17.6 Propeller Maintenance

Question 1

All propellers vibrate to some extent during operation. Assuming that the engine itself is not at fault, propeller roughness can be caused by:

Answer 1

Bent blades
Blades out of track due to an improper mounting of the propeller on the engine shaft
Imbalance
Propeller loosely mounted on the engine shaft
Blade angles between blades out of tolerance with respect to each other
Spinner imbalance due to improper mounting or to dirt, snow or ice inside the shell

Question 2

When working with propellers three different types of balancing are of importance. These are:

Answer 2

Static Balancing
Dynamic Balancing
Aerodynamic Balancing

Question 3

Static and dynamic imbalance are caused by unequal mass distribution while aerodynamic balancing is to ensure each blade delivers an equal amount of thrust.

Answer 3

In most cases, static balancing is sufficient. Only with larger propellers or with fast running propellers can dynamic balancing be necessary.

Question 4

Static Balance

A body capable of rotating about a fixed point is said to be in static balance when its centre of gravity lies on the axis of rotation. If a body is in static balance, each time it is rotated it comes to a stop in a random position.

Answer 4

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Question 5

Static balancing is carried out ‘off the aircraft’, either at the manufacturer, over hauler or in an approved propeller repair facility. The propeller is mounted on a mandrel which is placed across stable and perfectly levelled knife edges or rollers. The balance is checked in two planes, one horizontal and the other vertical

Answer 5

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Question 6

Fixed Pitch Wood Propellers

(Balancing)

Horizontal imbalance can be corrected by

Answer 6

applying small amounts of varnish or paint to the light blade or if larger amounts are required then solder can be applied to the metal tipping of the lighter blade.

Question 7

Fixed Pitch Wood Propellers

(Balancing)

Vertical imbalance can be corrected by

Answer 7

adding weights to the hub.

Question 8

Fixed Pitch Metal Propellers
(Balancing)

Answer 8

Fixed pitch metal propellers are statically balanced by removing some metal from the heavy side and then refinishing the propeller using a non-anodic protective coating such as Alodine ®.

Question 9

For propellers of aircraft up to 5700 kg (12 566 lbs), the general permissible tolerance is 2 gm (0.070 oz). However, the specifications of the manufacturer are binding.

Answer 9

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Question 10

Metal and Composite Variable Pitch Propellers (Balancing)

Answer 10

These types of propellers are balanced by placing lead washers onto a balancing stud within the hollow blade root/shank for horizontal balance while lead washers are placed in recesses of the hub for vertical balancing.

Question 11

Metal and Composite Variable Pitch Propellers

Minor adjustments to the propeller balance are corrected by placing lead wool into the balancing tube located within the hollow root of the blade.

Answer 11

.On smaller propellers the lead wool can be placed in the counterbored area of the hub bolt heads. These bolts are known as Welch bolts because of the Welch plug used to cap the bolt when lead wool is installed. Welch plugs must be in the bolt head regardless of whether or not lead wool is inserted in the bolt.

If a Welch plug is missing then the propeller is considered out of balance.

Question 12

Dynamic Balancing

Answer 12

Balancing the propeller to reduce the moment of imbalance is known as dynamic balancing. This must be carried out on a running engine.

Question 13

The term ‘balancing’ is not completely correct, because it cannot be done on all inertial axes as a change in mass is only possible in specific areas (blades, hub, spinner).

Answer 13

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Question 14

One method is a vibration pick-up on the engine and a defined weight which is attached alternately to each blade. In accordance with the result, a polar diagram is drawn.

Answer 14

The balancing weight is then attached at the position of greatest imbalance and a further ground run is carried out to ascertain the lowest level of vibration. For this balancing cruise RPM and cruise power are chosen.

Question 15

Small propellers are not normally dynamically balanced as any shift of the centres of gravity is only small.

Answer 15

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Question 16

There are four steps used to dynamically balance a propeller:

Answer 16

• Obtain in-flight vibration information.
• Ensure vibration is greater than permitted limits.
• Calculate the mass and location to reduce vibration to an acceptable level.
• Install balance weight(s) and confirm vibration levels are within limits.

