Analysis of Walking Vibration and Stability of High Strut Landing Gear

doi:10.12382/bgxb.2023.0629

Abstract

Abstract:

In order to improve the gear walk instability of high strut landing gear equipped with carbon ceramic brake discs, the rule of gear walk is analyzed thoroughly. The gear walk mechanism is explained. The braking torque with negative slope caused by the friction characteristics of the carbon ceramic brake disc can introduce negative damping to the longitudinal system of the landing gear, which causes the divergence of walking vibration. The effects of the brake torque parameters, the structural parameters of landing gear and the initial velocity of aircraft on gear walk are studied. Finally, a gear walk control strategy for reducing the braking pressure with the relative angular velocity of brake stators and rotors is proposed. The result shows that the decrease in the absolute value of negative slope of brake disc friction coefficient and the braking pressure, as well as the increase in the longitudinal stiffness and damping of strut will all contribute to the stability of gear walk. The stable gear walk can be achieved at any initial velocity of aircraft by increasing the minimum friction coefficient of brake disc to 0.186. The dropping slope of braking pressure is closely related to the initial velocity of aircraft. The simulated results of aircraft braking from 144km/h show that a 24.7% dropping in braking pressure can lead to the convergence of unstable gear walk and a 77.23% reduction in the longitudinal acceleration peak of wheel axle.

Key words: gear walk, brake vibration, carbon ceramic brake disc, braking torque with negative slope

CLC Number:

V214.3⁺3

DU Xiaoqiong, LI Bin, LUO Linyin, LIU Mujun, YANG Rong. Analysis of Walking Vibration and Stability of High Strut Landing Gear[J]. Acta Armamentarii, 2024, 45(8): 2793-2805.

Figures/Tables 21

Fig.1 Hazards of gear walk

Fig.2 3-DOF gear walk model

Fig.3 Relationship curve of ground adhesion coefficient and slip rate

Table 1 Structure and brake system parameters of high strut landing gear

参数	数值	参数	数值
m_a/kg	2×10⁴	R_g/m	0.49
m_g/kg	760	F_N/N	2.07×10⁵
m_ω/kg	280	p_bmax/MPa	10
L_g/m	2.7	S_p/m²	0.01
J_g/(kg·m²)	1.86×10³	N_m	8
J_ω/(kg·m²)	33	R/m	0.19
k_g/(N·m·rad^-1)	2.3×10⁷	r/m	0.12
c_g/(N·m·rad^-1)	7×10³

Fig.4 Flight test curve of longitudinal acceleration of wheel axle

Fig.5 Test curve of braking torque of carbon ceramic brake discs

Fig.6 Change of the friction coefficient of brake disc with the relative angular velocity of brake stators and rotors

Fig.7 Equivalent model of landing gear walk

Fig.8 Braking pressure-time

Fig.9 The influence of friction coefficient slope on the longitudinal acceleration of wheel axle

Fig.10 The influence of braking pressure on the longitudinal acceleration of wheel axle

Fig.11 Loading rate of braking pressure

Fig.12The influence of initial aircraft velocity on the longitudinal acceleration of wheel axle

Fig.13 The influence of strut stiffness and damping coefficient on the longitudinal acceleration of wheel axle

Fig.14 Relationship between the critical value and the initial velocity of aircraft

Table 2 Critical value bminc and initial velocity of aircraft

v_a0/(km·h^-1)	36	54	72	90	108	126	144
b_minc	0.186	0.181	0.176	0.174	0.170	0.167	0.164

Fig.15 The curve between bminc and the initial velocity of the fuselage corresponding to a 20% increase in stiffness and damping coefficient

Fig.16 Curves of the critical braking torque and the relative angular velocity of brake stators and rotors

Fig.17 Schematic diagram of braking pressure control system

Fig.18 The variables of control system

Fig.19 Simulated results

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