Purpose The purpose of this paper is to describe the approach for the design of a jet engine composite air inlet for a new generation of jet trainer aircraft from the perspective of airworthiness requirements regarding high-speed impact resistance. Design/methodology/approach Validated numerical simulation was applied to flat test panels. The final design was optimised and verified by validated numerical simulation and verified by testing on a full-scale demonstrator. High-speed camera measurement and non-destructive testing (NDT) results were used for the verification of the numerical models. Findings The test results of flat test panels confirmed the high durability of the composite structure during inclined high-speed impact with a near-real jet inlet load boundary condition. Research limitations/implications Owing to the sensitivity of the composite material on technology production, the results are limited by the material used and the production technology. Practical implications The application of flat test panels for the verification and tuning of numerical models allows optimised final design of the air inlet and reduces the risk of structural non-compliance during verification tests. Originality/value Numerical models were verified for simulation of the real composite structure based on high-speed camera results and NDT inspection after impact. The proposed numerical model was simplified for application in a real complex design and reduced calculation time.

Abstract. Bird or hail stone impacts are an important phenomenon that must be taken into consideration when designing aircraft. As engines are the sole thrust-providing mechanisms of an aircraft, it is critical that the effects of bird or hail stone strikes on engine inlets and systems be investigated and mitigated to the greatest extent possible. A combination of experiments and numerical simulations is necessary to properly understand the behaviour of a bird or hail stone during impact and the reaction of the impacted material with the structure. A simulation methodology is developed and validated to certify the bird or hail stone strike resistance of composite air ducts designed for a new generation of jet training aircraft. Physical impact tests were performed on real composite parts. Numerical simulation results were compared with test results. Numerical simulation was also used for test preparation and optimization of the test rig design from the point of view of the influence of the stiffness of the surrounding aircraft structure. The validated modelling procedure allows the analysis of numerous impact scenarios, improving the optimization procedures for aircraft component design and reducing the cost of development by reducing the need to manufacture test prototypes.

The material of an aircraft structure must resist a high-speed impact-an impact of a bird or hail at the flight speed (a bird strike or hail strike). The proof of this resistance can be provided in the experimental or numerical way. The recent development of numerical methods takes advantage of the numerical way. However, the necessity to verify the used numerical models creates new challenges for the experiments. The goal is to measure and record a great deal of data during the very short time of a high-speed impact. The use of high-speed load cells makes it possible to record the time-dependent force response of an impact event. However, the major difficulty of this approach is the existence of parasitic resonances. The experimental stand, the support of the studied specimen, exhibits an eigen dynamic response and in consequence, the final measured dynamic response is coupled with the stand-structure one. The objective of a stand design is therefore to minimize these parasitic resonances, occurring due to the stand-structure dynamics. In this way, special equipment for the experimental research of the dynamic response during a high-speed impact is designed and realized. The stand is to support the specimen during the impact of a projectile (a bird or hail) ejected from a pneumatic gun. The stand design enables an impact at any angle (from 0°to 90°), without changing the contact point. The dynamic-response measurement is realized by means of load cells. The equipment is designed and optimized by means of FEM numerical simulations with the aim to minimize the parasitic resonances of the stand structure. Keywords: high-speed impact, bird strike, hail strike, impact projectile, parasitic resonances, virtual-load-cell record Strukture iz materialov za letala morajo prenesti trke razli~nih predmetov, ki z veliko hitrostjo udarjajo vanje. To so lahko udarci ptic, to~e ali drugih delcev med potovanjem letala z veliko hitrostjo. Odpornost proti tak{nim udarcem lahko dolo~imo eksperimentalno ali numeri~no oz. z ra~unalni{kimi simulacijami, ki imajo z razvojem novih metod mnoge prednosti. Vendar pa je numeri~ne metode oz. modele potrebno eksperimentalno verificirati, kar predstavlja dolo~en izziv. Cilj je merjenje in zapisovanje velikega {tevila podatkov v zelo kratkem~asu, zelo hitrega udarca. Uporaba celic za merjenje hitrih obremenitev omogo~a zapisovanje odgovora~asovno odvisnih sil med trki. Vendar je pri tem glavna te`ava tega pristopa nastanek {kodljivih (parazitnih) resonanc. Izdelano eksperimentalno stojalo je bilo podpora za {tudiranje primerov z lastnimi vrednostmi dinami~nega odgovora in posledi~no kon~nimi izmerjenimi dinami~nimi odgovori v povezavi s strukturo stojala. Cilj oblikovanja stojala je zato zmanj{anje tak{nih {kodljivih resonanc zaradi dinamike strukture stojala. Na ta na~in so avtorji oblikovali in izdelali posebno opremo za eksperimentalne raziskave dinami~nega odgovora med udarjanjem zelo hitrih projektilov. Stojalo je prena{alo udarce razli~nih projektilov, ptic ali to~e, izstreljenih s pnevma...

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Bird strikes are an important phenomenon that must be taken into consideration when designing aircraft. A bird impact experiment provides a direct method to examine the bird strike resistance. However, the design of the aircraft structures usually involves many iterations of design-manufacturing-test and conducting bird impact experiments is not only time consuming but also costly. The aim of this work is to show the application of test verified numerical simulation for the design of composite cowlings of the high-speed helicopter.