Variable-Pitch Propellers

• Ground-adjustable propellers must have their blade angles adjusted on the ground to achieve performance characteristics.
• Propeller blades set at a low angle maximizes climb rate, enabling the engine to rotate at maximum speed and produce the greatest power.
• Early variable pitch propellers were two-pitch, having a low-pitch setting for takeoff and climb and a coarse setting for level-out and cruising.
• The blade angle shouldn't cause the engine to overspeed, but can be increased for efficient cruising at high altitude.

Variable-Pitch Propellers

• Variable-pitch propellers can change the blade angle while rotating, optimizing performance for flight conditions.
• The number of pitch positions can be limited (two-position propeller) or fully adjustable.
• As a propeller blade angle increases, the angle of attack increases, resulting in more lift, drag, and horsepower necessary to turn the propeller at a given RPM.
• Since the engine outputs the same horsepower, the propeller slows down
• Decreased blade angle results in propeller speed increase, thereby controlling engine RPM.
• Propeller governors increase or decrease propeller pitch by decreasing blade angle during climbs, allowing consistent engine output.
• When an aircraft dives, the blade angle increases to prevent over-speeding, maintaining constant power output and throttle setting.
• Constant-speed propellers change blade angle to maintain consistent engine RPM.
• Blade angle increases or decreases with throttle changes to keep the same RPM selected by the pilot.
• Blade angle automatically adjusts with a governor.

Hydromechanical Variable Pitch Propellers

• Mechanisms that change propeller pitch are housed in the propeller hub and operated by oil pressure using a piston-cylinder.
• Linear piston motion is converted to rotary motion, which changes blade angle using mechanical linkages or gears.
• Oil pressure comes from the engine's lubricating system and is boosted by a governor pump for quicker pitch changes.
• The governor is geared to the engine crankshaft and senses propeller RPM changes, directing pressurized oil to operate the pitch change mechanism.
• A propeller governor maintains constant engine RPM.
• When rotor value decreases or increases past a pilot's selected setting, the pitch will change to compensate.

Constant Speed Principles

• Constant-speed systems permit pilots to select a suitable propeller speed for flight conditions and maintain that RPM automatically.
• The pilot increases power during flight, which results in decreased engine RPM
• To fix this, the blade angle increases, increasing the torque required to counteract this to spin the propeller.
• Using a constant, pilot-selected RPM, engine torque and aircraft speed can change, thereby achieving the RPM setting.
• During economical cruising, the pilot can throttle back to the desired manifold pressure for cruise conditions and decrease the propeller's pitch while maintaining the RPM selected by the pilot.
• Full-feathering propeller systems are suitable for twin-engine aircraft.
• The propeller of an idle engine can rotate due to the aeroplane's forward movement, which causes increased drag.
• Feathering turns the propeller to a very high pitch, with blades almost parallel to the airstream, eliminating unequal drag forces.

Pitch Change Mechanisms

• The pitch of the propeller blades are changed through hydraulic, single-acting systems.
• Counterweighted systems reduce pitch with oil pressure; non-counterweighted systems increase it.
• Single-acting propeller systems use governor oil pressure to move a piston, countered by blade centrifugal twisting moment or counterweights.
• High-pressure oil moves the piston to adjust the blades toward high or low pitch based on the system.
• Oil flow stops when forces equalize, maintaining the blade pitch.
• Oil flows out of the propeller when the governor decreases pitch in non-counterweighted systems or increases it in counterweighted, returning oil to the engine sump.

Counterweighted and Non-Counterweighted Mechanisms

• Two basic types of constant-speed propellers includes counterweighted and non-counterweighted designs.
• As counterweight propellers rotate, centrifugal force moves the weights, increasing the pitch of the blades.
• The Pitch is controlled by a combination of oil pressure to increase pitch, and centrifugal turning moment and the force of an internal spring to decrease the pitch.

Moving Cylinders and Pistons

• Pitch change mechanisms come in two possible forms: moving cylinder and moving piston.
• Both types can be counterweighted or non-counterweighted.
• Counterweights turn blades to high pitch and adjust them to the feather position in mechanisms designed to do so.

Double-Acting Pitch Change Mechanisms

• Propellers on larger engines use more complex mechanisms due to engine specifications.
• Governors regulate oil pressure differences across the piston pushed through the engine reduction gear shaft's bore.
• Springs act on the piston, and counterweights are fitted to feather the propeller during flight engine failure.

