Fatigue life estimation of an aircraft used in airborne geophysical surveying

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Helsinki University of Technology | Diplomityö
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Date

2008

Department

Sovelletun mekaniikan laitos

Major/Subject

Lentotekniikka

Mcode

Kul-34

Degree programme

Language

en

Pages

ix + 125 s. + liitt. 38

Series

Abstract

In this thesis, the fatigue life of a DHC-6 aircraft used for airborne geophysical surveying is estimated with a tailored analytical approach. The approach is conservative since no detailed data of the aircraft structure or the original fatigue analysis was available. The study is focused on the wing which is the most fatigue critical structure of the aircraft. The loads induced to the wing in the low level survey flying differ from the loads of the normal use. In addition, the aircraft has had measuring equipment mounted to the wing tips which changes the static and dynamic characteristics of the wing. The wing load responses are studied with the finite element method. The static load responses are evaluated in the ground and airborne. A conservative method is created for evaluating the dynamic turbulence loads. Both classical turbulence representations, i.e. the discrete and continuous turbulence models, are applied. The differences between the dynamic responses of the original and modified wings are presented with dynamic load ratios. The landing impact loads are analyzed to some detail. In the fatigue analysis, normal commuter and air taxi operations are studied to approximate the loads used in the original fatigue analysis. The loads encountered in the survey use are created from the center of gravity accelerations recorded in actual survey operations. Results of the analysis reveal that the survey operations have decreased the remaining fatigue life of the aircraft. Some operations have consumed the fatigue life at an extremely high rate. However, the study verifies that the fatigue critical locations of the wing still have fatigue life left. All fatigue sensitive locations could not be verified since the developed method becomes unreliable when moving towards the tip of the wing. To decrease conservatism and to be able to analyze all fatigue sensitive areas, it is suggested that the dynamic analysis of the wing is renewed.

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Supervisor

Saarela, Olli

Thesis advisor

Ojala, Juha

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Citation

Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-2020120554173

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[dipl] Teknillinen korkeakoulu / TKK