Re: 747 with engines on the wings?

Date:         19 Feb 98 01:33:59 
From:         Carl Peters <cpeters@i1.net>
Organization: Internet 1st, Inc
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With the development of high bypass ratio engines, noise has been cut
several orders of magnitude. Sound attenuation is further accomplished
by special honeycomb linings inside the intake nacelle, bypass duct,
and tailpipe, optimizing low pressure fan blade to vane numbers and
spacing, using low noise combustors, optimizing turbine blade/vane
spacing, using an extended cowl (RR, V2500) and so on. With more
energy used from the core gas flow to drive the N1 fan, the overall
velocity decreases compared to older low bypass or turbojet engines.
This is very dramatic, as noise is proportional to the 8th power
of jet velocity while in flight.

Re-engineering engines to the top of the wing would prove to be
costly, and markedly worsen maintenance access. The noise in the
cabin would go up considerably if the engines were above the wing,
unless you now move the wing to a high mounting, such as the C-5
and C-141. Now, you have added total re-engineering of the wing,
wing carry through structure, and part of the fuselage, made
refueling and maintenance a bit more difficult, and have to totally
redesign the landing gear. All for what? I believe you will
find very little complaint with the great reductions in noise
with newer high bypass ration engines, especially compared to the
decibels we are exposed to in day to day urban life. (I assure
you, a 777 on takeoff is much kinder to my ears than children
can be).

>Lion's Pers Agentschap wrote:
(snip)
> but with overwing engines the wing can deflect a
> big portion of the noise for people living around airports.

Not exactly true. You have two types of noise - that which is high
pitch coming forward from the N1 fan, and the lower pitched rumble
from the rear. Optimizing placement of the engine so that the wing
will shield the exhaust (only from below, so a departing a/c on a runway
will still have nearly the same noise level from behind) will place
the front ahead of the leading edge, and provide no shielding. If you
move the engine back, then the efflux approaches the trailing edge,
losing any protection.

>  Why are Boeing and Airbus Industrie developing the wrong airplanes
> now: 737-600/700/800/900, 757-300, 767-400, 777-300, A340-500/600 and
> A3XX?

Are you implying that millions of man hours and dollars spent by the
a/c manufacturers over the years in R&D and market comprehension
led to this 'error in design'? With respect, I'll gladly accept the
work of thousands of engineers representing the top talent in the world
at Airbus, Boeing, etc. as having designed the 'right' airplanes.

Carl Peters