The present work explores some critical aspects of the numerical modeling of a rotorcraft seat and subfloor equipped with energy-absorbing stages, which are paramount in crash landing conditions. To limit the vast complexity of the problem, a purely vertical impact is considered as a reference scenario for an assembly made of a crashworthy helicopter seat and a subfloor section, including an anthropomorphic dummy. A preliminary lumped mass model is used to drive the design of the experimental drop test. Some additional static and dynamic tests are carried out at the coupon and sub-component levels to characterize the seat cushion, the seat pan and the honeycomb elements that were introduced in the structure as energy absorbers. The subfloor section is designed and manufactured with a simplified technique, yet representative of this structural component. Eventually, a finite element model representing the full drop test was created and, together with the original lumped mass model, finally validated against the experimental test, outlining the advantage of using both the numerical techniques for design assistance.

This paper describes the integrated analysis of energy absorbing stages of seat and subfloor in helicopters during a crash landing, and their influence on the occupant's response. Their optimisation, when performed considering both the stages and their mutual interaction, leads to significant reductions of the occupant's injury levels. The study is based on validated numerical models of an anthropomorphic test device, seat and subfloor developed in a multi-body technique. Beyond the optimisations, a series of response surfaces were generated that show the max lumbar spine load, seat stroke and subfloor deflection as functions of mechanical parameters of the seat and subfloor, pointing out the design regions. Different impact speeds were considered. The results suggest that the mechanical properties of the solutions currently adopted for helicopter energy absorption could be easily re-tuned to further improve occupant's protection during a crash landing.

A multiphase approach is considered for the design of an aircraft anti-skid braking control system. A four-phase scheme, based on angular acceleration thresholds and estimated slip rate values, is used to stabilize the aircraft system around an optimal braking condition. The change in vertical load due to variable lift force and the ensuing variable tire deflection are considered in the verification models. A hybrid controller is proposed, designed to achieve a stable wheel slip limit cycle. The simulations confirm that the proposed control scheme is a valid solution for the anti-skid of an aircraft main Landing Gear (LG). The actuator time delay and dynamic bandwidth influence on the aircraft stop distance has been studied.

This study aimed to investigate the impact resistance of monolithic and laminated polycarbonate plates for windshields in motorsport applications through a coupled experimental–numerical study. Both low- and high-velocity impact tests were performed by using a drop tower and a gas gun, respectively, considering a sharp-edged projectile impacting on flat panels. The response of the polycarbonate plates was evaluated in terms of the failure mode, perforation velocity threshold, and energy absorption mechanism. The experiments allowed for the assessment and the generalization of a 3D finite element modeling approach originally developed for supersonic application based on different state-of-the-art constitutive theories, including temperature-dependent and rate-dependent von Mises plasticity coupled with ductile damage, Mie–Grüneisen equation of state, and temperature variation due to energy dissipation under adiabatic assumptions. The approach was completed with a cohesive zone model for a laminate plate and studies were performed to highlight the relevancy of different aspects of material characterization. The tests and numerical analyses performed at different velocity ranges highlight the importance of viscoplastic behavior in a polycarbonate windshield. The numerical approach showed its capability to model the different failure modes for monolithic and laminated panels and capture the perforation velocity thresholds with appreciable accuracy, which were actually found to be quite similar for the two types of panels in the test conditions considered. A numerical investigation suggests that the development of delaminations could lead to the improved energy absorption of laminated polycarbonate. To further assess the numerical model, it was used to successfully predict the penetration threshold velocity of a polycarbonate windshield subjected to a gas gun impact test.