I finally got into the gear box today and found another issue.  In
 addition
to the sun gear pin failure inside the gear box, the flex plate
 came apart.  I found a piece of it in my cowl as a litte hint of
 what I was  about tofind..

Here are some pictures.  The plate was pretty badly broken up and
was onlybeing held together by Tracys aluminum damper plate and
the steel bolt  ring. Pin in sun gear was also broken.  No
apparent serious damage, just what Iassume is cosmetic galling of
the input shaft, adapter plate, and bellhousing from the loose
pin floating around.

Thinking back, I had an early sign of it at the Reno Pylon
School.  Afterone of the races I noticed that my home made cover
over the flywheel hadbeen marred by the flywheel but was not in
contact with it.  I attributed  itto the high air speeds (205 Kts
Indicated coming down "The Chute") somehowpushing my cover down
onto the flywheel.  I put some creases into the  coverto make it
stiffer which seemed to solve the problem, but perhaps the flex
 plate had broken at that time.  With a mis-tracking flex plate it
is easy  tosee that sun gear pins would be undergoing additional
stress.  So I amcalling the underlying cause of both issues the
flex plate failure.

The large washers that covers the rubber dampers between the
dampers and  theflex plate have made a significant groove into
the aluminum of theattachment plate.  I have never noticed that
before, possibly was a  functionof the twisting flex plate.
 Question is, does it need to be replaced?

My rubber dampers are noticeably worn and soft and need to be
replaced.  Iam getting quite a significant amount of oil coming
past either my rear  oilseal or the oil seal on the gear drive.

 That oil may have done in therubber dampers, that got too sloppy
and stressed the flex plate thateventually fatigued and broke,
 which further lead to the pin failure.

So I am undecided on what to do about the flex plate replacement.

 I agreethat the iorn flywheel is not the answer.  The machine
work would have to  bequite extensive, because the aluminum plate
rides inside the ring.  Afterall that machining, it would have to
be re-balanced but that would bedifficult because it has the rear
counter weight built in.

Using one of the aftermarket aluminum flywheels might work.  It would
 still
have to be machined to make space for the damper plate, but at
least itwould be aluminum (easy to machine) and could then be balanced
 symmetrically
(perhaps even with the damper plate installed so it is all nicely
 balanced.
 That would not be a low cost solution, however!

Paul, if I were to get an aluminum flywheel like this one:

http://www.racingbeat.com/RX7-**1986-

 1992/Flywheels/11465.html<http://www.racingbeat.com/RX7-1986-1992/Flywheels/
 11465.html
do you think that you could put it on your milling machine and
mill in theresesses for tracys damper plate?  Then would you have
any suggestion onwhere I could get it balanced?

I am also wondering if I have any business trying to make that
much HP.  Iwas about to install a water/methanol injection system
to be able to usemore boost at Reno.  But it seems I may not be
able to safely use the HPthat I already have...

-
--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net <http://n4vy.rotaryroster.net/
http://RotaryRoster.net <http://rotaryroster.net/

Wow Dave that is a game changer.

I have a guy up here in SZP with a really big lathe that can make
a new "flex plate" . As I recall the subject of flex plate run
out came up recently. Perhaps your plate was warped. Everybody
should check their plates for run out. Any run out puts a bending
stress on the plate due to dynamic imbalance. All parts of the
plate want to revolve in the same plane. If the plate does
not track it will introduce a bending stress in the material.

Also the alignment of the input shaft to the box must be
perfectly in line with the e-shaft axis. This is not easy to
check. Perhaps a low cost laser can be inserted into an empty
gear box starting at the prop bearing end and see where the light
spot falls on the counter weight. A holder for the laser can be
 made  and checked in a lathe for an aligned axis. If you UPS your empty
box,spacers and adapter plate  up I'll put Jim Poole on the job.

One quick and dirty way is to assemble Tracy's damper on the
input shaft with out bolting it to the flex plate. In fact
leave the flex plate out and off for the moment. Use the engine block
as an anchor for a dial indicator and check for damper plate run out.

Then measure the distance from the block to all four quadrants
of the damper plate.

Paul Lamar

 Dave if you look on the RX-8 flywheel as been redesign by Mazda
and those 4  holes 1" dia plus are located further apart  as the
center of the flywheel  and close to the ring gear It looks to me
Masda had similar fatigue problem  with the RX-7 flywheel.The
problem we can not fit  the Tracy damper plate  because it does not
fit the attaching holes and are to close of the ring  gear unless
someone have an other solution

 Jean Prudhomme

Yes, it is becoming pretty clear that any option other than the
 auto-  tran flex plate is going to take considerable extra work to
 get it  addopted.  I think the aluminum fly wheels are my first
 choice of  alternative at this time, but I may just put in the flex
 plate and  stop trying to make a lot of HP.
--
David Leonard

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

I would not use aluminum Dave. IMHO a better way is use fatigue  resistant
.065" thick  4130 sheet reinforcement tig welded in the center
diameter. I'll build you one out of a spare plate I have if you
 will  work on finding a replacement.

