Longitudinal Dynamic Characteristics of a Helicopter Rotor Blade: A Time-Based Modelling Method

This article represents a numerical approach for estimating the helicopter rotor’s blade longitudinal dynamic characteristics considering several operational parameters. A characterization regarding the blade’s longitudinal, flapping, and vertical responses is derived by solving a system of differential equations that fully describe the rotor’s longitudinal dynamics. Dependencies between the lagging (longitudinal) velocity, the flapping velocity, and the vertical velocity over time are illustrated, taking into consideration the varying flapping frequency in a hovering regime. Additionally, the blade’s longitudinal parameters were evaluated in ground effect conditions when hovering at <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mstyle scriptlevel="0" displaystyle="true"><mfrac><mrow><mi>H</mi></mrow><mrow><mi>R</mi></mrow></mfrac></mstyle><mo>=</mo><mn>1</mn></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mstyle scriptlevel="0" displaystyle="true"><mfrac><mrow><mi>H</mi></mrow><mrow><mi>R</mi></mrow></mfrac></mstyle><mo>=</mo><mn>0.5</mn></mrow></semantics></math></inline-formula>. The studied time domain variables represent the rotor’s natural reaction capabilities when a disbalancing condition occurs. Eventually, an increase in the blade’s flapping frequency leads to a rise in the required period for reaching a stable condition with regard to the longitudinal and vertical responses. The ground effect zone reduces the blade’s lagging and flapping reactions as well.