Nonlinear Stability Analysis and Shimmy Mitigation of Aircraft Nose Landing Gears
Bibliographic record
Abstract
Landing gear stability is crucial for aviation safety. Yet, it can be challenged through emergence of self-induced rotational-lateral oscillations designated as shimmy. The challenge of shimmy is more common in nose landing gears and is mostly addressed by addition of shimmy dampers. This presents two challenges and opportunities for improvement that are addressed in this thesis. Firstly, the gap between shimmy prediction from numerical simulations and physical tests can be narrowed by including more of the nonlinear phenomena. In this work, a representative nose landing gear model is constructed by accounting for chief degrees of freedom and major nonlinearities. Specifically, Coulomb friction in the shock absorber is modeled as a state-dependent resistive torque which varies with shock absorber compression and shimmy velocity. The effect of torque link freeplay nonlinearity is also investigated simultaneously with the Coulomb friction using the representative nonlinear model. Time domain numerical solution based on multi-body dynamics approach is used to obtain stability plots in a representative parameter space. Qualitative and quantitative effects of these nonlinearities are discussed. Coulomb friction is found to increase stability and switch the shimmy mode from rotational to lateral while freeplay diminishes stability and leads to more severe rotational vibrations. The second challenge addressed deals with shimmy damper performance analysis and designing an improved shimmy damper. Using the representative nose landing gear dynamic model and a generic damper sub-model, global trends offered by passive shimmy dampers are depicted and explained. Based on these trends and analyzing existing shimmy dampers, a novel shimmy damper concept is proposed which integrates the damping elements into the design of the torque links, offering a multifunctional torque link system with symmetrical load distribution and simpler maintenance. Designated as Symmetric Torque Link Damper (STLD), this shimmy damper is studied parametrically and optimized for an existing nose landing gear as a proof of concept. Using topology optimization and iterative studies, a prototype of STLD is sized and fabricated for experimental characterization and validation. Along with the analysis, the experimental results confirm the stability benefits offered by this novel shimmy damper design.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".