CASA B1-17 Propellers PDF, 2022

MODULE 17 Category B1 Licence CASA B1-17 Propellers  Copyright © 2020 Aviation Australia All rights reserved. No part of this document may be reproduced, transferred, sold or otherwise disposed of, without the written permission of Aviation A...

MODULE 17 Category B1 Licence CASA B1-17 Propellers  Copyright © 2020 Aviation Australia All rights reserved. No part of this document may be reproduced, transferred, sold or otherwise disposed of, without the written permission of Aviation Australia. CONTROLLED DOCUMENT 2022-08-24 B1-17 Propeller Page 2 of 228 CASA Part 66 - Training Materials Only  Knowledge Levels Category A, B1, B2 and C Aircraft Maintenance Licence Basic knowledge for categories A, B1 and B2 are indicated by the allocation of knowledge levels indicators (1, 2 or 3) against each applicable subject. Category C applicants must meet either the category B1 or the category B2 basic knowledge levels. The knowledge level indicators are defined as follows: LEVEL 1 Objectives: The applicant should be familiar with the basic elements of the subject. The applicant should be able to give a simple description of the whole subject, using common words and examples. The applicant should be able to use typical terms. LEVEL 2 A general knowledge of the theoretical and practical aspects of the subject. An ability to apply that knowledge. Objectives: The applicant should be able to understand the theoretical fundamentals of the subject. The applicant should be able to give a general description of the subject using, as appropriate, typical examples. The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject. The applicant should be able to read and understand sketches, drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using detailed procedures. LEVEL 3 A detailed knowledge of the theoretical and practical aspects of the subject. A capacity to combine and apply the separate elements of knowledge in a logical and comprehensive manner. Objectives: The applicant should know the theory of the subject and interrelationships with other subjects. The applicant should be able to give a detailed description of the subject using theoretical fundamentals and specific examples. The applicant should understand and be able to use mathematical formulae related to the subject. The applicant should be able to read, understand and prepare sketches, simple drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using manufacturer's instructions. The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate. 2022-08-24 B1-17 Propeller Page 3 of 228 CASA Part 66 - Training Materials Only  Table of Contents Propeller Fundamentals I (17.1) 10 Learning Objectives 10 Propeller Forces 11 Lift 11 Drag 11 Thrust 12 Total Reaction 12 Effects on Propeller Thrust 14 Blade Angle 14 Angle of Attack 15 Blade Twist 15 Pitch 16 Propeller Slip 18 Propeller Fundamentals II (17.1) 20 Learning Objectives 20 Effects on Aircraft Stability 21 Propeller Torque 21 Propeller Gyroscopic Effect and Slipstream 21 Contra-Rotating Effect 23 Forces Acting on a Propeller 23 Bending Forces 27 Force Coupling 29 Propeller Angle of Attack 30 Increased Rotational Velocity 31 Increased Forward Velocity 32 Blade Tip Speed Versus Efficiency 33 Blade Vibration 34 Propeller Construction I (17.2) 37 Learning Objectives 37 Construction 38 Construction Materials 38 Leading and Trailing Edges 38 Blade Back 39 Blade Face 39 2022-08-24 B1-17 Propeller Page 4 of 228 CASA Part 66 - Training Materials Only  Chord Line 40 Blade Stations 40 Hub Assembly 41 Root (Blade Butt) 42 Blade Shank 43 Blade 44 Tip 45 Cuff 46 Wooden Propellers 48 Wooden Propeller Construction Methods 48 Laminating 48 Varnishing 48 Leading-Edge Sheathing 49 Metallic Propellers 51 Steel Propellers 51 Aluminium Alloy Propellers 51 Anodising 52 Shot Peening 52 Metal Propeller Construction 53 Composite Propellers 55 Materials used in composite propellers 55 Fibre-Reinforced Plastic (FRP) Moulding 55 Composite Propeller Construction 56 Propeller Construction II (17.2) 58 Learning Objectives 58 Propeller Mounting and Installation Requirements 59 Types of Propeller Mounting Installations 59 Tapered Shaft 59 Flanged Shaft 60 Splined Shaft 61 Taper Bore 62 General Propeller Installation 64 Propeller Types 66 Tractor Propeller 66 Pusher Propeller 66 Fixed-Pitch 67 Ground-Adjustable 67 2022-08-24 B1-17 Propeller Page 5 of 228 CASA Part 66 - Training Materials Only  Controllable-Pitch 68 Constant-Speed 69 Contra-Rotating 70 Counter-Rotating 71 Feathering 72 Reversing 73 Propeller Effects on Operation 76 Propeller Selection 76 Engine Power Requirements and Performance Factors 76 Propeller Diameter 77 Number of Blades 78 Blade Shape and Section 79 Propeller Solidity 80 Spinner Installation 82 Propeller Spinner Types 82 Propeller Pitch Control I (17.3) 85 Learning Objectives 85 Pitch Change Mechanisms 86 Variable Pitch Propeller Applications 86 Manual Pitch Change 86 Mechanical 87 Electric 89 Propeller Electronic Control (PEC) 91 Counterweight and Hydraulic Combination 93 Two-Position Propeller (Bracket Type) 93 Governors 97 Purpose of a Governor 97 Single-Acting Governors 97 Single Acting Governor Operation 101 Governor and Propeller Operating Conditions 108 Governor Operation 108 Aerodynamic and Hydraulic Combination 108 Hydromatic 112 Feathering Propellers 117 Purpose of Feathering 117 Manual Feathering 117 Hartzell and McCauley Feathering Propellers 118 2022-08-24 B1-17 