Re: [PSUBS-MAILIST] fins on dragged naval sonar

["Cliff Redus" <dr_redus@devtex.net>]

Not exactly classic teardrop shape.  The classic teardrop shape has a length
to diameter ratio of approximately 6. The boat shown in
http://www.sfu.ca/casr/101-navvds.htm looks more like an L/D of  2.5.  To
drag (no pun intended) everyone back to school; for turbulent flow around an
axisymmetric body of revolution, there are two contributions to overall
drag, the first is skin friction and the second is form drag.  As the L/D
ratio increases for a teardrop shape, the form drag decreases and the skin
drag increases.  The total drag being a combination has minimum around an
L/D of 6.  Modern military boats use a higher L/D because even though not
optimum, at higher L/D's than 6, the total drag does not increase very
rapidly. With higher L/D's than 6, they can pack more kit in the boat
without paying to much of a drag penalty.  "Concepts in Submarine Design"
Burcher and Rydill (1999) pg 105.

Cliff
----- Original Message ----- 
From: <dinosnider666@spacemail.com>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, October 22, 2003 2:04 PM
Subject: RE: [PSUBS-MAILIST] fins on dragged naval sonar


>
>
> http://www.sfu.ca/casr/101-navvds.htm
>
> Classic teardrop. Pretty huge fin control panels. Reminded me of circular
band at back of original bazooka.
> Anyone else know any unorthodox fin configurations?
> D.