wrote:
On 7 Sep, 08:40, Thomas Borchert wrote:
Robert11,

Sure is unusual.
Unusual - maybe. New? No!http://en.wikipedia.org/wiki/VFW-614

My (not very well informed) understanding is that
rear mounted engines result in a quieter cabin
but that wing pylon mounted engines result in a lighter airframe
for the same size/power etc.

The reason for the weight saving is as follows:-

Consider the rear mount case. The wing root
must be strong enough and stiff enough to support the
whole weight of the plane. By moving
the engines to wing pylons the wing root structure
is relieved of some load since the weight of the engines
is now directly on the wing. The wing can therefore be
made lighter. I have read - on the internet
I guess - that the weight penalty in the case of the VC10
vs 707 was 10%. Then you need to add the extra fuel to
carry the extra weight if you want to go the same distance.
This multiplies the penalty further. And further, since
the extra fuel needs extra tanks ... Maybe the 10%
included all of that but my dodgy memory
of dodgy info says that it did not.

I suspect it is more marketing and being different than anything else.
You are correct that the wings have less fuselage weight to support when
on the ground, but they now have a lot more torsional load due to the
distance from the thrust centerline to the center of wing structure.

Without having the full specs and doing the calculations, I can't say
which one trumps, but generally resisting bending loads is easier than
resisting torsional loads.

Matt