Simulation of Ground Operations in Aircraft Design. Martin Spieck DLR - German Aerospace Center Institute of Aeroelasticity

Transcription

1 Simulation of Ground Operations in Aircraft Design Martin Spieck DLR - German Aerospace Center Institute of Aeroelasticity 1

2 Deep-Drawn Sigh of an Expert Ling gear is an invaluable aircraft system, albeit quite unpopular with most aircraft designers: In extended position, it spoils the aerodynamic shape of the aircraft. Retracted, it uses internal space which "could much better have been devoted to fuel or other useful things". Moreover, its dead weight impairs flight performance. Looking at ling gear from a structur point of view, it produces large concentrated loads provides for a lot of difficulties by requiring voluminous ling gear bays doors interrupting the smooth flow of loads stress. There is also the possibility that the optimal position of the ling gear with regard to e.g. nosewheel liftoff differs from that required for a satisfactory behaviour as a ground vehicle, both positions might be unfavourable with regard to structural attachment. A. Krauss DLR German Aerospace Center - Institute of Aeroelasticity 2

3 Motivation for Simulation of Aircraft Ground Dynamics rigid body oscillations structural strength dynamic loads on LG structural vibrations ling gear vibrations DLR German Aerospace Center - Institute of Aeroelasticity 3

4 Applications of Multibody Simulation as a Virtual Testbed 4 Applications in aircraft ground dynamics ling impact: dynamic ground loads ling impact: dynamic behaviour of overall system ground run: resonance effects, vibrations cornering: dynamic loads brake-gear interaction soft-soil operations ling gear positioning, kinematics evaluation of new concepts etc DLR German Aerospace Center - Institute of Aeroelasticity 4

5 Trends in Aircraft Ling Gear Design Calculation Enhancement for of simulation certifications capabilities, requirements, esp. in respect to: e.g. Advisory Circular AC (1998): 4Aircraft tyre properties (high lowintegrated speed) 4Aerodynamic effects (steady dynamic) Design Consideration of airframe flexibility ling gear dynamic characteristics For aerodynamic aspects of takeoff ling flight dynamics, current is necessary in most cases. analysis capabilities are not sufficient to detect avoid undesirable A deterministic dynamic analysis, based on dynamic characteristics. [ ] the San Francisco Runway 28R [ ] is an It is important that sufficiently accurate techniques be applied to predict acceptable method for compliance. dynamic characteristics from the beginning Airframe of the design effort Ling Gear Aeronautical Test Technologies for the Twenty-First Century Simulation Committee on Aeronautical Technologies of the Aeronautics Space Engineering Board, in: DLR German Aerospace Center - Institute of Aeroelasticity 5

6 Aerodynamics in Aircraft Ground Dynamics: Why? Problems of the stard approach of modelling simulation Modelling derives from FAR 25 certification requirements: lift = weight NWW (Newton-was-wrong) approach 4Complex ling sequences are not realisticly modelled. 4Airframe deformation at impact starts from the undeformed 0g-state, not from the pre-stressed +1g-state. 4Wing deformation (bending, torsion) causes aerodynamic effects which influence dynamic behavior loads. 4Pilot / FCS inputs cannot be modeled. 4Ground effect is being neglected. DLR German Aerospace Center - Institute of Aeroelasticity 6

7 Aerodynamics in Aircraft Ground Dynamics: How? Stard approach of MBS 4 Force elements sensor at marker frames of the flexible MBS body but: 4CPU time explodes 4a lot of work to set up the model 4much more work to modify the model in trade-off studies or optimizations DLR German Aerospace Center - Institute of Aeroelasticity 7

8 Aerodynamics in Aircraft Ground Dynamics: What? Requirements of MBS Aerodynamics of the Flexible, Maneuvering A/C 4Quick simple modeling: - computer-aided model set-up - use of existing disciplinary modeling 4Easy to modify if design changes 4Efficient computation of the job 4Adequate representation of high-lift aerodynamics 4Pilot controlled 3D-maneuvers 4Aerodynamic effects of structural deformation: - state-dependent - velocity-dependent DLR German Aerospace Center - Institute of Aeroelasticity 8

9 Integrated Design Process of Aircraft Ground Dynamics FEA model stress / strain modal data FEA dyn. loads AeroFEMBS airloads CFD CFD model LOADS SID file MBS model SIMPACK MBS results SOD file DLR German Aerospace Center - Institute of Aeroelasticity 9

10 Aeroelastic Preprocessing Step StepA CAx Models seizes seizes CAx CAx models, models, correlates correlates mcsm, mcsm, CFD CFD grids grids fluid-structure fluid-structure coupling coupling Step StepB defines defines reference reference configuration configuration rigid rigidbody reference referenceaerodyn. Step StepC selects selects relevant relevant rigid rigid body body modes modes rigid rigidbody attitude attitude & motion motion Step StepD selects selects rel. rel. control control surface surface deflections deflections control controlinputs Step StepE selects selects rel. rel. deformation deformation modes modes elastic elasticdefomation Step StepFF SIMPACK Input File sel. sel. approximation approximation method, method, at at sampling sampling points points ground groundeffect DLR German Aerospace Center - Institute of Aeroelasticity 10

11 Example: Ling of a Large Transport Aircraft 4 Model: large transport aircraft (basing on A ) 4 Scenario: hard touch-down, low wing DLR German Aerospace Center - Institute of Aeroelasticity 11

12 Example: Ling of a Large Transport Aircraft 4 Model: large transport aircraft (basing on A ) 4 Scenario: hard touch-down, low wing position of A/C reference frame z-position [m] A-RG A-EG A-RA A-EA 5 time [s] velocity of A/C reference frame z-velocity [m/s] A-RG A-EG A-RA A-EA time [s] DLR German Aerospace Center - Institute of Aeroelasticity 12

13 Example: Ling of a Large Transport Aircraft 4 Model: large transport aircraft (basing on A ) 4 Scenario: hard touch-down, low wing e e e+06 load on left MLG (mainfitting) z-load [N] A-RG A-EG A-EA -1.6e+06 time [s] -1.8e e e e e+06 load on right MLG (mainfitting) z-load [N] A- RG A- EG A-EA -1.8e+06 time [s] -2e DLR German Aerospace Center - Institute of Aeroelasticity 13

14 Example: Ling of a Large Transport Aircraft 4 Model: large transport aircraft (basing on A ) 4 Scenario: lift dumper deployment at rebound stroke of left MLG stroke [m] load on left MLG z-load [N] 0 D-WO D-LD no lift dumper deployment lift dumpers deployed 0 time [s] e e e+06 time [s] -1.6e DLR German Aerospace Center - Institute of Aeroelasticity 14

15 Computational Advantage of Aeroelastic Preprocessing SIMPACK-Simulation of Aircraft Ling Sequence Scenario NWW CPU Time FEL APP CPU Time Penalty NWW FEL APP A FAR (high AoA) s s s 100% 369% 26% B FAR (3-point) 81.8 s s s 100% 446% 42% C Left wing low (5.7 ) s s s 100% 434% 49% D Lift dumpers deployed s s DLR German Aerospace Center - Institute of Aeroelasticity 15

16 Summary New approach for aerodynamic effects has been applied in SIMPACK. Aerodynamic forces are causing appropriate structural deformation. Aerodynamic effects of deforming airframe are accounted for. Approach fits well into existing design process. Setting-up of SIMPACK model is fast simple. CPU time of SIMPACK analysis is significantly reduced. Aerodynamic effects have a big impact on dynamic behavior of the aircraft. DLR German Aerospace Center - Institute of Aeroelasticity 16