| dc.description.abstract | Small (< 25 kg) fixed-wing unmanned aerial systems (UASs) impacts can cause severe damage to manned aircraft. At impact velocities of ∼128.6 m/s, small UASs can perforate aircraft skins and damage underlying load carrying structures (ribs, spars, etc.) which can hinder flight safety. Severe impact damage is primarily due to an in-line arrangement of relatively heavy and stiff UAS components, i.e., motor, battery, and payload. In this work, a frangible design for a nominal 1.8 kg (4 lb) fixed-wing UAS was developed using finite element analysis to reduce the impact severity of airborne collisions to manned aircraft. The baseline UAS with a ‘tractor’ engine configuration (motor as the foremost part of the UAS) was modified to a ‘pusher’ engine configuration (motor in the aft of the fuselage) in developing the frangible design. A series of impacts were simulated in LS-DYNA with the pusher fixed-wing UAS configuration impacting a 1.59 mm thick aluminum 2024-T3 flat-plate target at 128.6 m/s to evaluate different frangible design concepts. A polymeric foam nosecone was introduced at the front of the UAS to absorb impact energy. Expanded polypropylene (EPP), polyurethane (PUR), and polystyrene based IMPAXX700 foams were assessed for the nosecone materials. Conical and semispherical nosecone geometries were considered for the preliminary analysis and subsequently, a topologically optimized nosecone geometry was designed for improved energy absorption. In addition, a payload drop mechanism was designed to initiate payload redirection from the in-line collision trajectory of the battery and motor. This minimized direct multi-component single-axis impacts on the target. These mechanisms reduced the target impact damage compared to the tractor configuration but were unsuccessful in avoiding the target plate tearing. Ultimately, crushable corrugated aluminum tubes positioned ahead of the payload within the fuselage and a crushable corrugated Al nosecone were designed to enhance impact energy absorption for the UAS which successfully avoided the target plate penetration and had a 39% safety margin based on the target plate strain-to-failure. This frangible UAS design will significantly reduce the impact damage to manned aircraft in airborne collision scenarios. | |
