Airworthiness Requirements Research Articles

Experimental Study on Ice Shedding Behaviors for Aero-Engine Fan Blade Icing during Ground Idle

Fan blade icing can affect efficiency and aerodynamic stability, and the shed ice may be sucked into the core of the engine, causing adverse effects or even damage to the compressor components. Ice accretion and shedding are among the key issues in engine design and tests. But they have not been clearly understood. In this work, ice shedding from rotating aero-engine fan blades during continuous icing is experimentally investigated under the relevant airworthiness requirements. The phenomena of icing and ice shedding under different ambient temperatures and engine speeds are recorded to obtain the ice-shedding time and the characteristic length of the residual ice. Force analysis is used to understand the corresponding behavior. The degree of ice-shedding balance Db is defined to explore the symmetry of ice shedding. The results show that the shedding time is significantly affected by the rotational speed, and the characteristic length will first shorten and then grow as the ambient temperature decreases. When the ice shedding is completed instantaneously, Db will show a violent shock. There is a critical ambient temperature, below which the ice accretion will worsen significantly as temperature decreases. For aero-engine fan blade icing tests during ground idle, the critical ambient temperature ranges from −5 ∘C to −9 ∘C. In order for the ice to shed faster, the engine speed has to reach a threshold. This study can shed light on the preliminary characteristics of ice shedding from rotating components and provide guidance and a data basis for the numerical simulation of fan blade icing and the design of an aero-engine.

Study on bird strike analysis of a civil aircraft equipped with satcom antenna

Abstract Civil aircraft have specific requirements for the anti-bird strike performance of the structure, so the installation of various types of antennas must carry out bird strike assessment to avoid catastrophic consequences because of bird strikes. In this paper, the anti-bird strike performance of a civil aircraft equipped with an antenna is studied by numerical calculation. It shows that the antenna adapter may be plastically deformed after a bird strike, but it will not be damaged or fall off from the body structure as a whole. Therefore, the satcom antenna will not cause catastrophic consequences after a bird strike and meet the airworthiness requirements.

Transient voltage performance and protection design of variable frequency ac three-stage generator for more electric aircraft

Abstract Nowadays, variable frequency AC generation system is widely used on more electric aircraft because of their advantages of simple structure, high power density, and high reliability. However, a variable frequency system has a wide range of operating speeds and frequencies, and its exciter field is designed to be highly saturated at low speed. Under the condition of a saturated exciter field at high speed, the generator can produce a very high voltage, which will cause damage to aircraft utilization equipment, leading to catastrophic failures. Therefore, to protect the safety of the aircraft, transient voltage regulation performance and voltage protection design are critical in the system design of variable frequency AC generation. This paper focuses on the design of voltage regulation and protection of variable frequency electrical power systems that can meet airworthiness requirements.

Novel Aluminum Alloy Tailored for Additive Manufacturing: Structural Characterization and Qualification Perspectives

The recent advances achieved in additive manufacturing (AM) technology demonstrate the potential to realize customized metal components, ensuring weight reduction opportunities. These benefits make AM attractive for high-cost aerospace applications, especially where high geometric complexity is required. In the context of an EU research scenario, the H2020 MANUELA (Additive Manufacturing Using Metal Pilot Line) project promotes the development of new technologies for design optimization by enabling the application of novel materials in AM. This paper illustrates recent advances in a new aluminum alloy (Al-HS1) with high strength emphasizing all of the characterization steps at the coupon level. This material has been employed in the re-engineering of a conventional hydraulic manifold using a powder bed fusion-laser beam (PBF-LB) process. Both the simulations and structural tests allowed for proving its compliance and technological maturity with industrial standards and applicable airworthiness requirements.