Constant-Speed Propeller Systems

• The engine is powered by the accessory gearbox and powered by the propeller reduction gearbox on a free-power turbo-prop engine system.
• Pilot valve position dictates oil flow to the propeller or a neutral, no-flow position.
• Varying oil flow conditions correspond to increased, decreased, or constant pitch for the propeller blades.
• The propeller governor controls propeller pitch, maintaining constant engine speed.

Governors

• The propeller and governor are key components of an engine system.
• The governor, geared to the engine/propeller, drives the gear pump and flyweight assembly.
• The gear pump boosts engine oil pressure for a quick propeller response.
• Flyweight assembly speed varies with propeller speed, controlling the pilot valve's position.
• Pilot valve position directs oil flow to/from the propeller, resulting in increased/decreased/constant pitch.
• The governor maintains constant engine speed via propeller pitch control with the engine speed selected in the cockpit.
• The governor combines a gear-type oil pressure boost pump and a spring-loaded governor to control oil flow.
• The boost pump elevates engine oil pressure and the spring-loaded governor manages a pilot valve for oil delivery to the propeller which is managed through ports in the drive shaft.
• The governor mechanism consists of L-shaped flyweights that lift under a ball-race in the pilot valve.
• Flyweights act against a pressure spring controlled from the cockpit.
• The 'speeder spring' is the typical name given to these springs.
• Oil from the governor is bypassed through a relief valve when it is unused by the propeller.
• The feathering valve in the governor sometimes admits oil from the feathering pump to the propeller with spring-loaded valves normally supplying oil from the governor boost pump.
• The speed at which an engine produces the appropriate adjustments depends on the governor RPM, in conjunction with the governor spring setting, which keeps constant pitch.
• A decrease in engine speed causes the governor spring force to exceed flyweight force, causing the pilot valve to drop and allowing high-pressure oil to exit the propeller.
• Pushing the cockpit feathering button activates the and supplies the feathering pump high-pressure oil to the propeller governor's base.
• Feathering oil routes to the feathering valve, feathering the propeller in place of governor oil.

Overspeed Protection

• The overspeed governor is a backup to the propeller governor in the propeller's reduction gearbox.
• Its flyweights and pilot valve release oil from the propeller when the propeller RPM exceeds a set limit.
• Flyweights lift the pilot valve when the propeller speed hits this limit, releasing propeller servo pressure oil into the reduction gearbox sump, increasing the blade angle, adding more to the engine, slowing the propeller.
• Overspeed protection can reduce fuel to the engine, preventing the engine from driving the propeller to the overspeed condition.
• Overspeed governors remain idle during the engine's normal operation and serviceability is tested regularly.
• The overspeed governor includes an electrical solenoid, and is operated by a cockpit switch.
• This will test serviceability since it can be unwise by testing by testing too vigorously since this will damage either propeller and/or the engine
• Solenoids simulate overspeed by lifting the pilot valve and drain the pitch change mechanism requiring propeller coarse pitch/feather movement.
• The test is a component of of pre-flight inspections by the pilot.

Pitch Locks

• Hydraulic pitch locks change pitch in double-acting propellers, suited for larger engine requirements.
• Construction mirrors single-acting propellers, but the cylinder is closed at both ends and the piston is moved by oil pressure.
• Links from the annular piston connect to a pin at each blade's base.
• Pistons use pins and rollers that connect to a cam track and bevel gear, with the bevel gear meshing with the bevel gear at each blade.
• Axial piston movement rotates the gear, thereby altering bade angle.
• Operating oil is conveyed to through concentric tubes in the bore of the engine reduction gear shaft.

Fine-Pitch Stops

• Fine-pitch stops reduce both the risk of propeller engine, as well as reduce the overall load during the starting and ground running phases.
• A spring collet supports in the flight fine pitch stop while the pitch lock piston remains forward.
• To use the ground fine pitch, a governor solenoid is energized, and oil pressure supports supporting the collet.
• Moving the throttles disarms the solenoid for take-off, and the pitch lock piston opens the spring collet when coarsen to constant speed.

Feathering

• Pilots feather the propeller, which stops the motor, by moving the propeller control lever through a gate in the quadrant,.
• This action allows oil to drain and fully raises the governor valve.
• This results in blades turning to a coarse (feathered) position with counterweights and a feathering spring.
• The double-acting propeller hydraulic actuation does not require assistance from springs or counterweights.
• Diagrammatically, double acting propellers use use a protected source of feathering oil, and includes a separate component of the main oil tank in a dry-sump lubrication system.
• Electrically-driven "Feathering Pumps" are used to send oil to the propeller.

