I have been working on a new flywheel proposal, based loosely around what Aeromomentum uses on their Suzuki engines. They did not provide me with a print so I am just going with something that is not too complicated to make, while keeping as much mass as possible out at the rim for best angular inertia vs total weight. I started out looking at Honda racing flywheels, but they are more focused on reducing mass and reducing rotating inertia - so not the same goal. But I did gather that their flywheels got down to about 8lb with the mass centered on the clutch friction face.
So far the weight is about 9lb (I have not simulated the teeth on the ring gear so its slightly heavier). The crankshaft flange area is 8mm and then the web thins to 6mm with the rim being 18mm wide. The OD of the ring gear is 11.125" 282.56mm.
When looking at the stress from only the RPM (centrifugal load) the peak stress is right around 100MPa in some small areas near the smaller lightening holes. So far so good. I then did a calculation for the gyroscopic torque reaction with the flywheel rotating at 5800rpm and yawing at 1 turn per second. With a mass of 4.08kg, a radius of gyration of 0.12m, rotational speed of 607.45 radians per second around x and 2xpi around z the torsional reaction works out to 196Nm.
Since I have discovered that I cant use 2 centrifugal constraints in the FreeCAD FEA I had to come up with another method to simulate the gyroscopic torque reaction. So what I did was to apply 2 forces direct to the rim of the flywheel 180 degrees apart and in opposite directions to create the torque couple. The loads were 819N each at a radius of 0.12m.
This ran successfully in the solver and has the appropriate effect of wanting to deform the flywheel web around the hub (a rotating bending moment) which is exactly what led to the flex plates cracking in the way that they did.
I might be inclined to taper the 8mm web out at a shallow angle into the 6mm surrounding web to reduce any stress concentration. These calculations have no factor of safety applied. I dont know how often people exceed the redline in a dive, for instance. The engines are not aerobatic either so hopefully a turn at 1 revolution per second is fast enough... Peak stress shows as 158MPa which is a safe "forever load" for a good quality piece of steel with a suitable surface finish. More than likely that finish will be protected by some good quality paint.
So far the weight is about 9lb (I have not simulated the teeth on the ring gear so its slightly heavier). The crankshaft flange area is 8mm and then the web thins to 6mm with the rim being 18mm wide. The OD of the ring gear is 11.125" 282.56mm.
When looking at the stress from only the RPM (centrifugal load) the peak stress is right around 100MPa in some small areas near the smaller lightening holes. So far so good. I then did a calculation for the gyroscopic torque reaction with the flywheel rotating at 5800rpm and yawing at 1 turn per second. With a mass of 4.08kg, a radius of gyration of 0.12m, rotational speed of 607.45 radians per second around x and 2xpi around z the torsional reaction works out to 196Nm.
Since I have discovered that I cant use 2 centrifugal constraints in the FreeCAD FEA I had to come up with another method to simulate the gyroscopic torque reaction. So what I did was to apply 2 forces direct to the rim of the flywheel 180 degrees apart and in opposite directions to create the torque couple. The loads were 819N each at a radius of 0.12m.
This ran successfully in the solver and has the appropriate effect of wanting to deform the flywheel web around the hub (a rotating bending moment) which is exactly what led to the flex plates cracking in the way that they did.
I might be inclined to taper the 8mm web out at a shallow angle into the 6mm surrounding web to reduce any stress concentration. These calculations have no factor of safety applied. I dont know how often people exceed the redline in a dive, for instance. The engines are not aerobatic either so hopefully a turn at 1 revolution per second is fast enough... Peak stress shows as 158MPa which is a safe "forever load" for a good quality piece of steel with a suitable surface finish. More than likely that finish will be protected by some good quality paint.
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