17.3.1 Speed and Pitch Control Flashcards
What are the two main types of propellers?
Propellers are designed as either pusher or puller (tractor) propellers.
What are the categories of propellers?
They are subdivided into fixed pitch, adjustable pitch, controllable, and constant speeding propellers.
How are constant speed propellers categorized?
Constant speed propellers are categorized by the method of pitch change: hydraulic, mechanical, or electrical.
What is the pitch change range in constant speed variable pitch propellers?
The pitch can be adjusted between the low (fine) pitch stop and the high (coarse) pitch stop.
What is the feathering position in multi-engine aircraft?
Blades can be moved into the feathering position to produce as little drag as possible when the engine is shut down.
What is reverse thrust in large aircraft?
Reverse thrust is produced by turning propellers into reverse pitch, accelerating air forwards while the propellers turn in the same direction.
What types of propellers commonly have hydraulic pitch change mechanisms?
Constant speed propellers, constant speed propellers with feathering position, and constant speed propellers with feathering and reverse.
What is disc braking in propellers?
Some propellers can move their blades to a very fine (low) pitch on landing, causing a negative angle of attack and a braking force.
What is power ON braking in propellers?
Some propellers can move their blades to a negative angle, offering resistance to rotation and allowing controllable braking force.
What is feathering in the context of engine failure?
Feathering reduces drag by moving the propeller blades to a coarse pitch, placing the leading edge into the oncoming airflow.
What is the BETA range in propeller pitch control?
The pilot controls the pitch on the ground.
What is the ALPHA range in propeller pitch control?
Also known as the constant speed range, where the propeller governor controls the pitch.
What are single acting propellers?
Propellers that operate with oil pressure changing the pitch in one direction only, with the opposite direction resulting from spring force.
How do single acting propellers for single engine aircraft operate?
Oil pressure moves the blades to high (coarse) pitch, and springs move them to low pitch for optimal engine restart.
How do single acting propellers for multi-engine aircraft operate?
Oil pressure moves the blades to low (fine) pitch, while springs and torsional moments move them to high pitch.
What is the role of centrifugal force in pitch change moments?
Centrifugal force produces a pitch change moment that turns the blade towards low (fine) pitch.
What are double acting propellers?
Large propellers with pitch change mechanisms that allow oil pressure to change pitch in both directions.
What is the function of a propeller governor?
It senses engine RPM and directs oil under pressure to the propeller hydraulic cylinder to maintain RPM.
What are the components of a propeller governor?
Includes a spur gear type pump, a pilot valve, and a safety spring.
What happens during the on-speed condition of a governor?
The governor is balanced, and the pilot valve does not direct oil pressure, keeping the propeller blades from changing pitch.
What occurs during the under-speed condition of a governor?
The pilot valve drains oil from the pitch change cylinder, allowing the pitch change spring to reduce the propeller brake moment.
What occurs during the over-speed condition of a governor?
The pilot valve directs pressurized oil into the pitch change cylinder, increasing the propeller brake moment to decrease RPM.
What is the governor’s behavior when the engine is stopped?
No centrifugal force acts on the flyweights, causing the speeder spring to push the landed valve down.
What happens when the engine power is increased to cruise?
Increased power raises propeller RPM, causing the pilot valve to move up and bleed away fine pitch oil.
What is the purpose of feathering the propeller?
To prevent windmilling in the event of an engine stopping in flight.
What happens when speeder spring force on flyweights is reduced?
When the pilot increases fuel flow by moving the throttle forward, it results in an under-speed condition.
What is a single acting, constant speed, counterweight propeller control?
It involves a counterweight attached at the root of each blade that overcomes CTM and exerts a force to turn the blade towards a coarser blade angle.
How does the pitch change mechanism work in a counterweight propeller?
It consists of a fixed cylinder housing a sliding piston subjected to spring force on its front face and oil pressure on its rear face.
What is the role of oil pressure in the pitch change mechanism?
Oil pressure at the rear of the piston creates a force to counteract spring and counterweight forces, moving the blades towards fine pitch.
How does the governor pilot valve control the pitch change mechanism?
The governor pilot valve routes boosted oil pressure to and from the rear of the operating piston in the pitch change mechanism.
What happens when oil pressure is routed to the piston?
It pushes the piston forwards, overcoming spring pressure and counterweight force to turn the blades towards fine pitch.
What is the function of the electrical control in pitch change mechanisms?
It employs a reversible electric motor that drives a bevel gear through a high reduction ratio gear train.
How is electrical power supplied to the pitch change mechanism?
Electrical power is supplied through a slip ring and brush assembly.
What is the function of the solenoid operated friction brake in the motor?
It is released whenever a pitch change signal is received.
How does the electrically operated pitch change mechanism differ from oil operated mechanisms?
The governor pilot valve supplies pressure oil selectively to either side of a servo piston in the governor instead of the propeller.
What do flight deck switches allow in the pitch change mechanism?
They permit manual control inputs and feathering.
How do some aircraft synchronize engine speeds?
A single propeller pitch lever controls the speed of a master electric motor, with each engine driving a generator producing three phase alternating current.
What is the ARINC 429 system used for?
It is used to pass information in digital form for avionics data bus systems.
What does the ECU do in an integrated digital electronic control?
It receives pilot-initiated engine speed demands and computes them against allowable engine parameters.
What is the function of linear variable differential transducers (LVDT) in the ECU?
They measure servo valve movement and provide feedback to the ECU.
What happens if the ECU detects an exceedance in torque, speed, or EGT?
It exercises a limiting function to reduce the parameter back into limits.
How is the ECU powered during engine start-up?
It is powered through its test circuits by 28V DC power until the generator reaches sufficient output.
What does the ECU do during approach and landing?
The servo valve will be bypassed, and the blade angle will be under control of the flight deck power lever.
What happens if the ECU fails?
The entire system reverts back to manual control under a power lever.
