Use of Euler parameters for the evaluation of ATD head trajectory from angular rate sensor and accelerometer data in aircraft seat certification testing

As part of the requirements of the US Federal regulations and the Society of Automotive Engineers (SAE) Aerospace Standard 8049B, when testing of the seat and adjacent parts of the aircraft may be impractical or unknown to the seat designer and cannot be determined if head contact is made, the head strike path and head velocity shall be documented. The head strike path, also known as head trajectory, is normally measured using software specifically designed to complete a photometric analysis from the high-speed video of the dynamic impact event. A procedure is presented in this paper to use accelerometers and angular rate sensors in the head centre of gravity (CG) location of the anthropomorphic test device (ATD); the head trajectory can be evaluated by using an algorithm utilising Euler parameters to transform the local accelerations into global accelerations. This can then be integrated to achieve global velocity and global displacement. The algorithm utilised to calculate the head trajectory provides results similar to a head trajectory by photometric analysis and can provide those results much quicker and independently of operator influence. It can also provide results without the need for interpolation due to the visual loss of a tracking target.