Paul, do you or anyone on the group remember the change in
crankshaft resistance after torquing down the RD 1C 12" an4 bolts at
final assembly?
The assembly instructions show a trial fitting without the 5 1/8
inch ring gear spacer o-ring. This worked well on my unit, with the
crankshaft turning easily by hand. However I found this oring was
missing from my unit.
Tracy's specifications are for a 5 1/8 inch outside diameter and
0.190 inch thickness, which corresponds to an AS568-351 (3/16"
thick). I ordered some of these, but found that the actual
thickness is 0.21 inches, not 0.190". I cannot find any metric or
other equivalent size that exactly matches the 0.190 specification.
When tightening down the drive bolts to the final torque, the
resistance to turn the crank shaft roughly doubled. I can still
detect just a little bit of backlash play, but the torque required
to turn the crank shaft without spark plugs installed is
approximately 20 foot pounds. It appears this is due to the
resistance of the ring gear pressing on the O-ring against the
adapter housing.
Does anyone know if this amount of resistance is normal, or perhaps
Tracy was using some o-rings that are exactly 0.190 inches in
thickness?
Thanks!
Scott Gettings
I assume that is the late one that does away with the torque damper.
I have no experience with that one. Send me a dwg or sketch if you
can. A picture or two would also help.
Typical of O-ring dimensions. It gets real critical when you are
dealing with the rotor housing O-rings. Too big and it will crack
the cast iron.
I this case it's not that bad.
Paul Lamar
The RD1 C still has the 4-bolt damper that mounts to the flex plate.
I added AN 970 large washers to the bolts on the engine side to the
plate, which was obviously highly stressed by the bolts and standard
washers on that side. It is also easy to inspect.
I have attached the expanded view of the RD1-C. The ring gear has a
45 degree cut on the outer circumference to accept the o-ring. The
oring just pushes against the solid adapter cylinder (the part that
bolts directly to the adapter plate), thus keeping the ring gear
tight. It seems this oring spins against one or the other surface
when running. So when trial assembling without the oring, the
gears spin freely. With the oring in place, there is pressure on the
ring gear as the bolts torque down.
Here is the scan and adapter pix.
Thanks, Scott Gettings
The ring gear is stationary. The bulkhead the ring gear splines on is
bolted to the gear box case. Nothing critical about that O ring.
Those bolts are flat heads screws. The early ones where known to
shear. I think the diameter was increased in the later versions.
The stock Ford bulkhead is powdered metal and SUPER hard. Makes a
good bolt shear :-)
Old message:
"I found that seven (7) of the eight (8) 1/4-20 bolts holding the
ring gear to the casting were broken. Only one bolt was still in
tact, and it was loose. After discussing this with Tracy, we agreed
to drill and tap them to 5/16-20 which I did. "
Please take one of those screws out an measure the diameter for me.
After you fly it for a few hours it disassemble the gear box and
check those bolts that bolt the ring gear bulkhead to the gear box
case.
Paul Lamar
Will do.
Scott Gettings
Paul,
I opened my RD1-C drive, and have included some pix. The ring gear
is on a splined shaft connected directly to the prop hub. It is not
fixed to the case and does not have the screws mentioned above. The
ring gear can easily be pulled out, as per the pic. The planet
carrier is fixed to the �spacer� part of the RD case (against the
flat adapter plate).
You can see the location of the o-ring. When in place, it sticks up
about 0.03� before compression. Since the surface on the
spacer/planet carrier where the o-ring contacts is rough (see pic) ,
it appears that the ring gear must rotate along the fixed o-ring
surface. There is nothing else other than the o-ring holding the
ring gear from impacting the prop side of the planet carrier.
Turning the engine over without compression requires about 10 ft-lb
of torque. When the o-ring is compressed, this doubles to about 20
ft-lbs. Do you think this is an acceptable amount of drag?
Thanks again?
Scott Gettings
Aw so my mistake. I thought all C versions were 3.12 to one. You
have a 2.12 to one I think. Power is out of the ring gear rather than
the planet carrier as in a 3-2-1.
An O-ring used in that fashion is very very unusual to say the
least. That is not what they are designed for.
Maybe Tracy did that to dampen some vibrations. I have NO idea what
he was thinking :-)
Paul Lamar
------------------------------------------------------------------------
There are two drawbacks to this box Scott.
Number one: the prop rotates in the wrong direction. I suspect but I
could be wrong props like that are hard to find. I happen to have a
nice one that I am willing to sell. Here is a picture. It is a
Warnake.
Number two: you will be quite a bit down on power. A turbo would be
cheaper than a new box if you can find one.
I have a box just like yours. I have new bearings on order with the
idea of upgrading it to 3-2-1. I need to check with my bearing
supplier tomorrow.
I'll have more info on this in a few days. It will need a new prop
shaft and prop flange.
Paul Lamar
Paul,
I pulled my 11-year old records and found that my RD is actually a
RD1-B. I just measured the reduction ratio and it is indeed (appx) 2.17:1.
The original rationale for this ratio may have been that the GG only has
a 62� prop. So a 2.17:1 drive can have the engine running at 7,250 and
the prop tip speed will be 616 mph, or 0.80 mach. 8000 rpm is 0.88 mach.
The turbo GG installations have had significant weight challenges. I
�only" need about 180 hp for this aircraft for water performance. The
easiest fix should this not work might be to revise my intake manifold.
Regarding the ring gear, I confirmed that the nylon �snubber� washer
spaces the ring gear away from the sun gear and planet carrier. So
these parts can�t hit even if the 0-ring failed. I confirmed the
measurement that the o-ring will compress about 0.04� against the ring
gear when the case tightens, which is creating the resistance. I have
pinged a couple of other rotary/GG builders to see if they have had
issues with the o-ring.
Scott Gettings
You won't see 7,250 RPM Scott. Not enough HP. Also 180 HP is a bit
optimistic.
Paul Lamar
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