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Message
Rusty,
at this stage I would try the following (all of it VWAG,
as I have no experience with Rotaries WSE, but a little with
track&balance):
a. Cheapest way is good: Mount a chunk of whatever to
go hopelesly beyond needed mass.
(I don't know what is cheapest in your corner - a chunk of
steel turned on a lathe, e.g. This way you can have it turned down bit by bit to
find the "critical mass")
b. Take off the prop, mount the mass to the
PSRU.
c1. If idle-problems/vibrations/shake&rattle&hum
(PVSRH) continue - remove PSRU and mount directly to the
engine.
d1. Confirm no problems with mass and engine alone -
remember, 2 rotors is NOT the same as 1 rotor and some flywheel mass, distances
are different, so different resonances can happen.
IF I remember right from Engineering school:
The faster you spin an assembly the smoother it gets, no
matter what the imbalance is - at some point it goes to zero, depending on
rpm/imbalance/inertia/mass - the problem is to get the rpm past the
resonance-rpms (you seem to see that at various rpm settings on your
1-rotor)
Just like your car wheels - generally they would show
imbalance worst around 70 - 100 km/h. Get past that speed and everything
smoothes out! Better solution: Get your wheels balanced
- I guess that's what we want here too: Smooth&low
idle, no shakes all through the rpm-band.
e1. Get the PSRU back on and start reducing the mass - if
PVSRH gets worse, you have a problem with the dampers.
c2. If there is no PVSRH, start to cut down mass little by
little to see if PVSRH starts at some
point.
d2. Once the weight is down to Prop/Hub/etc. weight and no
PVSRH is there, you have some resonance/vibration induced by the
prop/hub.
d3. If PVSRH is worse at some place before Prop/Hub/etc.
weight is reached, you have an idea how much weight you need to add at the
present prop/hub combo.
And you know you have resonance problem with the PSRU, be
it dampers or gear masses, etc.
f. Whenever you take off the mass for modification: Unplug
that ACES to re-charge it!! :)
You always want to see the spectrum and the
IPS/clock readings!! :)
Rusty (resistance is
futile) "I told you
so"
Rusty (trying hopelessly to resist) " What'd I say!!"
"If I'm smart, I'll just pull the prop, so
the engine runs well, and I'll run it every now and then when I go to the
airport. That will keep it healthy, and let me work on the RV-8 instead."
Ahh, forget that!!
You couldn't sleep at
night!!
Just find the fastest
way to get the mass on and off - this way you always do something on the Rotary,
while doing your RV/Lyc (Uagh!) thing.
However you could have the mass machined
with a couple of threads, so you can change weights fast!! You have an
electronic scale with your ACES, do you?
Thomas Jakits (finished 120 messages backlog of 3
days and putting the "scientist" back into Rusty - at least
trying!!)
----- Original Message -----
Sent: Friday, January 20, 2006 4:41
PM
Subject: [FlyRotary] Re: flywheel
weight?
10lbs. That is about the weight of a rotor. But
you'll be spinning it
3 times as fast, so it'll have 8 times the momentum
(momentum is
velocity squared, right?). The object is to keep the
shaft from
speeding up and slowing down, and I think increasing the
momentum 8
times would accomplish that well.
Hi
Ernest,
All WAG's
appreciated. I'm not sure the biggest problem is the missing mass of the
2nd rotor, but rather the missing firing pulse. If we were to continue
your momentum thought though, the flywheel advantage would be even
greater than you suggested. Remember that the center of the
rotor mass is traveling in a much smaller radius circle than the
mass of the flywheel ring that I proposed. Heck, maybe that 1.5 lbs of
weight that I had before would have made up for the missing rotor
:-)
other ideas: Have the disc water/laser cut. And
you don't need 4130,
so have the cutter use whatever steel they have on
hand. Have a brake
shop turn the disc and balance it, or you might
just be able to get a
brake rotor that would bolt right into place with
little or no
modification. The heavy duty Matco rotors I just bought
seem to be
around those dimensions if memory serves.
Interesting
thoughts. I'm still leaning toward trying to install 4 separate weights,
which makes it possible to do this without pulling the drive off. It
also makes balancing a simple matter of precisely weighing the added
weights. I can buy 1/2" steel discs in various diameters from McMaster
Carr, so I would just have to drill a hole in the middle, and bolt them
on. I wonder what the limit of a 7/16" bolt is for holding a
couple pound weight spinning at 8000 rpm. Probably don't want
to have anything in the arc of the flex plate the first time it was
run up :-0
Dale,
I thought about
flywheels, but aren't they always manual trans flywheels, made to install on
the shaft itself? I need something that coexists with the
current auto balance weight, flex plate, and Tracy's dampener
plate.
Thanks,
Rusty (trying hopelessly to
resist)
PS- Congrats to Joe! If this keeps
up, people are going to think that rotaries can only fly backwards
:-)
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