Date: 01 Feb 99 02:37:17 From: "Michael F. Lechnar" <email@example.com> Organization: nams References: 1 Followups: 1
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MCL757 wrote: > Someone asked me if Boeing enlarged the horizontal stab on the 747 when they > extended the upper deck to compensate for the CG change. I don't think the > stab was changed. I figure that considering the high weight of all the fuel > that could be in different places affecting the CG that the extra weight of the > extended upper deck really is relatively small. Does anyone know? Was there > any stab change or did they recalibrate the trim's zero setting? The external lines of the horizontal didn't change with the stretched upper deck. For the 747-400, provisions were made to carry fuel back there. In fact, you need the have that tank active to use the full 875,000 lb MTOW. The fuel isn't kept there for cg control, but rather it is moved into the CW tanks as soon as there is room. This is typically over by the time the airplane reaches cruise altitude. The drag benefit for keeping the cg aft is too small to justify the complexity of a fuel management system to keep the fuel back there. Mike Lechnar Aircraft Performance Engineer "If I was speaking for Boeing, I wouldn't be doing it here."