Propeller Page 6 of 228 CASA Part 66 - Training Materials Only  Unfeathering Accumulators 119 Auto-Feather System 120 Propeller Pitch Control II (17.3) 123 Learning Objectives 123 Reversible Propellers 124 Reverse Pitch 124 Propeller Auxiliary Systems 126 Negative Torque Sensing (NTS) 126 Safety Coupling 127 Propeller Brakes 129 Torquemeter 130 Pitch Stops 131 Counterweight Propellers 132 Hydraulic Propellers 133 Feather/Coarse Pitch Stop 133 Reversing Propeller Low-Pitch Stop-Lever Assembly 134 Overspeed Protection 135 Hydromatic Propeller System Operation 137 On Speed Governor Operation 137 Overspeed Governor Operation 138 Underspeed Governor Operation 139 Feather Propeller Operation 140 Unfeather Propeller Operation 141 Reversing Propeller Operation 142 Un-reversing Propeller Operation 144 Alpha and Beta Modes 147 Flight and Ground Range 147 Propeller Synchronising (17.4) 149 Learning Objectives 149 Synchronising Basic System 150 Purpose of a Synchronising System 150 Components of a Synchronising System 150 Synchrophasing 152 Purpose of Synchrophasing 152 Components of a Synchronising and Synchrophasing System 152 Synchrophasing System Operation 154 FADEC Synchrophasing 157 2022-08-24 B1-17 Propeller Page 7 of 228 CASA Part 66 - Training Materials Only  Propeller Ice Protection (17.5) 159 Learning Objectives 159 Propeller Ice Protection 160 Ice Protection 160 Fluid Anti-icing 160 Anti-icing System Components 161 System Operation 164 Electrical Thermal De-icing 165 Propeller Maintenance (17.6) 173 Learning Objectives 173 Propeller Vibration and Balance 174 Propeller Vibration 174 Propeller Balancing 174 Static Balance Review 178 Propeller Servicing Safety 179 Component Removal and Installation 179 Dynamic Balancing 179 Propeller Track 181 Checking the Track 182 Corrective Action 183 Propeller Maintenance 185 Types of Propeller Shafts 185 Flanged Shaft 185 Constant-Speed Propeller 187 Turboprop Propeller 188 Tapered Shaft Installations 189 Splined Shaft 191 Propeller Blade Angle 195 Universal Protractor 196 Propeller Damage Assessment and Repair Criteria 200 Damage Assessment 200 Damage and Repair Criteria 200 Major Damage 201 Minor Damage 202 Damage Assessment and Acceptance Areas 203 Wooden Propeller Damage 205 2022-08-24 B1-17 Propeller Page 8 of 228 CASA Part 66 - Training Materials Only  Aluminium Propeller Damage 209 Composite Propeller Damage 215 Testing After Installation 219 Propeller Storage and Preservation (17.7) 222 Learning Objectives 222 Propeller Storage and Preservation 223 Storage and Preservation Requirements 223 Wooden Propellers 224 Metal Propellers 225 Return to Service Maintenance for Controllable-Pitch Propellers 226 Composite Propellers 227 2022-08-24 B1-17 Propeller Page 9 of 228 CASA Part 66 - Training Materials Only  Propeller Fundamentals I (17.1) Learning Objectives 17.1.1 Describe propeller blade element theory. 17.1.2.1 Explain propeller high and low blade angle. 17.1.2.2 Explain propeller reverse angle. 17.1.2.3 Explain propeller angle of attack. 17.1.2.4 Explain propeller rotational speed. 17.1.3 Explain propeller slip. 2022-08-24 B1-17 Propeller Page 10 of 228 CASA Part 66 - Training Materials Only  Propeller Forces Lift Lift is the aerodynamic force caused by air flowing over an aerofoil. The aerofoil shape of an aircraft wing or propeller is designed to increase the velocity of the airflow over its cambered surface, thereby decreasing pressure above the aerofoil. This combination of pressure decrease above the aerofoil and a higher pressure below the aerofoil produces a force upward. This force is termed lift, and with propellers this forms the basis of blade element theory – with a blade element being any randomly selected area of the blade aerofoil. Lift 2022-08-24 B1-17 Propeller Page 11 of 228 CASA Part 66 - Training Materials Only  Drag Drag is a force opposing thrust, caused by the disruption or impact of airflow over, or onto, an aerofoil. Drag Thrust Thrust is a forward-acting force. It is the reaction to the mass of air being accelerated rearwards,. This force is felt on the blade face and forms the basis of momentum theory for propellers (Newton’s Third Law of Motion). Momentum is the quantity of motion of a moving body measured as a product of its mass and velocity. Thrust 2022-08-24 B1-17 Propeller Page 12 of 228 CASA Part 66 - Training Materials Only  Total Reaction Total reaction of a blade is the resultant of two pairs of forces: Lift and drag Thrust and torque. By plotting the vectors for lift and drag, thrust and torque, it is possible to derive the total reaction. The propeller is a rotating wing, and both pairs of forces are acting on the blade at the same time. Propeller Total Reaction An increase in rotational speed will increase these forces equally. Rotational speed is restricted to the point that the blade tip speed must remain below the speed of sound. Relevant Youtube link: The Propeller Explained 2022-08-24 B1-17 Propeller Page 13 of 228 CASA Part 66 - Training Materials Only  Effects on Propeller Thrust Blade Angle If you stand safely to the side of a stationary aircraft and view the rotating propeller, you will see the plane (path) in which the propeller is rotating. The angle between the chord line, which is an imaginary line drawn through the blade and the plane of rotation, usually measured in degrees, is termed the blade angle. Aviation Australia Blade Angle When blade angle is measured, it is measured with reference to a datum point (same as aircraft stations). A reference measuring point is necessary as the blade angle decreases from the root to the tip of the blade. The datum point is generally accepted as a measurement from the centre of the hub of the propeller to a position at 75% of the radius. The Aircraft Maintenance Manual (AMM) and the aircraft Type Certificate will give definitive angles and positions to carry out this task. For information only: For a Sensenich propeller designated M74DMS5-2-60, the ‘74’ component indicates the propeller diameter is 74 in. and the ‘-60’ designates the pitch of the propeller is 60 in. at the 75% station. 