Experimental Structural Validation of a Landing Gear System for High-Speed Helicopter Applications

The design and technological demonstration of a Landing Gear architecture were addressed for Airbus fast rotorcraft end application within the Clean Sky 2 Racer project. Numerical activities including advanced modelling approaches were carried out to substantiate the feasibility of structural concepts in compliance with industrial standards and CS-29 applicable airworthiness requirements. In order to demonstrate the goodness of design strategies, a true-scale prototype was manufactured and tested for demonstrating its capability to withstand static loads representative of the limit and ultimate cases expected in service. The paper will focus on the qualification of the Nose and Main Landing Gear systems. Sizing process was validated and verified by test whose results allowed for validating/calibrating the FE model. In such a way, the design database could count on a reliable tool available for analysing the effect of any further load condition change.

Liquid Hydrogen Storage Tank Virtual Crashworthiness Design Exploration for Civil Aircraft

Civil aviation industry is researching for alternative fuel energy sources to substitute current hydrocarbon-based aviation fuels. Carbon free emissions flights could be achieved with fuels like Hydrogen either through combustion or via electricity producing fuel cells. It is of great importance to explore the airframe designs to house Hydrogen in its cryogenic liquified state. The objective of the study herein was to provide a conceptual qualitative analysis related to the crashworthiness behaviour of civil aircraft carrying liquid Hydrogen fuel storage tanks. The design parameters of interest were the storage tank location in the airframe, the structural energy absorption following crash landing scenarios and the structural deformation of the structure surrounding the tanks, penetrating the survival space of the occupants. Several structural design arrangements were proposed and compared. Simulation results indicated that the optimal location for the fuel storage greatly depends on the actual aircraft layout as well as on the future civil aircraft airworthiness requirements that are still under development for that type of fuel energy source.

Multi-Phase Vertical Take-Off and Landing Trajectory Optimization with Feasible Initial Guesses

The advancement of electric vertical take-off and landing (eVTOL) aircraft has expanded the horizon of urban air mobility. However, the challenge of generating precise vertical take-off and landing (VTOL) trajectories that comply with airworthiness requirements remains. This paper presents an approach for optimizing VTOL trajectories considering six degrees of freedom (6DOF) dynamics and operational constraints. Multi-phase optimal control problems are formulated to address specific constraints in various flight stages. The incremental nonlinear dynamic inversion (INDI) controller is employed to execute the flight mission in each phase. Controlled flight simulations yield dynamically feasible trajectories that serve as initial guesses for generating sub-optimal trajectories within individual phases. A feasible and sub-optimal initial guess for the holistic multi-phase problem is established by concatenating these single-phase trajectories. Focusing on a tilt-wing eVTOL aircraft, this paper computes VTOL trajectories leveraging the proposed initial guess generation procedure. These trajectories account for complex flight dynamics, align with various operation constraints, and minimize electric energy consumption.

МЕТОД ПРОЕКТУВАЛЬНОГО РОЗРАХУНКУ НА МІЦНІСТЬ ПОПЕРЕЧНОГО СТИКУ ПАНЕЛЕЙ ВІД'ЄМНОЇ ЧАСТИНИ КРИЛА ТА ЦЕНТРОПЛАНА ТРАНСПОРТНОГО ЛІТАКА

Due to the limitation in the dimensions of the structural elements of the modeled wing contour and the possibility of increasing their cross-sections in the area of the transverse joint, only on the inside, there is a need to find an effective solution for the design, mass of the joint, as well as its statical strength at the modeling stage. The article presents the method and its application using the example of a preliminary analysis of the design calculation of the design of the flange connection of the center section with the outer wing section (OWS) of a transport aircraft. The method is based on the calculation of stresses caused by the discrete transmission of forces between elements. In the calculation method, a simplified statically indeterminate joint model is obtained according to the geometric characteristics and force transmission characteristics of each node section in the flange joint structure. During the calculations, the following are determined: diagrams of the bending moment and axial forces obtained using the force method, the distribution of force loads in each section of the model for subsequent analysis of the static safety factor. The resulting calculation results are compared with the airworthiness requirements to determine whether they meet the design requirements. For components with greater static strength, or those that do not meet the requirements, it is recommended to further modify the design parameters to ensure an effective design of the center section joint with the outer wing section and subsequent re-calculation. The calculation method used has practical value as a preliminary engineering analysis.The geometric characteristics of the junction of the center section with the negative part of the wing were modeled using the CAD/CAMCAE CATIA system.

