# Analysis of Carrier-Based Aircraft Catapult Launching Based on Variable Topology Dynamics
## 1 Introduction  
During the catapult and take-off process of a carrier-based aircraft, the catapult tackle is connected to the front landing gear pillar through the catapult rod, and the restraining rod is connected to the front landing gear antitorsion arm through the locking mechanism. In the initial stage of catapulting, under the action of the thrust of the aircraft engine, the landing gear and holding rod are tightened; after the catapulting starts, the tensioning force of the restraining rod increases with the increase of the catapult force. When the tensioning force of the restraining rod reaches the unlocking threshold of the locking mechanism, the restraining rod is separated from the nose gear, and the catapult tackle drags the nose landing gear of the aircraft to slide forward. When the catapult trolley reaches the end of its catapult stroke, the catapult rod separates from the catapult trolley, and the aircraft continues to accelerate and roll to take off under the thrust of the engine. Researchers have carried out a lot of research on the catapult and take-off process of carrier-based aircraft. [PERSON] [1] explained the advantages of dragging catapult from the front wheel and conducted catapult test research on the E-2A aircraft. [PERSON] [2] proposed that the shock of the front landing gear when the restraint lever is unlocked causes seriousfatigue problems to the landing gear structure. [PERSON] et al. [3] studied the adaptability of A6-A aircraft and aircraft carrier through experiments. They established mature design standards for the nose landing gear structure of carrier-based aircraft [4], restraining rods and unlocking devices [5; 6], and aircraft structure strength [7]. [PERSON] et al. [8] used the intelligent proxy model method to establish a launch model of carrier-based aircraft including the atmosphere, ocean, and ships. [PERSON] et al. [9] analyzed the predetermination of the disembarking attitude of the carrier-based aircraft, the design of the guidance law, and other related issues, providing a basis for the evaluation of the safety boundary of the disembarkation. [PERSON] et al. [10] studied the influence of the deflection angle of the carrier-based aircraft's elevator on the projection performance of the landing gear, and the influence of the movement of the aircraft carrier on the off-ship attitude of the carrier-based aircraft. [PERSON] [11] establishes a thermodynamic model of the steam catapult, analyzed the catapult process of the carrier- based aircraft with the dynamics model of the carrier-based aircraft, and compared it with the US military test. [PERSON] et al. [11] established a general whole nonlinear model by studying a carrier-based aircraft, and then designed a control scheme for climbing phase. Simulation results show a better control performance with the model and control scheme. [PERSON] et al. [12] and [PERSON] et al. [13] studied the catapult performance of the front landing gear of the carrier-based aircraft theoretically and experimentally, respectively. [PERSON] et al. [14] and [PERSON] et al. [15] studied the structural vibration of the front landing gear at the moment of sudden unloading of the hold bar load and also proposed a solution. [PERSON] [2] studied the performance parameters of five types of carrier-based aircraft. Results showed that for a given departure speed, some parameters had a critical interval. In this interval, small changes in ejection parameters may lead to great changes in track subsidence after taking off from the deck. [PERSON] [16] analyzed the impact load on the aircraft of low thrust-weight ratio during ski-jump take-off and described the work of designing and refitting the S-3A aircraft to adapt to the light aircraft carrier. [PERSON] et al. [17] conducted a simulation analysis on the ski-jump take-off ramp of the aircraft. The research showed that the use of a ski-jump take-off ramp does not affect the take-off performance of the aircraft.