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Figure 10. Shock absorber stroke vs time (left elastic leg). Slika 10. Ugib elastiéno-priguSnog elementa u ovisnosti 0 vremenu (lijeva elastiéna noga) Figure 10. Shock absorber stroke vs time (left elastic leg).

Figure 10 Shock absorber stroke vs time (left elastic leg). Slika 10. Ugib elastiéno-priguSnog elementa u ovisnosti 0 vremenu (lijeva elastiéna noga) Figure 10. Shock absorber stroke vs time (left elastic leg).

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1. Introduction airplane landing cases is briefly described. The model includes aircraft aerodynamic loads, discontinuous dynamics of shock absorbers oleo-pneumatic elements (main andnose landing gear) andaircrafttires 3D dynamics including longitudinal and lateral loading. Because of its great influence on the aircraft ground dynamic behaviour and structural loads determination, dynamic model of the main gear shock absorber is presented in more detail. Based on the developed model, landing cases of the large transport aircraft for different initial descent velocities are simulated and dynamic landing force and stroke of landing gear shock absorber are presented.
1. Introduction airplane landing cases is briefly described. The model includes aircraft aerodynamic loads, discontinuous dynamics of shock absorbers oleo-pneumatic elements (main andnose landing gear) andaircrafttires 3D dynamics including longitudinal and lateral loading. Because of its great influence on the aircraft ground dynamic behaviour and structural loads determination, dynamic model of the main gear shock absorber is presented in more detail. Based on the developed model, landing cases of the large transport aircraft for different initial descent velocities are simulated and dynamic landing force and stroke of landing gear shock absorber are presented.
Figure 1. Schematic landing aircraft global multibody model and details of shock absorber assembly model - low pressure gas chamber / oil chamber, upper and lower bearings, systems of orifices. The additional non-linear force couplers are added to model aircraft’s tire dynamics: it is assumed that the aircraft main gear is equipped with four tires of the conventional type and two conventional tires are mounted on the aircraft nose gear. Mechanical properties of the tires are estimated after [5] and manufacturer’s
Figure 1. Schematic landing aircraft global multibody model and details of shock absorber assembly model - low pressure gas chamber / oil chamber, upper and lower bearings, systems of orifices. The additional non-linear force couplers are added to model aircraft’s tire dynamics: it is assumed that the aircraft main gear is equipped with four tires of the conventional type and two conventional tires are mounted on the aircraft nose gear. Mechanical properties of the tires are estimated after [5] and manufacturer’s
Figure 2. Approach profile and aircraft velocity during the landing approach.
Figure 2. Approach profile and aircraft velocity during the landing approach.
Figure 3. Main landing gear elastic leg multibody model and schematic oleo-pneumatic shock absorber. The animation of dynamic simulation of “drop-test” - numerical testing of elastic leg dynamic characteristics and data validation (JAR- 25). Most commonly, a telescopic main landing gear of a transport aircraft comprises a shock absorber of oleo- pneumatic type [6, 11]. Considering a contemporary design, it is a several stage unit and contains four chambers: a first-stage oleo-pneumatic chamber containing low pressure gas and hydraulic fluid, a recoil chamber and compression chamber containing hydraulic fluid and a second-stage pneumatic chamber that contains high pressure gas (nitrogen) (Figure 3).
Figure 3. Main landing gear elastic leg multibody model and schematic oleo-pneumatic shock absorber. The animation of dynamic simulation of “drop-test” - numerical testing of elastic leg dynamic characteristics and data validation (JAR- 25). Most commonly, a telescopic main landing gear of a transport aircraft comprises a shock absorber of oleo- pneumatic type [6, 11]. Considering a contemporary design, it is a several stage unit and contains four chambers: a first-stage oleo-pneumatic chamber containing low pressure gas and hydraulic fluid, a recoil chamber and compression chamber containing hydraulic fluid and a second-stage pneumatic chamber that contains high pressure gas (nitrogen) (Figure 3).
Figure 4. Main gear elastic leg - shock absorber load characteristics and variable slip-friction characteristics of tire contact spin- up force. Slika 4. Elasti¢na noga glavnog podvozja — karakteristika opterecenja elasti¢no-prigusnog elementa i promjenjiva znaéajka sile trenja kontaktne dinamike gume. Figure 4. Main gear elastic leg - shock absorber load characteristics and variable slip-friction characteristics of tire contact spin- up force.
