Assessment of helicopter passengers' vibration discomfort: proposal for improvement of the ISO 2631-1 standard.

High levels of vibration exist in helicopters and manufacturers are seeking to quantify vibration discomfort. They use the ISO 2631-1 standard, proposed for all types of transport. This study aimed to verify the validity of this index in the specific case of helicopters. Perception tests were carried out in the laboratory. Volunteers assessed the discomfort of vibratory stimuli on test benches generating vertical and triaxial vibrations. Foot, seat, and backrest accelerations were measured for each participant according to each stimulus. The ISO 2631-1 comfort indices were then compared with the evaluations given by the participants. The results showed that the standard provided a good estimate of discomfort. However, it lacks precision in estimating the discomfort of stimuli which include amplitude modulations, as can happen in helicopters. A new discomfort index is proposed based on ISO 2631-1 and allows better prediction of subjective assessments. Practitioner Summary: An improved index based on ISO 2631-1 standard is proposed to estimate helicopter vibratory discomfort for seated passengers. It takes into account the amplitude modulations that can appear at low frequencies in helicopters. This modification allowed a significant improvement of the accuracy of ISO 2631-1 for such stimuli.