Date: 16 Sep 97 02:35:25 From: "Michael F. Lechnar" <firstname.lastname@example.org> Organization: nams References: 1
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Mark E. Ingram wrote: > On 8 Sep 1997, Marc Schaeffer wrote: > > > I wonder to what extend the hump of the 747 contributes to the total > > fuel consumption at cruise speed and cruise altitude. Can the > > aerodynamical disadvantages of the 747-hump be evaluated by some > > formula? > > An _AvWeek article of three or four years ago stated flatly that Boeing > aerodynamicists were totally surprised when the longer hump of the first > "extended upper deck" 747 (the -300) caused a *decrease* in drag over the > original design. Can anyone comment on (or verify) this? IIRC, we were pretty surprised by the increase in cruise speed between the 747-200 and 747-300. After we had thought about it for a while, we realized that we could have predicted it had we given it any thought. We had a previous example in the 747SP. The upper deck on the -300 helps area rule the airplane by extending closer to the leading edge of the wing. The SP accomplished the same thing by removing a section of the main fuselage, moving the wing closer to the upper deck. The SP cruises at Mach = 0.85 vs. 0.84 for the -200. Mike Lechnar Aircraft Performance Engineer "If I was speaking for Boeing, I wouldn't be doing it here."