PROPELLER

PROPELLERSPurpose to convert engine power to useful force termed THRUST.

Driven by either a turbine or reciprocating (piston) engine.

As technician, you must know the basic principles, maintenance, and repair of the propeller system.

IntroductionEarly propeller designs from simple fabric covered wooden paddles.Flat boards which merely pushed air backward, produce lift and pull a/c forward.New materials produced thinner airfoil sections and greater strength.Made from aluminum alloys.Old propellers constructed from wood.Improved design prop. with new airfoil shapes, composite materials and multi-blade configurations.

TERMINOLOGIESBasic terms and component names.Propellers consist of at least two blades are connected to a central hub.Blade that is nearest to hub referred to blade shank.Furthest from the hub is blade tip.Hub assembly is bored out to create a hub bore which permit a propeller to be mounted on the engine crankshaft.

Basic term and component namePropeller acts as a rotating wing to produce lift and pull an a/c through the air.Propeller blades have a:-

- leading edge. - trailing edge. - chord line. - blade back. - blade face. - blade angle.

ContsLeading edge. - most forward of an airfoil section. Trailing edge. - most aft of an airfoil section. Chord line. - an imaginary line drawn through an airfoil from the leading to the trailing edge.Blade back. - curved or cambered side of the blade.Blade face. - the flat face.Blade angle. - the acute angle formed by a propellers plane of rotation and the blades chord line.@ Propeller plane of rotation is always perpendicular to the engine crankshaft.

ContsClamping rings. That secures the removal blades to a hub assembly.Blade root. Flanged butt or shoulder which mates with grooves in hub assembly.

Blade shank. Typically round and extends out to at least the end of the hub assembly. However, in some cases the shank may extend beyond the hub assembly and into the airstream. When this is case, blade cuffs to be installed.

ContsBlade cuff. - An airfoil shaped attachment made of thin sheets of metal, plastic or composite material mounted on the shank to increase flow of cooling air to the engine. - Mechanical clamping devices or bonding agent such as rubber base adhesive or epoxy adhesive are utilized to attach the cuffs to the blade.

Conts.Blade station. A reference position on propeller blade that is a specified distance from the center of the hub. Gradual distance of 6 ins. from center of the hub to the tip.

Propeller TheoryPropeller rotates through the air: - low pressure area is created in front of the blade. - high pressure area behind the blade. - allow a propeller to produce thrust.Amount of thrust produced depends on; - the angle of attack. - speed of the blade. - airfoil shape.

Conts.Angle of attack. The angle formed by the cord line and relative wind (airflow). Relative wind. Determined by the speed an a/c moves through the air and rotational motion of the propeller.Propeller rotates on a stationary a/c, the direction of the relative wind is exactly the opposite, to the rotational movement of the propeller.Therefore, propeller blades angle of attack is the same as the propeller blade angle.

ContsA/c moves forward, relative wind changes direction.The combination of the rotating and forward motion produce a resultant relative wind that is not directly opposite the movement of the prop. blade. The angle of attack less than the blade angle.

# - In flight, a/c moves fm. A to B, prop. moves C to D. Prop. trailing edge follow the path fm C to D which represent the resultant relative wind. - This results in an angle of attack less than the blade angle.

ContsBased on forward motion effect the relative wind acting on a prop. blade.Faster a/c moves through the air, the smaller the angle of attack of the blade.If prop. speed increases, the trailing edge of the blade travels a greater distance for a given amount of forward movement.Prop. speed increases, relative wind strikes the prop. blade at a greater angle and the angle of attack increases.

ContsThe most effective angle of attack is between 2 and 4 degrees.Any angle of attack exceeding 15 degrees is ineffective because of propeller blade stall.A fixed pitch propeller is designed to produce an angle of attack between 2 and 4 degrees at either a climb or cruise airspeed with a specified rpm setting.Propeller section near the tip rotates much faster than the hub.Difference in rotational velocity along the blade can be calculating the circumference of the arc traveled by a point on that segment.Formula for blade velocity :- 2r

ContsFormula for blade velocity; 2r Circumference multiplied by engine rpm to find velocity.Blade velocity at point 18 ins. rotates at 1,800 rpm. velocity = 2r x rpm. = 2 x 22 x 18 x rpm 7 = 113.1 x 1800 = 203,575. Convert to miles per/hr divided by 63,360, no. of ins. in one mile. multiply by 60, the no. of mins. in one hour.

Velocity = 203,575 x 60 63,360 = 192.7 m/hr.

ContsTo compensate for the difference in velocity along the propeller blade.Blade is set at a difference angle.The gradual decrease in blade angle from the hub to the tip is called pitch distribution. This give the twisted appearance.Blade twist provides a fairly constant angle of attack along the length of the blade.

ContsPropeller are built with a thicker, low speed airfoil near the hub and thinner, higher speed airfoil near the tip.Combined with blade twist, permit a propeller to produce relatively constant amount of thrust along the propeller blades entire length.

FORCES ACTING ON A PROPELLERRotating propeller is subjected to many forces that cause tension, twisting and bending stresses within the propeller.

Centrifugal force.Causes the greatest stress which tries to pull the blades out of the hub. The amount of stress can be greater than 7,500 times the weight of the blade.

Thrust bending force.Force tends to bend the propeller blade forward at the tips.Occurs because blade are thinner at the tip. Thrust produced at the tip to flex the blade forward.Its also opposes centrifugal force to some degree.

Torque bending force.Air resistance opposes the rotational motion of the prop. blade.Force tends to bend the blades in the opposite direction.

Aerodynamic twisting force.Force tends to increase a blade angle.Help to change the blade on a propeller.

Centrifugal twisting force.Centrifugal force tries to decrease blade angle. Its also known as CTM.At operational speed centrifugal twisting force is greater than aerodynamic twisting force.

Blade vibration.Vibration occurs due to the aerodynamic and mechanical force that are present.Ex. aerodynamic forces tend to bend blade forward at the tips producing buffeting and vibration. On the other hand. mechanical vibration caused by the power pulses in a engine. Mechanical vibrations more destructive than aerodynamic vibrations.Engine power pulses tend to create standing wave patterns that can lead to metal fatigue and structural failure.Most critical location is about six inches from the blade tips.

ContsCritical range. - Is the operational range at which could result serve propeller vibration. - Combination of engine and propeller is indicated on the tachometer by a red arc. - Engine operation in this range must be limited to a brief passage from one rpm setting to another. - Extended period can lead to structural failure of propeller or a/c.

PROPELLER PITCH a) Geometric pitch. b) Effective pitch. c) Slip.

PROPELLER PITCH - The theoretical distance a propeller advances longitudinally in one revolution. a) Geometric pitch. - Define as the distance a propeller move forward in one revolution and did not encounter any loss of efficiency. b) Effective pitch. - Actual amount a propeller moves in one revolution.

d) Slip. - Is the difference between geometric pitch and effective pitch. - Propeller slip represents the total losses caused by inefficiencies. - If prop has a geometric pitch of 50 ins, its should move 50 ins in one revolution. - If a/c moves only 35 ins the effective pitch is 35 ins or 70% effective. - Slip represents 15ins or 30% loss of efficiency. - Most propellers are 75 to 85 % efficient.

PROPELLER CLASSIFICATIONSPropeller are typically classified according to their position on the aircraft. a) Tractor. - propellers are mounted on the front of the a/c and pull the a/c forward.

advantage:- - lower stresses are induced in the propeller as it rotates in relatively undisturbed air.

a) Tractor type propeller.

PROPELLER CLASSIFICATIONb) Pusher. - propeller are mounted on the aft end of the a/c and push the a/c forward.

disadvantage:- - little propeller to ground clearance. - subject to damage from rocks, gravel small objects that are dislodged by wheels are thrown or drawn into a pusher-type propeller.

Pusher type propeller

ContsPropeller are classified by the method used to establish pitch.Classification are:- a) Fixed pitch propeller. b) Ground adjustable. c) Controllable pitch. d) Constant pitch. e) Reversible pitch. f) Feathering propeller.

Contsa) Fixed pitch propeller. - Propeller are designed for a particular a/c to produce optimum efficiency at a specific rotational and forward speed. - A fixed pitch propeller with low blade angle often called climb propeller, provide the best performance for takeoff and climb. - A fixed pitch propeller with high blade angle often called a cruise propeller, for high speed cruise and high altitude flight. - Change in rpm or airspeed reduces the efficiency of the propeller.

Conts b) Ground adjustable propeller. - Similar to fixed pitch propeller, blade cannot be changed in flight. - Blade angle to be changed on the ground only (adjusted with eng stop). c) Controllable pitch. - Blade angle can be changed in flight between a minimum and maximum pitch setting to provide best performance for a particular flight condition. d) Constant speed propeller. - Sometimes referred to as automatic propeller. - Once pilot selects an operating rpm, propeller blades automatically adjust to maintain the selected rpm. - Pitch is control by a governor.