Figure 4. Main gear elastic leg - shock absorber load characteristics and variable slip-friction characteristics of tire contact spin- up force. Slika 4. Elasti¢na noga glavnog podvozja — karakteristika opterecenja elasti¢no-prigusnog elementa i promjenjiva znaéajka sile trenja kontaktne dinamike gume. Figure 4. Main gear elastic leg - shock absorber load characteristics and variable slip-friction characteristics of tire contact spin- up force.
Figure 5. The schematic layout of dynamic simulator “global” architecture. Slika 5. Shema dinami¢kog simulatora globalne arhitekture.
Figure 5. The schematic layout of dynamic simulator “global” architecture. Slika 5. Shema dinami¢kog simulatora globalne arhitekture.
Figure 6. The animation sequence of landing airplane with present lateral wind - one gear landing case.
Figure 6. The animation sequence of landing airplane with present lateral wind - one gear landing case.
Figure 7. Shock absorber total force vs time (right elastic leg). Slika 7. Ukupna sila elastiéno-prigu8nog elementa u ovisnosti o vremenu (desna elasti¢na noga). The discontinuities visible at the shock absorber total force characteristics in Figure 7. and Figure 9. are due to the orifices different working regime (inactive/active K3 orifices, Figure 3, Figure 4) and due to the change of the absorbers’ pneumatic force at the point where the floating piston of the second-stage pneumatic cylinder becomes active (Figure 4.).
Figure 7. Shock absorber total force vs time (right elastic leg). Slika 7. Ukupna sila elastiéno-prigu8nog elementa u ovisnosti o vremenu (desna elasti¢na noga). The discontinuities visible at the shock absorber total force characteristics in Figure 7. and Figure 9. are due to the orifices different working regime (inactive/active K3 orifices, Figure 3, Figure 4) and due to the change of the absorbers’ pneumatic force at the point where the floating piston of the second-stage pneumatic cylinder becomes active (Figure 4.).
Figure 8. Shock absorber stroke vs time (right elastic leg). Slika 8. Ugib elasti¢no-priguSnog elementa u ovisnosti 0 vremenu (desna elastiéna noga).
Figure 8. Shock absorber stroke vs time (right elastic leg). Slika 8. Ugib elasti¢no-priguSnog elementa u ovisnosti 0 vremenu (desna elastiéna noga).
Figure 9. Shock absorber total force vs time (left elastic leg). Slika 9. Ukupna sila elastiéno-prigu8nog elementa u ovisnosti 0 vremenu (lijeva elastiéna noga). As presented briefly here, a numerical simulaton algorithm of landing aircraft is based on dynamic response determination of the modelled aircraft for specified initial conditions, airplane aerodynamic data and runway contact loads. The aircraft dynamic model is designed as a multibody system with detailed non-linear dynamic model of landing gear assembly. Numerical simulaton procedures are modularly designed and dynamic models and algorithms of different structural subsystems (landing gear assembly, for example) are independently validated on the basis of technical documentation, JAA requirements and measured data. The airplane 3D aerodynamic model is estimated and used for dynamic simulation of landing approach in order to define initial conditions for aircraft multibody simulations after touch-down. The aerodynamic model is also used for determination of aerodynamic loads during system numerical simulation after touch-down and during taxiing.
Figure 9. Shock absorber total force vs time (left elastic leg). Slika 9. Ukupna sila elastiéno-prigu8nog elementa u ovisnosti 0 vremenu (lijeva elastiéna noga). As presented briefly here, a numerical simulaton algorithm of landing aircraft is based on dynamic response determination of the modelled aircraft for specified initial conditions, airplane aerodynamic data and runway contact loads. The aircraft dynamic model is designed as a multibody system with detailed non-linear dynamic model of landing gear assembly. Numerical simulaton procedures are modularly designed and dynamic models and algorithms of different structural subsystems (landing gear assembly, for example) are independently validated on the basis of technical documentation, JAA requirements and measured data. The airplane 3D aerodynamic model is estimated and used for dynamic simulation of landing approach in order to define initial conditions for aircraft multibody simulations after touch-down. The aerodynamic model is also used for determination of aerodynamic loads during system numerical simulation after touch-down and during taxiing.
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Computer ScienceAerodynamicsFlight Dynamics
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