Re: 747 hump

Date:         16 Sep 97 02:35:25 
From:         Gregory.A.Addington.4@nd.notrash.edu (gregory addington)
Organization: ND / AFRL
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In article <airliners.1997.2130@ohare.Chicago.COM>,
   crosby@cpc.me.up.ac.za (Charles Crosby) wrote:
>Marc Schaeffer (marcmsc@geocities.com) 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

>Area-rule considerations indicate that the hump causes very little (if any)
>additional drag at cruising speed.  At low speed there is more of a
>disadvantage, but this is fairly unimportant on a long-distance aircraft,
>which spends little time at low speed.  Kuethe & Chow (Foundations of
>Aerodynamics, Wiley) have a graph on page 298 of their book indicating
>that the change from short hump to longer hump (as on the -300 and -400
>models) pushed the drag-rise Mach-number up significantly.
>Considering the cross-section area plot on the same page, de-humping
>a 747 may well result in an increase in drag, in which case the hump causes
>negative fuel consumption ;-)

C.Y. Chow used this example for his lecture on the area rule when he taught
fluid mechanics at the University of Colorado. Quite interesting!

Which has made me wonder: from a picture I saw of the freighter version
of the 747-400, it looks as though it has the short-style hump.
Was it a bad camera angle, or is this true? I can understand why the long
hump would have no use from the cargo standpoint (really tough to get
pallets up those little stairs ;-) ), but why would the reduction in
drag not be advantagous? A weight vs. range trade, maybe?

GA

Greg Addington
Doctoral Candidate, University of Notre Dame | Any opinions,statements,
Aerospace Engineer, USAF Research Laboratory | etc, expressed herein are
USAF PALACE Knight recipient                 | not necessarily those of
email: Gregory.A.Addington.4@nd.edu          | the U.S. Government; they
www:   www.nd.edu/~gaddingt                  | may not be even my own.