Contse) Reversible pitch. - Propeller blade can be rotate to a negative angle to produce reverse thrust. - Permits a shorter landing roll and improved ground maneuvering. - Reduce brake wear and aid in aerodynamic braking.f) Feathering propeller. - Ability to rotate the blade so the leading edge is pointed forward into wind. - Selected to feather when engine fail in flight. - Eliminates drag cause by propeller wind milling. - Prevent further damage to the engine.

Propeller Quizs.1. State the purpose of the propeller. ans. Convert eng horsepower to propeller thrust. 2. The curved or chamfered sides of the propeller are known as . ans. Blade back.3. What is blade angle? ans. Angle between chord line and relative airflow.4. At what blade angle for an a/c efficiently during takeoff and landing. ans. Low pitch.5. Names the forces acting on the propeller. ans. - centrifugal force. - thrust bending force. - torque bending force. - aerodynamic twisting force. - centrifugal twisting force. 6. What make the a/c moves forward as the propeller rotates? ans. When a/c rotates low pressure is created in front of the blade and high pressure behind the blade.7. Where is the greatest force occurs at propeller and what cause the this stress? ans. At the propeller hub and cause by centrifugal force.8. What force that tends to increase propeller blade angle? ans. Aerodynamic twisting force.9. Actual distance of an a/c moves forward in one revolution of the propeller known as ? ans. Effective pitch. 10. What is the propeller classifications? ans. Classify by pusher or tractor propeller.11. The most forward edge of the blade aerofoil section is; ans. Leading edge.12. What is chord line? ans. An imaginary line drawn from leading edge to trailing edge.

PROPELLER CONSTRUCTIONPropellers are made of:-a) Woodb) Aluminum.c) Steel.d) Composite material.

a) Wooden propeller.Made from hardwood such as birch, mahogany, maple, cheery, oak, and black walnut or any several others posses the flexibility and strength required. Wood must be free from grain irregularities, knot pitch pocket and insect damage.Constructed of min 5 layers, kiln-dried and laminated together with waterproof resin glue to prevent warp.Each layer of the same thickness. Alternate different layers of wood types may be used.

a) Wooden propeller. Once laminated it forms Propeller Blank (A).

The Blank then cut to shape (B).

The finish exact airfoil and pitch dimension is called White (C).

Center bore bolt-holes are drilled.

a) Wooden propeller. - Metal Hub assembly inserted into hub-bore to accommodate mounting bolts and face plate. - White is sanded smooth, glued with cotton fabric to reinforce tip sections, then dope to prevent deterioration. - Amour coated with black or grey plastic coating to provide additional strength against chipping.

a) Wooden propeller.Monel brass or stainless steel tipping applied to leading edge and tip to prevent damage from small stones.The metal is notched to the blade to permit metal edging to conform to the contour of leading edge.Drill three small holes using no. 60 drill 3/16 in deep into tip of each blade to drain moisture from behind metal tipping and allow wood to breath.

b) Aluminum Alloy Propeller.Thinner blade and more efficient.Much stronger and flexible to accommodate high engine horsepower.Blades less susceptible to damage from gravel and debris on ground operation.Small damage such as nicks, dents can be easily dressed out with files.It may be repitched to approved blade angle by certified propeller repair station.It is susceptible to damage caused by resonant vibration.It requires vibration test during certification process.It is high strength aluminum forging.It is ground to the desired airfoil shape and blade is twisted to desired angle.Heat treated to relieve internal stress.

b) Aluminum Alloy Propeller conts.New propeller need to balance horizontally and vertically.Vertical balance achieve by removing metal from leading and trailing edges or by adding or removing balance weight to side of propeller hub.Horizontal balance is achieved by placing lead wool in balance holes near the boss.Finally blade is anodized and painted.

Propeller DesignationFederal Aviation Regulation require all propeller be identified with:- - Builder name. - Model designation. - Serial number. - Type certificate. - Production certificate number if there is one.Most manufacture of fixed-pitch propeller stamp all the required information on the propeller hub.

Propeller Designation conts.Need to be familiar with the information provided on the propeller.eg. McCauley propeller 1A90/DM 7651. - 1A90 - basic design. - DM - type of crankshaft. - 7651 - diameter is 76 ins, and the pitch at 75 percent station is 51 ins.

Propeller Designation conts.Sensenich propeller designated:- - M74DM-61 - diameter of 74 ins. - D designation identifies the blade design. - M special hub design with mounting information. - 61 blade pitch in ins. At the 75 percent station. - Number 1 stamped at the blade roots identifies as blade no. 1.

ADJUSTABLE-PITCH PROPELLERThe design and construction of adjustable pitch propeller permit the a/c operator to change the blade angle.Offers the advantage of maximum propeller blade efficiency from propeller/engine combination.Modern adjustable pitch propellers permit pilot to change the propeller pitch in flight.First adjustable pitch propeller offered two pitch setting, low and high pitch setting.Present adjustable propeller pitch systems are capable of a range of pitch setting.

GROUND-ADJUSTABLE PROPELLERSAllows the blade angle to changed when a/c on ground and engine shut down.Found on old a/c.Consist of two aluminum or steel halves that are machined to form a matched pair.The interior of it half is machined for shank of blades to be held between two hub halves.Blade is machined with shoulder that fit into grooves of hub halves to prevent centrifugal force pulls the blades out of the hub.If wooden blade, the shoulders are cast or machined into a metal sleeve and fastened to blade shank by lag screws.

GROUND-ADJUSTABLE PROPELLERS conts.Once the blades are inserted between the hub halves, bolts are used to secured the hub halves when steel blades are used.Wood or aluminum alloy blades are used, either bolts or clamp rings may be used to hold the hub halves together.

CONTROLLABLE-PITCH PROPELLERSHave an advantage over ground adjustable propellers.Allows the blade angle to changed while in flight (rotating).Provides the best performances for particular flight condition.Types in used: a) Two position controllable propeller. b) Constant - pitch propeller.

a) Two position controllable propeller.Permitted pilot to select one of the two position low pitch or high pitch.Low pitch used during takeoff and climb. - engine max. rpm and full power.High pitch for cruised flight. - permit more efficient high-speed flight while increasing fuel economy.Primary components:- - propeller hub. - propeller blades. - piston assembly.At the center of the hub is the spider.Spider consists of two or three arms on which the blades are attached. Blades are made from an aluminum alloy and have hollow end which fit over the arms of the spider.Once the blades are inserted on the hub, counterweight brackets are attached to the base of each blade.

a) Two position controllable propeller contsHamilton-Standard propeller consists of two piece hub encloses the spider and holds the propeller blades in place.To allow blades to rotates between low and high pitch stop, each blade ride on a set of roller bearings, counterweight bracket is installed at the base of each prop. blade.Blade angle on Hamilton-standard is changed by combination of hydraulic and centrifugal force.Hydraulic force decrease the blade angle.Centrifugal force acting on a set of counterweight, increase blade angle.

Two position controllable propellerdecrease (low) blade anglehigh (increase) pitch position

a) Two position controllable propeller contsHydraulic force to decrease blade angle:- - eng. oil that flows out of the crankshaft and acting on a piston assembly that mounted on the front of the propeller hub. - eng. oil flows into the piston controlled by 3 ways selector valve from the cockpit. - Valve forward - decrease propeller blade angle. - oil is routed into the piston assembly to force the piston outward. - piston moves out, pulls the counterweights in and decreased blade angle. - oil pressure hold blades in position once the blades reach their low pitch stop.

a) Two position controllable propeller contsTo move the blades to a high (increase) pitch position. - propeller control lever is moved backward (aft). - rotate selector valve to release oil pressure in the prop. hub. - oil pressure removed, centrifugal force acting on the counterweights causes them to move outward. - rotate the blades to high pitch position. - oil is forced out from prop cylinder and returned to the engine sump. - blade stop rotating when they contact high pitch stops.

contsThe pitch stops on a two-position propeller can be adjusted.Adjust pitch stop nut to desired blade angle.Operational requirement:- - before engine shut down, propeller should be place in high pitch position, to protect corrosion, accumulation of dirt and prevent from congealed in cold weather (oil is out from piston).

b) Constant Speed Propeller.It also called variable pitch or controllable pitch propeller.Common type used on a/c today.Advantage:- a) converts a high percentage of engines power into thrust over a wide range of rpm and airspeed combinations. b) allow operator to select most efficient eng. rpm for given condition. c) it maintains selected engine rpm under all flight condition by means a governor automatically adjust prop. blade angle. d) low pitch for takeoff and land. e) high pitch for climb and cruise.