Question 17

Propeller Balancing Systems

Modern electronically controlled Turbo prop systems use some form of Propeller Balance Monitoring System (PBMS).

Answer 17

The information required to provide a balance solution is derived from data provided by a Magnetic Pickup Unit (MPU) and the Active Noise Control Unit (ANCU) controller. This information together with engine RPM and aircraft altitude is processed to determine the level of propeller imbalance.

Question 18

Aerodynamic Balancing

Answer 18

Propellers can be affected by vibrations because of the differing aerodynamic loads of the blades resulting from the different blade angles. No two blades are manufactured to 100% accuracy. This means that each blade can produce slight variations from the standard theoretical values for torque and thrust

Question 19

A propeller is described as being in aerodynamic balance when the aerodynamic forces acting on the blades result in no periodic vibrations in the mountings. This means that each blade will be producing an equal value of thrust.

Answer 19

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Question 20

one blade of a four bladed propeller is producing more thrust than each of the other blades. As this propeller rotates, it will experience an alternating force. When the subject blade is at the top, it will try to push the propeller shaft down. When the blade rotates through the bottom, it will try to force the shaft up

Answer 20

this vibration does not increase with increasing engine speed. It does, however, become worse with increasing pitch and thrust.

Question 21

The forces of thrust and torque are perpendicular to each other. This makes it difficult to correct for both forces simultaneously

Answer 21

The blades are therefore balanced for either thrust or torque. The choice will be marked on the blade as an Aerodynamic Correction Factor (ACF), preceded by the letter ‘T’ if the correction is for thrust, or ‘Q’ if it is for torque.

Question 22

All the blades on a single propeller are balanced for the same force and must not be mixed with blades that have been corrected for the other force.

Answer 22

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Question 23

Aerodynamic balancing is only necessary for propellers with high performance. Manufactured blades are compared individually with a master blade and receive, according to deviation from the zero lift angle, an aerodynamic correction factor in the form of a reference to the blade angle difference necessary to the basic setting.

The whole process is also known as

Answer 23

blade indexing

Question 24

Aerodynamic Correction Factor

Aerodynamic balancing is achieved by adjusting the basic setting angle of each blade relative to the others during the assembly of the propeller. The action is known as ‘Blade Indexing’ and there are two methods used to achieve it, each dependent on the type of propeller.

Answer 24

The amount to be added or subtracted from the basic setting is expressed in degrees and minutes fine or coarse and is known as the Aerodynamic Correction Factor (ACF). This figure is marked on the blade.

One method of making adjustments, for example is by means of a vernier adiustment on each blade root

Question 25

Universal Blade Protractor

Answer 25

The protractor is used to measure the propeller blade angle at a specific blade station to determine if the propeller is properly adjusted. The blade angle is referenced from the propeller plane of rotation, which is ninety degrees to the crankshaft centreline.

Question 26

hen using this device and before measuring the angle of a propeller blade, the reference blade station must be determined from the propeller or aircraft manufacturer’s maintenance manual. This reference station is normally set at either the 30-inch, 36-inch, or 42-inch measurement on the propeller blade. The reference station must be marked with

Answer 26

a chalk or grease pencil on the face of each blade.

Question 27

The reference plane is not based on the airframe attitude because of the canted Installation of some engines.

Answer 27

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Question 28

Blade tracking is the ability of one blade to follow the other in the same plane of rotation. Tracking is held to reasonable limits to prevent roughness and vibration.

Answer 28

A tracking check may be called up after a propeller has been installed or, if there is any reason to suspect the dynamic balance. A propeller that has suffered an impact from an object would be a classic case, particularly if vibration occurs.

Question 29

(Blade Tracking) Measurement is usually conducted at the master station. The fixed reference point can be mounted on the engine or placed on the ground

Answer 29

The distance between a blade and the pointer is measured. The propeller is then turned by hand to enable measurements to be taken of the distances between each blade and the reference pointer propeller chapter (Chap 61)

Question 30

It is important that the propeller blade angles are all set at the same value before doing a tracking check. The maintenance manual will specify the actual setting. Usually, the check is done with the blades on the fine pitch stop.

