Perry Mick wrote:

Paul wrote:

Perry,
There is a simple test you can perform to see if your prop
tips are running into the mach brick wall.

Dive the airplane and watch the tach. If the RPM increases
you are merely HP limited by too much pitch. If not your
tips are up there near the mach barrier for the airfoil used.

One thing that makes me think I'm not against the brick wall
is my max rpm with duct2 is 5300+, but the max rpm with duct3
is only 5000.  You would think it would accelerate with duct3
until 5300 also if I weren't HP limited.  The aerodynamics of
duct3 puts more load on the engine somehow.

I'm back to flying duct2, in level flight I don't like to leave
it at 5300 too long because the vibration level increases,
at 5000 it's pretty smooth.  Now maybe some of that vibration
at 5300 is the brick wall (?), or maybe just imbalance showing
up at the higher rpm (v^2/r), a square function of rpm.  Seems
to be a lower frequency vibration, maybe also fan/duct interaction
of some sort I thought.

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

Could be wake affects from the wing. I expect those would be proportional 
to the square of airspeed.

How is the run out on that e-shaft extension?

You really need to do some pressure measurement around the lips of those
ducts to see what is going on. Inside and out side. If the lip on duct 2 is
stalling the resultant low pressure area on the outside could be reducing
the airflowing into the duct.
 
Paul Lamar
 
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