Landing Gear Model Research Articles

Lateral Response of Nonlinear Nose Wheel Landing Gear Models with Torsional Free-play

Nose-wheel landing gears can, under certain conditions, exhibit instability in lateral dynamics, causing divergent coupled lateral flexural and torsional oscillations called shimmy. The stability of the system depends on the dynamic characteristics of the gear and tires, nonlinearities in the system, and vibratory modes of the vehicle as a whole, as well as the degree of coupling that exists between them. Shimmy may be caused by a number of conditions such as low torsional stiffness of the strut, free play in the gear, wheel imbalance, or worn parts. Free play in the steering degree of freedom has the potential to significantly reduce the divergent shimmy velocity. Nonlinear behavior of landing gear makes the evaluation of the shimmy phenomenon more complex and its prediction more difficult. This work presents a study of the shimmy instability of a three-degree-of-freedom simplified nose-wheel landing gear model with linear flexible tire model and nonlinearities arising out of torsional free play. Response results are presented for a typical range of values of various problem parameters. Numerical studies bring out several interesting features of the shimmy and its dependence on free play.

Lateral Response of Nose-Wheel Landing Gear System to Ground-Induced Excitation

Nose-wheel landing gears can become laterally unstable during takeoff, taxiing, and landing, exhibiting divergent coupled lateral flexural and torsional oscillations called shimmy. The system stability is governed by the gear and tire dynamic characteristics, system nonlinearities, and vibratory modes of the vehicle, as well as by the degree of coupling that exists between these modes. Ground unevenness can produce significant lateral excitation on the landing gear and results in adversely impacting its lateral stability. To evaluate a nose-wheel landing gear system for its stability and response, it is necessary to model system components to capture the contributions of the landing gear structure, the tire, wheel configuration, system nonlinearities, and its interaction with the runway. This paper examines the lateral response of linear and nonlinear simplified nose-wheel landing gear models to ground-induced lateral excitation. Considering torsional free play as the source ofnonlinearity and external excitation due to runway roughness, modeling and analysis of nose-wheel landing gear shimmy is presented. The spatial variation of the runway surface is modeled as a continuous profile, obtained as a combination of sinusoids to represent a randomlike ground-induced excitation with the specified power spectral density. Time-domain simulation studies on the linear landing gear system show that unacceptable levels of lateral accelerations may be caused even at subcritical velocities. Studies on nonlinear nose-wheel landing gear systems bring out the fact that the free play can result in a significant reduction of the critical shimmy velocity and the need for such simulations in the subcritical ranges of velocities.

Simulation model of an aircraft landing gear considering elastic properties of the shock absorber

For the investigation of elastic bending of the landing gear shock absorber of an aircraft under dynamic loads upon landing and subsequent braking during roll out, an MBS-based model of the landing gear is introduced. To separate effects of the elastic bending of the main landing gear the fuselage is considered rigid. After performing a flare with subsequent landing, the aircraft is stopped by means of an antiskid system. For comparison, an analytical-numerical study of a finite-element model of the main landing gear shock strut components is done for simple static and dynamic loads considering Bernoulli's hypothesis. Simulation of a rough-landing manoeuvre reveals that vibrations due to the elastic properties of the shock absorber not only increase loads on the components but significantly affect the braking process as well.

헬리콥터 강착장치 비선형 충돌해석 및 실험결과 비교

본 연구에서는 헬리콥터 스키드형 강착장치에 대한 비선형 충돌해석을 수행하였으며, 실제 운용중인 헬리콥터(SB427)의 강착장치 시스템이 해석에 고려되었다. 재료의 소성 거동특성과 두께변화를 고려한 3차원 유한요소 모델을 구축하였으며, LS-DYNA(Ver.970)를 활용하여 다양한 충돌 조건에 대한 전산충돌해석을 수행하여 특성을 검토하였다. 지면충돌에 기인한 강착장치의 비선형 천이응답이 설계요구조건에 대해 검토되었다. 다양한 충돌조건에 대해 비선형 충돌해석으로 예측한 최대 구조 변형량을 실험결과와 정량적으로 비교하였으며, 마찰의 영향을 고려하는 것이 해석결과의 정확성에 매우 중요함을 보였다. In this study, nonlinear crash analyses have been conducted for the skid landing gear of a helicopter. The realistic landing gear model of the commercial helicopter (SB427) is considered. Three-dimensional dynamic finite element model with variable thickness and material plastic behavior is constructed and LS-DYNA(Ver.970) is used to conduct nonlinear transient crash analyses for different impact conditions. Characteristics of nonlinear transient responses due to the ground crash are investigated for typical structural design criteria of a skid landing gear system. In addition, comparison results for maximum crash deformations of the skid landing gear are presented and the important effect of ground friction for numerical accuracy is described.

