Fisher P-75 Eagle Brochure from May 1944

[PR19_Kit]

With FOUR guns and SIX prop blades, half of which are going the other way, the interruptor gear would be working overtime! I wonder if any shells would make it past the nose in fact!

[pyro-manic]

It does seem like the rate/weight of fire would be quite badly limited, doesn't it? Perhaps a better option would be to put the guns in the wing, and/or have a heavy-ish cannon firing through the spinner?

[icchan]

Are there any contra-rotators that have axial guns?  I've been wondering that myself.

[Jschmus]

Are there any contra-rotators that have axial guns?  I've been wondering that myself.

Seems like that would make things needlessly more complex.  I mean, you'd have an engine driving contra-rotating propellers, with a gun firing through the shaft.

[rickshaw]

Are there any contra-rotators that have axial guns?  I've been wondering that myself.

Seems like that would make things needlessly more complex.  I mean, you'd have an engine driving contra-rotating propellers, with a gun firing through the shaft.

Not that much more complex.  As you need a hollow shaft to allow the forward propeller to be driven, why not simply make the forward propeller's shaft hollow as well?   The real problem would be placement and type of powerplant.  The German/French aircraft with motor cannon were upright v's.  The P-39/P-63 were mid-engined.   So, you could make it work with either.  The mid-engined with two auxiliary drive shafts, one each side of the cannon to drive each prop?  The upright V's would have to put the cockpit a loooooong way back from the nose.  A gas turbine would be interesting - air intakes, auxiliary shafts - where does the cockpit go?   

[icchan]

Go Bell and cockpit-forward.  Never seemed to have a problem with the long shafts, though it might hurt overall torque just because of the higher shaft mass and therefore inertia.  That's a backhanded guess, though.

[jcf]

The Junkers Jumo and Daimler-Benz engines with motor-cannon were inverted-V.

[kitnut617]

With FOUR guns and SIX prop blades, half of which are going the other way, the interruptor gear would be working overtime! I wonder if any shells would make it past the nose in fact!

Hi Kit,

I've tried to explain before on another forum while discussing my Crecy Fighter concept (F-86D with contra-props), that firing synchronized guns through a contra-prop isn't as difficult as it seems.  It's not much different than just firing through a single prop, 3-blade or 4-blade.  The thing to remember is that the props do not free-wheel, they are geared together at the PSRU, which means that the front and rear blades will exactly cross over each other six times during a 360 degree rotation.

In this pic below I show that during just 60 degrees of rotation, there's at least two guns with a clear shot between the blades in all but one instance, that when the blades have move 30 degrees each way off the zero degree point.



The solid black blades are the front ones and where I show solid black and a shaded one together, that's where the two props are lined up exactly one behind the other.  I've added a small circle in one blade of each prop so you can see where it's position is when turning through the various degress I've set them at.

[IanH]

ARRRRRRRRGH my head hurts