ContsAfter selecting a desired rpm during flight, an increase in airspeed or decrease in propeller load will cause; blade angle to increase as to maintain selected rpm.If reduction on airspeed or increase in propeller load will cause blade angle to decrease.

ContsConstant speed range (constant speed propeller) is the range of blade angle travel define by high and low pitch stops:a) RPM will maintain as long as blade angle not touching the high or low pitch stop.b) Once prop blades contact a pitch stop, the engine rpm will increase or decrease with changes in airspeed and prop load.If a/c speed decreases, rotate blade to contact low pitch, any further decrease in airspeed will cause engine rpm to decrease.As a/c accelerates, prop blade angle increases to maintain the selected rpm until high pitch stop is reached.Blade cannot increase any further and engine rpm increases.

ContsA/c equipped with constant-speed propeller, engine power output is control by the throttle and indicated by a manifold pressure.Propeller blade angle is controlled by a propeller control lever and the resulting change in engine rpm caused by a change in blade angle is indicated on the tachometer.Providing the operator a means of controlling both engine power output and propeller angle, for most efficient combination of blade angle and engine power output at all a/c flight conditions.

ContsEx. During takeoff; - engine to maximum power. - throttle and prop control fully advanced (blade low pitch). - engine turns to maximum rpm on takeoff. - Established in cruise flight; - throttle can be retarded for engine runs at a more economy speed. - prop angle can be increased to increase propeller efficiency for higher speed flight. note:- - when operating a constant-speed propeller at given rpm setting, there is a max allowable manifold pressure. - operating above this level may cause internal engine stress. - avoid high manifold pressure with low rpm setting.

Operating principlesMost constant-speed, non - feathering propeller; - rely on combination of hydraulic and centrifugal forces to change the propeller blade angle. high pressure oil to increase blade angle. centrifugal twisting force to decrease the blade angle.

Feathering propeller utilize counterweight and centrifugal force to pull the blades to high pitch.Oil pressure to force the blades to low pitch. to prevent confusion between the operation of feathering and non-feathering propellers, discussion will focus on non-feathering and non-counterweight propeller assembly.

ContsThe device that regulate the flow of high-pressure oil to the propeller is called governor.Governor does three thing:- a) boost engine oil pressure before it enters the propeller hub. b) controls the amount of oil flows to the propeller. c) senses engine rotational speed and adjust blade angle to maintain a constant rpm.Propeller governor is mounted either on the front of the an engine near propeller shaft or on the engine accessory case.Governor consists of: 1) gear-type boost pump. 2) pilot valve. 3) flyweight assembly.

Conts1) Gear-type boost pump. a) Installed in base of the governor. b) Boost oil pressure between 180 psi to 300 psi depend on the system requirement. c) Gear type boost pump (constant displacement pump). d) Incorporated with relief valve to prevent damage to seals and other components. e) Relief valve route excess oil back to the pump inlet.

2) Pilot valve. a) Responsible for routing oil into and out of the propeller hub. b) Pilot valve is a shutter valve type that covers and uncovers oil passages allowing oil to flow into or out of the propeller hub. c) Located inside the drive shaft extends into flyweight assembly where it rest on the toe of each flyweight assembly. d) Flyweight tilt in and out, the pilot valve up or down.

Conts3) Flyweight assembly. a) It senses engine speed. b) Consist of: i) Flyweight. - mounted on flyweight head. ii) Speeder spring. - is provided to adjust amount of pressure acting on the flyweights and pilot valve. iii) Flyweight head. - a set of flyweight mounted on it.Assembly driven by the same shaft that drive the boost pump. c) When flyweight tilt in or out will move pilot valve up or down to allow oil in or out of the propeller. d) Speeder spring adjust amount of pressure acting on flyweight and pilot valve.

3) Flyweight assembly conts.

When propeller control push forward low pitch position: a) speeder spring compressed. b) flyweight will tilt inward. c) pilot valve move down. d) no oil pressure into propeller hub.With no oil pressure acting on the pitch change mechanism in the prop hub, centrifugal twisting force hold the blades in the low position, typically used during takeoff with max eng power output.

Cont,sWhen propeller control pull aft. - speeder spring pressure decreased. - flyweight will tilt outward due to centrifugal force. - pilot valve move up. - governor oil pressure directed to propeller hub. - cause blade angle to increase. - RPM will decrease reduction of centrifugal force acting on the flyweights. - allow flyweight to tilt inward and lower pilot valve to cutoff oil to the propeller. - speeder spring pressure and centrifugal force acting on the flyweight balance, the governor is on-speed.

Cont,sOnce the rpm is selected, the governor automatically adjust the propeller pitch to maintain selected rpm.Changes in load and airspeed on the propeller will change in blade angle.A/c initiated in climb from level flight will decreased in airspeed and prop load increases.As engine speed decreases in turn reduces centrifugal force acting on the flyweight.Speeder spring pressure force the flyweight to tilt inward.Governor will be in an under-speed condition.Flyweight inward pilot valve moves down and oil is ported out of the prop hub back to the engine.

Cont,sAs the oil is ported out of the prop hub, centrifugal twisting force moves the blade to the lower pitch.Lower pitch reduces the load on the prop and allow the engine to accelerate.As the engine rpm increases, the centrifugal force acting on the flyweight also increases and cause the flyweight to tilt outward and return the governor to an on-speed condition.When airspeed increases or the load on the prop decreases, centrifugal force acting on the flyweight to increase.Flyweight tilt outward creating an over-speed condition. As the flyweight move outward, the pilot valve moves up and boost pump oil is directed to the propeller hub to increase blade angle.

ContsThe increased pitch increases the load on the propeller and slows the engine.As engine rpm decreases, the centrifugal force acting on the flyweight also decreases.Centrifugal force acting on the flyweight decreases, cause it to tilt inward and return the governor to an on-speed condition.Safety feature to protect engine from over-speed; - governor incorporate an adjustable stop screw that limits how low the blade pitch on a given constant-speed prop can go. - incorporate a balance speeder spring that automatically sets the governor to produce a cruise rpm should the propeller control cable break.

McCAULEY CONSTANT-SPEED PROPELLERS.Mostly used on light and medium size aircraft.Two types of constant-speed propeller.a) Threaded series. - uses retention nut which screws into the propeller hub and holds the blade in the hub.b) Thread less series. - employ a split retainer ring to hold each blade in the hub.Both use the same pitch change mechanism in the propeller hub.Method used to attach the propeller blades into the hub does differ.

ContsBoth series are non-feathering and non-counterweighted.Use oil pressure to increase the blade angle.Centrifugal twisting force and internal spring pressure to decrease (low) blade angle.- High blade pitch is selected:- high pressure oil is routed to the propeller hub.- it pushes against a piston.- overcome the spring pressure inside the hub and the centrifugal force exerted on the blade.- the piston slides back toward the hub.- rotate the propeller through blade actuating link to actuating pin on the blade butt.

ContsPropeller blades, hub and piston are made from an aluminum alloy.Propeller cylinder, blade actuating pin, piston rod and spring are made from chrome or cadmium plated steel.Most actuating links are made of a phenolic material to prevent metal particles from wear off the actuating links and trapped inside the propeller hub.To prevent pitch change oil leaking into the center of the hub and down the propeller blade, O-ring seals are installed.Propellers pitch change mechanism can be lubricated with grease.

McCAULEY GOVERNORSGovernors direct high pressure oil to the propeller hub to increase the propeller blade angle.This is directly opposite from the Hamilton-Standard system.The other thing is: - MaCauly governor oil pressure approximately 290 psi. - Hamilton-Standard oil pressure is 180 200 psi.Governor use a control arm instead of a pulley to adjust the speeder spring pressure acting on the flyweight and pilot valve.

McCauly non-feathering Governor

Governor contsFor safety purpose: - Governor control lever is spring loaded to the high rpm setting (low blade angle/max power output) should control cable break.Incorporated with high rpm stop to prevent propeller and engine from over speeding. Both high and low rpm stop arc adjustable by set screw on governor head.Depend on engine and governor combination, one turn (screw) will change the rpm 17, 20 or 25 rpm.Ability to interchange the governor with other.Full explanation of a given designation refer to McCauly maintenance manual.

HAMILTON-STANDARD CONSTANT-SPEED PROPELLERSTwo position counterweight propeller system transformed into a constant-speed propeller system by installed flyweight governor.Propeller used with Hamilton Standard constant speed is essentially the same counterweight propeller used as the two position propeller discussed earlier.Counterweight propeller used oil pressure to decrease (low or fine) blade angle.Centrifugal force acting on the counterweight to increase (high or course) blade angle.Governor divided into three parts; 1) Head - contains flyweight and flyweight assembly. 2) Body - house pilot valve. 3) Base - house booster pump.

