Turbine Aircraft Systems - Propeller Flashcards
What is a propeller governor?
A governor is an engine RPM-sensing device and high-pressure oil pump. In a constant-speed propeller system, the governor responds to a change in engine RPM by directing oil under pressure to the propeller hydraulic cylinder or by releasing oil from the hydraulic cylinder. The change in oil volume in the hydraulic cylinder changes the blade angle and maintains the propeller system RPM. The governor is set for a specific RPM via the cockpit propeller control, which compresses or releases the governor speeder spring. Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 15). Aviation Supplies & Academics, Inc.. Kindle Edition.
Explain the “beta range” of operation on a turboprop engine.
The beta range of operation consists of power lever positions from flight idle to maximum reverse. Beginning at power lever positions just aft of flight idle, propeller blade pitch angles become progressively flatter with aft movement of the power lever until they go beyond maximum flat pitch and into negative pitch, resulting in reverse thrust. In a fixed shaft/constant-speed engine, the engine speed remains largely unchanged as the propeller blade angles achieve their negative values. Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (pp. 15-16). Aviation Supplies & Academics, Inc.. Kindle Edition.
Explain the term “reverse pitch.”
In the “reverse” pitch position, the engine/propeller turns in the same direction as in the normal (forward) pitch position, but the propeller blade angle is positioned to the other side of flat pitch. In reverse pitch, air is pushed away from the airplane rather than being drawn over it and results in braking action rather than forward thrust of the airplane. It is used for backing away from obstacles when taxiing, controlling taxi speed, or to aid in bringing the airplane to a stop during the landing roll. Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 16). Aviation Supplies & Academics, Inc.. Kindle Edition.
Describe a typical autofeather system.
An autofeather system automatically feathers a propeller when engine power loss results in a propeller thrust drop to a preset value. This system is switch-armed for use during takeoff and can function only when the power lever is near or in the “takeoff” position. When an autofeather system senses an engine failure, it will automatically begin dumping oil from the propeller servo of the failed engine to enable the propeller to go into a feathered condition with assistance from feathering springs and counterweights. A very important feature on turboprop aircraft, considering the size of the propellers and the amount of drag they produce in the event of an engine failure. Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 16). Aviation Supplies & Academics, Inc.. Kindle Edition.
Explain how a propeller synchrophaser / synchronizer system functions.
A propeller synchrophaser/synchronizer automatically equalizes rotational speeds of both propellers by comparing the control engine’s propeller RPM/phase angle to the slave engine’s RPM/phase angle, electronically adjusting the prop governor of one engine to the other in order to keep the propeller RPM and/or blade phase angle relationship the same. Greatly reduces the noise level and vibration within the airplane and eliminates the unpleasant beat produced by unsynchronized propeller operation. Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 16). Aviation Supplies & Academics, Inc.. Kindle Edition.
What is a reduction gearbox?
The increased brake horsepower output of gas turbine engines requires reduction gearing to limit the propeller rotation speed (relative to the speed of the power turbine) to a value at which efficient operation is obtained. Whenever the speed of the blade tips approaches the speed of sound, the efficiency of the propeller decreases rapidly. Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 17). Aviation Supplies & Academics, Inc.. Kindle Edition.
