Parameterizations of main rotor hub required for blade damping lead-lag oscillations

Aeronautical engineering


Аuthors

Pavlenko N. S.

National Helicopter Center Mil & Kamov, 26/1, Garshina str., Tomilino, Moscow region, 140070, Russia

e-mail: npavlenko@mi-helicopter.ru

Abstract

During the engineering design all kinds of self-oscillations should be excluded, including «chord flutter» and ground resonance.

The importance of structural main rotor hub parameterization is determined by helicopter safety during the flight and on the ground.

The article is devoted to the research of impact of available damping over the main rotor stable operating. The flutter calculation was made by means of isolate blade disturbance motion analysis. The equations of flexural-torsional oscillations are contemplated in the stability analysis.

The solution stability of differential equation system with periodic indexes, describing blade oscillations, is considered by means of numerical Floсk technique.

It’s shown, that unsteadyness of main rotor blades, in mode with dominating blade oscillations in plane of highest stiffness («chord flutter»), can’t be excluded only owing to relative first lag-mode frequency of free oscillations, . It’s essential to bring into construction a damper with the required damping value.

A type of construction of light helicopter bearingless main rotor (BMR), without in-plane damping and with it, is reviewed in this article. The insufficiency of only structural damping due to exclusion of «chord flutter» instability is also revealed in this article. The analytical model that can be used for the wide range of bearingless rotors during the stability analysis is also proposed. The method of calculation of elastomeric damper parameters is adduced in this article. The formulas that define requirement damper stiffness for relative damping calculation were developed. The linear dimensions are defined using them. The value of damping required for the exclusion of «chord flutter» is shown.

Keywords:

main rotor, damper, flutter, differential equations, differential equations, blade oscillations, stiffness, main rotor hub

References

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