RAH'er has forced landing

Corky Scott wrote:
On Wed, 22 Dec 2004 03:11:51 GMT, "Blueskies"
wrote:


Doesn't the 'mazda' rotary mnimize this pulsation?


Not if the Powersport saga is to be believed. Their initial efforts
resulted in a LOT of psru failures.

See:
http://www.powersportaviation.com/Ho...on%20drive.htm

Ross Aero, on the other hand put together a planetary gear design and
seemed to suffer no torsional problems at all. They told me that some
engineer stopped in to tell them that he'd analized their reduction
unit and claimed that it would destructively vibrate at 300 rpm. Of
course the engine only sees that rpm during startup or shut down. The
rest of the time it's operating well above that.

The Ross Aero psru is what Tracy Crook initially used in his Mazda
powered RV-4. I gather he substantially modified it since then and
may now offer one of his own.

Corky Scott


Tracy does in fact offer his own, now in two versions, a 2.17:1
reduction and a 2.89:1 reduction.

The torsion properties of the rotary is very small compared to a piston
engine. It still has to compress the gas, and then withstand an metered
explosion. But it doesn't have pistons completely reversing direction,
and it has a rather large rotating mass (the rotors and eccentric
shaft), which will absorb much of the pulse in inertial effects.

You can read about it on Tracy's website, but there are basically two
different design philosophies. Building the PSRU gearing tight, with
very small clearances moves the resonant frequency up. Build it loose,
and the resonant frequency goes down. The 13B has a RPM range of
something on the order of 800 to 7000 RPM (depending on tuning and how
hard the pilot wants to push his luck).

Powersport chose the former philosophy. Build it tight enough to put
the resonance above the 6000RPM range. This required incredibly tight
tolerances, which drove the price into the ridiculous range.

Ross Aero, by design or dumb luck, went the other direction. The amount
of play that is in the gears as taken from the truck's transmission is
enough to push the resonance down below the idle speed (ie, into the who
cares range).

Tracy Crook's design is based on the Ross, but with several improvements
that came about due to several problems that Tracy ran into. Several of
these units have been flying for years without problems.


--
http://www.ernest.isa-geek.org/
"This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

"Ed Sullivan" wrote in message
...
On Wed, 22 Dec 2004 22:39:59 GMT, "Blueskies"
wrote:
(snip)

I remember someone talking about a damper that was filled with steel shot
or similar, but I cannot find a reference to
it now.


I can't recall the name, but they were used by Molt Taylor in his
pusher designs and were also used with the Honda Civic engine in some
BD-5s

Ed Sullivan


Dodge Flexidyne dry fluid coupling.

http://www.dodge-reliance.com/pdf/ma.../flexidyne.pdf

http://www.mini-imp.com/drive_train_and_starting.htm
-Bob

On Wed, 22 Dec 2004 12:31:10 -0500, "George A. Graham"
wrote:



Go ahead with your "I told you so's", just remember that there was not a
good alternative six years ago, and my junkyard gearbox has been good to
me.

you are one of aviations pioneers george.
not all pioneering efforts lead to anything in the long term.
honing anything useful takes time and often many dead end attempts.
we applaud your efforts.
what you have shown is that the approach is not too far off the mark.

6 years isnt too informative though.
how many hours were accumulated in those years?
how much work had the gearbox done before finding a home in your
aircraft?
Stealth Pilot
Australia.

On Fri, 24 Dec 2004, Stealth Pilot wrote:

6 years isnt too informative though.
how many hours were accumulated in those years?
how much work had the gearbox done before finding a home in your
aircraft?

The gearbox was used, over 80,000 miles when I got it, I installed new
bearings. It flew 415 hours in the six years. I suspect that the bearings
may have worn enough to disturb the gear lobe fit (but I don't know).
In hindsite, I wish that I had replaced the bearings at annual.

To share my understanding on other issues raised on RAH:

The Mazda Wankle has very low amplitude (strength) power pulses, since the
power stroke is over 130 degrees of the output shaft.

The frequency of power pulses is the same as a four cylinder four stroke
as there are two per revolution. However, if it starts on one rotor,
then every other pulse is removed, which lowers the frequency by one half.
That is not likely to happen on any other engine.

If you know the moment of inertia of each component, and the rate of
spring of the revolving mass, then you can compute the frequency during
which torsional resonance is likely. In my setup, that is 200 to 300 rpm
with both rotors running (double that on one rotor). The forces generated
by resonnance, approach infinity, so no "stronger" gears help much.

I did use an elastomeric dampener (clutch hub), and a quill shaft on
the tranny input (came with it).

Thanks for all of your kind words, I'm off to retrieve my airplane today.

George Graham
RX-7 Powered Graham-EZ, N4449E
Homepage http://bfn.org/~ca266