17.3.1 Speed and Pitch Control Flashcards
(44 cards)
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.
