> > Ken Welter wrote:

 > >
 > >    The Ross gearbox that I had was a 3.17 to 1 and I don't think they
 > > were the same gear set as the 2.17 to 1 but cant be for sure.
 > >   That was the best ratio that I have run, much better than the 2.95
 > > that I am currently running but its not practical get any lower with
 > > the cog belts I am running.
 > >
 > >   Ken Welter

 > The 2.17 takes the power from the ring gear. I think if you take the
 > power from the planet carries and hold the ring gear fixed you
 > will get 3.17 out of the same planet set. This is also how the
 > 2.85:1 works but that is an entirely different planet set.
 >
 > The one on the left is the 2.17 planet carrier and the one on the
 > right is the 2.85 planet carrier. The sun gear shown fits both.
 > So the sun gear diameter is smaller for the 2.17 giving a greater
 > reduction when power is removed from the planet carrier.
 >
 > Paul Lamar

 Ken could you give us a brief description of your setup and results. What is
 your cruise, climb and max rpm? What engine mods from stock have you done
 (i.e. oil pressure, rotor weight/balance, etc). I gather from other posts
 you use NOX. How long is the NOX on and at what rpm. How many hours on
 engine and any other comments on rpm? Also why did you prefer the 3.17 to
 the 2.95?

 Thanks
 Graydon Woods

Ken Welter wrote:

   My plane is a slow boat compared to most of you, it only cruises at
about 110 mph but I takeoff at a gross weight up to 3100 lbs.
  The engine that I am running 86 13b e-shaft and rotors with the
rotors cut for 3mm seals, 85 GSELE rotor housings and 12a side
housings and uses a Weber carb.
  The nitrous is only used for about 5 to 10 seconds to lift it on the
step and get it out of the water.
  I run the engine up to 7000 to 7500 rpm on takeoff, climb out at
6500 to 6800 and cruise at 6000 to 6500 rpm.
   The most I have put on one engine in the 1000 hrs on the old coot
is about 400 hrs, had lots of engine failures with that ross gearbox
but doing good now.
  The reason I like the low ratio is if you run a 2 to 1 ratio you
double the torque to the prop and a 3 to 1 you triple the torque and
it takes torque to get static thrust and the more torque the bigger
the prop you can swing to develop the thrust.
  Now I admit that torque and thrust are not everything if you want to
go fast but to lift gross weight especially out of the water its
everything.
  Check out my web site and there are some photos of my old coot that
burned up a year ago, the new four place one is do to fly any day now.

I looked at some old photos of my 3.17 ross and it does look like the
2.17 is the same gear set.

  Ken welter
  http://homepage.mac.com/rotarycoot/

 
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