Paul,

   I think you got the 13B aluminum bare block weight wrong, or
  thisfellow
   is super strong.
   Next is  what the  Bell 47 final drive looks like in use as designed.
   Amazing the final thrust bearing collar and hence the whole
  helicopter
   is hanging on  eight 1/4 " steel studs threaded into the magnesium
   housing.

   Doug in Japan


   Yes you are right. I was thinking of the cast iron version.

   Paul Lamar

  Here is one for you.  What kind of Hp can the Bell 47 take?  Normal
  operating and max?
  Jeremy

  Bell engineers estimated 1000 HP at 6000 input RPM when
  Dave Garber checked with Bell back in 1973. Dave Garber was
  the original rotary powered airplane  builder using Bell 47 gear
  boxes.
  These are 12A engines.

  Paul Lamar

Paul,

So I have called around and I found quite a number of Bell 47 gear
boxes.  Now I have more questions!  :)  Ok, so which one do I use??
Any idea which one Dave used?  There are some for the Franklin 165
and then more for another engine....  ??  Then another guy said that
he didn't think the transmission would work horizontally.   I know we
can use an oil spray type unit for that.
Well, so far I have found a large number out there, just depends on
which one.  One guy in FL would sell me all the parts to rebuild one
(which is what we would have to do anyway) for $6500.  He has a bunch
and he is trying to get rid of them.  He also has a fresh rebuild
with the clutch and fan, which you don't need for $23,000.   :)
This same guy has a SeaWind kit for sale that is @ 50% done.
$65,000, or with the engine and prop $89,000.
Thanks for your help.
Jeremy

That is good news Jeremy. Good work. Several people on here
are interested in that gear box. I was under the impression
the cost was much higher than that. I suspect just about
any version would be OK because it is so over kill. So strong.
The box is very light weight for its size. About the same
weight as Tracy Crooks.

Doug might know the version Dave used as he knows Dave very well.

Paul Lamar

--

Careful guys,

What you need is the end gear set of the Bell 47 helicopter. i believe
Dave Garber bought three of them for about $500 each back in the early
seventies.
"G" model though newer ones might work.

Actually the Bell gear box 'as is' still needs a LOT of work. The best
part of it is the compact magnesium housing and very robust ring gear.
Total length is about 140mm.   From there after everything has to
modified, although Dave was running it as is.  He was told not to exceed
5,000 engine rpms which is too fast for the standard type of roller
bearings. Bearings in the unit I have are all flatspotted. Even Bell
Corp. issue AD to inspect after 200 hours in this helicopter model
version, and that was at design rpms around 300. Dave was lucky he could
actually fly his plane with those bearings IMHO  and not have the box
seize.

In the original form the gear box had TWO planetary gear sets back to
back for a total gear reduction was 9:1. Dave and I are using only the
final drive set.  There the similarity ends.

I have ordered new planetary gears cut to accept high speed needle
bearings.  I am tossing the splined output connection as it is of little
merit to make three inch long  splined shaft only to have to bolt a prop
on to the outside end of it. Why introducge more slop in the system was
one of my thoughts. I am ordering a prop shaft with flange that bolts to
the planetary set on the inside but has a taper and threaded shaft to
accept the prop plate on the outside. Dave used the spline plate on the
inside and a modified shorten, welded-up shaft from a old Bell 47 rotor
shaft.  To this he STILL had an outer spline (no taper) and bolt a prop
flange on.

The sun gear as Dave used is actually one half slice of the first
planetary gear retainer.  It can be attached directly to a modified
counter weight or in my case to the turbo compount intermediary shaft
which is in turn  is splined into a torque absorber/TC compound
pulley/counter weight.

The final radial/thrust bearing ( 3inches ID) has to be replaced with a
more appropriate design.  Dave used the Bell TGK bearing which I doubt
would last long at high revs. I could be wrong however on this point
because I am looking for alternatives.  Oiling is not a problem because
there are several locations that oil both the front bearing.

If any one is interested I could finally be modivated to bring the case
down to company I do business with and see it they could create a Solid
Works 3-D point cloud file from the housing.  If desired the housing and
hollow 3 inch final shaft could be modified to accept a hydraulic prop
thought personally I might just go with a MT electric prop.

Doug in Japan

Got any dwgs on these mods Doug?
Have you looked into silicon nitride rollers for the planet gears?
Widely used in machine tools running up to 20,000 RPM.
Also widely used in Formula 1 cars.

Paul Lamar