Contra - Rotation Schematics

http://en.wikipedia.org/wiki/Contra-rotating_propellers

http://cr4.globalspec.com/thread/45769, plus it denies other readers the chance of learning from, or commenting on, what has been written.

Picture shows a possible transmission for 2 counter rotating propellers which get power from only one engine.

The principle is :

a- The number of external meshing has to be uneven and the number of internal meshing can be either even or uneven.

b- In the first stage rpm are increased and in the second reduced to initial value.

There are a couple of conditions to be respected:

- The gears have to be assembled and if parallel pairs Z2+Z3 are used which often the case for reduction of the transverse dimensions then for more than 2 also lateral conditions have to be considered.

If we assume that Z1/Z2= I and if the radial gap between Z3 and center line is Δ then we get a couple of equations leading to limitations in the choice of values.

The first limitation is that "I " MUST be >2.

The second coming from the assumption that The number of parallel paths is 3 leads to:

Δ/Z1 >0.5*(1-sin(60°))*(1+1/i).

Although according to Wikipedia there are 2 engines for 2 propellers I thought that for the student you are it will be interesting to know how such a transmission could be when only one engine (or motor) would be used. This can help you in other cases when you could be confronted with similar question.

thank you, i believe i understand your schematic. the last on the right, is it an inner cut gear? ( if thats what you call it).

YES

Is it the only question?

This idea is used also in marine high performance systems. I think Volvo Penta is doing something along those lines.