Paul wrote:

I think your fan tips are up against the mach # brick wall.

I calculate a vector sum of 909 fps with 5300 rpm and 160 knots in the
fan.
Doesn't seem like the brick wall should start that early.  Maybe it
does.
Isn't mach one around 1100 fps?

Depends on a lot of things such as temp and air density not the
least of which is the airfoil used. What are your tip airfoils
now a days?

It's ClarkY, which according to Bill is bad above mach 0.8 or so.
My tips are only 2.6 inch chord, 6% thickness.  But it's also true
that I can't go much higher in RPM or I will hit that wall.  That
means even smaller diameter fan and duct.  Someday projects.

That is the problem in a nut shell. You are between a rock and a hard spot.
If you go smaller on the duct to get more RPM and power the disk loading goes
up and the thrust efficiency goes down. You need a gear box to exit this 
viscous circle. I know that is not want you want to hear. You could also
pump up the power at this RPM with a turbo and use wider blades. That would 
help. A high displacement light weight engine running at 3600 RPM with high 
HP is what you really need IMHO. That is close to a typical aircraft engine
but no cigar. They will not live at 3600 - 4000 RPM. Some of the GITSO's might
live. Take off the gear box. 

GITSO = Geared Injected Turbo Supercharged Opposed.

PL

Assuming with more power I could get to 6000 RPM and 200 knots inside
the duct, 154 knots airspeed, the tip speed would be 982 fps, 200
knots is 338 fps, and the vector sum is 1039 fps.

Maybe I can reshape the airfoils at the tips.

What you need is real thin... less than 3% thick,  titanium blades 
running at mach 1.4. with the right airfoil. This will give you a 
lower disk loading, more RPM, more HP and more thrust efficiency IMHO. 

Reshaping the blades is the easiest thing to try. Way less time
consuming than making yet another duct. PL

I know you know that but for others that might not.
BTW 600 MPH is 880 fps. 700 MPH is 1027 fps. You are up there.

Paul Lamar

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

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