Answer 30

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Question 31

There are two main methods for check a blades tracking:

Answer 31

Flat Bench Method Block or Pointer Method

Question 32

To check tracking, place a smooth board just under the tip of the lower blade

Answer 32

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Question 33

Flat Bench Tracking Method On controllable props, move the tip fore and aft carefully through its small range of movement, making small pencil marks at each position. Centre the blade between these marks and draw a line the full width of the blade. Rotate the propeller so that the next blade is in the lower position and repeat this procedure at the blade tip.

Answer 33

The lines should be separated by not more than 3 mm (1/8 inch) or by the measurements designated in the maintenance manual.

Question 34

Block or pointer Tracking Method rotate one of the blades so it is pointing down. Place a solid object (e.g., a heavy wooden block that is at least a couple of inches higher off the ground than the distance between the propeller tip and the ground) next to the propeller tip so that it just touches or attach a pointer/indicator to the cowling itself

Answer 34

Rotate the propeller slowly to determine if the next blade tracks through the same point (touches the block/ pointer). Each blade track should be within the tolerances defined in the maintenance manual (i.e., within 1/16 inch (plus or minus) from the opposite blade’s track.

Question 35

Blade Damage Damage to a propeller can be divided into airworthy and unairworthy damage. Airworthy damage can be repaired in the field. Unairworthy damage is any damage that exceeds the limits of the airworthy damage.

Answer 35

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Question 36

Damage to blades can take many forms. Some of the terms used to describe blade damage are as follows:

Answer 36

Fatigue: Fatigue failures normally occur within a few inches of the blade tip: however, failures also occur in other portions of the blade when dents, cuts, scratches or nicks are ignored Split: is a delamination of a composite blade extending to the blade surface, normally found near the trailing edge or tip. Distortion: is an alteration of the original shape or size of a component Debond: is a separation of the metal erosion shield from the composite material in the blade.

Question 37

Normal airworthy damage does not affect the flight safety characteristics of the blades, although airworthy damage should be repaired to maintain aerodynamic efficiency.

Answer 37

To determine if the damage is airworthy or unairworthy, the aircraft maintainer should refer to the information in the blade repair manual.

Question 38

Airworthy damage limits are usually described within AMM ATA chapter 61 of the related aircraft.

Answer 38

Always refer to the manufacturer manuals to determine serviceability and methods of repair.

Question 39

Some of the inspection techniques that are or may be required are

Answer 39

Visual Inspection Tap Test Penetrant Inspection Ultrasonic Inspection Eddy Current Inspection Magnetic Particle Inspection

Question 40

Magnetic Particle Inspection

Answer 40

Magnetic particle inspection is conducted at an appropriately approved maintenance facility. It is useful for finding cracks, inclusions, and imperfections at or near the surface of ferrous parts

Question 41

Eddy Current Inspection

Answer 41

Eddy current inspection uses specialised equipment to generate and measure an electric field that detects flaws at or slightly below the surface of the component being inspected. Eddy current inspection is conducted by appropriately certificated engineer. used on ferrous and non ferrous metals

Question 42

Ultrasonic Inspection

Answer 42

Ultrasonic inspection uses specialised equipment to send, receive, and process sound waves to detect flaws on or below the surface of the component being tested. Appropriately certified engineers conduct ultrasonic inspections. Ultrasonic inspections are very specific and require specially designed probes and calibration standards to obtain reliable results. Ultrasonic inspections can be conducted on composites, wood, ferrous, and non-ferrous metals.

Question 43

Penetrant Inspection

Answer 43

Fluorescent penetrant is far superior to non-fluorescing penetrant (visible dye penetrant), particularly for detecting small surface cracks on propeller blades. The use of visible dye penetrant is not recommended. Penetrant inspection on propellers is usually conducted in an approved repair station.

Question 44

Tap Test Composite blades are inspected for delaminations and debonds by tapping the blade or cuff (if applicable) with a metal coin. If an audible change is apparent, sounding hollow or dead, a debond or delamination is likely

Answer 44

Blades that incorporate a 'cuff' have a different tone when coin tapped in the cuff area. To avoid confusing the sounds, coin tap the cuff area and the transition area between the cuff and the blade separately from the blade area.

