The heliomatc works thus
The hub body is a fore runner of the cassette system we now know and love/hate(delete acordingly)
Its like an ordinary screw on hub with bearings in the same place, onto that is fixed a splined body that the freewheel goes on, the difference being from a cassette is that the splines are very fine and run in a helical pattern like the rifling of a gun barrel
You slide the freewheel over the splines and then use the knurled lockring to lock it in place, forward pressure on the drive train pushes the freewheel down against hub body ensuring a that the freewhhel stays put and doesnt attempt to come off on its own
The upside of this design is that the freewheel locking its self into the hub body under drive means that the lock ring will hold the freewheel in place safely with little more than finger tightening of the lock ring, this makes them very easy to change in the field with out any major tools
Sadly the whole system is a bit fragile as all the splines are too fine and the moving parts on too small a scale for them to be robust and reliable
If you upscaled it it would work very well indeed
Edit - They are a doddle to remove, just use a mole grip on the lock ring, you dont need a lot of pressure, its easy to see how it works once you take it to bits