2022-08-24 B1-17 Propeller Page 14 of 228 CASA Part 66 - Training Materials Only  Sensenich Propeller Designation Chart Angle of Attack The angle between the chord line and angle of relative wind/airflow is termed the angle of attack. For best results, this should be 2° to 4°. It is within this angle of attack that the incoming air is compressed, then allowed to expand as it leaves the trailing edge of the blade, resulting in thrust. The angle of attack is a combination of two airflows due to the forward motion of the aircraft True Air Speed (TAS) and the rotational speed of the propeller, revolutions per minute (rpm). Aviation Australia Propeller Angle of Attack 2022-08-24 B1-17 Propeller Page 15 of 228 CASA Part 66 - Training Materials Only  Blade Twist The further away from the hub along the propeller blade, the faster that section of the blade is travelling. If the tip reaches the speed of sound, then that portion will not produce any thrust. Therefore, if a propeller had no twist along its length when viewed from the side, then only part of it would produce any useable thrust. To ensure all sections of the propeller blade produce equal thrust, the blade is manufactured with a gradual twist from hub to tip. Maintaining this gradual twist also ensures that the correct angle of attack is maintained at 2° to 4° along the length of the blade. Propeller blade twist 2022-08-24 B1-17 Propeller Page 16 of 228 CASA Part 66 - Training Materials Only  Pitch Pitch is the distance moved forward by the propeller in one revolution. This can vary with different blade angles on variable pitch propellers, as illustrated. Aviation Australia Low and high propeller pitch 2022-08-24 B1-17 Propeller Page 17 of 228 CASA Part 66 - Training Materials Only  Aviation Australia Propeller pitch positions 2022-08-24 B1-17 Propeller Page 18 of 228 CASA Part 66 - Training Materials Only  Propeller Slip Slip is defined as the difference between geometric pitch and effective pitch. Geometric pitch is a calculated distance a propeller advances forward through a solid medium in one revolution. Effective pitch is the distance a propeller actually advances forward in one revolution due to moving through air. Slip is the difference between geometric pitch and effective pitch. If a propeller has a geometric pitch of 50 in., in theory it should move forward 50 in. per revolution through a solid medium. If the aircraft moves forward only 35 in. per revolution in air, the effective pitch is 35 in. and the propeller is 70% efficient. Slip represents 15 in. or a 30% loss of efficiency. In practice, most propellers are 75% to 85% efficient. © Aviation Australia Propeller Slip 2022-08-24 B1-17 Propeller Page 19 of 228 CASA Part 66 - Training Materials Only  Propeller Fundamentals II (17.1) Learning Objectives 17.1.4.1 Explain propeller aerodynamic forces. 17.1.4.2 Explain propeller centrifugal forces. 17.1.4.3 Explain propeller thrust forces. 17.1.5 Explain propeller torque. 17.1.6 Explain relative airflow effect on propeller blade angle of attack. 17.1.7 Explain propeller vibration and resonance. 2022-08-24 B1-17 Propeller Page 20 of 228 CASA Part 66 - Training Materials Only  Effects on Aircraft Stability Propeller Torque If a propeller is being driven anti-clockwise, the torque that is being developed to drive the propeller has an effect on the aircraft structure and will tend to roll the aircraft clockwise. R QUE REACTIO TO N ELLER ROTA P T O IO PR N Aviation Australia Torque reaction effect on aircraft stability 2022-08-24 B1-17 Propeller Page 21 of 228 CASA Part 66 - Training Materials Only  Propeller Gyroscopic Effect and Slipstream Propeller Gyroscopic Effect An example of gyroscopic effect is spinning a bicycle wheel while holding the axle, then trying to tilt the axle in one direction while it is spinning. You will note that it actually tilts at 90° in the direction intended. The rotating mass of the propeller may cause a slight gyroscopic effect. A rotating body (propeller) tends to resist any change in its plane of rotation. In straight and level flight, the propeller will resist a turn to either the left or right. If such a change does take place, there is a tendency for the plane of rotation (straight and level) to change in a direction at right angles (90°) to where the force was applied. Aviation Australia Gyroscopic and slipstream effects 2022-08-24 B1-17 Propeller Page 22 of 228 CASA Part 66 - Training Materials Only  Propeller Slipstream A rotating propeller will impart a rotational motion to the slipstream in the same direction as the propeller. This rotation of the air has an adverse effect on the aircraft’s fin. The diagram shows two airflows flowing rearwards, represented by one solid and one dotted line. The solid portion firstly curls over the top of the aircraft, then under it, prior