A gas turbine by-pass system is used between a gas turbine generator outlet nozzle and the inlet of a heat recovery steam generator. A method comprises towing marine geophysical equipment having a surface covering, comprising a textural attribute of shark skin, attached thereto. A self-standing inertia body whose bottom surface is placed on the supporting surface is installed inside the sensor case in a self-standing condition, and which tilts when a horizontal acceleration is exerted. The power and control unit may include at least one energy source, be electrically connected to the at least one propulsion unit, and be configured to control operation of the at least one propulsion unit to control flight of the toy aircraft.