when you consider the enormous gyro forces placed on the crankshaft and its support brgs (mains), and the flywheels, it is fairly easy
to see that we don't want the crank to move at all if possible. (If i remember correctly this is the prime concern of GuyF, in that he has concern over movement of the crankshaft inducing stresses that might lead to failure). So if we want to stabilize the crankshaft we have to center the rocking component at the centerline of the crankshaft, then the rocking can rock and roll all it wants to without effect on the crankshaft, brgs or the flywheels.
This is the bit I've always had trouble with.
For reference, I'll define my axes. Looking at listeroid side on, directly facing the flywheels with a generator off to the right, x is left and right, y is up and down, z is in and out of the image. From there, you can define planes - the x-y plane is the one looking side on at the flywheels, the x-z plane is the view from the top, the y-z plane is the view from the side. All of those can be taken as 'slices' along the missing axis, eg the x-y plane is an infinite number of slices in the z-plane. If you want to sketch out a listeroid on a bit of paper and label the axes, it'd probably help with what's to come.
So, we're all looking at the same thing? Good.
If :
- The forces are generated from the crankshaft/reciprocating mass due to imbalance between reciprocating/rotating masses and power pulses.
- The bulk of these forces are in a plane at 90 degrees from the crankshaft, that is a plane defined by the x and y-axis.
- The forces that are parallel with the crankshaft that would cause the engine to rock outside of this plane (in the z-axis) are minimal. If your two flywheels are imbalanced with respect to each other, you'd get some. Of course, all listeroid manufacturers pride themselves on the extremely high quality and balance of their machines, so this is rarely an issue.
Then:
It doesn't matter how you mount/hang/swing that engine as it's still rotating and the forces are still present. Gyro forces only occur when when a flywheels axis is rotated. You can move a spinning flywheel without any gyro forces in all axes. It's only when you try and rotate the axis that gyro forces occur. As long as you don't get any rotation (turning) of the flywheel axis in the y/z planes (in our scenario, you can't rotate the axis in the x plane, it's just visible edge-on as a point in that plane).
This explains to me when I was watching that video of the loveson startup - it was very slowly creeping clockwise. One of his flywheels is slightly imbalanced compared to the other, causing a rocking moment in the y-z plane and rotating the flywheel axis, creating gyro forces which try and twist the machine around.
Following from that, it's very important to note that gyro forces all come from somewhere. Grossly simplifying gyro mechanics, one can say that a gyro is a thing that will convert forces 90 degrees. Twist a spinning flywheel about it's axis and it will want to lean. Lean a spinning wheel and it will want to twist. All the forces that make a gyro move are already applied somewhere - 90 degrees on another plane. If you take the loveson startup video, the forces are a rotation of the flywheel axis in the z-plane (front on to us in the video). These forces get translated to a clockwise movement of the base on the floor. So the forces are still there - instead of trying to rock the engine, they've been shifted to try and rotate the engine.
Finally (!) from all that, seeing as the crankshaft is already rotating, it doesn't really matter if the forces are applied in one plane or another - they're 90 degrees out, but the shaft rotates continuously past both planes anyway. So the gyro forces are just forces that would have been applied 90 degrees earlier/later anyway.
There. That's the problem I have with that bit. Can anyone sort it out for me?
(And a blackboard would be a really, really handy thing to have right now.)