Paul,

What is the ball park figure for radial and thrust dynamic load rating for 240 hp in a 3.17 box. Milo


I need the distance between the bearings.

In simple theory the radial load is zero in a planetary gear box but what happens
the load starts happening when you yaw the airplane. Worst case scenario
you spin. A stall is pretty bad too. Based on a 50 pound prop the bending
load is about 650 foot pounds. If the bearings are one foot apart one
bearing sees and up or side load of 325 pounds and the other sees
the same load in the opposite direction.


The thrust load is related to HP and is a max roughly when climbing out.

Lets say you are climbing out at a forward speed of 100 feet per second and you
are generating 250 net HP at the prop to make it simple.

HP is a thrust times a velocity. Velocity in this case 100 feet per second.
HP is 250 so thrust HP is 250 pounds times 200 FPS or 50,000 pound feet per second.

So the thrust is  simply found by dividing that by 100 feet per second or wonders
of wonders 250 pounds of thrust. In this one case only the same as the HP number.

I like to use 1000 pounds because in simple theory the thrust is infinte at
zero speed. The prop efficiency enters into the equation and props don't start to
bite until about 60 MPH or so which is 88 FPS.

So the thrust on the bearing is a max at lower speeds and tapers off as
you go faster and faster.  For a 2 inch ID needle thrust bearing this is a piece of cake.
Price about a dollar :)


Paul Lamar

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