Buoyancy engine is a device which changes net buoyancy of an underwater vehicle by attracting and expelling water. Underwater gliders equipped with buoyancy engines can be driven by net buoyancy forces to travel in the vertical plane. Existing underwater gliders, such as Seaglider, Spray and SLOCUM are configured with single buoyancy engine and a longitudinally mass shifting device by which pitch angle are varied by moving their center of gravity. The buoyancy engine on Seaglider,and Spray include a high-pressure reciprocating pump and an external bladder [1,2]. For SLOCUM Battery, buoyancy engine is a piston driven by a motor. Modeling and control of ocean gliders driven by buoyancy engines and mass-shifting device can be found in [3]. Nonlinear dynamic equations are derived, and feedback control laws for the linearized system were developed in [4]. The stability of this nonlinear system using linearization control was shown by numerical simulations. Equilibrium points of the nonlinear glider model were also derived in [4]. An estimation of energy cost for the buoyancy engines operating at different water depths was shown in [5]. In [6], design considerations of gliders and wings were described. Maximum velocities of gliders with various body sizes and buoyancy engine capacities were studied in [6].