Perry Mick wrote:

Paul wrote:

Bill Freeman wrote:

Paul,

I must strenuously object!   This is what has been claimed
was the problem with Mr. Parkman's prop!   You do NOT
want to see max or even very near max RPM at static
conditions with a fixed pitch prop.

With a fixed pitch prop, you pitch it so it is efficient at
cruise or climb speed, both much higher than either static
(zero) or early in the takeoff roll.   As you accelerate the
prop will be more effective and TO RPM will be higher
than static, increasing the HP available and the thrust.

Bill

I am not so sure a ducted fan works exactly like a prop
Bill. Perry's RPM does not pick up that much
RPM between static and 90 mph taxi speed as I recall.

What does happen Perry? What is max RPM static and
what is the RPM at 90 MPH?

The duct is invisible as far as static rpm goes.  It's
around 4150-4200 static, increasing to 4400 at 90 knots.
The duct is increasing velocity to the fan plane, so I
don't get that much rpm increase unducted at 90 knots.

That is characteristic of a converging duct.

I would rather have 5000 rpm for takeoff, the two-blade
prop would do that, but I don't want to exceed 6000 rpm
during cruise.  Redline is 7000.

6500 rpm might be ok static if you have an 8000 redline
engine (later engine).

If the duct/fan was even smaller I suspect the RPM would
pick up even less. In other words it would be near constant
RPM. I could be wrong.

In any event it is still bogged way down at 90 MPH
at only 3700 RPM or so as I recall.

The original prop was 3300 static, around only 80 HP, which
I consider not nearly enough.  The new prop is 4200, around
100-110 HP, probably just enough.

Also the rotary is unlike a piston engine and power continues
to increase beyond 6500 RPM because it breathes so much better.

Another factor could be the 15% or so Clark Y airfoil blades
tip tops may be going transonic and running into a drag brick
wall at only 3700 RPM. Perry has a strongly converging
inlet duct on there.

I know what you're talking about here, but I don't think it's
happening yet at 3700, maybe at 5500.

It is not going to climb well at 70-90 HP and 3700 RPM
at 90 MPH the way it is.

How about 100-110 HP and 4400 rpm, the real numbers?

Perry

Still not enough IMHO.
What worries me is the acceleration is down to only 
0.05 G or so. Not far off top speed. Have you had a chance 
to check those numbers using the old fashion stop watch and 
time to distance?

I think you have mentioned this before Perry but I forgot.
What is the current fan diameter again?

Paul Lamar
 
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