# Landing Impact Load Analysis and Validation of a Civil Aircraft Nose Landing Gear

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## Abstract

**:**

## 1. Introduction

## 2. Theoretical Model and Tool

#### 2.1. Landing Gear Structure

#### 2.2. Landing Dynamic Model

_{1}is the up and down of the un-sprung mass, q

_{2}is the up and down of the sprung mass, q

_{3}is the wheel rotation, and q

_{4}is the forward and afterward of the un-sprung mass, namely the gear walk phenomenon caused by strut flexible bending. The corresponding mass definitions are as follows: m

_{1}and m

_{4}represent the un-sprung mass, m

_{2}represent the sprung mass, and m

_{3}is the inertia moment of wheels.

_{V}is the vertical load inside the shock absorber, consisting of the gas spring force, oil damping force and bearing friction forces; F

_{T}is the vertical load on the tire; D

_{T}is the longitude friction on the tire; L is the airlift force assumed to be equal to the gravity of the reduced mass; Q

_{H}is the strut bending force; b is the fixed pitch angle of the pillar; R is the tire radium; d is the tire deflection; g is the gravity coefficient.

_{1}is the distance between the upper and lower bearing; L

_{2}is the distance between the lower bearing to the wheel axle center; μ is the bearing friction coefficient; S is the shock absorber stroke; k is the structural stiffness in the bending direction; c is the structural damping coefficient (assumed to be 5%).

#### 2.3. Landing Analysis Tool

## 3. Preliminary Analysis

#### 3.1. Analysis Cases

#### 3.2. Performance Verification

_{V}is the vertical force along the strut direction; S is the stroke travel; Q

_{VM}is the maximum vertical force; S

_{m}is the maximum stroke. The results corresponding to cases L1, L2, and L3 were 65.3%, 67.6%, and 68.8%. This shows that the shock absorber efficiency of the gear can meet the minimum shock absorber efficiency requirement (greater than 65%). Compared to the other cases [4,8,17,33], the curve shapes and the absorber efficiencies are basically similar. However, if the vertical loads before 250 mm can be optimized from 100 kN to about 150 kN by redesigning the damping parameter, the absorber efficiencies may be better.

#### 3.3. WA and GC Loads

## 4. Drop Test Validation

#### 4.1. Test Facility and Preparation

#### 4.2. Test Cases

#### 4.3. Processing of Test Results

#### 4.3.1. Parameter Tuning

#### 4.3.2. Load Validation

#### 4.3.3. Performance Validation

## 5. Conclusions

- The results of the drop test show that the landing simulation analysis model established by the assumption of the two masses (sprung and un-sprung), four degrees of freedom, and a rigid airframe can accurately analyze the landing impact loads.
- Through both the simulation and the test, the difference between the wheel-axle and the ground-contact loads was revealed to be non-negligible.
- If one takes reasonable consideration in the pre-test preparation of the structure’s stiffness and the during-test measurement of the wheel-axle loads, the drop test validation can be accurate and comprehensive, and both the vertical and the longitudinal loads, as well as the wheel-axle and ground-contact loads, can be fully validated.
- The importance of structural flexibility and tire friction modeling, as noted in this paper, should be considered in the current popular dynamic analysis methods based on ADAMS or other software, and the corresponding multi-body modeling methods can be further investigated to accurately analyze longitudinal loads.
- The lateral loads and the detailed attachment point loads may also need to be investigated further via both simulations and tests, including the motion equations for the lateral degrees of freedom, the lateral mechanics model of the tires, and the experimental validation of attachment point loads, especially for main landing gears with more complex asymmetric structures than the nose landing gear.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Landing gear and shock absorber: (

**a**) nose landing gear structure; (

**b**) internal schematic of shock absorber.

**Figure 10.**Load comparison between the simulation and test: (

**a**) WA loads of case 1; (

**b**) GC loads of case 1; (

**c**) WA loads of case 2; (

**d**) GC loads of case 2; (

**e**) WA loads of case 3; (

**f**) GC loads of case 3.

Preliminary Analysis Case | A1 | A2 | A3 |
---|---|---|---|

Reduced mass (kg) | 13,400 | 13,400 | 13,400 |

Sinking speed (m/s) | 3.05 | 3.05 | 3.05 |

Longitudinal speed (m/s) | 0 | 58 | 96 |

Test Case | T1 | T2 | T3 |
---|---|---|---|

Reduced Mass (kg) | 13,472 | 13,472 | 13,472 |

Sinking Speed (m/s) | 3.10 | 3.08 | 3.08 |

Longitudinal Speed (m/s) | 0 | 58.6 | 96.5 |

Key Factor | Pre. | T1 | T2 | T3 | Tuned |
---|---|---|---|---|---|

Gas polytrophic (−) | 1.1 | 1.13 | 1.05 | 1.12 | 1.08 |

Oil discharging (−) | 0.8 | 0.82 | 0.84 | 0.79 | 0.8 |

Bearing friction (−) | 5% | 5% | 9% | 8% | 7% |

Tire dynamic (−) | 1.08 | 1.04 | 0.97 | 1.07 | 1.08 |

Performance Index | T1 | T2 | T3 |
---|---|---|---|

Load factor (−) | 1.69 | 1.62 | 1.63 |

Absorption efficiency (−) | 65.9% | 67.8% | 67.4% |

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**MDPI and ACS Style**

Liu, W.; Wang, Y.; Ji, Y.
Landing Impact Load Analysis and Validation of a Civil Aircraft Nose Landing Gear. *Aerospace* **2023**, *10*, 953.
https://doi.org/10.3390/aerospace10110953

**AMA Style**

Liu W, Wang Y, Ji Y.
Landing Impact Load Analysis and Validation of a Civil Aircraft Nose Landing Gear. *Aerospace*. 2023; 10(11):953.
https://doi.org/10.3390/aerospace10110953

**Chicago/Turabian Style**

Liu, Wenbin, Youshan Wang, and Yuchen Ji.
2023. "Landing Impact Load Analysis and Validation of a Civil Aircraft Nose Landing Gear" *Aerospace* 10, no. 11: 953.
https://doi.org/10.3390/aerospace10110953