> > > 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
>

 Perry,
 14" is a lot of clearance, is that because it's a pusher? I'm working on
10"
 for my tractor application with a minimum of 6". The more the better is an
 'understood', provided you have the capability to extend the undercarriage
 legs. Which is something I'm considering.
 George (down under)

As a pusher rotates, the ground clearance is reduced - because the
prop is behind the main gear.  Also, many of the canard airplanes have
pretty squishy main gear.  Flop it in fairly hard (with the nose up)
and a prop strike is fairly easy.


Regards,

Matt-



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