Paul Lamar

 Hi Dave,

 I gather from your e-mail and web that you are a Naval Aviator. This
 would
 tell me you are used to aerobatics, which will put assorted higher
 stresses on
 the airframe. I was having a morning coffee and contemplating navel
 lint when
 I came to the idea to check your web and construction photos. Also this
 came
 to the forefront after the pylon school with high stresses.

 Your PSRU mount on the plate has a fairly small diameter ring of bolts.
 During
 aerobatic manoeuvres, there will be a large torque on the prop that
 will be
 transmitted through the PSRU to the mount plate. I believe the flex
 should be
 determined and dealt with.

 So, how to measure and calculate the flex force. A hydraulic cylinder
 like
 used with a pump for body work can be modified to have a pressure gauge
 and
 the cylinder diameter is easy to find.  This will tell the pounds
 force. If
 this cylinder is extended a bit (1/2 stroke) and a bottle jack is
 used under it to apply force, then a dial indicator will show the
 amount of flex. Put the hydraulic jacks under the front of the PSRU
 just behind the spinner. A piece of angle or channel iron bolted on
 the top of the engine (the lift bracket bolt hole) will provide a
 mount for a dial indicator, to read movement on the top of the front
 of the PSRU. Paul should be able to do a quick calculation of the
 force applied through the prop during turns.

 You may need to install braces from the front of the PSRU back to the
 engine
 bellhousing bolts to stiffen it up. A small amount of flex is like a
 misalignment and under load it will not take long to break the flex
 plate.
 Brace to the sides as well.

 Dale Davies

David I sent an idea of using the RX_8 flywheel with an additional
 aluminum
plate,the RX-8 look a stiffer design

Jean Prudhomme

Yes it does look stiffer Jean but it would require a new Tracy
 style damper  plate because I suspect it is larger in diameter.

I think the cracks started in these holes.
The 13B plate is only 1.5 mm thick or about .059".
I think the holes could be filled in with .065" thick 4130
and it would be much stronger. Also a 4130  doubler plate
could be added to the center. This is all low cost.

Aluminum is not a good material for this use.

Paul Lamar

--Hi, a flex plate will flex.  Our experiance with an odd fire
 Chevy V-6 on a dyno showed more than 1/2" deflection at the ring
 gear on a heavy duty racing flex plate judging by the notches cut
 into the ribs at the back of an expensive aluminum block. The ring
 gear is effectively the rim of a gyroscope.  The unbalance of the V-
 6 excited it.  With the better balance of the Wankel that would not
 be a problem but maneuvering in the aircraft would be.  It needs to
 be stiffer to minimize deflection and fatigue.  Look forward to
 seeing you all on Saturday.  Free lunch after meeting.

 Murry Rozansky

 Like some fast 2 G laps at Reno? :)
 A one radian per second spin will bend a Lycoming crank shaft flange.
 Good call Murry. Aluminum is not what you want when continuous
 bending is present.

 ---------------------------------------------------------
 Here is what the Skyranch Engineering Manual has to say about it.

 It is obvious from this point of view Tracy's large nuts and bolts
 out near the rim add to the moment of inertia. Helicopters deal with
 this by putting hinges in the blades near the hub. Obviously it is
 not a good idea to use a solid and stiff disk such as an aluminum or
 steel flywheel as that adds a lot of weight. Stresses in the solid
 hub go up to high levels. It is better for the rim of the flex plate
 and ring gear to find its own plane of rotation and allow the plate
 to flex. If it is laminated from two or more thin spring steelplates
the cyclical bending stress on any one plate will be lower.

 Does anybody wish to comment on this analysis or scenario?

 * Sky Ranch Engineering Manual. This book presents an excellent
 overview of the problems of aircraft engines. It is 500  pages and a
 bargain at only $23. There are many details on the materials and
 processes used to build a successful aircraft engine. There is a
 very good and exhaustive discussion of destructive  torsional
 vibrations and fatigue. The telephone number  to buy this book is
 (916) 421 7672. The author is John Schwaner. John is highly thought
 of in the experimental aircraft community.

 Paul Lamar


I would caution against re-inventing the wheel. I think the flex of the plate
between the PSRU and the rear iron/bell housing bolts needs to be checked. The
flex plates between a 600HP diesel and a generator are four thin discs about
0.020" thick. That boils down to about 1750 lb-ft at 1800RPM. The alignment
MUST be checked or the plates will buckle under load.

If 600 to 700 pounds does not flex the aluminum plate much, then OK. The
pounds is from the gyro force calculation and is pounds force not PSI. Use the
method I described in my previous post to measure the flex. If the initial
alignment with the bolt-up to the flex plate is good as per OEM standards,
then the flex plate should not break! I believe it is the PSRU mount flexing
because the gyro forces go through it and are counteracted by the engine
mount. When the PSRU plate flexes, the force is transfered to the flex plate
which eventually fails. Planes that are not flown as aggressively likely  will
not have a problem with this. Putting a doubler in will not hurt, but the
welding could be a concern. If it could be put in as a sandwich between the
existing bolts would work well.

Again, I suggest measuring the PSRU mount plate flex.

Dale Davies


We did that Dale and the half inch 6061 plate was amazingly stiff.
Tracy's spacers between block and plate could be better.

One could also make a simple flat 4130 flex plate and space it out
out from the counter weight to get the ring gear in the right location.
Here is a 3D.

Paul Lamar