Multi-body coupling dynamic research of carrier-based aircraft catapult launch based on natural coordinate method

There is an increasing demand for predicting the dynamic behaviours of carrier-based aircrafts(CBAs) during catapult launch. This paper presents a maximal parameterised dynamic model of the launch process from a new perspective, and conducts a detailed study of its mechanical behaviours. Based on the topological analysis of the multi-body catapult launch system, the natural coordinate method is adopted to establish a comprehensive model including steam catapult, landing gears, ship motion, aerodynamic and multi-body modules. The predictive capability of the model is demonstrated by presenting the CBA launch dynamic properties under different conditions. First, effects of steam flow area rate and the coupling carrier movement in different directions on catapult performance are discussed. Second, the take-off characteristics as well as the initial catapult attitude are analysed. Then, by investigating Lagrange multipliers, the loads of torque arms, holdback bar and launch bar are compared. Finally, the loads of buffer struts and tyres during launch are also discussed. The results show that it is reasonable to keep the steam flow area increasing in a linear way, but the opening velocity needs to be strictly controlled. When the CBA departs from the deck, the possible sink of the bow is the major threat to the take-off safety, the larger the sink is, the more dangerous the flight becomes. The upwash at the bow may be the primary reason of stall and cannot be ignored. The model established is reliable with capacities of capturing the coupled behaviours between different sub-modules as well as the load change of each component in detail. The natural coordinate method proves to be efficient and accurate, which should be given more attention.