Question 45

Visual Inspection

Answer 45

The primary defence against early failure of propellers. Some areas may require the use of a 10x magnifying glass to identify small features or find cracking.

Question 46

Types of Propeller Damage

Answer 46

Erosion Corrosion Impact damage Composite or wood propeller Delam

Question 47

Erosion

Answer 47

the loss of material from blade surface by the action of small particles such as sand or water and is usually present on the leading edge close to the tip. This damage destroys the blades’ corrosion protection, which might lead to blade failure. If metallic blades appear to show erosion beyond limits, the propeller should be removed from service and evaluated by an approved maintenance facility Composite blades have an erosion strip attached to the leading edge of the blade to reduce the effects of erosion. However, extensive damage to the ‘strip’ or any degradation of the protective paint finish will require extensive repairs in accordance with the relevant maintenance manual or at an approved maintenance facility.

Question 48

Corrosion on metal propeller compoents can be classified into three distinct types these are

Answer 48

Surface Corrosion Pitting Intergranular Corrosion

Question 49

Surface Corrosion

Answer 49

The loss of surface metal due to chemical or electro-chemical action with visible oxidation products usually having a contrasting colour and texture to the base metal. Surface corrosion, as shown, generally results when the corrosion protection on a metal surface has been removed by erosion or by polishing. Therefore, removing paint and corrosion protection, such as when polishing blades, is not recommended

Question 50

Pitting

Answer 50

Pits consist of visible corrosion cavities extending inward from the metal surface. They can grow on the surface, under decals, or under improperly installed de-ice boots. Pitting can appear to be relatively minor - 0.010 inches (0.254 mm) deep and still cause major problems since the pits could be a precursor to the initiation of cracks.

Question 51

Intergranular Corrosion

Answer 51

Occurs in grain boundaries. The presence of intergranular corrosion may be the result of the continued presence of moisture such as under a decal, in a fastener hole, or where the anodise and paint protective barriers have been lost. Exfoliation is a form of intergranular corrosion that occurs more often in forgings or rolled sheets, and less often in castings. Exfoliation is sometimes visible as metal flaking and cracks on a blade leading edge.

Question 52

Impact Damage

Answer 52

A conservative approach in evaluating the damage is required because of the possibility that there may be hidden damage that is not readily apparent during a superficial, visual inspection.

Question 53

Composite or Wood Propeller Delamination

Answer 53

Although not susceptible to corrosion like metal propellers, wood or composite propellers have special problems that can lead to an unairworthy condition. Wood or composite propellers are susceptible to internal damage from small stone strikes that can create delamination or microcracks and permit intrusion of moisture. Moisture will cause expansion of existing cracks and delaminations. When moisture freezes within the blade, it causes delamination. When inspecting wood or composite propeller blades, look for cracks or delamination on the blade surface and at blade edges.

Question 54

in wooden propellers, check the glue lines for debonding; look for warp and loss of protective coating (paint or varnish). If drain holes are present, it is imperative that they be inspected since they may become clogged with insects and debris. Clogged drain holes can cause moisture retention.

Answer 54

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Question 55

wooden proplellers insepction criteria:

Answer 55

The centre bore should be examined for cracks and de-lamination of the plies. The mounting hub should be examined for corrosion, cracks, correct fit on the crankshaft and for the condition of the attachment bolts and nuts. Where mounting cones are fitted, these should be checked for corrosion. Fit between the hub and cones may be checked using engineer's blue, an 80% contact normally being required.

Question 56

Repairs to Wooden Propellers When examining the blades the surface protection coating must be inspected. It must be 100% intact so that no moisture can penetrate

Answer 56

Cracks in the paint across the blade are signs of flexural vibrations. Cracks through the leading edge tipping are the result. If the tipping is cracked in this way, it must be replaced immediately. In the case of riveted tipping, loose rivets are a sign that the wood beneath it is damaged. The propeller must be taken out of service immediately.

Question 57

Less significant damage on the trailing edge or on the blade can be filled with plastics. Indentations in the metal tipping can be filled by soldering. In this case the use of any significant heat is to be avoided and balance must be taken into consideration. Perforated tipping must be replaced.