to arriving at the tail. The dotted portion initially curls under the aircraft until it reaches the trailing edge of the wing. It then rotates back up, hitting the right side of the tail. This force acting on the tail will cause the aircraft to turn to the right. Contra-Rotating Effect The fitment of a contra-rotating propeller basically eliminates the effects of propeller torque, propeller slipstream and propeller gyroscopic effect. The second propeller straightens the slipstream of the first, causes a straight high-speed flow of air over the fin and improves control. Propeller torque is cancelled because the propellers are spinning in opposite directions, therefore neutralising the gyroscopic effect. Contra-rotating propellers 2022-08-24 B1-17 Propeller Page 23 of 228 CASA Part 66 - Training Materials Only  Forces Acting on a Propeller As a propeller is rotating, it is acted upon by certain forces. These forces are: Centrifugal force Centrifugal Twisting Moment (CTM) Aerodynamic Twisting Moment (ATM) Bending forces Thrust and drag. Aircraft propeller 2022-08-24 B1-17 Propeller Page 24 of 228 CASA Part 66 - Training Materials Only  Centrifugal Force Centrifugal force is a force that tends to throw the rotating propeller blades away from the propeller hub. This force can amount to many thousands of newtons. Aviation Australia Centrifugal force on a propeller blade 2022-08-24 B1-17 Propeller Page 25 of 228 CASA Part 66 - Training Materials Only  Centrifugal Twisting Moment Centrifugal Twisting Moment (CTM) is a force which tends to rotate propeller blades toward a fine blade angle on variable pitch propellers. This is the result of the mass of the propeller, located in front of the rotational axis, trying to align itself with the plane of rotation. CTM will always be a greater force than ATM. CTM is a force that propeller manufacturers use to alter blade angle from coarse to fine. Aviation Australia Centrifugal Twisting Moment (CTM) on a propeller blade Force Accentuation Both ATM and CTM (torsional stresses) are increased with an increase in revolutions per minute (i.e. if rpm is doubled, these stresses are quadrupled). 2022-08-24 B1-17 Propeller Page 26 of 228 CASA Part 66 - Training Materials Only  Aerodynamic Twisting Moment Aerodynamic Twisting Moment (ATM) is a force that tries to move the propeller blades to a coarser blade angle. The centre of pressure is in front of the rotational axis of the blade, which is at the mid- point of the chord line. This force tends to increase the blade angle.. Some propeller designs use this force to aid in feathering the propeller. Aviation Australia Aerodynamic twisting moment 2022-08-24 B1-17 Propeller Page 27 of 228 CASA Part 66 - Training Materials Only  Bending Forces Bending force is divided into two components: Torque bending force (caused by drag) Thrust bending force (caused by thrust). Torque Bending Force Torque bending force is a resultant force from the load that air resistance (drag) places on the blades. It bends the propeller blades opposite to the direction of rotation. Torque Bending Force 2022-08-24 B1-17 Propeller Page 28 of 228 CASA Part 66 - Training Materials Only  Thrust Bending Force Thrust bending force is a force which bends the blades forward as the aircraft is pulled through the air. This bending forward of the blades is exerted by the thrust that propels the aircraft forward. Thrust bending force 2022-08-24 B1-17 Propeller Page 29 of 228 CASA Part 66 - Training Materials Only  Force Coupling The coupling of centrifugal force and thrust creates severe stresses which are greater near the hub. The blade face is exposed to tension from centrifugal force as well as from bending. Therefore, the propeller needs to be designed to withstand these stresses, which increase proportionally with rpm. A simple scratch or dent in the blade can have severe repercussions. Stress Analysis of a 2-Blade Propeller 2022-08-24 B1-17 Propeller Page 30 of 228 CASA Part 66 - Training Materials Only  Propeller Angle of Attack To understand how a propeller’s performance can vary, you will need to understand vectors. You should remember from your study of vectors that where a line is drawn to scale, it shows a velocity or force. These lines are drawn to represent speed (i.e., the longer a line is drawn, the faster an item’s speed). The performance (thrust) of a fixed-pitch propeller will vary with variations in: Rotational velocity (rpm) Aircraft velocity (TAS in kt). If a propeller is designed to produce the correct angle of attack (2° to 4°) at say, 1500 rpm and 50 kt forward velocity, then it will produce the required amount of thrust until either rotational velocity or forward velocity alter. Aviation Australia Resultant Angle of Attack Relevant Youtube link: Angle of attack animation 2022-08-24 B1-17 Propeller Page 31 of 228 CASA Part 66 - Training Materials Only  Increased Rotational Velocity If forward velocity is maintained but rotational velocity is increased to 2000 rpm, then it can be seen that the angle of attack has increased. Aviation Australia Increased Rotational Velocity 2022-08-24 B1-17 Propeller Page 32 of 228 CASA Part 66 - Training Materials Only  Increased Forward Velocity If forward velocity is increased (i.e. in a dive) and rotational velocity maintained, then it can be seen that the relative airflow has decreased the angle of attack. This can sometimes give the rotating blades a negative angle of attack, which produces no forward