> Paul,
> I am commited to using the P port configuration and started
looking at
> specs for props. I do not think a 74" prop will fit on a pusher even
> though I have 48" from the ground to the thrustline. I went to your
> website where you have two P Ports with different runner lengths. Is
> there any advantage running the 2.85 PSRU over the 2.17? The curve on
> the higher performance runner looks flat in the range from 6500 to
> 7800. I think I could swing a 68" prop. Just trying to find the
right
> combination.
>
> Joe Berki
> Limo EZ
>
> Yes. There definitely is a HP advantage. If you can not handle 74
> inches think
> of a wider blade or 3 bladed prop that will absorb 240 HP of lower
> diameter.
>
> Just explain things to the prop builder and he will build a prop
> for 240 HP as little as 65 inches in diameter. Could be as many
> as four blades if he does not have a wide blade version.
--
Paul Lamar ...No rotor no motor.
With a 2.85 psru and a "small" diameter prop, you are turning the prop
slower than if you had a 2.17, so the tip speeds would be relatively low
- good for noise reduction. To go fast with a "slow" turning prop will
require a lot of pitch, which might tend to stall more at the start of
takeoff roll. But you have lots of power so a prop can be built that
will work. What is max RPM you want to operate the engine?
Perry
Perry,
I do not want to go much beyond 7500 RPM and would go lowest at 5000
I have 48 " from the thrustline to the ground and the prop flang is
41.5" to
42" from the firewall. Right now this is theoretical as I have not
purchased the PSRU because I am trying to decide on a ratio. Thanks
for any
input.
Joe Berki
I think mine measures about 48" from thrustline to ground at the prop,
but I lowered the thrustline a couple inches because of the ducted fan.
When I build the new engine mount I plan to raise it back up where it
should be. And your prop is farther aft than mine and probably most
Long-EZs. So I don't think you can go larger in diameter than the
recommended 62 to 64 inches on the prop. Max. RPM on a 62" prop is about
3000, exceed that and you start to go above 800 fps at the blade tips.
3000 prop RPM is 6510 engine RPM with the 2.17 drive, which is where I
run mine. My engine redlines at 7000. If you want to go higher than 6500
engine RPM you would need the 2.85 drive. 7500 / 2.85 = 2630 prop RPM -
reasonable. But you will still be stuck with the small prop diameter to
avoid prop strike with nose high attitude on landing or takeoff.
To go 220 mph with your 2630 RPM prop and your engine running at 7500
RPM you will need 88" of pitch, which might give you some grief on takeoff.
Perry
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site.
http://www.rotaryeng.net
Copyright 1998-2007 All world wide rights reserved.