Retracting Blade Stall Phenomenon - Review of Investigations Performed during the PZL W-3A Serial and New Blade Projects

Abstract

One of the key phenomena of importance for the final determination of the operating envelope of classic design helicopters is the flow separation appearing on the retracting blade. This study presents specific is-sues related to the occurrence of this phenomenon on the main rotor of the PZL W-3A “Sokó?” helicopter, which blades are characterized by relatively low torsional stiffness. Aspects related to the prediction of the conditions for the occurrence of the stall phenomenon using different levels of complexity of aerodynamic models in comparison with the test results are presented. The results of selected flight tests of the PZL W-3A “Sokó?” helicopter conducted to determine it’s safe operating envelope are presented. The results of meas-urements carried out in the conditions of a developed phenomenon of retracting blade stall and the identified influence of external parameters on the intensity of the phenomenon are noted. Selected analyzes carried out to determine the limitations for the newly designed main rotor blades for the PZL W-3A helicopter are presented, showing the possibility of the helicopter operating envelope extension. The results of these ana-lyzes was the starting point for the anticipated flight tests of the helicopter and will be checked for the final MR blade configuration.