Hartzell Constant-Speed PropellersWide used in modern a/c and share market with McCauly.Two type: A) Steel hub propeller. - Similar to the Hamilton- Standard constant-speed propeller. - Pitch change mechanism is exposed. B) Compact propeller. - Hartzel compact propeller is housed inside the propeller head. - Regardless of the type of hub used, model designation code stamps on both the propeller hub and the propeller blade.

A) Steel Hub PropellerIts pitch change mechanism is exposed.Its may or may not be counterweight.If has counterweights, use oil pressure to decrease blade angle and centrifugal force to increase blade angle.No counterweight, oil to increase and centrifugal force to decrease blade angle.Central component of a Hartzel steel hub propeller is a steel spider.Spider consist of central hub and two arms.Arms provided attachment for blades with bearing assembly that allow blades rotate to change blade pitch angle.

A) Steel Hub PropellerTwo pieces steel clamps use to screw blades on spider arm. Aluminum piston placed over the cylinder.Piston is connected to the blade clamps on each blade by a sliding rod and fork system. This way, as oil is directed into and out of the propeller hub will change the blade angle.

B) Compact Propeller.Pitch change mechanism is enclosed in the hub.Hub is smaller, lighter and more dependable.Hub is forged aluminum alloy as two separate halves.Each half is machined out so that the shank of each propeller blade can be held between the two hub halves.Entire pitch change mechanism can be contained.Bolts are used to secure the halves together.

B) Compact Propeller.Its utilized either a Woodward governor or a modified Hamilton-Standard governor.Woodward governor produce 275 psi of oil pressure from engine oil 60 psi.Hartzel governor pressure setting refer to Hartzel maintenance manual.

Feathering PropellersEngine fail in flight, propeller continue to windmill.Feathering help to eliminate drag created by windmilling propeller.Prevent further damage to the engine by rotate the propeller to 90 degree angle.Control in the cockpit, when selected to feathered position.Blade will move from low to high then to feathered position.If from high angle, blade will move from high pitch to the feathered position.On most system, feathering functions are independent.In other word, the operator can feather the propeller at any time.In fact, some system the propeller can be feathered without engine running.

Hartzel Compact Feathering Propellers.The constant-speed operation of a Hartzel compact feathering propeller is the same as the constant-speed model with one difference; - feathering propeller uses both governor oil pressure and centrifugal force to low blade angle. - nitrogen gas, an internal spring or counterweight to increase blade angle.

Another type:- high pressure nitrogen and mechanical spring to increase and feather.- high pressure nitrogen charge stored in the propeller hub.

Safety feature:- - Governor oil drop to zero. - Propeller automatically move to the feathering position. - Prevent windmilling and further damage to engine and drag.

ContsPrevent propeller from feathering on ground during shut down, most Hartzel compact propellers utilize an automatic high pitch stop.Latch mechanism is comprised of spring-loaded latches fastened to the hub which engage high-pitch stop plates bolted to the movable blade clamps.Propeller rotate above 800 rpm, centrifugal force allow the pin to overcome spring pressure and disengage the latches from the high-pitch stop plate. Propeller pitch may be increased to the feathering position.Below 800 rpm, the latch spring engage the latches with high-pitch stop and prevent the propeller pitch angle from increasing.To feather a Hartzel compact feathering propeller. - Control to feather position. - oil pressure out from the hub. - nitrogen charge and either spring pressure or centrifugal force rotate the blades to feather position. - the speed (time taken) depends on how fast the oil drain out. - Hartzel propeller takes about 3-10 sec to feather.

ContsUnfeathering.Propeller control to normal flight range and restart the engine.As engine turn, governor starts to unfeather the blades.Once partially unfeathered, the propeller start to windmilling and accelerate the unfeathering process.To facilitate engine cranking with blades feathered, the feathering blades angle is set at 80 to 85 at the point on the blade.Some a/c utilize accumulator to speed up the unfeathering.Accumulator stores oil under pressure until it is needed to unfeather the propeller.Accumulator allows operator to unfeather before start.

Unfeathering contsAccumulator stores oil under pressure until it is needed to unfeather the propeller.Accumulator allows operator to unfeather before start. One side of the accumulator is charged with nitrogen and the other is filled with oil.Normal operation, accumulator valve open, oil flows in.To feather valve closed, trap oil in accumulator.Control to unfeather, oil flows out to propeller hub and moves the blades to unfeather position.

HAMILTON-STANDARD HYDROMATIC PROPELLERA non-reversing, full-feathering propeller is made up of three major assemblies: a) Hub/barrel assembly. b) Dome. c) Distributor valve. - Not much in used today.

ContsHub/Barrel assembly.Its consist of:- - Two halves hub. - Spider. - Propeller blades.Each propeller blades has sector gear mesh with pitch change gear in dome assembly.Each blades slips onto spiders arm.Spider/blade assembly placed between two hub halves.To allow each blades to rotate freely within the hub and hold the blade in place, combination of bearing and spacers are installed between the blade butt and hub.

ContsDome Assembly.Houses the pitch mechanism:- - Piston. - Rotating cam. - Fixed cam.Dome assembly threaded into propeller hub.Oil pressure act on the piston to move it fore and aft within the dome.When piston move, a set of cam roller will rotate the rotating cam within the fixed cam.Rear of the rotating cam is attached with beveled gear meshes with blade sector gear, causes the blade angle changed as the cam rotate.

ContsDistributor valve.Acts as extension to engine crankshaft.Installed in the center of dome assembly.Purpose:- - to direct both governor oil and engine oil into and out of the dome assembly. GOVERNORS.A hydromatic governor contain high pressure transfer valve that disables the governor constant-speed function when the propeller is feathered or unfeathered.An electrical pressure cutout switch is located on the side of the governor.Cutout switch automatically stop oil pressure once the blades have reached their full feathered position.

ContsOPERATING PRINCIPLES.

Hydromatic propeller differs from other constant-speed propeller. - its has no spring or counterweights to change blade angle. - engine oil pressure act one side of the piston while governor oil pressure act on the opposite side.Depending on the propeller model, governor oil pressure can be directed to either the inboard or outboard side of the piston.For the purpose of this discussion; - Governor oil pressure to the inboard side of the piston while engine oil pressure to the outboard side. - engine oil pressure (60 90 psi) with centrifugal force decrease blade angle. - governor oil pressure (200 300 psi) increase blade angle.

ContsDuring constant speed operation. - governor oil pressure, controlled by the pilot valve. - if the load on the propeller or a/c speed increases, propeller rotate faster creating an over-speed condition. - centrifugal force tilts the flyweights outboard, raising the pilot valve. - governor boosted oil pressure is routed to backside of the piston. - at the same time, oil in front of the piston is routed through the distributor valve and back to the inlet side of the governor. - difference in oil pressure between the front and back sides of the piston cause the piston to move forward.

Conts- as the piston moves, it causes the cam rollers to move forward.- cam roller engage a set of slots in the rotating cam, movement of the cam roller causes the rotating cam to turn.- as the rotating cam turn, bevel gear on the cam engage the gears affixed to the blade and rotate blade to high pitch.- blade angle increase, rpm decrease and flyweights begin to tilt back to inward to lower the pilot valve.- the piston stops moving system return to an on-speed condition.

ContsWhen an under-speed condition exits. - centrifugal force decrease flyweight tilt inward. - pilot valve move down (lower), governor oil pressure from back side of the piston is ported back to the governor then back to engine. - at the same time, engine oil pressure continue to exerted on the front side of the piston. - back side pressure decrease below than the engine oil pressure and centrifugal force acting on the blades. - rotate cam in opposite direction (back). - propeller blade angle decrease. - blade angle decreases, rpm increases and flyweight tilt outward raise the pilot valve. - piston stop, system on-speed condition.

FEATHERINGUnlike most other feathering propeller rely (depend) on counterweight, spring or compressed nitrogen.Hydromatic propeller requires high pressure oil to feather the blade.Utilize high pressure oil to feather the blades: - consist of:- - oil reservoir. - electric pump. - shut-off switch. - feathering button.

ContsFeathering sequence;- feathering button depressed in the cockpit.- holding coil hold button in until feathering complete.- solenoid relay energized feathering motor.- feathering pump draw oil from reservoir and boost it to 600 psi.- oil shift the high pressure transfer valve and isolate the governor system.- auxiliary oil pressure flow through oil passage to in-board side of the piston, piston and cam rings move outward until propeller blades reach the feathered position.- when fully feathered, piston stop by high pitch stop.- oil pressure continue buildup and sense by oil pressure cutout switch on the governor.- reaches 650 psi, feather button holding coil opened and de- energize the relay and shut-off the oil pump.