thrust and the propeller now acts like a brake. Aviation Australia Increased Forward Velocity Therefore, changing either rotational velocity or aircraft forward velocity will alter the propeller’s angle of attack. Varying the propeller angle of attack outside its designed parameters will lower the efficiency of that blade and therefore the propeller as a unit. 2022-08-24 B1-17 Propeller Page 33 of 228 CASA Part 66 - Training Materials Only  Blade Tip Speed Versus Efficiency To allow propellers to absorb the enormous power that engines can develop, larger propellers were made. It was found that the increase in propeller diameter did not necessarily increase efficiency. In fact, the larger propellers lost performance through tip vibration or flutter. This flutter or vibration is caused by shock waves as the tip of the propeller approaches the speed of sound, which is approximately 1200 ft/s (or 660 kt) at sea level on a standard day of 15 °C. It was therefore necessary to keep blade tip speed below the speed of sound. This meant the propeller tips had to be below the speed of sound and still be able to absorb the available engine power. This can be achieved in several ways, such as by increasing the number of blades or by increasing blade shape and section. © Aviation Australia Blade tip speed versus power coefficient 2022-08-24 B1-17 Propeller Page 34 of 228 CASA Part 66 - Training Materials Only  Blade Vibration The final force that is exerted on a spinning propeller is blade vibration. When a propeller produces thrust, blade vibration occurs due to the aerodynamic and mechanical forces that are present. Aerodynamic forces tend to bend the propeller blades forward at the tips, producing buffeting and vibration. Mechanical vibrations are caused by the power pulses in a piston engine. Of the two, mechanical vibrations are considered more destructive than aerodynamic vibrations. The reason is that the engine power pulses tend to create standing wave patterns in a propeller blade that can lead to metal fatigue and structural failure. While concentrations of vibrational stress are detrimental at any point on a blade, the most critical location is about 6 in. from the blade tips. Most airframe-engine-propeller combinations have eliminated the detrimental effects of vibrational stresses by careful design. Nevertheless, some engine/propeller combinations do have a critical range in which severe propeller vibration can occur. In this case, the critical range is indicated on the tachometer by a red arc. Engine operation in the critical range should be limited to a brief passage from one rpm setting to another. Aviation Australia Critical RPM Range 2022-08-24 B1-17 Propeller Page 35 of 228 CASA Part 66 - Training Materials Only  Relevant Youtube link: Propeller resonance 2022-08-24 B1-17 Propeller Page 36 of 228 CASA Part 66 - Training Materials Only  Propeller Construction I (17.2) Learning Objectives 17.2.1.1 Explain construction methods and materials used in wooden propellers. 17.2.1.2 Explain construction methods and materials used in composite propellers. 17.2.1.3 Explain construction methods and materials used in metal propellers. 17.2.2 Explain blade station, blade face, blade shank, blade back and hub assembly. 2022-08-24 B1-17 Propeller Page 37 of 228 CASA Part 66 - Training Materials Only  Construction Construction Materials Propeller blades are usually made of one of the following: Wood Steel Aluminium alloy Composite (non-metallic fibre). Although they are made of different materials, all propellers have common design features. Aviation Australia (DK) Mustang 4 blade propeller maintenance 2022-08-24 B1-17 Propeller Page 38 of 228 CASA Part 66 - Training Materials Only  Leading and Trailing Edges Leading Edge The leading edge of a blade (aerofoil shape) is the thick edge that first meets the air as the propeller rotates. Trailing Edge After air has passed the leading edge, it leaves the aerofoil at the trailing edge. The trailing edge of a propeller blade is the rear edge of the blade, the point where the blade camber face and the blade thrust face join. Blade edges Blade Back The blade back is the curved face of the propeller aerofoil and joins the leading and trailing edge. Blade Back Aviation Australia Blade back 2022-08-24 B1-17 Propeller Page 39 of 228 CASA Part 66 - Training Materials Only  Blade Face The flat side of a propeller blade is the blade face. It is on this face that the thrust produced by the blade is felt. Blade Face Chord Line To assist in determining propeller blade angles, all aerofoils have an imaginary straight line drawn through them. This straight line cuts through the centre of the leading edge and the centre of the trailing edge and is known as the chord line. Chord Line 2022-08-24 B1-17 Propeller Page 40 of 228 CASA Part 66 - Training Materials Only  Blade Stations To assist maintenance personnel in locating relevant positions on a blade, the blades have designated distances along their length as measured from the centre of the hub out to the tip of each blade. These ‘blade stations’ are normally measured in 6-in. intervals. If you refer to damage in the leading edge of the propeller at the 20-in blade station, you would normally say it is located between the 18- in. and 24-in. blade stations. Blade Stations 2022-08-24 B1-17 Propeller Page 41 of 228 CASA Part 66 - Training Materials Only  Hub Assembly The hub assembly provides a means of attaching the propeller