On the choice of axes systems for aircraft dynamic calculations

Extract

In the places in the UK where these things are discussed, there is a reconsideration of the pros and cons of the two axes systems commonly used for aircraft dynamic calculations.

The first of these is a system fixed in the body and moving therefore with it: this system is referred to as ‘body axes’ and is used by the ‘stability and control’ specialists for assessing rigid aircraft behaviour.

The second is a fixed inertial frame fixed in the earth and is used by the flutter specialists for assessing a variety of behaviours of the flexible aircraft. It is the purpose of this paper to point out the very simple correspondence between these two systems in the case of small perturbations from an equilibrium position of the rigid aircraft flying straight and level. The first section presents unpublished work from the Vickers Aircraft Company’s files done in 1952 which is confined to the symmetric motion at constant speed (i.e. with the phugoid suppressed).