Unfeather

ContsTo unfeather. - the feather button is pressed and manually held in to prevent it from popping back out when the pressure cutout switch open. - electrical oil pump, pumping auxiliary oil to the inboard side of the piston causing the pressure to built up. - pressure greater than spring pressure and oil pressure holding the distributor valve, distributor valve will shift. - allow high oil pressure to flow to outboard side of the piston. - a passage is provided to drain oil from the inboard side of the piston back to the engine. - piston move aft (backward) rotate blade to lower blade angle. - once the blade angle is decreased, propeller starts to windmill. - allowing the engine to be restart. - feather button is released and system return to constant-speed operation. - relief valve off-seats and release oil pressure over 750 psi from the outboard side of the piston and rotating cam contacts the low blade angle stop.

Turboprop aircraft

TURBOPROP ENGINE TPE-331

TURBOPROP ENGINE

TURBOPROP ENGINE

TURBOPROP PROPELLERIt is a new design and technique to improve reliability and efficiency of the propeller powered by TURBINE ENGINE.Basic design and operational characteristics are common to all turboprop engines.

Propeller Speed ReductionAlthough reciprocating engine and turboprop engine system are similar but there is a difference, mostly on operational.Turboprop engine operate at high rotational speed compared to piston engine.Reduction gear assembly is necessary to convert engine high speed, low torque to a usable low speed high torque.Reduction gear system perform under extreme operational condition.Turboprop engine operates more than 40,000 rpm, and propeller turns at approximately 2,200 rpm so reduction gear ratio for certain aircraft is about 14:1

Power SectionThe combination of reduction gear assembly and propeller referred as POWER SECTION.There are two methods used to drive a turboprop power section: a) Direct driven by integral turbine through fixed shaft. b) Driven by power turbine or free turbine. - No mechanically connection with the gas generator.

POWER SECTIONPower section generally refers to:a) Power turbine.b) Reduction gearbox.c) Propeller.

Propeller governingAll turboprop engine utilize constant-speed, feathering propeller and propeller are controlled by one or more governors.Use the same governing principle to control propeller pitch and maintain constant rpm.Propeller pitch change more extensively with turboprop engine to produce changes in thrust.Unlike reciprocating engine , turboprop engine takes more time to react to fuel flow and power changes.Due to slow reaction, gas generator speed is held constant while propeller pitch is varies to produce desired amount of thrust.

Reversible-Pitch PropellerIn addition to constant speed and feathering, most turboprop propeller is reversible.Capable of operating beyond the low pitch limits, blade rotate to a negative blade angle.Propeller thrust is directed forward instead of aft.Advantages of reversible:- - reduce a/c landing distance. - reduce brake wear. - improve landing performance. - better control taxi speed and back the a/c up. - improve maneuverability on ground.

Reversible-Pitch PropellerTurboprop propeller has two operating ranges:-a) Alpha range operating under constant- speed mode (from flight idle to full power or from 95 100% N1)b) Beta range operating on ground, when the blade is rotated so they produce zero or negative thrust. - beta range may be divided into two ranges; i) Beta for taxi range. ii) Beta plus power range.

Reversible-Pitch Propelleri) Beta for taxi range. - blade angle that fall between the bottom of the Alpha range to zero thrust blade angle. - used primarily for taxiing and gas generator operate at high rpm and limiting the amount of thrust produced by the propeller. - a/c operator has better control the a/c speed an the ground.

Reversible-Pitch Propeller ii) Beta plus power range. - represents the range of blade angle that produce negative thrust. - in this range power lever also control the fuel flows to the engine. - farther back you move the more reverse thrust produced. - power lever quadrant is generally either striped or a placard is provided.

Disadvantages of reversible propeller. = stir up FOD in front of the a/c, will be ingested into the engine. = damage the propeller blade due to FOD. = difficulties in rear viewing. = be accomplished on smooth, clean surfaces and limit the speed to a minimum. = moving backward rapidly and when brake applied, a/c nose to rise off the ground and cause the tail to strike the ground.

Note:- Reversing the propeller during flight is prevented by electro hydraulic stop.

Reversible-Pitch PropellerThe quadrant range for:-

Alpha range.

Beta range. a) beta for taxi range. b) beta plus power range. max pwr 90Alpha rangeflt idle 34 Grd. Idle 16 0 veBeta range.

Reversible-Pitch PropellerA reversible propeller is very similar to typical constant-speed propeller. i) Oil pressure used to either increase or decrease blade angle. ii) Combination of spring pressure, centrifugal force acting on counterweights and nitrogen pressure on the opposing side. The only difference between reversing and non-reversing propeller is the absent of fixed low pitch stop (blade can pass through it to reverse).Appropriate blade angle must be maintained by creating a hydraulic lock with the propeller governor can be change as necessary. Once a desired angle is achieved, oil pressure in the hub balances the sum of the acting forces acting on the propeller blade.Primary pitch lock mechanism prevent blade from rotating to reverse pitch.Secondary pitch lock as back up should primary system fails.

TURBOPROP FUEL CONTROLFuel control working conjunction with propeller governor to control blade angle.Speed above flight idle, power lever control fuel flow and propeller blade.When power lever advance further, more fuel flow and increase blade angle to maintain its optimum efficiency and vise-versa.Speed below flight idle, propeller blade angle is controlled by power lever (exclusively) and governor incapable handling it.

HARTZEL REVERSING PROPELLER SYSTEMThis propeller is used on Allied Signal TPE-331 and Pratt & Whitney PT6 engine.This engine is constant-speed engine; operate at or near 100% rpm throughout operational cycle.Reduction gear on the front of the engine with a fixed shaft coupled directly to the gas generator turbine.Its reduction gear ratio is about 14:1

HARTZEL REVERSING PROPELLER SYSTEMNegative torque sense (NTS) incorporated in reduction gear assembly to prevent propeller drive the engine.When engine power decelerated rapidly (by automatically increase the blade pitch) enough to prevent propeller drive the engine.If engine fail NTS senses the loss of engine torque and rotate the blade to high pitch position.Some engine are incorporated with Thrust Sensitive Signal (TSS) automatically feathers the blades should engine fails.

PropellerThe propeller used on a TPE-331 engine is a flange mounted three or four bladed Hartzel steel hub, feathering and reversing propeller.Blade is moved to low pitch and reverse by governor oil pressure.Centrifugal force acting on counterweight and spring pressure increase blade angle.Set of retractable pitch stop prevent blade to feather during shutdown.Spacer or Beta Tube in place of low pitch stop acts as reverse pitch stop.Beta tube serve as oil transfer tube between the propeller pitch control and propeller dome.

Propeller ControlDuring flight: - engine power, control by fuel control unit and propeller blade angle control by governor. - governor permits operator to set a desired engine rpm by direct oil into and out of the propeller hub and change the angle.During ground operation: - under speed governor control fuel flow to the engine (Beta mode).Propeller pitch control meter oil in and out of the propeller hub to control the blade angle, because propeller governor has no ability to select angle to reverse.

Cockpit Control Consist of two engine controls: a) Power lever. b) Speed or Condition lever.

Cockpit ControlPower lever has four position: a) Reverse. b) Ground idle. c) Flight Idle. d) Maximum.During flight power lever directly adjust fuel control unit.On ground power lever has three position connected to primary and under speed governor through mechanical linkage is to control rpm and manually cut-off fuel and feather the propeller. a) Cut-off. b) Low rpm. c) High rpm.

Cockpit ControlSome a/c feather valve connected to condition lever, some with separate feather handle.Moving condition lever fully aft, will feather the blade or moving the feather handle to feather position.During flight condition, lever is set by pilot and the propeller governor will maintain rpm by changing blade angle.In beta range condition lever adjusts underspeed governor on fuel control unit through power lever adjustment.

Cockpit ControlMost TPE-331 include an unfeathering button.Unfeathering switch or button used to unfeather the propeller, when attempting to restart the engine.Unfeathering switch is activated, electrical unfeathering pump forces oil into the propeller dome to rotate the blades out of the feathered position.

System operationTwo basics operating mode of TPE-331are; - a) Beta mode. - includes all ground operations: = engine starting. = taxing. = reverse thrust. - in most cases, the Beta range includes all power settings from 65 to 95 percent N1. - b) Alpha mode. - all operation from flight idle to full power or from 95 to 100 percent N1.To begin, TPE-331 is sitting at idle on an a/c with propeller blades resting against the pitch stop.

System operationOnce engine starts:- Propeller latches are retracted by easing power lever toward the reserve position.- Mechanical linkage connecting the power lever to the propeller pitch control (PPC) slides the follower sleeve in the PPC forward.- Open the port in the oil transfer or beta tube allowing high pressure governor oil to be ported to the propeller hub.

System operationOnce the governor oil reaches propeller hub, oil pressure overcomes both spring pressure and centrifugal force acting on the counterweight to force the piston outward.Piston move out, propeller blades move to shallow pitch, in turn removes the weight of the blades from the pitch stop.Weight removed, centrifugal force retracts the pitch stop.Beta tube is attached to the propeller piston; - propeller piston moves, the Beta tube also moves.

