FREEPLAY INDUCED LIMIT CYCLE OSCILLATION PREDICTION BY USING EQUIVALENT STIFFNESS METHODOLOGY

Date

2023-12-11

Author

Aydın, Murat

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This study examines the aeroelastic instability effect of freeplay on an aircraft using the equivalent stiffness methodology. The main motivation of the equivalent stiffness method is that it is also applicable for actuators implemented finite element model. The offset moment requires the modelling of total rotational stiffness around the hinge line with spring element which is CBUSH element in Nastran. The equivalent stiffness methodology is applicable for both bush and actuator implemented finite element model. The 3 DOF airfoil case and AGARD 445.6 wing with loosened root connection are used to validate the equivalent stiffness approach. In the validation phase, ZAERO Nonlinear Flutter Module (NLFLT) is used. METU Very Light Aircraft Model (VLA) is selected to apply the equivalent stiffness methodology on a complete aircraft for both bush and actuator implemented finite element model. The structural and aeroelastic models are created in MSC Nastran/Patran. A set of points are selected from the envelope, and analyses are performed for different flight conditions with different freeplay angles. The maximum free-play limits of control surfaces are determined by following the maximum pilot seat acceleration limitation that it should not exceed the ± 0.12g. The results show that the effect of elevator freeplay on the pilot seat acceleration is the highest one, and it should have the smallest freeplay limit. The rudder has no LCO behavior due to the absence of the flutter mechanism in the envelope for both zero and nominal rotational stiffness around the hinge line. Apart from the determination of allowable maximum freeplay limits of each control surface alone, the combined control surface freeplay analysis is also conducted in this study. The results show that the combined freeplay case is the most critical one while determining the maximum allowable freeplay limits.

Subject Keywords

Aeroelasticity, Freeplay, Fictitious mass approach, Equivalent stiffness, Limit cycle oscillation

URI

https://hdl.handle.net/11511/107770

Collections

Graduate School of Natural and Applied Sciences, Thesis