Thread: Kammback size?
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Old 01-19-2013, 04:38 PM   #17 (permalink)
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Originally Posted by ennored View Post
The 115 point is 25 after the 90 top (or bottom). That's just past 4 seconds (4.17 actually). So the 4 second circle I made in my graph is close to that. Hmmmm.

I did a little more playing, the curve of the template follows almost exactly a 6 second circle until about halfway down the template. Given that a truncated boattail is nearly as effective as a full one, that critical part of the template is very closely approximated by a circle. It might be arguable that any boattail, no matter the length, should start with a circular form? I need to play with my graph and see how circular the Dryden tail is...
I played around with the 'Template' and found that its profile can be defined by degrees of arc of rotation of four different radii,which emanate from the same Y-ordinate on a Cartesian grid.
The original 'Template' contour mimics the aft-body of a streamline body of revolution of 2.5:1 fineness ratio which Hucho portrayed in one of his drag tables.
NACA (NASA) described these forms as hyperboloids.And there would be a formula for that particular contour.I don't have it.I just do graphical solutions based on the architecture.I believe that it is the reason aerodynamicists present these forms for us.
If you haven't seen the thread for W.A.Mair's boat tail you might want to check it out as well.
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