Abstract: A novel multi-stage pneumatic and hydraulic catapult device with oil buffering structure，which utilizes compressed air as impetus and hydraulic fluid as transmission medium, is introduced and its ejection performance is researched by analyzing two typical catapult devices involving pneumatic and hydraulic catapult. According to the complex polytropic process of gas, the flow nonlinearity of hydraulic fluid in enclosed chamber, motion uncertainty of multi-stage cylinders and the self-buffering structure, a mathematical model describing multi-stage pneumatic and hydraulic catapult process is established based on real gas thermodynamic effect. Meanwhile, the dynamic variation model of oil pressure in enclosed chamber and the nonlinear dynamic model of multi-stage cylinders are constructed. The motion laws and working performance of multi-stage pneumatic and hydraulic catapult cylinder are obtained through numerical simulation. The results show that the proposed multi-stage pneumatic and hydraulic catapult device can generate the appropriate pressure quickly and accelerate the load up to 19 m/s within 0.2 s with the speed-up distance of 2.4 m, and thus the overload is less than 16 g and the relative velocity between two adjacent cylinders is less than 15 m/s.

Key words: ordnance science and technology, compressed air, multi-stage cylinder, pneumatic and hydraulic catapult