RE: Aero rule of thumb (was: RE: More three wheeler stuff)

[Roger Stockton <rstockton@delta-q.com>]

Without my books handy to refer to I can't be 100% certain, but
as I recall Kamm's specific discovery was not so much "taper as
far as possible then cut it off flat", or "taper at 17 degrees
or less", but that it was aerodynamically superior to truncate
the body abruptly once it had been tapered down so that the
cross-sectional area at the truncation is about 1/3 of the
vehicle's frontal cross-section.  ("Superior" in the sense that
there was little or no benefit to continuing the body beyond
this point and/or trying to round it off attractively.)

I think the 17 degrees or less part may be a guideline that
fell out of later airfoil research (not necessarily by Kamm).

Roger.

-----Original Message-----
From:	Chris Tromley [SMTP:chris_t@microtrac.com]
Sent:	Monday, April 30, 2001 4:52 AM
To:	ev@listproc.sjsu.edu
Subject:	Aero rule of thumb (was: RE: More three wheeler stuff)

Peter Vanderwal wrote:

> There was a fellow (can't remember his name) who discovered
> that if your
> back end is too close to taper all the way to a point (at no
> more than 17
> degrees), you are better off tapering at 17 degrees as far as
> possible and
> then sharply cutting it off (flat back end).  This actually
> works well for
> vehicles because it gives you a place to put tail lights and
> license plates,
> etc.

The fellow's name was Kamm, I believe.

I've seen this 17 degree rule of thumb before, and I'm curious where it
comes from.  I'm not challenging it, I'd just be more comfortable with a
source before using it to design a body.  To what range of road speeds does
the rule apply?  And just to clarify, do you mean 17 degrees included
(between upper and lower, or right and left sides of the body) or 17 degrees
to the centerline (i.e. between the roof and the ground)?

Chris