Perry, Have you seen this web site?

Paul Lamar

http://www.gdsys.net/WWWmembers/unicorn/DUCTED_FAN/ducted_fan.htm

Perry Mick wrote:

Not until now.  Looks like it's Richard Sohn's site, the guy who makes
the oil injection pumps.

There are a lot of different definitions of what is a ducted fan and
what is
a shrouded propeller.  By Marc's definition a ducted fan is anything
with
a duct longer than the diameter.  By that definition mine is a shrouded
propeller.
But I disagree to the extent that my "propeller" isn't really anything
like an open
propeller.  It was designed and built as a ducted fan (non-linear pitch
across
the blade), a real airfoil all the way to the hub.  I only have three
blades and
low solidity, because with my low HP (120) that is all I can turn to
5000 RPM.

It looks like Richard's definition of ducted fan requires a high
solidity fan,
with a lot of blades. I don't think Marc would necessarily agree with
this definition.

But it really doesn't matter to me what it's called.  Shrouded prop or
ducted fan, really just variations of the same beast.

I also don't agree with his statement about blade twist.  The ducted fan
has more blade twist than a fixed pitch prop.  The inner, slower moving
portion of the blade has more angle of attack than the outer portion.  The idea
is to keep the air velocity constant accross the diameter of the duct.  At
cruise.

Look at the rc model ducted fans, you will see incredible twist.

My cowling is such a mess because of the shape of the engine, that I'm
certainly not achieving this, and is probably the main cause of my low
performance (lots of drag).  But I hope to improve it next time around
(see drawing).

--
Perry J. Mick
Duckt N7XR
http://www.ductedfan.com

 
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