Surface Topology on the Wheels of a Generic Four-Wheel Landing Gear

The analysis of shear stress lines in surface oil flow can provide attachment and separation characteristics on three-dimensional configurations about which flowfield data are often difficult or time consuming to acquire. This technique, in conjunction with mean surface pressure data, was utilized to determine the surface topology on a fore and aft wheel of a generic four-wheel landing gear model. Tests were performed at a Reynolds number of 6 × 10 5 based on wheel diameter. Because noise is produced when fluid attaches to or separates from a surface, the detailed analysis highlights regions on the wheels where further investigation may be warranted. The surface characteristics on the wheels determined in this study correlate well with the mean flowfield data acquired in a previous study. A relationship is hypothesized between observed changes in the state of separation on the ground side of the fore wheel in the present study, with the changing streamwise location of a midwheel vortex discovered in a previous study

Finite Element Simulation of a Full-Scale Crash Test of a Composite Helicopter

Finite Element Simulation of a Full-Scale Crash Test of a Composite Helicopter

Full-scale crash test and simulation of a composite helicopter

A finite element model of the Sikorsky Advanced Composite Airframe Program (ACAP) helicopter was developed using the non-linear, explicit transient dynamic code, MSC.Dytran. Analytical predictions were correlated with experimental data obtained from a full-scale crash test of the Sikorsky ACAP helicopter flight test article that was conducted in June 1999 at the Impact Dynamics Research Facility of NASA Langley Research Centre, Hampton, Virginia, USA. The helicopter was impacted at 11.58 m/s vertical and 9.9-m/s forward velocity with an attitude of 6.25° pitch (nose up) and 3.5° left roll. Due to the relatively long crash pulse duration, a rigid-body helicopter model with an energy absorbing landing gear model was executed initially. Prior to fuselage contact, a deformable structural model was executed with the rigid-body nodal displacements and velocities used as initial conditions.

A Comparison of the Moreland and Von Schlippe-Dietrich Landing Gear Tire Shimmy Models

ABSTRACT A detailed review of two classical landing gear tire shimmy models is presented. First, derivations of each of the two models are presented along with the detailed definitions of the various tire parameters used in each model. A mathematical derivation is presented which establishes a clear mathematical connection between these two tire models. Also, a mathematical connection between the Moreland tire parameters and the Von Schlippe-Dietrich tire parameters is established.

A Comparison of the Moreland and Von Schlippe-Dietrich Landing Gear Tire Shimmy Models

ABSTRACT A detailed review of two classical landing gear tire shimmy models is presented. First, derivations of each of the two models are presented along with the detailed definitions of the various tire parameters used in each model. A mathematical derivation is presented which establishes a clear mathematical connection between these two tire models. Also, a mathematical connection between the Moreland tire parameters and the Von Schlippe-Dietrich tire parameters is established.

TIRE MODELS IN AIRCRAFT LANDING GEAR SIMULATION

Abstract This report discusses the development of a simulation model of an aircraft landing gear describing its typical non-linear behaviour. The development of the design tool -which correlates the actual design parameters with the performance of the gear- is a part of the research project that investigates the estimation of the nonlinear dynamical system, which an aircraft landing gear is. This project is a joint effort by the Eindhoven University of Technology and DAF Special Products. The non-linear parts of the simulation model are implemented in the general purpose multi body program DADS, which is based on time integration procedures.