Experimental and simulation of tetrafluoroethane catapult UAV

In response to insufficient aerodynamic power in traditional Unmanned Aerial Vehicle（UAV）pneumatic catapults, a method is proposed to use tetrafluoroethane（R134a）instead of air as the pneumatic medium for catapulting UAVs. Tetrafluoroethane is characterized by its high safety, ease of undergoing phase transition for expansion with heating, and higher thermodynamic potential compared to air. The feasibility of using tetrafluoroethane for UAV catapult is validated through catapult experiments, and an aerodynamic thermodynamic numerical model is established with tetrafluoroethane as the catapult medium. After model verification, the catapult ability of compressed air and tetrafluoroethane is compared, and the impacts of high-pressure gas storage chamber volume, valve diameter, and low-pressure chamber volume on the trajectory parameters of tetrafluoroethane catapult UAVs are further explored. The results indicate that tetrafluoroethane can catapult the UAV out of the tube within milliseconds, exhibiting superior catapult abilities compared to compressed air, and is capable of catapulting UAVs with a mass of over 500 pounds（1 pound = 0.453 6 kg）. When the liquid injection density is constant, the pressure of the low-pressure chamber, the acceleration of the UAV, and the catapult velocity of the UAV gradually increase with the grow in the high-pressure gas storage chamber volume, while the velocity increase gradually declines. When the numerical example increases to 500 L, the velocity increase is close to 0. While meeting the specified requirements, reducing the volume of the high-pressure gas storage chamber can decrease the pressure peak and temperature peak in the low-pressure chamber, so can ensure catapult safety. For a specific catapult system, there exists a critical release diameter for the valve; exceeding this diameter will only increase the peak acceleration instead of the UAV catapult velocity. Under unchanged conditions, appropriately increasing the volume of the low-pressure chamber effectively reduces the acceleration peak of the UAV, with a minimal decrease in catapult velocity when the UAV exits the tube.