System operationPropeller blades angle will stop changing when the port in the Beta tube moves forward enough to be blocked by the follower sleeve.This is referred as neutral position and represents the point where oil pressure within the propeller hub balances both spring pressure and centrifugal force acting on the counterweight.

System operationOnce propeller reached to a lower pitch and the pitch stop retract, the power lever is move forward to increase blade pitch.As the power lever moves, a mechanical linkage pulls the sleeve in the propeller pitch control aft, unporting the Beta tube.Beta tube oil port open, oil is free to flow into the gear reduction case.Combination of spring tension and centrifugal force on the counterweight to force oil out from the hub to increase the blade angle.Blade angle increase, the propeller piston and beta tube moves aft until Beta tube return to its neutral position in the PPC.Blade angle change proportional to the degree of power lever movement.

System operation

System operationTake-off: - condition lever to high setting. - power lever to the flight idle.Condition lever in a high rpm position, under-speed governor is fully opened and no longer controls fuel flow.In addition, when power lever to FLT> IDLE, the followers sleeve in the propeller pitch control is slide forward that no longer cover the port in the Beta tube.This effectively eliminates the ability of the PPC to change the propeller pitch giving the propeller governor full control over the propeller blade angle.In this mode, power lever is used to control fuel flow from engines fuel control unit and has no effect on propeller pitch change.

System operationIn Alpha / flight mode. - Propeller governor adjusted by condition lever to set rpm setting. - Power lever control the amount of fuel delivered to the engine. - Power lever forward, increase fuel flow that will increase engine power. - Governor control constant rpm. - increasing engine power causes propeller governor to increase propeller blade angle. - decrease engine power causes propeller governor to decrease propeller blade angle.

System operationTo feather the propeller on TPE-331 engine: - condition lever is moved aft or pulled the feather handle. - this causes the feather valve to shift and allow the oil in the hub to return to the engine. - with no oil pressure in the hub, spring tension and centrifugal force acting on the counterweight rotate the propeller blades to the feather position.

System operationTo unfeather the propeller on TPE-331 engine. - activate an electric unfeathering pump in the cockpit. - pumps on, it pumps oil to the propeller hub forces the piston forward. - piston moves outward, the blades rotate out of the featherd position and into high pitch.As the blades unfeather, the propeller begin to windmill and aid in an air start attempt. - unfeathering pump can be used on ground to unfeather the propeller.

PRATT & WHITNEY PT6PT 6 is a free or power turbine engine.Produces more than 600 hp at 38,000 rpm gas generator speed.Free turbine engine, has no mechanical connection between gas generator and power turbine.Power turbine is driven by the hot gases produced by the gas generator section.The power is transmitted through a shaft to a reduction gear to drive the propeller.Reduction gear reduce propeller speed to 2200 rpm, from engine operation at 100% output.Main difference between free turbine and a fixed shaft engine is that a free turbine engine is shutdown, the propeller are placed in the feathered position.During normal engine start, the compressor and turbine are rotated while the free turbine remains motionless.This reduce the starter load and eliminates the need for a set of pitch stops.

PRATT & WHITNEY PT6 Propeller.Type in used is the Hartzel HC-B3TN-3.It is flange mounted, three blades, steel hub and reversible.Governor oil pressure to low or reverse blade angle.Feathering, spring and counterweight to high pitch and feather position.To provide blade angle information to the propeller governor and fuel control, a feedback ring or Beta slip ring is installed on the rear of the propeller assembly when operating in the Beta range.

PRATT & WHITNEY PT6 Governor.Utilize a primary and over speed governor, in some engine use topping governor.Located at 12 oclock position on top of the reduction gear case.Component include: - a gear-type oil pump. - rotating flyweight. - speeder spring. - pilot valve.In addition depending on model, governor incorporate either Beta valve or a Beta lift rod that control blade angle when propeller is operated in the Beta range.

GovernorPrecaution - in the event of primary propeller governor fails to limit the propellers speed to normal maximum rpm. A over-speed governor act as backup (rpm above 106%). - to prevent the propeller from over-speed by using a speeder spring and flyweight arrangement.Speeder spring tension cannot be controlled from the cockpit nor is it field adjustable.Adjustments by manufacture or approved repair station.

GovernorOperation of the over-speed governor. - speeder spring applies a predetermined amount of pressure to a set of flyweight. - engine accelerate, centrifugal force pulls the flyweight outward and raises a pilot valve. - engine speed exceeds its maximum rated speed, centrifugal force acting on the flyweights pulls the flyweights out to raise the pilot valve so oil can escape from the hub. - spring tension and centrifugal force acting on the propeller counterweights to increase the blade angle and slow the engine. To check the over-speed governors operation; - momentarily close toggle switch will activate the electrical test solenoid. - on ground engine running at high rpm and switch is depressed, the propeller maximum rpm will be less than the normal amount. - care should be taken, test switch is not released while power lever is advanced or a real over-speed will occur.

GovernorPrevent propeller overspeed condition, a fuel topping governor is installed. In the event propeller rpm exceeds the limit, fuel topping governor sense it and dumps a portion of the bleed air in the fuel control unit to tricked that the gas generator is not developing as much power as it really is and send less fuel to the engine.The engine gas generators rpm reduces, in turn reduces propellers rpm.

PRATT & WHITNEY PT6Fuel Control Unit. - it is installed on the rear of the engine. - it is linked through a cam assembly to Beta valve on the primary propeller governor and to the Beta slip ring on the propeller. - the purpose for interconnecting the fuel control unit with Beta valve and Beta slip ring is to provide input to the fuel control unit when operating in the Beta mode.

PRATT & WHITNEY PT6 Cockpit control.Cockpit control consist of:a) power lever.b) propeller control lever.c) fuel cut-off or condition lever.

a) Power lever. - it is connected to cam assembly and through mechanical linkages to the fuel control unit and Beta valve on the primary governor. - in the Alpha mode, power lever controls engine power output by adjusting the fuel flow to maintain desired gas generator speed. - Beta mode, power lever controls both the fuel unit and the propeller blade angle.

b) Propeller control lever.It is connected to the primary propeller governor.Adjusts the tension applied on the speeder spring.Full aft movement will dump oil pressure from the propeller piston to feather the blade.Full forward will cause oil pressure to be directed into the hub and decrease blade angle.

c) Fuel cut-off or condition lever. Utilized on reversing propeller installation. Has two function:- - i) positive fuel shutoff at the FCU for engine shutdown. - ii) sets the gas generators low and high idle rpm. = Low Idle provides 50% gas generator during ground operation. = High Idle provides 70% gas generator rpm during flight.

PT6 engine control

PRATT & WHITNEY PT6 System Operation.PT6 turboprop engine has two operation mode. 1) Alpha Mode. - all operation from 95 100%. 2) Beta Mode (Beta range). - all operation from 50 and 85%.To begin, engine not running propeller blades in the feathered position.To start; - power lever idle position. - propeller control lever in feather position. - condition lever - fuel cut-off position.Starter engaged and the N1 reaches to specified speed, move condition lever to Low Idle position. Engine starts and ready to taxi; - control lever moved to high rpm setting. - power lever adjusted as necessary for a/c taxi speed.

PRATT & WHITNEY PT6System Operation.Beta mode, the primary governor is in a under speed condition and pilot valve in the lowered position.This allows the power lever to control fuel flow and blade angle.As power lever moved aft into Beta range, Beta valve is pushed into the governor to allow governor oil into the hub.Oil in, piston moves outward and propeller to fine angle.As piston move outward, the feedback ring moves forward and beta valve to neutral position.

PRATT & WHITNEY PT6System Operation.Movement of power lever aft, increases fuel flow and reverse thrust during ground operations. Power lever forward to Beta range, Beta valve is pulled out of the governor.Oil is released from propeller piston.Centrifugal force acting on counterweight moves piston inward to increase blades angle.As piston moves aft the feedback ring moves aft until the Beta valve returned to the neutral position.

PRATT & WHITNEY PT6To feather. - propeller lever to full aft. - pilot valve in the governor rise allow oil in hub to return to the engine. - spring tension and centrifugal force acting on the counterweight rotate blade to feather position.

To unfeather. - the engine must first be started. - propeller control lever forward, out of the feather position. - pilot valve down, governor oil directed into the hub. - pressurized oil rotate the blades out from feathered position to the selected blade angle or governor rpm setting.

AUXILIARY PROPELLER SYSTEMS Purpose:-To improve propeller performance and enhance the a/c all-weather capabilities by: i) Reducing propeller noise and vibration. ii) Removing ice from propeller should it occurs.