to the engine and supports the blades. The hub is divided into forward and rear barrel halves to enable fitment of the blades onto the spider, which provides bearing support for the blades for variable-pitch propellers. Hub Assembly 2022-08-24 B1-17 Propeller Page 42 of 228 CASA Part 66 - Training Materials Only  Root (Blade Butt) The round blade root, also known as the blade butt, is the part of the propeller blade which fits into the propeller hub. Blade Root 2022-08-24 B1-17 Propeller Page 43 of 228 CASA Part 66 - Training Materials Only  Blade Shank The blade shank is the cylindrical part of the blade near the blade root. It is usually thick for strength and contributes little or nothing to thrust. Blade Shank 2022-08-24 B1-17 Propeller Page 44 of 228 CASA Part 66 - Training Materials Only  Blade The blade is the aerofoil part of the propeller that converts the torque of the engine into thrust. Blade 2022-08-24 B1-17 Propeller Page 45 of 228 CASA Part 66 - Training Materials Only  Tip The propeller blade tip is the portion of the blade farthest from the hub assembly. It is usually referred to as the last 6 in. of the blade. Blade Tip 2022-08-24 B1-17 Propeller Page 46 of 228 CASA Part 66 - Training Materials Only  Cuff Propeller blade cuffs are designed to restore the round section of the blade shank to an aerofoil shape and thereby increase airflow to the engine. Blade cuffs are usually constructed of metal, wood or plastic and are either clamped or bonded to the blades. Blade Cuff 2022-08-24 B1-17 Propeller Page 47 of 228 CASA Part 66 - Training Materials Only  Wooden Propellers Wooden Propeller Construction Methods The earliest propellers fitted to aircraft were constructed of timber. These propellers were made from several layers of hardwood glued together with high-quality wood glue. Timber Laminated Construction Laminating Timber used for the manufacture of propellers is specially selected, well-seasoned hardwood. The timber should be free from imperfections such as: Holes Loose knots Decay. The timber is layered and glued. The propeller is then placed in a kiln, where the pressure and temperature are carefully controlled for a prescribed time. The propeller is then shaped to its final form using templates and protractors to ensure it meets design specifications. Blade Shaping After shaping, various protective coatings are applied to the propeller, such as varnish, fabric covering and sheathing. 2022-08-24 B1-17 Propeller Page 48 of 228 CASA Part 66 - Training Materials Only  Varnishing Wood, due to changes in moisture content, is subject to: swelling shrinking warping. A protective coating of varnish is applied to the finished propeller to prevent rapid changes in moisture content. Wooden Construction 2022-08-24 B1-17 Propeller Page 49 of 228 CASA Part 66 - Training Materials Only  Leading-Edge Sheathing During take-off and taxiing, small stones and sand can damage the leading edge of the propeller. To protect wooden propeller blades, a metal shield is secured around the tip and along the leading edge. This metal shield is known as either leading-edge tipping or leading-edge sheathing. Small drain holes in the tipping near the blade tip allow moisture from condensation to drain away. Leading-edge sheathing can be made from: Terneplate Monel Brass Stainless steel. The installation of metal sheathing on a propeller blade is shown. Metal Sheathing Relevant Youtube link: Wooden propeller manufacture 2022-08-24 B1-17 Propeller Page 50 of 228 CASA Part 66 - Training Materials Only  Metallic Propellers Steel Propellers Steel propellers and blades are found mainly on antique and transport aircraft. Normally they are of hollow construction but can also be produced as a solid unit. The hollow steel blades are constructed by assembling a rib structure, attaching steel sheets to it, and filling the outer section of the hollow blade with foam to absorb vibration and maintain a rigid structure. Solid steel propellers are forged and machined to the desired contours and the blades are then twisted to achieve the correct pitch. Many of the early solid propellers were manufactured from a lightweight alloy called Duralumin, an alloy of aluminium with copper, manganese and magnesium. These propellers provided better cooling for the engine because of the effective pitch near the hub. These types of propellers are now manufactured from aluminium alloy. Fixed Pitch Steel Propeller Aluminium Alloy Propellers A fixed-pitch aluminium propeller is usually manufactured by forging a single bar of aluminium alloy to the required shape by machine forging, copying the shape of a master blade (sometimes referred to as a profile) onto the bar of aluminium. These propellers incorporate a centre bore to allow fitment of various steel hubs or adaptors, providing for different types of installations. Fixed Pitch Metal 2022-08-24 B1-17 Propeller Page 51 of 228 CASA Part 66 - Training Materials Only  Due to the high strength and malleability of aluminium alloy, the aerofoil extends to the propeller hub. This will not increase thrust as the engine is located immediately behind this area, but it does act to provide increased flow of cooling air to the engine. Anodising Anodising is used to add extra protection to alloy blades. It is an electroplating process that provides a hard coating which is: Corrosion resistant Waterproof Airtight. Anodised metal (aluminium) 2022-08-24 B1-17 Propeller Page 52 of 228 CASA Part 66 - Training Materials Only  Shot Peening This process is itself a finishing treatment and normally requires no other treatments. Nicks, gouges and other minor blade damage can quickly lead to stress cracking. This is predominantly evident on steel propellers due to their relatively brittle characteristic. Shot peening of metals is designed to distribute stresses more evenly in the surface (e.g. around the blade shank) and to increase fatigue strength. The area of a metal propeller which is usually shot peened is shown. Shot (beads/balls of glass, steel, etc.) of a known size are thrown by centrifugal force or air blasted through a nozzle at a prescribed pressure onto the required area. The impact of the shot causes plastic deformation of the surface to a depth of a few thousandths of an inch. If the depth of work needs to be increased, all that is required is for the velocity or size of the shot to be increased. Various types of shot can be used; two common types are steel and glass beads. Shot Peened Areas 2022-08-24 B1-17 Propeller Page 53 of 228 CASA Part 66 - Training Materials Only  Metal Propeller Construction Relevant Youtube link: Hartzell metal propeller manufacture 2022-08-24 B1-17 Propeller Page 54 of 228 CASA Part 66 - Training Materials Only  Composite Propellers Materials used in composite propellers Composite blade construction involves the use of special plastic resins. These resins are reinforced with fibres or filaments composed of one of the following: glass Kevlar carbon boron. There are two ways of constructing a composite blade. One way is to use one of the materials listed above and shape it around an aluminium-alloy spar with foam placed in the leading and trailing edges of the propeller. Composite construction with alloy spar The second method is to use a composite material shell to form the blade profile, into which a foam core is placed to resist distortion. Composite construction using shell 2022-08-24 B1-17 Propeller Page 55 of 228 CASA Part 66 - Training Materials Only  Fibre-Reinforced Plastic (FRP) Moulding The FRP moulding is a variation of the composite blade. The FRP blade consists of a laminated Kevlar shell into which is placed a foam core. To boost the strength of the shell, Kevlar is layered not only lengthwise but also multidirectionally. The leading and trailing edges of the blade are reinforced with solid unidirectional Kevlar. Two unidirectional Kevlar shear webs are placed between the camber and the thrust face surfaces of the shell to resist flexing and buckling. FRP Moulding The polyurethane foam filling supplies additional resistance to any distortion caused by operating stresses that the propeller encounters. Composite materials are commonly retained on the shank primarily by external composite windings. The secondary form of retention is the clamping action of the hub halves. Composite material retention 2022-08-24 B1-17 Propeller Page 56 of 228 CASA Part 66 - Training Materials Only  Composite Propeller Construction Relevant Youtube link: Hartzell composite propeller manufacture 2022-08-24 B1-17 Propeller Page 57 of 228 CASA Part 66 - Training Materials Only  Propeller Construction II (17.2) Learning Objectives 17.2.3 Explain propeller types including fixed pitch, controllable pitch and constant speeding propeller. 17.2.3 Explain types of propeller and spinner installations including; tractor, pusher, contra rotating, and counter rotating (S). 17.2.4 Explain factors that affect propeller selection including engine type, engine power, aircraft type and aircraft performance (S). 17.2.4 Explain mounting requirements of flanged, tapered and splined propeller installations (S). 17.2.4.1 Explain how spinner installations are used to suit the various propeller types. 2022-08-24 B1-17 Propeller Page 58 of 228 CASA Part 66 - Training Materials Only  Propeller Mounting and Installation Requirements Types of Propeller Mounting Installations Correct installation of the propeller onto the engine propeller shaft is critical to safety and to avoid vibration (some props have come off in flight). There are basically three types of installations: Tapered shaft Flanged shaft Splined shaft. Smaller engines have either tapered or flanged propeller mountings, while the bigger engines usually have splined shafts. Tapered Shaft Found mostly on older aircraft of lower horsepower, the engine crankshaft is extended, in a tapered form, to mate with a similarly shaped prop hub. The interference fit of these two surfaces provides the primary transfer of power to the propeller. Ground threads at the end of the shaft accommodate the prop retention nut. The safety holes allow for locking of the nut. The keyway is a long-milled slot in the tapered shaft, and the mating key ‘indexes’ the hub to the shaft to prevent rotary motion between hub and shaft only during installation. In service, the keyway is subject to wear and small cracks – especially in the sharp corners. Close inspection is essential using either dye-penetrant or magnetic particle methods. Safety holes and snap ring of a tapered propeller installation The key to a good fit between hub and shaft is full metal-to-metal contact, with the prop retention nut fully tightened. 