Paul,

I understand that your mission is the turbo compound rotary project, yet
you occasionally
express an opinion on the rotary torsional vibration issue. It's the
latter issue I wanted
to discuss...
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I have two lines of inquiry...
1. Why are the Mazda rotary cars with auto transmissions not exhibiting
fatigue failures
of flex plates or other drive train components? Some possible answers...
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2. Why are the Mazda rotary cars with manual transmissions not exhibiting
fatigue failures
of flywheel/clutch/pressure plate or other drive train components? Some
possible answers...
packs

I've read Tracy Crook's discussion discounting any pulse dampening effect
from the clutch
disk spring packs. I am unable to provide a technical basis to support or
dispute his
views on this topic.

A topic I have not seen discussed and want to explore is the effect of the
increased
rotating mass that can be attributed to the total combined mass of Flex
Plate + Torque
Converter assembly or the total combined mass of flywheel/clutch/pressure
plate assembly.
I feel an increase in rotating mass would certainly affect the torsional
vibration
amplitude and also the critical speeds, but it is just speculation that
the change would
be beneficial for our aircraft application.

In automobiles the rotating mass is minimized (via light weight flywheels,
drive shafts,
mag wheels, etc) in support of enhancing acceleration performance. This
acceleration
performance is less important (maybe negligible) in aircraft engine
applications. So we
might propose a heavier flywheel between the rotary engine crank shaft and
the PSRU input
shaft.

I'm just brainstorming here, but if we can find a clutch disk with the
correct spline
shaft interface, I suggest that a Mazda flywheel/clutch/pressure plate
could be used as
the coupling between the rotary engine crank shaft and the PSRU spline
input shaft. Maybe
use the manual transmission bell housing too. I see no need for
disengaging the clutch so
the throw-out bearing, linkage, and hydraulic slave cylinder would not be
installed.

If that idea is not feasible, then I suggest we consider bolting Tracy
Crook's plate to a
manual transmission flywheel with integral starter ring gear rather than
the auto
transmission flex plate with welded on starter ring gear. The stock manual
transmission
flywheel is much heavier than the flex plate (improved flywheel mass for
torsional
dampening effect) and it's stronger than the flex plate (probably immune
to the fatigue
failures seen in the flimsy flex plates).

Of course the PSRU mounting plates and spacers would need to be modified.
Might add inches
to the PSRU length.

Your thoughts?

John Lindinger
Bede-4 Builder
1993 RX7 Owner
1951 Piper TriPacer Owner


1. The flex plate is bolted to a fluid coupling type of torque
converter. That absorbs torsional vibration. There is a fluid
coupling in the DD15 TC gear box I just bought.

2. The manual transmission cars have springs in the clutch plate
that mitigates the torsional vibration. These
work and have been used in the Ross gear. The springs are not the
best however. It is like having a car with no shock absorbers
(damper is a better description of shock absorbers).

It works but not as well as having some damping.
Rubber works like springs but also has damping built in. The rubber
heats up because of the damping so you need high temp rubber like
silicone. That is what we are working on.

BTW the torsional vibration of a  2  rotor rotary is much lower than
that of a 4 cycle piston aircraft engine. The frequency is much higher as
it revs much faster.

Heavy flywheels are also used in man tx cars of course.
Heavy fly wheels have been used in a Chevy engine when used with
a gear box in an aircraft. Adding a heavy fly wheel is the sledge
hammer approach to aircraft design :)

Paul Lamar


If we are brainstorming, ...
In Diesel trucks and pickups, the impulses are so hard, that gears can be
ground up.  To counter-act this, I use the example of the 7.3L Ford Diesel
in the 1990s manual F250/350/450/550/etc.  The flywheel has what Ford calls
a mass dampener I think.  It consists of a light flywheel (as trucks go),
with dense, heavy duty, high-temp rubber bushing around each of the flywheel
attach bolts with bushings.  They last on an average of 200-250K miles or
about 10 years of average use.  The mass-dampened flywheels can cost around
$1,000 depending on the exact application.

A similar dampener is used on the Cummins of the Dodge variety.  Some
mechanics at the Dodge Boys, say that the option to have a flex-plate and
torque converter is less damaging since the impulses are absorbed in the
fluid. (I understand this is not good in aircraft.)

Just my 2 cents worth...
Dan

Diesel's have particularly sharp and steep torque pulses.
The aircraft diesel engines out now have been known to destroy props.

BTW Dan I suspect the battery maintaining the real time clock in your
PC is dead. Your messages are coming in out of sync.
No real problem for me so you don't need to fix it right away.

Paul Lamar