## 1 Introduction
At the same time, with the increase in the water-soaked area of the propeller, the additional frictional resistance of the end plate part due to the increase in the area increases, resulting in the increase in the torque coefficient of the propeller as a whole, and the benefit of the end plate blocking the backflow of the blade tip is limited, resulting in the reduction in propeller efficiency. In this paper, a series of Kappel propellers were combined with an underwater glider (UG) to form a hybrid-driven underwater glider, and the application analysis was carried out. Therefore, it is necessary to discuss the research status of traditional underwater gliders and hybrid-driven underwater gliders in this section. For the limitations brought about by the traditional drive mode, the researchers put forward the concept of the hybrid-driven underwater glider, that is, on the basis of the traditional underwater glider applying other strong propulsion devices. [PERSON] et al. [20] proposed to install a propeller in the stern of the _Slocum_ underwater glider to improve the maneuverability of the underwater glider. For the _Folaga_ hybrid-driven underwater glider, propulsion devices were installed in both the bow and stern according to [PERSON] et al. [21]. [PERSON] et al. [22; 23] developed a flat rectangular underwater glider named _AUV-Glider_, which adopted an open-frame design and installed multiple propulsion devices to realize bidirectional motion. In the early stage, the researchers did not focus on the design of suitable propellers for the hybrid-driven underwater glider. [PERSON] [24] installed a propeller with high propulsive efficiency in the stern of the _Hybrid Slocum_ hybrid-driven underwater glider. This propeller can maintain the horizontal speed of 2 kn while ensuring the working efficiency is roughly equivalent to the gliding motion mode, which effectively solves the energy consumption problem of the hybrid-driven underwater glider. In view of this, this paper also tries to combine a series of Kappel propellers with high efficiency into the underwater glider to carry out application research. At present, there is little research on propellers suitable for hybrid-driven underwater gliders. [PERSON] et al. [25; 26] developed and designed a collapsible propeller for the hybrid-driven underwater glider, aiming at the problem of increasing the drag of the propeller when gliding. The propeller is a double-blade propeller; the blade can be shrunk and folded to the center, and the opening and closing angle can be adjusted. [PERSON] et al. [27] combined a hybrid-driven underwater glider with a rotatable folding propeller, and the hydrodynamic simulation results of the hybrid-driven underwater glider showed that, during navigation in gliding mode, if the blade of the foldable propeller is shrunk and folded, the glide resistance of the body will be reduced by more than 45%, and the resistance reduction can even reach 60% under low speed conditions. The above provides a guide to solve the propeller drag increase problem encountered in the application research of the Kappel propeller in this paper. In this paper, we focus on the tip rake of the blade; adjust, modify, and design the tip rake distribution of the series Kappel propellers; and study the effect of the tip rake on the open water propulsion performance and sheet cavitation performance of the series Kappel propellers [19]. At the same time, the self-propelled propulsion performance of the series Kappel tip rake propeller in the wake field of the underwater glider was further studied from the perspectives of actual propulsion efficiency and companion current fraction, and the optimal tip rake value in different flow field conditions was obtained, which provided guidance for the practical application of Kappel propellers.