Wings Taking weight out of composite fulelage
Quoting WINGS (Reply 34):
It might very well be overweight. The difference being that the A350X fuselage, wont be completely be made out of CRFP. This fact may make things easier for Airbus to trim down weight apposed to Boeing.
Exactly the opposite is true. Metal fuselage is a highly mature technology - once the initial design is completed, very little can be done to optimize the design any further. You may squeeze a few drops out, but the fuselage will be designed very close to the minimum weight since day one. On the other hand. composite fuselage is a new technology, and as with everything new, substantial safety factor is build-in into the design to account for the unknowns of an emerging technology. As more operational and manufacturing experience will be gained over the few first years, Boeing will be able to start shaving the extra safety margins. I would not be surprized to see that 5 years after EIS date, Boeing will be able to reduce OEW by as much as 5%, or increase MTOW by an equivalent amount without increasing OEW.
787 Engineer Reply 39. You seem convinced that decreasing the weight of a composite fuselage will actually be more difficult than a metal fuselage which is well simply untrue. If the loads change or if there's a more accurate iteration you would have to decrease the thickness of an aluminum fuselage to save weight. In doing so the IML (inside mold line) will change while the OML (outside mold line) will likely stay the same for aero purposes. This means every single part, shear ties, stringers, frames, whatever that is attached to the skin will have to be modified. With composites you can decrease weight (and strength) by changing the spacing of the fibers (decreasing # of fibers) yet keep the OML and IML exactly the same. Of course with composites there's a lot more a designer has to consider (fiber density and direction), and of course there's a learning curve. However as far as making changes and taking out weight from the fuselage I would say it is theoretically easier with composites. It may not be easier now, but once everyone has a good understanding of composites it will go a lot smoother.
http://www.airliners.net/discussions/general_aviation/read.main/2952025/6/#ID2952025
It might very well be overweight. The difference being that the A350X fuselage, wont be completely be made out of CRFP. This fact may make things easier for Airbus to trim down weight apposed to Boeing.
Exactly the opposite is true. Metal fuselage is a highly mature technology - once the initial design is completed, very little can be done to optimize the design any further. You may squeeze a few drops out, but the fuselage will be designed very close to the minimum weight since day one. On the other hand. composite fuselage is a new technology, and as with everything new, substantial safety factor is build-in into the design to account for the unknowns of an emerging technology. As more operational and manufacturing experience will be gained over the few first years, Boeing will be able to start shaving the extra safety margins. I would not be surprized to see that 5 years after EIS date, Boeing will be able to reduce OEW by as much as 5%, or increase MTOW by an equivalent amount without increasing OEW.
787 Engineer Reply 39. You seem convinced that decreasing the weight of a composite fuselage will actually be more difficult than a metal fuselage which is well simply untrue. If the loads change or if there's a more accurate iteration you would have to decrease the thickness of an aluminum fuselage to save weight. In doing so the IML (inside mold line) will change while the OML (outside mold line) will likely stay the same for aero purposes. This means every single part, shear ties, stringers, frames, whatever that is attached to the skin will have to be modified. With composites you can decrease weight (and strength) by changing the spacing of the fibers (decreasing # of fibers) yet keep the OML and IML exactly the same. Of course with composites there's a lot more a designer has to consider (fiber density and direction), and of course there's a learning curve. However as far as making changes and taking out weight from the fuselage I would say it is theoretically easier with composites. It may not be easier now, but once everyone has a good understanding of composites it will go a lot smoother.
http://www.airliners.net/discussions/general_aviation/read.main/2952025/6/#ID2952025
posted by Tom Bucceri at 9:21 AM
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