In-flight tailload measurements

Fatigue load spectra that are used for the design of aircraft tail structures are based on simplifying assumptions with respect to external disturbances, such as gusts, turbulence and control inputs, as well as aircraft response behaviour. Past service-load measurement programs have been restricted to measuring the vertical acceleration of aircraft at the centre of gravity, which gives ample information about main wing loads but lacks a proper correlation with tailloads. In general the relation between aircraft tailloads and aircraft motion parameters (lateral or vertical acceleration, pitch or yaw rate) is insufficient. Therefore the best way to obtain this information is by direct measurement of these tailloads by means of calibrated strain gauges. This paper describes tailload measurements carried out using a commercially operated civil aircraft that has been equipped with a compact micro-processor based data recorder. The measured tailload data is combined with flight parameters from the Aircraft Condition Monitoring System (ACMS), in order to create a database for further analysis. Some results are presented to illustrate that valuable information can be obtained with a relatively simple and straightforward procedure, which is easy to install in an aircraft and does not interfere with other aircraft systems.