The Modeling and Simulation of Turbulence for Civil Aircraft Compliance Verification Test

For the airworthiness compliance verification of civil aircraft, the response of the aircraft in turbulence is one of the most important tests. Turbulence is mentioned in many airworthiness regulations for civil aircraft, but there are no clear requirements. To study the compliance of civil aircraft response in an atmospheric turbulence environment, the airworthiness requirements of civil aircraft were analyzed. The turbulence model that can be used for airworthiness compliance of civil aircraft was determined for the first time. In this paper, the principle of the atmospheric turbulence model is studied. The evaluation process of the model is proposed, which indicates that the turbulence model meets the airworthiness requirements. At the same time, the model was integrated on a certain simulator, and the correctness of the integration was proved through integration testing. The modeling, evaluation, and integration process of the turbulence model proposed in this paper can be used for the airworthiness verification of civil aircraft.

Airworthiness Compliance Verification of Bird Strike on Civil Aircraft Windshield Frame

With the frequent occurrence of bird strikes, minimizing the impact damage effect of birdstrike on flight always is the goal of airworthiness certification. As a large windward component in front of the aircraft, the windshield, and frame have more probability to be suffered from birdstrike. This paper introduces the common connection forms of the windshield frame structure of civil aircraft, and through the interpretation of the airworthiness requirements related to windshield in CCAR-25, puts forward the process and method of compliance verification of windshield frame birdstrike. Based on the SPH method, the dynamic analysis of bird impact on windshield window frame is carried out, the test is carried out to verify that the analysis method is reasonable and conservative, and the results show that the bird impact performance of the windshield frame structure meets the airworthiness requirements.

Harmonising and standardising military airworthiness in Europe: a review of key aspects and achievements

AbstractThe distinct operational characteristics of military aircraft, relative to civil aircraft, have impeded the standardisation of airworthiness management practice across Europe. Standardisation has been further deterred by the intertwined certification and qualification activities specific to military aircraft. The management of airworthiness in European military aviation has undergone significant changes over the past 15 years, with the progress made attributed to the harmonisation efforts driven by the European Defence Agency (EDA). The creation of a Military Airworthiness Authorities Forum and the development of the European Military Airworthiness Requirements (EMAR) have been instrumental in creating a more homogenous regulatory landscape. The examples of five main players of the European aerospace sector, namely France, Italy, Germany, Spain and the United Kingdom, are examined from the point of view of adoption and implementation of an EMARs-based system. Their regulatory structures have revealed similarities and primary differences. The EMAR’s framework has enabled a gradual build-up of technical knowhow within the European countries who embraced this, civil-based, framework. All five countries have adopted EMARs, though through a variety of regulatory constructs. Their regulatory structures exhibit diverse practices, especially in how initial and continuing airworthiness is managed. Some countries have also elected to have more than one authority overseeing/been responsible for airworthiness. Closer collaboration between national Military Aviation Authorities (MAAs) can be achieved through standardisation at regulatory structure level. The establishment of a joint MAAs may be the next logical step in the harmonisation process, in line with EDA objective’ for a EU-wide authority with greater powers.

Airworthiness Requirements for Drainage Ground Test of Flammable Liquids from Transport Aircraft

The leakage and ignition of flammable liquids such as fuel and hydraulic liquid on transport aircraft are extremely harmful to aircraft and passengers. The drainage design is an effective means to reduce the probability of ignition and the resultant hazards if ignition does occur. The drainage test is required to show compliance with Article 25.863, and the drainage ground test must be performed before the flight test. This paper deeply studies Draft AC 25.863 and gives the airworthiness requirements for the drainage ground test of flammable liquids in combination with model practice. It provides a reference for the ground drainage compliance verification in the flammable liquid leakage area of transport aircraft.

