SATCAS

SIMULATION OF THE ASSEMBLY TOLERANCES FOR COMPOSITE AIRCRAFT STRUCTURES

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 Obiettivo del progetto (Objective)

'One of the challenges that currently exists for the design of large aircraft structures under natural-laminar-flow (NLF) regime is the extremely high requirements that must be achieved in terms of tolerances with the aim of ensuring that the flow will be sufficiently stable. In systems composed of many parts (such as the Smart Fixed Wing Aircraft torsion box object of study), the assembly processes acquire a special relevance, taking into account that, depending on how they are executed, the tolerances of each part might accumulate and generate deviations much larger than those of the parts taken individually. The objective of the present project is the development of a numerical methodology for the analysis of the assembly tolerances of aircraft components designed to operate under natural laminar flow (NLF). The methodology should allow determining the maximum acceptable components deviations to obtain assemblies within the specified tolerances, evaluating the influence of the joining techniques and the jigs, and determining the best assembly strategy or bolting sequence. For that, the proposed approach integrates tolerance accumulation techniques and mechanical/structural tools in order to consider in the analysis the parts compliance and other possible relevant effects associated with the joints.'

Introduzione (Teaser)

Natural laminar flow (NLF) technologies for reduced drag on aircraft require very smooth surfaces. Methods for simulating the entire assembly process will ensure that cumulative deviations in individually acceptable tolerances do not lead to rejection of the assembled configuration.

Descrizione progetto (Article)

Modern and advanced NLF aircraft technologies such as those under development within the European Commission's joint public-private partnership Clean Sky will significantly decrease drag, fuel consumption and emissions. When multiple parts or components are joined together in complex configurations, meeting individual tolerances may not be enough to meet the overall tolerance as deviations from design can accumulate.

EU-funded scientists working on the project SATCAS (Simulation of the assembly tolerances for composite aircraft structures) developed analysis tools based on finite element (FE) calculations to predict overall deviations in complex assemblies which can be produced by the accumulation of the deviations of the constituent parts and/or by the assembly operations itself. The team developed simulations of the whole assembly process in which individual parts are considered as flexible bodies, to take into account that during such processes they can deform. The focus was on the wings of the Low Drag Demonstrator of the Smart Fixed Wing Aircraft Integrated Technology Demonstrator.

It required consideration of detailed assembly processes and fixtures, from the local analysis of the fastening techniques to the simulation of each of the main assembly operations expected to be used for the Low Drag Demonstrator. The output is the cumulative tolerances analysis.

Following validation on small lab-scale assemblies enabling comparison of experimental and theoretical results, the numerical methodology was applied to two large aircraft wing torsion box concepts. The tests not only confirmed the ability of the FE numerical strategy to simulate assembly processes accurately, they also showed its potential to highlight improvements in processes or even in design of assembly hardware. Further optimisation will focus on reduction of computation time.

The SATCAS simulation platform will be an important tool in design of new NLF concepts for the EU aerospace sector, ensuring that finished assemblies meet overall tolerances to achieve required drag reduction. As a cumulative tolerance evaluator, it will no doubt find applications in numerous other manufacturing environments as well.