Abstract: An apparatus includes a transmission system for an aircraft structure, in which the aircraft structure includes a first propeller assembly and a second propeller assembly, and an engine assembly. The transmission system is configured to (A) be coupled to the engine assembly, (B) be coupled to the first propeller assembly and the second propeller assembly. The transmission system is also configured to urge, in use, the first propeller assembly and the second propeller assembly to (i) operatively rotate in opposite directions relative to each other, and (ii) operatively rotate at different rotational speeds relative to the rotational speed of the engine assembly. The different rotational speeds of the first propeller assembly and the second propeller assembly, in use, urge the aircraft structure to move along a desired flight path.