RC, you do not have to combine and connect these objects if you do not wish too, the thing to do with them is group them and name the group as one object.
It is normal practice to combine and join geometry that is part of a single whole but if you have an object made of different parts i.e your propeller with it's blades and shaft then grouping is fine and you can simply locate the group pivot to allow the whole thing to rotate as it should if it needs to be animated.