A negative torque sensing and control system is disclosed which is useful with a differential geared or fixed shaft gas turbine engine of the type installed in general aviation aircraft. Negative torque is sensed in the gear train between the propeller and the aircraft engine whenever there is a powerplant failure. When the reverse torque exceeds a selected threshold, hydraulic valves are actuated which remove oil pressure from the pitch control mechanism of the propeller. Loss of oil pressure causes the propeller to assume the feathered position.
An alternator, powered by a wind rotor having pitch changeable blades, is maintained at a fixed speed despite variations in wind speed and cyclic perturbations in rotor shaft speed due to rotor dynamics. In one embodiment, a geared speed increaser, coupling the rotor to the alternator, is mounted for reversible rotation relative to the rotor shaft. A fluid transfer means, such as a torque motor, coupled to a pressurized accumulator, applies such a torsional reaction to the speed increaser to permit its rotation at a rate which accommodates the difference between the instantaneous rotor shaft speed and that rotor shaft speed corresponding to the alternator's fixed speed. The fluid transfer means and accumulator means together permit a maximum angular displacement of the speed increaser sufficient to provide a time interval in which the rotor blade pitch may be corrected and the rotor shaft returned to normal speed. Pitch changes are effected, in part, responsive to rotation of the speed increaser.
An improved electronic hydraulic propeller control designed as a retro-fit kit for existing Hamilton Standard Division 54460 and 54H60 propeller controllers includes an apparatus for controlling the pitch angle of a propeller blade. The retro-fit kit includes an electro-hydraulic servo valve, an electronic controller, a protection valve, and a propeller maintenance interface panel. These components functionally replace the existing hydromechanical propeller control system without reconfiguration of the existing interface. The apparatus converts mechanical inputs of the propeller and airframe systems to electronic signals, which can be measured by the electronic control. The apparatus also receives and converts the electronic control's commands into hydraulic pressure and flow changes through an electro-hydraulic servo valve. The electronic controller performs the required calculations to interpret and then react to changes in the propeller/airframe systems. The electronic controller has two channels in a master/slave configuration to provide back up control of 90% of all functionality. Back-up systems are implemented through a protection valve, which can override hydraulic inputs from the electro-hydraulic servo valve. The propeller maintenance interface panel provides a link between the aircraft personnel and the propeller system to allow for calibration, fault interrogation, and real time data display.
Overspeed conditions in a ram air turbine are eliminated through a novel blade pitching mechanism. The mechanism includes a rotatable shaft with a hub mounted thereon for rotation therewith. The hub rotatably mounts at least one blade and a hollow blade pitch control shaft extends generally concentrically about the rotatable shaft and is mounted for reciprocating movement in a path toward and away from the hub. A reciprocating to rotary motion converting mechanism interconnects the control shaft and the blade so that the pitch of the blade can be controlled by controlling the position of the control shaft in the path. A first motor is provided for incrementally moving the control shaft within the path and a second motor is provided for rapidly moving the control shaft within the path to a position therein corresponding to a feathered position of the blades.