Research on Monte Carlo simulation of CAT III auto-landing system

Approach/Landing is the phase of most accidents occur to endanger civil aircraft safety. CAT III autoland operation can improve the safety and reliability of aircraft when approach and landing in bad weather conditions, and reduce pilot’s working loads, so CAT III autoland control law design is an important task in advanced flight control system research. However, the most of the related researches are requirement based rather and scenario based. Firstly, the article analyzes the Monte Carlo simulation requirements based on airworthiness requirements of auto-landing system and proposes a Monte Carlo simulation model scheme considering the uncertainty of aircraft dynamic model and the actuator model, the error of sensors and the disturbance of wind, then implements the simulation based on a desktop simulation platform. The simulation result shows that the designed auto-landing system can assure the safe and stable landing of the aircraft on the condition of all kinds of uncertainty, the touchdown point, the vertical landing speed and the attitude are all compliance with the expectation criteria, satisfying the requirement of airworthiness items.

Technical analysis on airworthiness compliance of lighting components for civil aircraft emergency evacuation slides

The emergency landing safety of emergency evacuation slides can be improved greatly by using lighting components, especially in dark environments. To design a required lighting system, two problems need to be solved, which are also the focus of this paper. Firstly, what airworthiness compliance work should be planned and how to do it. Secondly, how to design to meet the airworthiness requirements should be considered. A complete and effective airworthiness compliance method was proposed by analyzing various performance characteristics such as self-opening function, lighting duration, illuminance, and installation environment. Airworthiness requirements are decomposed into design features, and the design requirements of lighting components are put forward. This study can provide verification methods and design ideas for the lighting components of civil aircraft emergency evacuation slides.

The influence of Work Health Safety on Australia’s military aviation regulatory framework

In 2016, the Australian Defence Force (ADF) Defence Aviation Safety Regulations (DASR) came into being, in part to harmonise with the Australian Work Health and Safety Act 2011 (WHSA). Defence aviation is too complex to be regulated completely by Work Health Safety (WHS) legislation; therefore, amplification is required to ensure safe and legal outcomes. The DASR provides the necessary amplification, managing aviation safety through technical and operational airworthiness. ADF technical airworthiness is based on the European Military Airworthiness Requirements (EMAR), with an overlaid Aviation Safety Management System (ASMS) modelled by the International Civil Aviation Organization. Australian WHS legislation directly influences Safety Risk Management (SRM), mandating how hazards and risks must be controlled by duty holders in all industries. For ADF aviation, this means a shift from a standards-based SRM to a legislative-based SRM, culminating in implementing a seven-step process integrated into all risk management activities. This paper examines how WHS legislation can directly influence the safety regulation of a high-risk industry such as military aviation. Further, safety management from a military perspective is a novel area of research, as military and civil safety management have historically been non-aligned and disparate. This research helps close the knowledge gap and offers an opportunity to disseminate and explore military safety management processes resulting from changes to the overarching WHS legislation. The authors believe such insights may prove useful to other states transitioning to an EMAR-based regulatory structure.

Damage sensitivity of a wing-type leading edge structure impacted by a bird

On the windward side of an aircraft, the components with higher probability of impact with birds are the wing-type leading edge structures, such as the wing and tail. A study on the damage sensitivity of a wing-type leading edge structure under bird strikes was presented in this paper. First, a bird strike test was carried out on a wing. The principles of the bird strike test equipment and method were introduced in detail, including the bird strike test system, bird projectile production process and data acquisition system. The dynamic strain measurement results, the high-speed camera videos, and the final deformation and damage morphology observations of the structure were obtained. Based on the coupled Smooth Particle Hydrodynamics (SPH) - Finite Element Method (FEM), the commercial software PAM-CRASH was used to simulate the process of a bird strike with the wing. The good agreement between the finite element simulation results and the experimental results shows that the calculation method and the numerical model presented in this paper were reasonable. On this basis, wing-type leading edge structures can be designed by adding triangular support. The bird strike resistances of an original structure and improved structure were studied by numerical simulation. The calculated results show that the improved wing-type leading edge structure is less damaged than the original structure under bird strike. The improved leading edge structure satisfied the anti-bird strike airworthiness requirements, as the thickness of the triangular support was 1.2 mm, and the weight of the structure was reduced by 0.87 kg compared with the original structure. This indicated that the bird strike resistance of the improved structure is better than that of the original structure, and the improved design of the wing-type leading edge structure presented in this paper is reasonable.