Answer 57

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Question 58

After installation of a new fixed-pitch wood propeller the attachment bolts must be re-tightened after 25 hours with the torque prescribed. After the initial re-tightening, the torque must be checked at least every 50 hours as humidity causes the wood to shrink and expand.

Answer 58

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Question 59

Wooden propeller must be checked for

Answer 59

- Delamination - Surface damage (damage to the protective - --coating allows the wood to become damp). - Protective strip damage and loose screws or rivets. - Root/shank damage (no repairs are permitted). - Distortion of the propeller mounting boss. - Damage or distortion to mounting bolt holes. - Blade warp. - Chips or splits.

Question 60

Surface damage to propeller blades can be repaired using a wood filler or a mix of sawdust and aero glue (casein). On completion of the repair the blades surface finish must be restored. All work must be carried out in a warm dry atmosphere. Casein cement (Aerolite 306) is a two part mix which sets quickly but requires an 8 hour cure time.

Answer 60

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Question 61

The following damage cannot be repaired and renders the propeller unusable:

Answer 61

- Cracks across the grain - A splintered blade - Delamination - Missing material - Cracks in the hub - Enlargement of the hub shaft bore - Elliptical bolt holes

Question 62

Metal Propellers Metal propellers are particularly subject to metal fatigue. This is caused by the high dynamic loads they are subjected to.

Answer 62

Scratches, hairline cracks, impact marks and the effects of corrosion are potential stress risers for cracks. As a result of additional bending and centrifugal forces the crack extends, usually over the matt black sprayed back side of the propeller blade.

Question 63

In order to avoid a failure of the propeller blades the following measures are recommended: (Metal Propellers)

Answer 63

RPM limitations are to be observed. Never taxi at high power if sand, stones or other material can be sucked into the propeller. Do not cover the propeller (moisture forming can cause corrosion). When pulling small aircraft do not use the outside of the propeller blades but the propeller root Every 100 hours or at least at every annual check inspect the propeller thoroughly for damage after cleaning. In case of doubt use a magnifying glass or other methods of checking for cracks (using dye penetrant).

Question 64

Repair of Damage Information on permissible repairs can be found in the manufacturer's manuals. If no information is available, the following source can be used:

Answer 64

Certification Specification (CS) CS-SR801a which refers to FAA Advisory Circular (AC) AC 4313-B Aircraft Inspection and Repair. Permissible repair on the blade width is normally 1.2 mm from the root to 0.6 R and from 0.6 R to blade tip is 2.4 mm, however not under the permissible blade width Permissible repair on the blade thickness is 0.7 mm over the whole blade, however not under the minimum blade thickness nor across the whole of the blade.

Question 65

No repair whatever is permissible on the blade root.

Answer 65

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Question 66

Steel propellers are extremely durable and resistant to damage, but any damage is critical due to the brittle metals used. Consequently, damage must be located and corrected as soon as possible.

Answer 66

All repairs to steel propellers and blades, including slight dents and nicks, are major repairs and must be performed at an approved repair facility.

Question 67

Permissible Bending of Metal Blades If a blade has been bent, the angle of the bend and the blade station of the bend centre can be measured and, by using the proper chart, an evaluation can be made as to the repairability of the blade.

Answer 67

firstly identify the centreline of the bend, then measure from the centre of the boss (or use the blade master station mark) to determine the blade station. Next, mark the blade one inch on each side of the bend centreline and measure the degree of bend by using a protractor Use the appropriate chart to determine if the bend is repairable. When reading the chart, anything above the graph line is not repairable.

Question 68

Inspection of the Hub During periodical inspections the hub must be checked for cracks and corrosion. Exterior parts of the change mechanism and the hub must be freed of corrosion Grease leaks point to damage to the blade attachment seals

Answer 68

Oil leaks are a sign of damaged seals in the pitch change cylinder or of damage to the blade attachments (oil-smeared blade bearings) As a protection against corrosion lubricant spray can be applied to the hub after cleaning.

Question 69

If there is excessive play on the blade tips or the blade angle, the cause can be damage to the blade attachment or the pitch change mechanism. It is equally serious if the blades stick (stiffness can be due to construction).

Answer 69

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Question 70

composite Propellers Damage is classified into two groups, acceptable and unacceptable.