Two types of auxiliary system: i) Synchronization system. ii) Propeller ice control system.

Synchronization System. This system is utilized to equalize the propellers rpm should the dissimilar rpm occur between engines. The matching of this rpm is called synchronize.

Types of synchronization system; a) Master motor synchronization. b) One engine master control system. c) Synchrophasing system. System control engine rpm, reduce vibration by setting all propeller at exactly the same rpm used for all flight operation except take-off and landing.

a) Master motor synchronization.Used in WW II four engine a/c.Consists of:- i) Synchronizer master unit (which consist of master motor). ii) Four alternators. iii) Master tachometer. iv) Tachometer generator. v) Contactor unit for each engine. vi) RPM master control lever. vii) Switches. viii) Wiring.

a) Master motor synchronization.When switch is activated the master motor in synchronizer master unit drives contactor units that electrically connected to alternator (three phase generator).The alternator is driven by engine accessory drive.The voltage produced by generator is directly proportional to engine speed.The desired engine rpm is selected manually by adjusting the rpm control lever until master tachometer indicates the desired rpm.Once engine is set, any difference in rpm between engine and master motor will cause corresponding contactor unit to operate the pitch change mechanism until engine speeds match.

b) One engine master control system.Today many twin engine a/c used this propeller synchronizer system.Consists of:- 1) Control box. 2) Master governor (on left engine (# 1 eng). 3) Slave governor (on right engine). 4) Actuator.Both governor incorporated frequency generator that produces frequency proportional to the engine rotational speed.

One engine master control system

Control box compares rpm signal from slave engine to rpm signal from master engine.If difference in engine speed exists, the control box will send signal to actuator to adjust the slave governor until engines match.The comparative circuit has limited range of operation in which the difference of slave engine to master engine within approximately 100 rpm for synchronization to occur.

c) Synchrophasing system.

It is a refinement of propeller synchronization system.Pilot can control the phase angle (angular difference in the plane of rotation between propeller blades) from synchrophasing control panel in the cockpit.It known as the phase angle.Can be adjusted by the pilot to minimizes noise and vibration levels.

c) Synchrophasing system.This system consist of magnetic pick-up device (pulse generator).Pulse generator on each engine is keyed to the same blade of respective propeller for comparison purposes.As the designated blade of each propeller passes the pulse generator, an electrical signal is sent to phasing control unit which determines the relative position of each respective propeller.A propeller manual phase control in the cockpit allows the pilot to manually select the phase angle.If a difference exits, the phasing control unit electrically drives the slave generator to establish the selected phase angle between propellers.

Propeller Ice Control Systems.Propeller are susceptible to ice buildups when flying in cool weather.Must be equipped with system to remove ice accumulation.Ice accumulation can distort a propeller blades airfoil shape and loss efficiency and thrust.Cause propeller blade unbalance and vibration.

PROPELLER ICE CONTROL SYSTEMPurpose:- - to improve a/c performance during flight in cold weather condition either to prevent or remove ice.Types:- a) Anti-icing prevents ice accumulation. b) De-icing removes ice after it has accumulated.

a) Fluid anti-icing system. Consists of:-

i) Rheostat in control unit, ii) Tank. iii) Pump. iv) Slinger ring. v) Feed shoes vi) Anti icing fluid either isopropyl or phosphate compound.

a) Fluid Anti-icing.Operation:- - Fluid is pumped out from tank to stationary nozzle behind the engine nose case. - From nozzle it enters a slinger ring (U-shape channel) mounted at rear of propeller assembly. - Due to centrifugal force the fluid is dispersed into delivery tube to feed shoes (narrow rubber strip from shank to 75% of propeller radius). - As anti-icing fluid flows along the channels the relative wind carries the fluid laterally over the leading edge of each blade. - Anti-icing fluid is isopropyl alcohol or phosphate compounds.

Electric De-ice.It is electrical operated.Consists of:- a) Power source. b) Power relay. c) Resistance heating elements. d) System controls. e) Timer or cycling unit.Resistance heating element may be mounted either internally or externally on each propeller blade.Externally mounted heating elements is called Deicing Boots.The deicing boots is bonded to each blade with approved bonding agent.System control consists of: a) On-off switch. b) Load meter. c) Protective device either current limiter or circuit breaker.The load meter monitors individual circuit current and verify proper timer operation.

System Operation.Switch on electrical power is supplied to propeller hub through a set of brush block and slip rings.Brush block mounted on an engine case just behind the propeller.Slip rings mounted on the back of propeller hub assembly.Flexible connectors on propeller hub transfer power from slip ring to each heating element.

System Operation.The icing systems are designed for intermittent application of power to heating element to remove small ice accumulation.Should ice accumulation is excessive the de-icing effectiveness is diminished. When base of the ice melts it becomes loose and due to centrifugal force the ice is flung off the blades.

System Operation.Proper control of the heating intervals is critical to prevent runback.Runback refers to a condition where melted ice reforms behind a blades leading edge.Heat should be applied long enough to melt the ice.Insufficient to evaporate the water can run back over unheated surface and freeze again.

System Operation.Runback may result in a dangerous build-up of ice on blade areas which have no de-icing protection.Prevent runback, heating intervals carefully control to avoid vibration.Cycling timers energize the heating element for periods of 15 to 30 sec with a complete cycle time of 2 mins.De-icing boots, check for proper warming sequences during pre-flight inspection by turning the system on and feeling the boots. (applied for short time only).

Propeller Inspection, Maintenance, and InstallationAs an aviation maintenance personnel, your knowledge, experience and familiar with propeller maintenance is required to perform routine maintenance.A certified mechanic with powerplant rating only are authorized to perform minor repairs and minor alternations to propeller.

Maintenance RegulationFAR Part 43, maintenance, preventative maintenance, rebuilding and alteration, defines the different classes of maintenance for propeller systems.Appendix D list the minimum requirement for 100 hr and annual inspection of propellers and their controls.

Example:- In between annual and 100 hr inspection, propeller assemblies must be checked for; - cracks, nicks and oil leakage. - inspect bolts for proper torque and safetying. - anti-icing system for proper/improper operations. - propeller control mechanisms for operation, travel and security.

Maintenance Regulation Appendix A of FAR 43 lists propeller major alteration and repair which must be performed by the manufacture or a certified repair station. Propeller major alterations include:- - changes in blade design. - hub design. - governor or control design. - installation of a propeller governor. - feathering systems. - de-icing systems. - parts not approved for the propeller.

Maintenance RegulationMajor repairs include:- - retipping. - replacement of fabric covering. - inlay work on wood propeller. - replacement of outer laminations. - repair of elongated bolt holes in the hub. - any repair to straightening, repair to or machining of steel hubs. - shortening, straightening of blades, and repairs to dents, cuts, scars and nicks on aluminum propellers. - repair and replacement of blades de-icing heating elements.

Inspection and maintenanceSpecific inspection items and minor maintenance depend on the type of propeller and its accessories.Always consults the appropriate aircraft or propeller maintenance manuals and service bulletins for specific instructions and service limits.

Wood PropellerFor both annual and 100hr inspection:- - check for cracks, nicks, properly torque and safetied bolts.If excessive vibration:- - remove propeller to check for elongated mounting bolts or proper balance.To facilitate an inspection:- - wood propellers may be cleaned with warm water and a mild soap, using brushes or a cloth.Common defect found:- - separation of the lamination. - dents or bruises on the surface. - cracks or scars across the blade back or face. - broken section, wrapping and worn or over size center bore and bolts hole.If a dent, bruise or scar is found on a blade surface, inspect the damage with magnifying glass while flexing the blade to help expose any cracks.

Wood PropellerWhen inspecting metal tipping look for:- - looseness or slipping. - loose screws or rivets. - cracks in the solder joints.If crack is found in a solder joint near the blade tip, it may be indication of wood deterioration. - closely inspect the crack while flexing the blade tip. - no crack, the joint may be resoldered. - tip should be inspected at regular interval.Blade installed on ground-adjustable propeller, special attention should be given to the metal sleeve and shank area.Any crack presence may indicate broken or loose lag screws.

Wood Propeller

RepairSmall cracks parallel to the grain or small cuts may be repaired by:- - working resin glue into the crack. - once glue is dry, sanded with fine sandpaper. - refinished with approved varnish or other coating.Tip fabric surface defects of in. or less:- - no breakdown in the wood structure. - filled with several layer coats of lacquer. - once lacquer dried, the defect should blend in with the fabric surface.Defects larger than in. referred to repair station.Repair must be done by a certified repair station or manufacture such as:- - separated on the outside lamination. - large cracks that require an inlay. - restoration of elongated bolt holes with metal inserts.Any repair work done a protective coating must be applied.Blades balance to be carried out and apply more protective coating as required to balance the blade.