A Novel Framework for Qualification of a Composite-Based Main Landing Gear Strut of a Lightweight Aircraft

The determination of suitable testing and qualification procedures for fiber-reinforced polymer matrix composite structures is an active area of research due to the increased demand, especially in the field of aerospace. This research illustrates the development of a generic qualification framework for a composite-based main landing gear strut of a lightweight aircraft. For this purpose, a landing gear strut composed of T700 carbon fiber/epoxy material was designed and analyzed for a given lightweight aircraft having mass of 1600 kg. Computational analysis was performed on ABAQUS CAE® to evaluate the maximum stresses and critical failure modes encountered during one-point landing condition as defined in the UAV Systems Airworthiness Requirements (USAR) and Air Worthiness Standards FAA FAR Part 23. A three-step qualification framework including material, process and product-based qualification was then proposed against these maximum stresses and failure modes. The proposed framework revolves around the destructive testing of specimens initially as per ASTM standards D 7264 and D 2344, followed by defining the autoclave process parameters and customized testing of thick specimens to evaluate material strength against the maximum stresses in specific failure modes of the main landing gear strut. Once the desired strength of the specimens was achieved based on material and process qualifications, qualification criteria for the main landing gear strut were proposed which would not only serve as an alternative to drop test the landing gear struts as defined in air worthiness standards during mass production, but would also give confidence to manufacturers to undertake the manufacturing of main landing gear struts using qualified material and process parameters.

Study on the facility airworthiness requirements and conformity verification method of aircraft leveling meanings

The aircraft measurement is the inspection of the relative position of the various parts, the installation quality of the parts and their deformation in the process of use, and the airworthiness regulations have clear requirements for this. This paper carries out the research based on the requirements of the airworthiness regulations, clearly determines the facility airworthiness technical requirements of the aircraft level, gives the suggested design requirements, clarifies the practical and feasible compliance verification methods, and provides a reference for the airworthiness certification of the civil transport aircraft.

Considering Thermal Diffusivity as a Design Factor in Multilayer Hybrid Ice Protection Systems

Icing is a major problem that affects the aeronautical sector, which is forced to use anti- and de-icing systems to ensure flight safety. The currently used systems are effective but exhibit high energy consumption. Resistive heating is used to prevent ice accretion or to release it once it has formed. To satisfy all the imposed airworthiness requirements, such as low aerodynamic impact, resistance to lightning strikes, no overheating, etc., multilayer systems are commonly configured with different layers fulfilling specific functions. For example, the Boeing 787 Dreamliner uses dry woven glass fiber fabric on top of the heating element to provide galvanic insulation and dielectric resistance. It satisfies the above-mentioned requirements, but its thermal conductivity is very low, therefore reducing energy efficiency. The thermal distribution of two materials (AA6061 aluminum alloy and PTFE) with significantly different thermal and electrical properties in contact with a heating element was studied. Finite element calculations and experimental testing in an icing wind tunnel were carried out at −12 °C under different convection conditions: natural (0 m/s) and forced (35 and 70 m/s), using specimens of different sizes. Heating elements areas were also varied. AA6061 showed homogeneous heating, whereas differences of up to 80 °C were observed when using PTFE. In addition, the test results highlighted the effect of forced convection and the need to evaluate these systems “in close to operative” conditions. The calculation results proved to it be an interesting tool for studying the behavior of the systems avoiding extensive testing.

Avionics Architecture Design for Military Unmanned Aerial Vehicles

This paper describes the design of the avionics architecture for military unmanned aerial vehicles considering the airworthiness requirements for the first time. This design considers the redundancy in the system data bus and the power system and the data link system to meet the system safety requirements of the airworthiness requirements of military UAVs. This avionics architecture design has been verified through the system integration test and the flight test after manufacturing the UAV.