DEVELOPMENT OF A FRANGIBLE DESIGN OF SMALL FIXED-WING UNMANNED AERIAL SYSTEM
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Existing studies show that small fixed-wing unmanned aircraft systems (FWUASs) mid-air collisions with aircraft can cause substantial damage. Upon a 250 knots impact, a ~1.8 kg tractor configuration of FW-UAS can perforate aircraft skin, thereby damaging the internal structures such as ribs, frames, etc., posing severe threat to manned air fleet. Significant damage is primarily caused by FW-UASs heavy and rigid components such as motor, battery, and payload especially due to their roughly in-line arrangement and proximity with one another. In this work, a modified FW-UAS finite element (FE) model was developed that included a pusher engine (i.e., motor in the aft of the forward fuselage) configuration to reduce the impact severity during airborne collisions. A polymeric foam nosecone was attached to the front of the FW-UAS FE model to dissipate impact energy. To assess its energy absorbing capacity, a comparative study with expanded polypropylene (EPP), polyurethane (PUR), and polystyrene (IMPAXX700) foams was performed. Conical and semi-spherical nosecone configurations were studied as part of this research. A series of LS-Dyna impact simulations were performed with the pusher configuration of FW-UAS impacting a 1.59 mm thick aluminum 2024-T3 flat plate sandwiched between a rigid target frame. In addition, a frangible design of the FW-UAS, in which the payload is diverged from the in-line collision trajectory of battery and motor upon impact, was implemented and assessed. Force generated during the initial stage of impact is leveraged through lightweight and friable structural links to diverge the payload to avoid impact along the single axis as of the battery and motor. Damage severity is evaluated through target plate tear, and velocity of payload during impact, it being the major damage causing component.
