----- Original Message -----
Sent: Friday, July 13, 2007 8:59 PM
Subject: [FlyRotary] Re: Single Rotor
Run
What torque pulses? Today was the first run
with the complete engine in flight configuration, meaning engine - psru -
prop. No vibration out of the ordinary. It, off curse, is shaking at 1300 RPM
idle, just as my Soob does. Once it goes over 1700 running like an electric
motor, almost.
Sounds great Richard. What prop are you
running?
A couple thoughts come to mind about why you might not
have the same torque reversal problems I have. One is the damper in the
Hirth gear box. It might just be that it's exactly right for the
job.
The other possibility I've mentioned before is that maybe
you're benefiting from one of the PP shortcomings. As I understand it,
PP engines tend to have less power down really low
in RPM's. Perhaps this lack of torque is what's keeping you from
having the torque reversal problems. I don't see a down side to this,
and it would be THE reason to go with PP for me (if indeed it has
anything to do with it).
Cheers,
Rusty
I am using a
75" three blade Powerfin set at the tip to 13deg.
The key to
eliminate the influence of the power pulses is to have all natural frequencies
in the power train well below the rpm operated. This meaning high rotational
inertia and soft couplers.
We can't do
much about the inertia except bigger flywheel, and that would be weight. So we
can only Play with the coupler. Early on, I determined that the coupler used
on the two rotor is way too stiff for single rotor. Even with the
softest rubber, you can not get the freedom needed for low enough natural
freuency and sufficient damping factor. The only way to achieve that is with a
much smaller radius for the location of the coupling
elements.
I don't know
what your coupler looks like, but I would suspect that it is very close to
what is used on the two rotors.
If every
thing else fails, the Hirth comes with the option for a clutch. And the price
is right.
Richard