Answer 70

The blade repair section of the Propeller Maintenance Manual will define the limits that apply to these classifications.

Question 71

composite Propellers Sub-classification of damage may also be sub-divided as either ‘skin perforated damage’ and ‘skin not perforated damage’.

Answer 71

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Question 72

Skin not perforated damage:

Answer 72

Abrasion Scratches Gouges Nicks Debonding Delamination Dents

Question 73

Skin perforated damage:

Answer 73

Lightning strike Holes

Question 74

Composite Propellers When the propeller remains attached, only minor repairs are possible, such as the re-coating of the polyurethane finish.

Answer 74

If struck by foreign material the edges can be smoothed and the missing material replaced..

Question 75

Field repairs to composite propeller blades are restricted because of the extensive training required to qualify an engineer in composite repair techniques

Answer 75

Composite repairs have to be conducted within a clean environment where humidity and temperature values are carefully controlled. The normal environments that are associated with aircraft operations rarely meet these standards.

Question 76

Delamination of surface layers on the outer half of the blade may be acceptable if within the area limit specified.

Answer 76

his would typically be around 2 in2 (50.8 mm2). It would be unacceptable, however, if the delaminated area is accompanied by black or brown

Question 77

Gouges or delamination occurring on the inner half of the blade would be unacceptable

Answer 77

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Question 78

composite propellers Gouges on the outer half of the blade surface may be acceptable providing they are within a specified length and depth. This would typically be

Answer 78

less than two inches long and 0.02 in (0.508 mm) deep.

Question 79

Small crushed or split sections on the trailing edge outer half, typically less than one inch long (25.4 mm), may be acceptable providing it is only the resin matrix that is crushed and not the fibres.

Answer 79

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Question 80

Some erosion of the paint finish and primer may be classified as acceptable, providing it has not progressed into the resin layer.

Answer 80

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Question 81

The leading edge erosion shield may have small gouges. These may be acceptable providing they do not penetrate through to the blade underneath.

Answer 81

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Question 82

Small cracks may be acceptable, providing they are not accompanied by a failure in the bond between the shield and the blade.

Answer 82

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Question 83

Nicks, small cracks and depressions on the blade cuff may be acceptable if within specified limits. It may be necessary to apply a sealant over these to prevent water ingress to the foam.

Answer 83

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Question 84

Lightning strike damage normally occurs near the tip of the leading edge metal erosion shield. This reveals itself as a blackened area often accompanied by pitting. It is important to check if the shield to blade bond has failed, or whether there is any delamination in the surrounding area. A coin tap test may be used to determine this.

Answer 84

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Question 85

Before carrying out a ground run certain checks need to be carried out with the engine not running. Therefore, these checks are known as Static Checks.

Answer 85

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Question 86

Static Checks Certain checks on the propeller and control system can be carried out without the need to run the engine. These checks are:

Answer 86

Flight Fine Pitch Stop (FFPS) Auto-Coarsening Manual Feather Autofeather Unfeather

Question 87

Static checks can be carried out using the electric feathering pump to pressurise the oil to move the pitch change mechanism. It must be noted that, when using this method to move the propeller blades, oil being returned from the propeller pitch change mechanism cannot be returned to the engine oil tank because the oil scavenge pumps are not rotating

Answer 87

To prevent flooding the engine with oil, a dry motoring cycle is required to operate the scavenge pumps.

Question 88

These static checks are normally carried out prior to an engine ground run following:

Answer 88

Engine installation Propeller installation Propeller Governor installation Propeller control adjustments When called for by the servicing schedule

Question 89

Piston engines, otherwise known as reciprocating engines, are further classified as normally-aspirated or supercharged engines.

Answer 89

The power developed by these engines (power ratings) are related to the air pressure in the engine air induction manifold. This is known as Manifold Air Pressure (M.A.P.).

Question 90

The M.A.P. produced in a normally aspirated engine is always below ambient air pressure whilst that of a supercharged engine (known as boost pressure) can be greatly in excess of ambient pressure.

Answer 90

American engines measure their boost pressure in inches of mercury (in. Hg.) where the standard atmospheric pressure of 14.7 psi is taken as 29.92 in Hg. Therefore, 1 psi equals approximately 2.04 in Hg.

