Why does every pro flail mower person automatically site the reason to get a flail over a rotary is because a rotary can "sling objects from underneath the mower." If you don't think a flail can throw things your kidding yourself. Most flails have a roller on the back that does a good job at stopping things but they also have about an 8" gap above that to shed clippings that lots of hard objects can come flying out at very high rates of speed. Plus if you think about it, with a flail you've got all those knives spinning vertically in line with tractor operator, if one of them breaks free it has to go somewhere. I've seen used high end Alamo flails beat to he!! just like a well abused rotary. I'm not bashing flails, I simply think they can be just as dangerous as other mowers.
For what it is worth I know you are not bashing
flailmowers.
The properly designed geometry of a flail mowers
hood AND ITS THICKNESS in construction where
the steel is rolled into the desired shape and length
of the formed piece prior to welding the end weldments
and structural tubing to the mowers hood weldment.
This in turn creates the air flow and induces the
aerodynamic forces which create the pressure
gradient that increase the ability of the rotor
and knives to lift and suction the clippings up
and over the rotor back to the ground.
It taks a lot to break a stamped and or a heat
treated grass slicer, and the mowers hood covers
an area greater than 180 degrees in the total
circumference reducing the chance of
an ejected grass slicer or hammer knive.
The other item is the potential trajectory of
a grass slicer knive after it breaks (if it breaks),
as the knive will hit the interior of the hood then
the ground and stick there before it can be
bounced out from under the mower hood.
Most of the time the shackle will break-which it is
designed to do as it wears at greater rate than
the knives stamped mounting hole.
The thirty year old grass slicers I have have very
little if any wear in the mounting slots and we have
never had a knive failure from a stamped mounting hole.
The only time a grass knive or hammer knive moves to
some degree is when either of two things happens,
when the flailmowers rotor is spun up to operating speed
and then back down to a stop or being when the grass or
hammer knive and knive hanger impacts and object and
folds back as it passes over the object and it may contact
an adjacent knive or the knive behind it.
Iif the grass slicers are long in size or a finish mower flail rotor
has a high knive count and or a large diameter rotor like my flaimower
where the knives may bump into each other when the centrifugal forces become less and less with relation to the slowing speed of the flail mowers rotor from the destruction of the drive belts or the disengaging of of the Power Take Off at the end of a mowing session.
The disdvantage of a smaller flail mower rotor is that is has to spin faster have longer knives typically than a flail mower with a larger diameter rotor
which does not have to spin as fast as it takes less centrifugal force to move a knive that is smaller in total length as the mass of the rotor itself is greater and the diameter of the flail mowers rotor is larger.