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Newsgroups: sci.military
Subject: Ducted Fan Sub props
Message-ID: <1990Jun6.142332.5428@cbnews.att.com>
Date: 6 Jun 90 14:23:32 GMT
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From: att!jsugate!nak
    We just had this discussion under another guise about a month ago -
Status: R

remember the bypass ratio turbine discussions?  The final word I heard was
that for maximum thrust, move a lot of air at a lesser speed.  This is why
the turbofan engines have such huge diameters.  As far as the ducted prop
enlarging the sub envelope too greatly, there is another answer - don't
enclose the prop in the main hull of the sub: (poor diagrams follow)
	    _	                      _          __
	 ___/ \________            __/ \________/  \
        (              \-/  |     (            | || |-/| <- fins at back
	(______________/-\__|     (____________| || |-\|
                                                \__/
			   ^                     ^
			   |                     |
			ducted fan       large, solid center ring

    Put the ducted fan at the rear end.  We can get the diameter needed for
good efficiency without growing the sub in diameter.  For a really big
diameter, make the fan a ring around the sub since the center of the fan
contributes least to the thrust (less area)

Besides, from what I've read of Seawolf proposals in the press, the
expanded diameter (forty feet?) is a great advantage for the design
compared to the Los Angeles class.  Much less cramped, more interior
volume.

    Neil Kirby
    ...att!jsugate!nak