Abstract: A heat exchanger includes a silicon nitride substrate. Electronic components may be surface mounted to the substrate. A fluid passageway in the heat exchanger allows a coolant to flow therethrough and carry away heat from the electronic components.

Abstract: A ceramic nozzle for a gas turbine stage of a turbomachine (e.g., a turbopump) includes a splined mounting surface. Ceramic splines on the nozzle mounting surface are interlocked with metal mating splines on a surface of a turbine housing to prevent the nozzle from rotating relative to the housing. Both sets of splines extend in a radial direction, are straight and have trapezoidal shapes in transverse cross-section. These splines maintain a constant contact angle during large temperature excursions, when inherent thermal growth mismatches between ceramic and metal occur.

Abstract: Blade pitch of variable pitch blades is changed by an actuator having first and second ac machines. The first ac machine is excited with ac power to apply a motoring torque to a control shaft of the actuator, thereby causing blade pitch to change in one direction. The second ac machine is excited with appropriate power to apply a braking torque to the control shaft, thereby causing blade pitch to change in an opposite direction. When the second ac machine is an induction machine, dc excitation will brake the control shaft. When the second ac machine is a synchronous machine, an ac excitation causing a retarding magnetic field will brake the control shaft.