Re: 747 hump

Date:         16 Sep 97 02:35:26 
From:         b.domke@coruscant.b.shuttle.de (Burkhard & Birgit Domke)
Organization: WiNShuttle, DFN - Deutsches Forschungsnetz eV
References:   1 2
Followups:    1
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On 10 Sep 97 19:38:45 , David Lednicer <dave@amiwest.com> wrote:

>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 ?
>
>	Actually, the hump slightly improves the drag of the 747.  If the hump
>wasn't there, the cross-sectional area distribution would have a chunk
>missing and the wave drag would be higher.  I have data showing that the
>extended hump on the 747-300 and -400 improves the area distribution
>slightly, further reducing wave drag.

Saw some graphics depicting that the hump moved the drag divergence
Mach number slightly up, although there's no information how the
non-hump reference was defined. Nevertheless, the same graphics showed
that total drag was slightly up at lower Mach numbers, most probably
due to an increase in skin friction.
BTW, the (slight) reduction in wave drag due to the 747's elevated
flight deck is a sort of smart excuse, as the hump seems rather
related to the 747's origins as a freighter with a hinged nose, isn't
it?

Another reference stated that further extending the upper deck
(-500/-600) would aggravate the problem of (instable, asymmetric)
vortices being shed by the hump at low speed/high alpha, deteriorating
airflow around the tail. Anyone to confirm/deny/comment that?

Burkhard