The Use of the Open-Loop Onset Point (OLOP) to Predict Rotorcraft Pilot-Induced Oscillations

The Open-Loop Onset Point (OLOP) criterion has, for many years, been successfully used as a method to predict quasi- non-linear pilot-induced oscillations (PIOs) for fixed-wing aircraft. Only limited research has been conducted using the criterion for prediction of PIOs occurring in rotorcraft. These efforts have shown OLOP to be too conservative for this application. This paper details a study to extend the application of OLOP to rotorcraft, using the combination of control inputs appropriate for the task and a suitable pilot model. Results are compared between pilot subjective opinion and OLOP predictions, from tests performed in a ground-based simulation facility. Using 'task specific' application of OLOP, results obtained in the investigation are encouraging. From results obtained, a modified boundary is presented.