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)."