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This page gives an insight of the methods used to analyse the main Tradewind aircraft structure. The sheet below is taken from a stress report into the fuselage structure and shows a typical hand calc. This particular investigation is to determine the strength of the aft fuselage longerons in both compression and tension due to flight loads and an inertia of 3.8g. A quick estimate of the loads expected in the structure for a given loading condition means that any finite element model used can be verified for realism. Exporting geometry from the 3D CAD model it was a straightforward task to model the framework and plywood skin using finite element software.

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model

A coarse finite element model was constructed using CBars to represent the timber framework and CShears for the plywood skins. It has been assumed that the timber frame will resist all the bending loads and the plywood skins will take the shear. Care has been taken with bar element axis systems and to ensure quads associated with 2D orthotropic materials are properly aligned.

barelems

The table below is taken from the output file and indicates the compression in the lower longerons. The maximum axial loads of 2154 lbs compares well with the 2285 lbs estimate in the hand calculation. The longerons are thus fit for purpose.

The contour plot below shows the shear stress in the fuselage side skins for the most severe asymmetrical vertical and horizontal tail load case. The skin in this region has been found to be plenty strong enough for instability (buckling) and rupture.

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NOTICE: The Tradewind design is protected under international copyright law. No part of the Tradewind plans may be reproduced or distributed in any form or process without written permission of the designer.

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