Defects that cannot be repaired.For wooden propellers these include:-Crack or deep cut across the grain.A split blade.Separated lamination, except for the outside laminations of a fixed-pitch propeller.Empty screw or rivet holes.Any appreciable wrap.Portion of wood missing.Oversize crankshaft bore in a fixed-pitch propeller. Cracks between crankshaft bore hole and bolt holes.Cracked internal laminations.Oversize or excessively elongated bolt holes.

StorageWhen wood propeller in stored, it should be placed in a horizontal position to keep the moisture evenly distributed through the wood.Storage area should be cool, dark, dry and well ventilated.Do not wrap the propeller, that seals it from the surrounding airflow.Any airtight wrapping wood propeller promotes wood decay.

Aluminum PropellersThe properties of aluminum alloys make aluminum propellers durable and relatively inexpensive to maintain.Some types of damage can be serve enough to cause blade failure.Propellers must be carefully inspected at regular intervals.Any damage jeopardized the integrity of the propeller.Must be repaired before flight.

Blade InspectionFor both annual and 100 hrs inspection:- - check for cracks, nicks and properly torque or safetied bolts. Inspection with the blades in place or sometime required to be remove.Before inspection, clean with mild soap and water using soft brush or cloth to remove dirt and grease.Do not use acid or caustic cleaning materials, could lead to corrosion.Avoid using power buffers, steel wool, steel brush or abrasive that may scratch or mar the blades.Expose to salt water, flash/wash with fresh water.Aluminum blades, inspected for pitting, nicks, dents, cracks and corrosion.Inspect leading edge and blade face for damage.Use dye penetrant inspection for suspected crack area. Inspect the hub boss for damage and corrosion.Light corrosion can be cleaned with sandpaper, treated and painted to prevent corrosion.Propellers with damage, dimensional wear and heavy corrosion in the boss referred to a repair station for appropriate repairs.

RepairsSurface damage such as nicks, scratches or gouges (groove/cut/hole) on aluminum alloy blade to be repairs as soon as possible to eliminate stress concentration points.These helps prevent cracks and fatigue failure.Defects on leading or trailing edge can be dressed out using round or half round files to smooth contour.Repair of surface defects on aluminum blades must be parallel to the length of the blade.Maximum allowable size repair on a propeller edge is 1/8 in deep by no more than 11/2 ins in length.

RepairsRepair on surface and back of the blade with spoon-like riffle file.Max. allowable repair size on blade face or back is 1/16 in. deep by 3/8 in. wide by 1 in. long.Finished by polishing with very fine sandpaper.In a direction parallel to the length of the blade.Surface should be treated with Alodine, paint or other approved protective coating.Damage on the shank area cannot be repaired in the field and should referred to the overhaul facility.

Repairs

RepairsDamage in the propeller blades shank area cannot be repaired.Referred to the overhaul facility for correction action.Transverse cracks on aluminum alloy is unrepairable.Contrary to popular belief, bent blades can be repaired by:- - measuring the thickness of the blade where the bend is located. - determine the blade station (ctr of the hub and ctr of the bend located). - with center of the bend located, mark the blade one inch on each side of the bend and place the protractor tangent to the one inch marks to determine the bend angle. - any bend below the graph (chart) line is repairable. - above the line is unrepairable.Proper chart not available, take the measurements and contact propeller repair station before send for repair.Cold straightening repairs on bent aluminum propeller, send to repair station or manufacturer.Once repaired, cleaned with solvent to remove all dye penetrant painted with zinc chromate and two coat of flat black lacquer from 6 ins. station to the tip. Last 4 ins of the tip painted with zinc chromate primer and two coat of a high visibility color.

Repairs

Ground-Adjustable PropellersInspect closely on the Hub area for cracks.Use dye penetrant is recommended during routine inspection,100 hrs and annual inspection.To reduce wear and tear, disassembly is not recommended during inspection.

McCAULEY CONSTANT-SPEED PROPELLERSConstant-speed propellers require a more detail inspection.Oil leak from the propeller hub may indicate a defective piston-to-cylinder O-ring. - leaking O-ring can be change in the field as laid down in the service manual. - some model, must return to a propeller repair station. - any seal other than O-ring leaking require replacement by a propeller repair station.On certain model of McCauley, there is a hub breather holes are sealed and hub is partially filled with oil that is dyed red. - any evident red dye oil makes, indicate cracks and propeller should be removed from service.

Hartzell Constant-speed PropellersRequire the same types of inspection, maintenance and repair.Check on steel hub for cracks; - preferable method is magnetic particle inspection.Grease leakage cause by; - loose, missing or defective grease fitting or zerks (grease nipple / grease point ). - loose blade clamps. - defective blade clamps. - over lubrication on the blade to hub joint.If zerk fitting loose, missing or defective, it should be tightened or replaced.Loose blade clamps should be retorque and resafetied.Check blade angle does not change during retorque. Lubricating the blade-to-hub joints to prevent damage to the seal:- - remove one of the zerk and grease through the remaining zerk point. - service until grease comes out on the other end. - this prevent pressure buildup in the chamber and damage on the seal. - reinstall the zerk fitting, replace the protective cap and safety the cap to the zerk fitting. (if any).

Hartzell Feathering Compact PropellerInspection, maintenance and repair procedures is the same as constant-speed system.One additional check during 100 hrs inspection is the nitrogen charge within the propeller hub.If too low propeller not feather or response properly to constant-speed operation and tendency to overspeed or surge. If too high propeller system may not reach full rpm. -- may feather during engine shutdown.Checking nitrogen charge (pressure), ensure the blades are latched in the low pitch position.Any servicing follow the manufacturers instruction.

Hamilton-Standard Hydromatic PropellerInspection and check for proper operation, oil leak and oil lines for deterioration or abrasion.Oil leak in the propeller caused by a defective gasket or loose hard wear.Oil leak around rear cone usually indicates a defective spider-shaft oil seal.Leak from the barrel behind the dome leak from gasket or dome nut loose.From blade shank or barrel halves; - loose hub bolts retorque. - defective gasket replaced by overhaul facility.Lubricating oil from engine oil itself.

Propeller LubricationAll the adjustable pitch propeller system require inspection and servicing at regular interval.Lubricating or greasing is part of the servicing to be carried out.To reduces frictional resistance of the moving parts. Grease in use to service the propeller must have the proper anti-friction and plasticity characteristics.Specification of the lubrication and grease in use refer to manufacturers instruction (manual).

Steel and Composite PropellersPropellers are made of steel or composite material.May be cleaned and inspected in the same manner as wood or aluminum propellers.Cleaning techniques and inspection are unique to composite materials.Restricted to inspection, cleaning only and follow the manufacturers instruction.Any repairs made to correct the defect must be accomplished by repair station or the manufacturer.

Blade Cuff InspectionPropellers blades fitted with blade cuffs are to improve:- - airflow over the blade shank. - cooling airflow through the engine.Blade cuffs must be inspected and checked for:- - damage. - proper clearance.Longitudinal clearance of constant-speed propeller blades or cuffs must be at least in between propeller parts and aircraft stationary parts.Clearance must be measured with the propeller blades feathered or in the critical pitch position.

GovernorsInspection of governors is limited to:- - checking for oil leak. - security of mounting.Maintenance consists of:- - properly rigging the governor controls. - control freedom of movement. - removal and installation.Overhaul carried out by certified repair station or manufacturer.

BalancingExact propeller balance is critical to proper engine and propeller performance.Anytime maintenance is conducted or repair is made that add or removes weight from a propeller must check the propeller balance.Example:- - wood propeller is refinished with new coat of varnish. - any repair on the metal propeller. - tip damage shortened the blade. the opposite blade tip requires shorting to maintain balance.Propellers are balanced both statically or dynamically:- 1. Statically balance. - when the propellers center of gravity coincides with its axis of rotation. 2. Dynamic balance. - when the centers of gravity of the blades in the same plane of rotation.

1. Static balanceStatic balance is accomplished by using either:- a) knife-edge method (simpler and accurate) or. b) suspension method.Using knife-edge method, a test stand consist of two hardened steel edges. Carried out in a room that free from air motion or heavy vibration.Before carried out verify the blades angle are all the same.Blade angles are correct then follow the listed sequence of operation:- a) insert a bushing in the propeller hub bore hole. b) insert a mandrel or arbor through the bushing to support the propeller on the balance knife. c) place the propeller assembly so that the ends of the arbor are supported on the test stand. d) the propeller must be free to rotate.

1. Static balanceOnce on the stand, the propeller should be check for:- a) vertical. b) horizontal balance.

a) Vertical balanceTo check two-bladed propeller for vertical balance, position one blade in the vertical position.Next, position the opposite blade in the same manner.If propeller is balanced vertically, it will remain in a vertical position regardless of which blade is pointing up.If imb