of design weights to allow
a common structure.

In practice, the drag and aeroelastic effects of the outer engines has
meant that the A330 has a slightly better drag, but the difference is
peanuts - around 1%. The design loads for the two aircraft are also
within 1 or 2%, so tuning for two or four engines is not really relevant.

Clive Leyman