Auto-feathering

• Autofeathering automatically feathers propellers using a torque switch and the aircraft's power levers are set above the idling range
• Engine torque needs to falls below a certain level.
• Closing the torque operates the feathering pump as well as the valve lifting solenoid within the governor.
• The solenoid directs the oil moving the governer to opening the ports from the feathering pump through the pitch change piston auto feather.
• Automating feathering, manual feathering isolates the engine, and is able to shut off the feathering pump effectively.

Unfeathering

• A propeller has to have oil pressure to unfeather, but this will only be possible if there is not oil pressure available because the engine is currently off.
• Starting a direct-coupled turboprop poses a risk for complete destruction due to the high resistance of the propeller.
• Similarly, attempt to start with a piston engine's propeller in feather can cause damage to the starter motor.
• Supplying necessary oil pressure to unfeather propeller comes from an electric pump or feather accumulator.

Reverse Thrust and Beta Control

• Beta controls all negative pitch angles, including ground fine and finer.
• The propeller system contains a ground flight-fine pitch stop allowing its descent, to a position/pitch below normal but safety measures will prevent that selection mid-flight.
• The throttle levers have either a mechanical gate or an electrical system.
• Oil pressure withdraws fine-pitch stop to increase pitch, switching lever operation to increase reverse power.
• Switches indicate stop withdrawal with warning lights.
• To reselect positive angle, the throttle has to be in normal idiling range, using oil to activate the system.
• Upon completion the blades move to an angle.

Beta Operation

• Beta range is for used ground operations; lowering the aircraft's speed after landing.
• Blade pitch is directly controlled by Power levers set below flight idle.
• System includes a system called a "coordinator" containing interlinked cams.
• Governor does not operate, instead a "beta tube" is used, controlling propeller pitch, based on pilots,input.
• Fuels input matches any needs by variations on the propeller Pitch.
• Beta stops, the system will go the to flight level, the govenor with be active in flight with the pilot.
• Coordinators can inverts control, with the blade angle increasing on rear thrust for engines with greater negative levels.

Hartzell Counterweighted Propeller

• Two Hartzell single-acting, counterweighted variations use pre-charged nitrogen pressure instead of a spring to push the piston and blades to coarse pitch, countered with oil pressure.

Dowty Rotol Double-Acting Propeller

• This Propeller is typically on commuter aircraft.
• Its pitch is controlled using propeller governor and counterweights.
• It is adjustable in the position for feathering, thrust and reverse thrust.
• The key components include Piston, cylinder and combinedyoke assembly
• The piston and yoke move together because the cylinder is up front but the yoke sits toward the inside.
• The system has has the propeller under normal pressure which allows correct pitch due to greater force than weights on the opposing sides.
• The piston and crosshead will move at same rate in response while the proppeller blades are turning and adjusting them.
• Pitch is related to output , piston up font blades, to alter blades using Beta tube by altering the angles.

Hamilton Standard Hydromatic

• The invention served purpose for use on multi-engine that came to light in the late the 30's.
• Added level of safety allowing pilots move blades for one to feather with and the angle was optimal
• In its most basic description, It is enclosed in a sealed with no arms.
• Propellers are secured using high stength shafts including rolling bearing, along with extending into root, all conneccted.
• The dome comes containing has segment bevel inner and oil boosted by valve.
• During underseed passages send oil the first time and then oil the drains
• Overspeed the oil engine boost is reversed and passes flows the other direction.

Electrically Operated / Controlled Propellers

• Hub on shaft with reversible motor/gear that rotates blades and receives power.
• Electrical brake prevents overrun.
• Engine-driven governors are controlled by a switch and supply oil to various sides of a piston to complete circuit for pitch changes.

Electric Control

• Electric control systems in multi-engine aircraft use a motor that controls each engine's contactor unit stator.
• Individual engine alternators drive the stator winding within contactor generating a frequency.
• A magnetic field is created around stator for frequency.
• This rotation can close circuit by to to switch motor , there provided various enable switch feathering action.
• Use hydro systems opposed the system is uncommonly.

FADEC Controlled Propellers

• The Full Authority Digital Engine Control (FADEC) system controls each aspect of the engine's electrical power, including from start to power off.
• The FADEC is an electrically operated servo valve using signals for thrust and lever conditions transmitted via transducers .
• An electronic system receives RPM, torque, and blade position inputs and is a computer that controls the engine's operation.
• The EEC housing has a dual two channel system can switch failure sensors that has any data failure computer to switch the other equal each start.
• EEC channels compute based information commanding the servo value take scheduler position.