Evaluation Of The Representativeness Of Flight Mechanics Models During Vortex-Ring-State Entries And Recovery Manoeuvres

Abstract

Vortex-Ring-State (VRS) remains a dangerous regime leading to several accidents every year. Many studies have been conducted on the phenomenon, but the representativeness of flight mechanics models for prediction of the vortex ring boundaries, and their capability to reproduce the helicopter behaviour during VRS and recovery manoeuvres is still questionable. Therefore, developing fast numerical models able to reproduce this specific aerodynamic rotor regime and validating their representativeness compared to flight tests is an important task to train pilots to VRS in real-time simulator. The 'VRS-Helicopter Vortex Ring State Experimental Research', led by EASA and bounded by a contract signed between the EASA and ONERA/DGA-EV, aims to enhance understanding of VRS across two helicopters types, exploring analytical, simulation, and flight test methods. Additionally, it assesses the different recovery manoeuvres. As part of the objectives of this project, the main subject of the paper is to evaluate the correctness of flight mechanics code, VRS models and the reproducibility of recovery techniques. Off-line simulations are compared against flight test data, gathered from the eight flights performed during this project. Additionally, simulator trials were realized in the ONERA research simulator in order to evaluate the representativeness of two different VRS models through piloted simulations. The objective is to highlight the potential shortcomings of the VRS models and thus the reservations to be taken into account when the vortex phenomenon and associated recovery techniques are evaluated through simulations.