NOVELTY - The turbine includes a control valve which generates a control signal based on hydraulic signal obtained from speed changes of blades and pressure dropping orifice (114). A hydraulic pump driven by blades, produces pressurized fluid output to drive the load and has a displacement control element which responds to the control signal to vary the displacement of hydraulic pump.    USE - For generating power to drive aircrafts during emergency.    ADVANTAGE - As pressure dropping orifice is provided, emergency power output is not varied depending on temperature variation during sustained flight and so emergency power to maintain flight control of aircraft when propulsion engines are not operating, is constant. As turbulence producing structures are provided in orifice, constant coefficient of discharge of fluid through the orifice is enabled.    DETAILED DESCRIPTION - The orifice has a turbulence producing structure in the fluid flowpath in the upstream of orifice so as to create turbulent flow along cross direction of orifice. The turbulence producing structure is either curved surface or partially spherical surface or a rod which extends into the flow path. The orifice produces coefficient of discharge of liquid independent of viscosity. The pump is driven by the rotational velocities of the blades for producing pressurized output. A spool mounted in bore of valve, moves between two positions with respect to the hydraulic signal coupled it to control flow of fluid. A pair of loads spaced apart along the longitudinal axis of spool. The hydraulic signal causes the land to move to control the output of control signal. The displacement control element is an antistall piston (60) which varies the displacement of hydraulic pump in secondary rotational velocity range which is below the primary range. A stroking piston (62) responds to control signal to vary piston displacement during primary velocity range.    DESCRIPTION OF DRAWING(S) - The figure shows the illustration of variable displacement hydraulic pump.    Antistall piston (60)    Stroking piston (62)    Pressure dropping orifice (114)