An Analytical Method for Coaxial Helicopter Ground Resonance

Xiangyi Liu,Guocai Hu,Shansong Song,Jing Wu,Shuyan Liu,C.H Su

doi:10.1051/matecconf/202031604005

Xiangyi Liu, Guocai Hu + Show 4 more

Open Access

https://doi.org/10.1051/matecconf/202031604005

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Abstract

A time-frequency analytical method is presented to analyze physical mechanism of coaxial helicopter ground resonance. Eigenvalue calculation and numerical integration of disturbance equations of motions are used to obtain modal characters and time-domain response characters of coaxial helicopter ground resonance, and the interaction between rotors and body is revealed according to response of various DOFs. The analysis results show that regressive lag mode with upper rotor character is the most instability mode. In dynamic instability region, coaxial helicopter ground resonance is mainly due to energy transferred between periodic lag motion of upper rotor and body roll rotation. For this instability mode, energy transferred between periodic lag motion of lower rotor and body roll rotation is also existed, and it can enhance ground resonance instability of coaxial helicopter.

Highlights

Helicopter ground resonance is one of dynamics problems must be solved in model design
Lag sinusoidal component ζ2s of upper rotor and body roll angle φx are close to opposite phase, so there is almost no energy transferred between φx and ζ2s, and they are mainly provided positive or negative "spring" constraint. For this LR2 mode, instability of helicopter ground resonance is mainly due to energy transferred between periodic lag motion of upper rotor and body roll rotation
According to equation (11), for this lower rotor, there is only lag cosinoidal periodic motion has inertia moment effect on body roll motion, too, the size is M RB1 NSbhx 1c 2, when 1c and x are in the opposite phase, lower rotor provides negative damping to body; As rotary direction of lower rotor is opposite to that of upper rotor, and center of rotor gravity lags lag vector 90°, moment body inertia has an incentive effect on periodic lag motion of upper rotor, that is, body transfers energy to rotors

Summary

Introduction

Helicopter ground resonance is one of dynamics problems must be solved in model design. For a single rotor helicopter with tail, the domestic and foreign scholars have done a lot of research about ground resonance, from Investigation analysis for ground resonance[1,2], the influence of the design parameters[3,4,5], nonlinear analysis of the helicopter ground resonance[6,7,8], active or passive control[9,10] and ground resonance test verification[11,12]. Many well-known conclusions have been made and the problem of ground resonance in model development has been well solved[13,14,15,16]. We find that there is no systematic analysis and explanation about the influence of physical investigation and design parameters of upper/lower rotor in ground resonance, this poses potential uncertainties in the design analysis、use and maintenance of coaxial helicopter

Analytical model

Analytical method