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Chapter 3 | Turbine Engine and Propeller Systems
There are several types of propeller synchronizing systems, but they fall into two basic categories: the propeller synchronizer, which matches propeller RPM between multiple engines, and the propeller synchrophaser, which in addition to matching propeller RPM also matches propeller blade positions between engines for maximum noise reduction. The “brains” of a propeller synchronizer or synchrophaser system is the control unit. The control unit compares electronic signals generated from two different magnetic “pick-ups,” one mounted on a stationary location, such as the propeller gear box assembly, and one mounted on the rotating propeller hub backplate. To control prop RPM, the prop synch control unit signals magnetic synchronization coils mounted on the propeller governor flyweights, thereby magnetically controlling them for precise positioning. In this way, whenever RPM or phase corrections are required, the governor is guided to adjust propeller RPM in a normal manner, by increasing prop blade angle to reduce RPM or decreasing prop blade angle to increase RPM. In-f light operation of prop synch systems is simply a matter of manually synchronizing the propellers within a predetermined RPM range and selecting prop synchro “ON.” The control unit will
then match prop RPMs between engines, greatly reducing propeller noise levels. Some prop synch systems require the pilot to manually synchronize the propellers to within a few RPMs of each other and then manually select propeller blade phase to the quietest blade position. Other units automatically adjust blade phase position to a predetermined setting that is identified as the quietest during flight testing (see Figure 3.23).
Propeller Supplement for Transitioning Military Jet Pilots Whether in fighters, bombers, or tanker/transport aircraft, most recent military pilots have spent their careers piloting pure jet aircraft. Therefore, if that’s your background basic propeller theory is probably not familiar to you. Like it or not, there is still a possibility that your first civilian flying job will be in a turboprop aircraft. Familiarity with basic propeller characteristics is important, especially in engine-out operations, because these characteristics affect both handling and performance of the aircraft. For this reason, we review some basic propeller theory for those who
primary propeller governor
primary propeller governor
prop synch control unit
Propeller synchronizer/synchrophaser systems reduce pilot workload, noise and “prop beat” by matching propeller speed and/or position. Prop synchronizers compare rpm of each propeller, then automatically adjust one primary propeller governor to match the other. Propeller synchrophasers additionally compare and adjust relative propeller positions to further minimize noise.
FIGURE 3.23 | Propeller synch on multiengine aircraft.
