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Welcome to Arrow Guide. In this video,
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we'll explore the aircraft propeller
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governor, a critical component in
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constant speed propeller systems that
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manages engine RPM automatically. Let's
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dive in. A propeller governer is an
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engine RPM sensing device combined with
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a high-pressure oil pump. It plays a key
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role in constant speed propeller systems
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by keeping the engine running at a set
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speed even when flight conditions
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change. It works by adjusting the oil
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flow to a hydraulic piston connected to
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the propeller blades. This changes blade
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pitch, which in turn regulates engine
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load and speed. In a constant speed
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propeller system, the governor typically
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supplies oil to move the blades into a
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low pitch position. However, a few
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non-feathering propeller designs may
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operate in the opposite direction. The
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blade angle is controlled by a
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combination of mechanical, aerodynamic,
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and hydraulic forces. Let's break down
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Centrifugal twisting moment. A component
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of the centrifugal force acting on a
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rotating blade that tins at all times to
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move the blade into low pitch. Propeller
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governor oil on the propeller piston
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side balances the propeller blade
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flyweights which moves the blades toward
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high pitch. Propeller blade flyweights
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always move the blades toward high
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pitch. Air pressure against the
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propeller piston pushes toward high
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pitch. Large springs push in the
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direction of high pitch and feather.
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Centrifugal twisting force moves the
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blades toward low pitch. Aerodynamic
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twisting force moves the blades toward
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Not all of these forces are equal in
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strength. The governor oil pressure
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acting on the piston is the most
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powerful. This piston is mechanically
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linked to the blades. So as it moves, it
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rotates the blades accordingly. If the
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governor reduces or removes oil
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pressure, the opposing forces like
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springs and centrifugal twisting take
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over and move the blades in the opposite
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direction. The propeller governor used
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in constant speed systems is engine
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driven and single acting. It receives
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oil from the engine's lubricating system
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and boosts its pressure to the level
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required to operate the pitch changing
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mechanism. The governor includes several
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key components. Gear pump boosts engine
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oil pressure. A pilot valve controlled
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by rotating flyweights that directs oil
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to or from the propeller piston. A
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relief valve system that regulates the
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operating oil pressure inside the
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governor. A speed sensitive flyweight
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assembly that tells the pilot valve
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which way to move. A key part of this
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mechanism is the speeder spring which
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resists the outward movement of the
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flyweights as they spin. The tension on
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this spring can be adjusted by the
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propeller control on the control
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quadrant. The tension of the speeder
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spring sets the maximum RPM of the
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engine in the governor mode.
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When RPM climbs to that set point,
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centrifugal force pushes the fly weights
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outward, overpowering the spring. The
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pilot valve shifts, oil is released from
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the propeller piston, blade pitch
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increases, and the added load slows the
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engine back toward the selected speed.
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Conversely, if RPM falls below the set
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value, the spring wins, the pilot valve
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meters high pressure oil back into the
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piston, pitch decreases, and the engine
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accelerates. By constantly metering oil
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into or out of the propeller piston, the
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governor keeps the opposing forces in
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balance and holds the blades at the
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exact angle required for constant speed
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The governor operates in three
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conditions, under speed, over speed, and
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on speed. When the engine runs slower
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than the RPM set by the pilot through
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the propeller control, the governor
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enters an under speed condition. In this
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situation, the centrifugal force on the
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flyweights is too weak to push them
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outward. As a result, the speeder spring
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pushes the pilot valve downward. This
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downward motion opens the governor's oil
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metering port, allowing high pressure
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oil to flow into the propeller piston.
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As oil fills the piston chamber, the
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blades shift to a lower pitch angle,
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reducing aerodynamic resistance. This
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lightens the load on the engine,
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allowing it to speed up and return to
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the target RPM. This typically happens
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when nose of the aircraft is raised or
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the blades are moved to a higher blade
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angle. This increases the load on the
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engine and the propeller tries to slow
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down, but the governor senses this drop
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and responds by lowering blade pitch to
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maintain a steady RPM. When the engine
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RPM rises above the value set by the
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pilot, the governor enters an oversp
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speed condition. In this state, the
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centrifugal force acting on the
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flyweights becomes greater than the
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opposing speeder spring force. This
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causes the flyweights to tilt outward,
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lifting the pilot valve. The upward
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movement of the pilot valve opens the
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governor's metering port, allowing oil
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to flow from the propeller piston. As
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oil leaves the piston chamber, the
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propeller blades shift to a higher pitch
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angle. This increase in pitch raises
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aerodynamic drag, which helps to slow
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down the engine RPM, returning it to the
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selected setting. This is how the
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governor responds to an oversp speed
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condition by adjusting blade pitch to
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stabilize engine speed. When the engine
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is operating at the RPM set by the
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pilot, the governor is said to be in an
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onsp speed condition. In this balanced
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state, the centrifugal force from the
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flyweights is equal to the opposing
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force of the speeder spring. As a
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result, the pilot valve remains centered
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and no oil is directed to or from the
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propeller piston. Because the oil flow
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is neutral, the blade pitch stays
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constant and the propeller maintains the
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selected RPM. However, if anything
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disturbs this balance, like a change in
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aircraft attitude or the pilot adjusting
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the propeller control, the system will
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shift into an under speed or over speed
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condition and the governor will respond
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Most propeller governors can maintain
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RPM within a range of about 200 RPM.
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Beyond that, they lose control accuracy.
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Some aircraft include oversp speeded
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governors, backup protection against
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excessive RPM, feathering systems for
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shutting down engines in flight,
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synchronizing units, match multiple
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angines prop speeds. To wrap up, the
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propeller governor is an automatic RPM
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controller. It adjusts blade pitch using
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oil pressure and fly weights. The system
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keeps RPM constant even when flight
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conditions change. It's a key part of
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constant speed propeller operation and
