A simple way to make a group of objects a single animated unit is to use groups. As an example have made a simple helicopter, made of three objects, the body and two rotors. The rotors are animated to spin using a simple
rotation_euler[axis] = frame driver on their rotation axis. (Could be keyframed instead). There is no parenting or armature involved.
Select All the objects that make up the helicopter and press CtrlG This will make each member have a green outline indicating it's in a group. Default group name is "Group".
Move the objects to an unused layer.M select a layer.
Image shows 3 objects that make up heli, added to group "Group" and moved to layer 20
In object mode, adding a group instance to your scene will add a helicopter keeping all the animations of the original. The instances can be translated, rotated, scaled.
adding group instance "Group" into layer 1. The original objects are on layer 20.
Sample file, with simple driver based rotation on rotors.