Study on the interior ballistic characteristics of UAV ejection by CO2 phase transition catapult.

In response to the development demand for miniaturized portable and lightweight of UAV ejection system, a new technological approach for UAV ejection based on CO2 phase transition is proposed. A thermodynamic model for CO2 phase transition ejection system was established and solved, a 115 mL CO2 phase transition catapult was trial-produced and the ejection experimental system was built. The 8.8 kg UAV was accelerated to a exit velocity of 25 m/s and the peak acceleration was 1077.7 m/s2, the simulation and experimental results showed that the maximum error of exit velocity and peak acceleration were 2.35%, 3.68%, which effectively verifying the accuracy of simulation model. To further reduce the launch overload of UAV, the effects of ejection system's CO2 working fluid filling parameters, valve diameter, and initial volume of launch tube on the interior ballistic performance during ejection process were simulated and studied under the condition of constant total system energy. The research results indicate that the filling density of CO2 which inside catapult has the greatest impact on the exit velocity, and the valve diameter has the greatest impact on the peak acceleration. Reducing the valve diameter, increasing the filling density of CO2 and the initial volume of launch tube are beneficial for reducing the projectile overload while ensuring the exit velocity. By adopting key parameter optimization design, the UAV achieves an exit velocity of 25.5 m/s and a peak acceleration of 733 m/s2, the peak acceleration can be reduced by 31.98%, which can significantly improve the safety of ejection process.