Question 91

At any given air density, a propeller at a fixed pitch always stabilises at a particular RPM to absorb the engine power. This means that if the engine throttle is advanced, then as well as the RPM increasing the M.A.P. increases allowing the performance of the engine/propeller combination to be checked using known reference figures at the reference RPM.

Answer 91

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Question 92

To check this reference RPM, it is simply a matter of setting the propeller to fine pitch, advancing the throttle until the manifold pressure reads zero boost and checking that the RPM is the same as that published for the reference RPM. This is called the reference power check.

Answer 92

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Question 93

To compensate for an airfields height above sea level and temperature differences, reference RPM corrections can be found in Ch 71 of the A.M.M

Answer 93

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Question 94

Fixed pitch propellers do not attain maximum RPM when ground running in nil wind conditions. This is to prevent over speeding during take off.

Answer 94

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Question 95

Turboprop engine power is measured in shaft horsepower (SHP) and determined by the amount of torque produced. Whereas a piston engine uses boost pressure to determine RPM a turboprop produces a selected RPM for a given torque.

Answer 95

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Question 96

Turboprop To determine that the engine is operating correctly then the engine exhaust gas temperature (EGT) and fuel flow (Wf) must be monitored against the referenced torque and RPM. This allows the relationship between the propeller and engine to be checked.

Answer 96

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Question 97

Performance checks Turboprop unlike piston engine reference RPM checks, performance checks can be carried out at the maximum power setting or a lower value. The important point to note is there is always a relationship between the torque, RPM, Fuel Flow and EGT.

Answer 97

This is the same whether the operation of the engine/propeller is by single or twin lever operation.

Question 98

Trouble-shooting Piston Engine Propellers Engine does not attain reference RPM at Zero boost.

Answer 98

Engine power low. Incorrect blade angle (Coarse). Weak governor speeder spring. Advancing the throttle until reference RPM is reached indicates how low the engine performance is.

Question 99

Engine attains reference RPM before Zero boost (Piston Engine prop)

Answer 99

Incorrect blade angle (Fine). Incorrect propeller governor setting. High ambient temperature.

Question 100

Maximum take off RPM low (Piston engine prop)

Answer 100

Maximum RPM stop on governor incorrect Tail wind

Question 101

Troubleshooting General (Constant Speed Propellers) Vibration =

Answer 101

1.Incorrect Blade Angle (Aerodynamic balance) 2.Out of Track 3.bearing Grease Leakage 4. propeller Security 5.Damaged Blade Bearings

Question 102

Troubleshooting General (Constant Speed Propellers) Minimum RPM too low

Answer 102

PCU valve sticking in high (coarse) pitch position. PCU speeder spring weakened, allowing centrifugal weights to operate earlier.

Question 103

Troubleshooting General (Constant Speed Propellers) Minimum RPM Too High

Answer 103

PCU valve sticking in low (fine) pitch position. Restriction can prevent the minimum RPM position from being reached by PCU.

Question 104

Troubleshooting General (Constant Speed Propellers) Maximum RPM Too Low

Answer 104

Check the setting of Maximum RPM stop on PCU If Maximum RPM stop correctly set, check the range of movement of controls.

Question 105

Troubleshooting General (Constant Speed Propellers) Maximum RPM Too High

Answer 105

Maximum RPM stop incorrectly set.

Question 106

Troubleshooting General (Constant Speed Propellers) Propeller Control Unit (PCU) Fails To Control

Answer 106

If new installation, check quill drive. PCU seizure, sheared quill drive. Pressure relief valve (PRV) open producing low oil pressure. Stiff operation of blade bearings or linkages

Question 107

Stiff operation of PCU or propeller moving parts can produce RPM surges

Answer 107

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Question 108

Turbo-propeller Engines High Torque with normal EGT and Fuel Flow (Wf)

Answer 108

Suspect Torque Indication.

Question 109

Turbo-propeller Engines Low Torque with Low EGT and Low Fuel Flow (Wf)

Answer 109

Over-speed Governor.

Question 110

Turbo-propeller Engine Low Torque with High EGT and Low Fuel Flow (Wf)

Answer 110

High ambient air temperature.