A SMA based Landing Gear conceived for Unmanned Aerial Vehicles

Different aspects make SMA materials good candidate for aerospace applications: ability in transmitting large forces and displacements, compactness, capability of the material in absorbing loads (this way cooperating with the surrounding hosting structure), potential simplification of the system (reduction of the global system complexity and of the failure events). Among the different typologies of applications, one recalls the morphing actuation of aerodynamic surfaces like leading and trailing edges [1-3], the adaptive deformation of chevrons, the reconfiguration of rotor blades, the deployment systems of rotor tabs, the adaptive variation of engine inlet [4]. In the paper at hand, moving from other applications present in literature [5-6], the design of a SMA based landing gear, oriented to unmanned aerial vehicles, is described. The landing gear is constituted by four legs, supposed to be completely included within the fuselage during the cruise regime and to deploy during the take-off and landing phases. Each leg is constituted by a rod element rotating around a pivot, included in the fuselage domain; one edge of the rod (the internal one) is connected to a SMA spring integrated in the fuselage chassis, while the other edge is linked to the heel through an hub. The activation (heating) of the spring elements and the consequent contraction, transmitted as rotation around the pivots, causes the deployment of the legs. A dedicated scheme was defined to describe the two fundamental working configurations of the legs: the retracted (horizontal) and the deployed (vertical) attitude. After setting the equilibrium equations around the leg pivot, the definition of the main design parameters was dealt with: SMA spring features (external diameter, wire diameter, number of coils) the location of the pivot along the leg and the dimensions of the angular spring demanded for hindering SMA action and to assure the gear retraction when the SMA is not activated.