<p>While zigzag gliding is the most common motion mode for underwater gliders (UGs), turning and helical gliding are also necessary motions, yet their principles remain poorly understood. This paper performs dynamic modeling of the UG to investigate the principle of turning and helical gliding and analyzes the factors influencing the roll rudder performance. A helical gliding model is developed, and computational fluid dynamics simulations of constrained-based testing are conducted to evaluate the various hydrodynamic coefficients associated with the hull, wings, and vertical stabilizers. The principles of turning and helical gliding are analyzed based on motion simulations, which reveal that UGs also achieve turning and helical gliding through rolling operations, similar to air gliders. Unlike air gliders, which generate centripetal forces to turn with the horizontal component of the lift on wings, UGs rely on sideslip hydrodynamic force from the hull to realize turning and helical gliding. For UGs, the horizontal component of lift on wings can initiate sideslip through its moment of the center of buoyancy, like the function of vertical rudders in submarines. Finally, the relationships between the roll rudder performance and the influencing factors of the net buoyancy, pitch angle, and roll rudder angle are established, followed by a sensitivity analysis via Monte Carlo simulation. The results indicate significant coupling between the roll rudder angle and the pitch angle, suggesting that reducing the pitch angle can enhance turning maneuverability. This conclusion is further validated through a sea trial.</p>