The rudder is one of the few aircraft primary composite structures that experience relatively low external aerodynamic loading during regular flight conditions. This renders the rudder shell the perfect candidate to study the possibility of introducing sustainable materials with lower mechanical properties in primary structures. However, high internal loads are introduced in the shells during actuator jamming events, which occur with low frequency. Locally redesigning the rudder spar as a torsion box to take up the jamming loads and alleviate the shell loading could enable the safe usage of green materials in the rudder shells. The aim of this thesis is to study the design feasibility of three rudder torsion-box spar concepts to separate the aerodynamic and jamming loads in the rudder and provide a preliminary optimised structural design based on a parametric study of the torsion-box spar design variables and static FEM simulations.