I went through the calculation for the front shaft using an online
java calculator here:
http://www.tech.plym.ac.uk/sme/desnotes/shaftMandT.htm
The attached screen shot shows the result of the calculator and would

indicate that the front shaft is indeed capable of taking the full
torque pulse of a 2 rotor, even if you add a significant fudge factor.
If you only ask it to take ½ the load?  Dual prop amphibian?
Decker, Michael

What stress level or material did you enter the program with?

Paul Lamar
UTS 800 Mpa
Decker, Michael


800 megapascal = 116 030.190 41 pounds per square inch Nobody designs
a crank shaft or e-shaft to run at 116,00 psi.

19 mm is a 3/4" diameter e-shaft. That is crazy :)

Yes it might not break if applied once but no engine designer would
use that number. 30,000 is more like it.

Paul Lamar

Even using 206.842(30000) it still works, and that is for the full max
torque
pulse, not half load max which would be 200ftlb.

Are you telling me that when they ask for UTS in these calculators
they don't really mean UTS?
Decker, Michael


Stop mixing and matching measuring systems. If you use foot pounds then
use psi instead of Kpa. I have to convert things and that takes time.
We got to the moon on inches... as my old friend Vance Jaqua RIP was fond
of saying :)

No but engineers don't always design things to ultimate tensile strength.
There are fatigue and deflection considerations.

If you want to try this be my guest. It is a free country. Just
please don't kill your self in a rotary powered air craft.

I don't want to waste any more time on this scheme. There are more
productive things for me to do.


Paul Lamar

If I may add a little here I would say this to Decker, Michael:

Industry practice is 8000 psi for line shafting that is ~ 58 MPa,
nowhere near 800 MPa.
For high strength steel you may go up a little, but not too much.
Even the 30,000 psi Paul was suggesting is too high in my opinion for a
propeller drive shaft.

UTS is one thing. That is when the shaft brakes. Endurance loads,
especially with load reversals is another, and is way lower, ~ 10 - 20 %
of UTS.

Although the polar moment of inertia of a shaft is D to the power of 4,
the polar section modulus, which determining the torque capacity, is a
cube function of the diameter D. So torque is proportional to D^3 (and
don't forget the pi/16 factor).

Secondly, what is the advantage of driving two propellers with one engine?
There is none, only more complications, as one propeller can easily
absorb the power the engine puts out.
The other way around, using two engines driving on large propeller would
make more sense. But then, we just make the one engine bigger and save a
lot of trouble.

Two engines and two propellers provide added safety that is all. Two
propellers and one engine does nothing but complicate things.

Rolf