The internal ballistics analysis of underwater solid motor with protective nozzle caps
DOI:
https://doi.org/10.54939/1859-1043.j.mst.110.2026.169-176Keywords:
Solid motor; High-pressure chamber; Low -pressure chamber; Underwater solid motor; Internal ballistics.Abstract
This paper investigates the performance of a solid motor (SM) operating in underwater environments, specifically accounting for the influence of the protective nozzle closure cap assembly. A mathematical model for the internal ballistics is established, incorporating the critical phase of the seal-breaking process. During this stage, the partial combustion of the propellant increases the combustion chamber pressure, leading to the failure of the pressure seal. Concurrently, a portion of the combustion gas flows into the cavity formed between the closure cap and the nozzle, resulting in a pressure buildup within this region. Once the pressure in the low-pressure cavity reaches a threshold sufficient to shear the retaining bolts, the closure cap is jettisoned. Following the ejection of the cap, the combustion gases are discharged through the nozzle into the surrounding medium, transitioning the SM into its conventional operating mode. The findings of this study provide a theoretical foundation for the calculation, design, and structural fabrication of a solid motor intended for underwater applications.
References
[1]. Tran D. Dien, “Internal Ballistics of Special Weapons”, vols. 1–2, Military Technical University, Hanoi, Vietnam, (1975).
[2]. Pham T. Phiet, “Theory of Rocket Engines”, Military Technical Academy, Hanoi, Vietnam, (2006).
[3]. Dang H. Trien, “Theory of Solid Rocket Motors”, Science and Technology Publishing House, Hanoi, Vietnam, (2016).
[4]. Trien D. H., Thanh N. T., “Application of the Inverse Internal Ballistics Problem for the Design of Replacement Propellant Charges in Solid Motors”, Journal of Military Science and Technology, pp. 137–144, (2007).
[5]. Thanh N. T., Dung H. T., et al., “Study on the Effect of Pressure on the Thrust Force of a Solid Propellant Engine Operating in a Water Environment”, Journal of Military Science and Technology, vol. 102, pp. 137–144, (2025).
[6]. Hoang T. Dung, “Investigation of the Effects of Combustion Chamber Parameters on the Performance Characteristics of Solid Motors”, Ph.D. Dissertation, Institute of Military Science and Technology, Hanoi, Vietnam, (2018).
[7]. Le S. Tung, Hoang T. Dung, “Fundamentals of Calculation and Design of Solid Propellant Engines”, People’s Army Publishing House, Hanoi, Vietnam, (2015).
[8]. Орлов Б. В., “Термодинамические и баллистические основы проектирования РДТТ”, Издательство Машиностроение, Москва, (1968).
[9]. “Переносный противотанковый комплекс 9К111 – Техническое описание”, Военное издательство Министерства обороны СССР, Москва, (1981).
[10]. “Техническое описание и инструкция по эксплуатации ПТУРС 9М111М”, Военное издательство Министерства обороны СССР, Москва, (1975).
