Re: 747 hump

Date:         10 Sep 97 19:38:45 
From:         crosby@cpc.me.up.ac.za (Charles Crosby)
Organization: University of Pretoria
References:   1
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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 ;-)

--
Charles Crosby                                  Ph: (27)-(0)-12-4202861 (w)
Dept of Mech and Aero Eng                           (27)-(0)-12-3451586 (h)
University of Pretoria, South Africa            Fax:(27)-(0)-12-436540
cros-cp@fanella.ee.up.ac.za, crosby@cpc.me.up.ac.za, meg0023@upvm2.up.ac.za