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Date: Fri, 3 Feb 2012 13:23:20 -0500
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Subject: New Flywheel for RD-1x redrives
From: Tracy <rwstracy@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Finally got around to flight testing the aftermarket flywheel setup for the
RWS redrive.

The cracked flexplate issue some builders experienced came up at the same
time as my CNC source for input shafts lost the ability to make them
anymore due to loss of specialized spline making machinery.  Since I had to
line up a new source I took this opportunity to review the design from the
input shaft back to the engine.   Because the damper has been such an
expensive and labor intensive part, it was looked at as well.   As a
result, there have been enough changes to warrant a change in the name so
the new drives will be RD-2B & RD-2C.

In rethinking the drive I had the thought that since the relatively low
frequency primary resonance range of the drive train is taken care of by
the system lash, that left only the high frequency harmonics that the
damper is responsible for.  This high range is the factor that creates the
red zone in rpm ranges found on some certified engines and metal prop
combinations.   As far as I know, no one has used a metal prop on an RD-1x
drive so I decided that it was an unneeded requirement.  The new design has
no damper at all and consequently it has a "No Metal Propeller"
restriction.

Replacing the damper is a flanged spline that is bolted directly to the
flywheel using the same bolts (longer bolts required) that attach the
flywheel to the counterweight.  The spline is a different spec (15 splines
instead of 30) so it is not compatible with the RD-1 damper but the new
shaft itself is backward compatible with the remainder of the drive.  I
retrofitted the same RD-1C that was on my RV-4 for these tests.

The flywheel was an aluminum racing flywheel with the replaceable iron
friction surface unbolted and removed.  Really looks pretty and
professional compared to the flexplate.  Any of the aftermarket RX-7 & RX-8
racing flywheels (steel or aluminum) that utilize the auto counterweight
may be used.

As David Leonard found, these flywheels place the ring gear about .2"
closer to the engine than the flexplate.  To compensate, I milled .2" off
the front surface of the adapter plate where the starter mounts.  No
changes were needed to the starter itself.   I did not bother to grind the
lead-in bevel on the ring gear teeth as discussed earlier.   Starter
engagement was smooth anyway.

The RV-4 drive had over 700 hours on it and everything looked beautiful
inside.  No signs of wear other than a shallow groove (~.002") on the input
shaft where the 1mm thrust bearing race between the two needle bearings
rides.  Others have reported more than this in fewer hours so this is an
area to inspect carefully.  The new input shaft is a harder alloy (post
machining through hardened 4340) than the the RD-1 which was pre hardened
4140.  This should reduce the wear in this area.   The old flexplate with
over 1000 hours was still crack free.   The input shaft oil seal still
looked and felt new so it was not replaced as planed.  Others have reported
these leaking in much fewer hours.  Don't know the reason but I suspect
that oil temperatures out of range may be a factor.  NEVER allow oil temps
to exceed redline.  If they go higher, back off the power then land and
correct the cooling system.

Only 1 hour of flight testing so far but all indications were good.
Operated the engine through the full range of rpm up to 7100 looking for
telltale signs of resonance.   I was sort of expecting to feel, sense or
hear some indication of increased harshness in the drive with no rubber
anywhere in the system but if anything, it felt smoother.  There was none
of the 'Waaa --- Waaa' warbling sound (like a twin engine with the engines
out of sync) that I had with the Ross drive years ago.  So far I'm very
satisfied with the results but it's still early in the tests.

Tracy Crook

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Finally got around to flight testing the aftermarket flywheel setup for the=
 RWS redrive. <br><br>The cracked flexplate issue some builders experienced=
 came up at the same time as my CNC source for input shafts lost the abilit=
y to make them anymore due to loss of specialized spline making machinery.=
=A0 Since I had to line up a new source I took this opportunity to review t=
he design from the input shaft back to the engine.=A0=A0 Because the damper=
 has been such an expensive and labor intensive part, it was looked at as w=
ell.=A0=A0 As a result, there have been enough changes to warrant a change =
in the name so the new drives will be RD-2B &amp; RD-2C.=A0 <br>
<br>In rethinking the drive I had the thought that since the relatively low=
 frequency primary resonance range of the drive train is taken care of by t=
he system lash, that left only the high frequency harmonics that the damper=
 is responsible for.=A0 This high range is the factor that creates the red =
zone in rpm ranges found on some certified engines and metal prop combinati=
ons. =A0 As far as I know, no one has used a metal prop on an RD-1x drive s=
o I decided that it was an unneeded requirement.=A0 The new design has no d=
amper at all and consequently it has a &quot;No Metal Propeller&quot;=A0 re=
striction.<br>
<br>Replacing the damper is a flanged spline that is bolted directly to the=
 flywheel using the same bolts (longer bolts required) that attach the flyw=
heel to the counterweight.=A0 The spline is a different spec (15 splines in=
stead of 30) so it is not compatible with the RD-1 damper but the new shaft=
 itself is backward compatible with the remainder of the drive.=A0 I retrof=
itted the same RD-1C that was on my RV-4 for these tests.<br>
<br>The flywheel was an aluminum racing flywheel with the replaceable iron =
friction surface unbolted and removed.=A0 Really looks pretty and professio=
nal compared to the flexplate.=A0 Any of the aftermarket RX-7 &amp; RX-8 ra=
cing flywheels (steel or aluminum) that utilize the auto counterweight may =
be used. <br>
<br>As David Leonard found, these flywheels place the ring gear about .2&qu=
ot; closer to the engine than the flexplate.=A0 To compensate, I milled .2&=
quot; off the front surface of the adapter plate where the starter mounts.=
=A0 No changes were needed to the starter itself.=A0=A0 I did not bother to=
 grind the lead-in bevel on the ring gear teeth as discussed earlier.=A0=A0=
 Starter engagement was smooth anyway.<br>
<br>The RV-4 drive had over 700 hours on it and everything looked beautiful=
 inside.=A0 No signs of wear other than a shallow groove (~.002&quot;) on t=
he input shaft where the 1mm thrust bearing race between the two needle bea=
rings rides.=A0 Others have reported more than this in fewer hours so this =
is an area to inspect carefully.=A0 The new input shaft is a harder alloy (=
post machining through hardened 4340) than the the RD-1 which was pre harde=
ned 4140.=A0 This should reduce the wear in this area. =A0 The old flexplat=
e with over 1000 hours was still crack free.=A0=A0 The input shaft oil seal=
 still looked and felt new so it was not replaced as planed.=A0 Others have=
 reported these leaking in much fewer hours.=A0 Don&#39;t know the reason b=
ut I suspect that oil temperatures out of range may be a factor.=A0 NEVER a=
llow oil temps to exceed redline.=A0 If they go higher, back off the power =
then land and correct the cooling system.<br>
<br>Only 1 hour of flight testing so far but all indications were good.=A0 =
Operated the engine through the full range of rpm up to 7100 looking for te=
lltale signs of resonance.=A0=A0 I was sort of expecting to feel, sense or =
hear some indication of increased harshness in the drive with no rubber any=
where in the system but if anything, it felt smoother.=A0 There was none of=
 the &#39;Waaa --- Waaa&#39; warbling sound (like a twin engine with the en=
gines out of sync) that I had with the Ross drive years ago.=A0 So far I=
9;m very satisfied with the results but it&#39;s still early in the tests. =
<br>
=A0=A0 <br>Tracy Crook<br>

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