Re: 747 hump

Date:         16 Sep 97 02:35:25 
From:         "Michael F. Lechnar" <michael.f.lechnar@boeing.com>
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."