Today had a failure of my RD-1B gear drive.  It
couldn't have happened at a
better time, I was just taxiing off the runway at my home
airport.  I just
finished flying 200 mi. to Santa Paula to help Paul with
the getting of Mike
Wills airplane back into the air.  Flight home was
otherwise unevenful and
beautiful.  I didn't bother taking it apart, but will
do so tomorrow.  Feels
like I may have broken the sun gear pin again but will have
to wait until
tomorrow to be sure.  The strange thing is that
nothing particularly
stressed it.

Sorry there is not cause I can report... a little suspense
until tomorrow.

-- David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net

Both Lycoming and Continental have produced "geared, opposed" engines.
This paper summaries the best practices for your geared power plant.

http://www.republicseabee.com/Files/GO-480%20ops%20big.pdf

"In a nutshell, the secret to long life of your GO-series Lycoming is to
NEVER EVER let the air turn the prop!"

Erik

Erik, have Chris Schuermann check the Ford C6 parts. Looks like Ford C6 parts to
me. Lycoming is known to use certain automotive parts like sodium
cooled diesel engine valves and old Cadillac V8 hydraulic valve lifters.

The difference between the Lyc GO and Tracy's box is the rubber torque isolator
missing in the GO. As Vance used to quote some famous English racing
engineer "An ounce of rubber is worth a pound of engineering". That is
pound sterling.

However there is a chatter resonance below 1800 engine RPM in Tracy's box.
Mike's RV4 idle screw is therefor set above that. Dave told me he has
seen 7100 or 7300 RPM down hill which is not reachable in straight and level
flight with the 2.17:1 box  so that could have something to do with it.


Paul Lamar

Why is 7100-7300 rpm much different than 6500?  This failure isn't a line speed issue, is it?  Straight overload?  Fatigue?

Is the gear reduction on a GO significantly different from that of a Merlin or Allison, other than the Lyc is about 20 years newer by my account...  All are spur gears, I think.  I guess the Lyc has proportionally higher torque pulses than the V12's..


Matt-

Well 7300 implies the air is driving the engine to a certain extent
whhich reverses the torque direction..

Merlin and Allison are spur gears.

" Wright Field was not enamored with the overhung crankshaft pinion design of the internally driven spur type reduction gear. This was a design feature looked upon as having questionable reliability and one that would cause problems for the crankshaft. Allison claimed the feature provided weight-saving construction, though Wright Field believed there was a reasonable chance that the saved weight might need to be added in the crankshaft or crankcase to prevent failures such as those occurred on two crankshafts in the earlier Navy GV-171O-A engine, both of which were believed to have been induced by this cantilever feature."

http://www.rotaryeng.net/psrus.html

Gear line contact compressive stress is critical to the life of a gear
box. A planetary has six times the length of a spur gear for the same
gear width.


Here is a real old message on the subject.
---------------------------------------------------

-------- Original Message --------
Subject: Mazda manual transmission PSRU
Date: Mon, 06 Dec 1999 14:01:09 -0500
From: Paul <rotaryeng@earthlink.net (by way of plamar@echelon.ca)
To: plamar@echelon.ca

norm doty wrote:

 the spalling and temp problems can usually be avoided by using an oil blend.
 ive used castrol 90w hypoid gear oil mixed with stp in a 50/50 mix.
 this was used in our race car, and our race boats, we also used the mazda
 tranny.
 all gears in race and it was locked like goerges for the race boats,(we used
 3rd).
 we tried every brand on the market at the time 1970-75, this was the best
 for us.
 some of the newer synthetics might be of help, but im not sure and ive never
 tested any of them.
 norm

This may help norm but the fundamental problem is the length of line
contact and the force on that line length. (In other words the diameter
and width of the gear and the RPM and torque)

In the case of the Ford C6 planetary set there are four line
contacts about two inches long each for a total of
eight inches. In the case of the Mazda 2nd gear
there is only one line contact about about one inch long.
All other things are roughly equal. For this reason it is
difficult to beat a planetary gear reduction.

Tracy has noticed some gear deterioration in 600 hours of use
when the Ford planetary was used
with splash lubrication. He has changed the Ross design to use
postive lubrication in his new design.

Paul Lamar

The Aircraft Rotary Engine Newsletter.              Powered by Linux.

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------------------------------------------------------
There have been many more since.

Paul Lamar

Woops..  I thought the Lyc GO was spur drive like a Continental GO, but looking at some pictures suggests the Lyc GO is planetary geared..

Why does 7300 imply the prop is driving the engine unless the throttle is reduced or there's some other limit in the engine?  Shouldn't the engine go to 9000 or higher if not loaded by the prop?  Or was Dave avoiding going through Vne?  Also, 7300 should have put the prop tips through trans-sonic?


Matt-