2022-08-24 B1-17 Propeller Page 59 of 228 CASA Part 66 - Training Materials Only  Before mating the parts, apply a coating of Prussian blue to the crankshaft end. Carefully mate the two and fully torque the retention nut. Then separate the joint and inspect to see that there is at least a 70% transfer of the blue ink to the hub. If there is less transfer, lapping of the shaft is allowable to manufacturer’s specifications. The key must be inserted into the keyway each time the hub and shaft are mated. Taper shaft applications generally incorporate a snap ring located in the retaining nut and attached to the hub. This item acts as puller, aiding in the removal of the hub by overcoming the interference fit. Flanged Shaft A flanged shaft is a thick, circular flange at the front of the engine crankshaft with a ring of holes, either plain (dowel pins) or threaded. The prop is attached by bolts. A skull cap spinner is fitted to small aircraft as an aerodynamic fairing. Flanged shaft and Skull Cap of a flanged propeller installation 2022-08-24 B1-17 Propeller Page 60 of 228 CASA Part 66 - Training Materials Only  Pre-installation checks include: Inspect the flange for distortion and surface defects (do a ‘run-out’ check on the flange if distortion is suspected). Ensure bolt holes/threads are in good condition. Apply a light coat of oil or anti-seize to the flange and propeller mounting surfaces to aid in the next removal. Conduct a close inspection of attachment bolts – use NDT dye penetrant or magnetic particles to be sure. Ensure retaining nuts are new when replacing self-locking nuts. Splined Shaft A splined shaft is commonly found on the larger turboprops. The splines are evenly pitched and there is usually a master (wider) spline which mates the shaft to the hub in only one position. A tight, but sliding fit is required to prevent fretting and subsequent wear. This wear is checked with a go-no-go gauge and by careful inspection for small cracks, especially in sharp corners (dye penetrant or magnetic particle methods). Splined Shaft Go No-Go gauge Tapered cones are used, front and back, to centre the hub on the prop shaft. The rear cone is one piece, made of bronze, while the front is split, made of steel and manufactured in two matched halves with matching serial numbers. As with tapered-shaft installations, Prussian blue is used on cone faces/hub faces to check the degree of mating after the prop-retaining nut has been fully torqued to pull the surfaces together. 2022-08-24 B1-17 Propeller Page 61 of 228 CASA Part 66 - Training Materials Only  Sometimes the data requires the cones to be fitted ‘dry’, while others specify a light oil coating. When offering the prop to the engine, it is good practice to first fit a protector to the prop shaft screw threads, as it is easy to damage them while installing the propeller. Aviation Australia Propeller splined shaft installation 2022-08-24 B1-17 Propeller Page 62 of 228 CASA Part 66 - Training Materials Only  Taper Bore In variable-pitch applications, a removable bushing is fitted into a forging (taper bore) at the centre of the blade butt to provide a bearing surface for the blades to turn on when blade angle changes occur. This bushing also allows for fitment of a plug which is used to initially balance each blade statically. Taper bore forging This forging, along with the bushing, permits fitment of each blade onto the spider, which is located within the hub of the propeller. Spider Forging 2022-08-24 B1-17 Propeller Page 63 of 228 CASA Part 66 - Training Materials Only  Modern six bladed propeller hub construction 2022-08-24 B1-17 Propeller Page 64 of 228 CASA Part 66 - Training Materials Only  General Propeller Installation Installation checks include: Offer the prop to the shaft in the correct indexing position. Usually, there is a dowel hole or pin to ensure this. Most splined shafts have a master spline. On a small engine without indexing, fit the prop so that the blades are at the 4 and 10 o’clock positions to facilitate hand starting. Insert the bolts, nuts and washers, then lightly tighten the nuts. Tighten the nuts progressively, in the sequence given in the maintenance manual. Note the balance washers may be installed under the bolt head or nut. Correctly torque the prop retention nuts to the tension specified in the manual. For wooden props, a circular faceplate is installed at the front of the hub boss to spread the compression load and thereby protect the wood from crushing. On completion of the installation, a track test will show that blade tips are describing the same tip path plane. Propeller Types. A typical propeller tracking arrangement 2022-08-24 B1-17 Propeller Page 65 of 228 CASA Part 66 - Training Materials Only  Propeller Types Tractor Propeller Tractor propellers are those conventionally mounted in front of the engine powerplant. Tractor propellers ‘pull’ the aircraft through the air. Most aircraft are equipped with this type of propeller. Tractor Propeller 2022-08-24 B1-17 Propeller Page 66 of 228 CASA Part 66 - Training Materials Only  Pusher Propeller Pusher propellers are mounted on a drive shaft from the rear of the engine, producing thrust to ‘push’ the aircraft forward. To reduce the chance of blades being damaged, many pusher propellers are mounted above and behind the wings. Many seaplanes and amphibious aircraft use pusher propellers. Pusher Propeller Fixed-Pitch A fixed-pitch propeller is one whose blade angle cannot be changed. It is designed for a specific purpose (cruise or acceleration). A propeller’s performance will drop off rapidly when it is operated outside of its designed purpose. Fixed-pitch propellers, metal and wooden, are shown. Wooden and metal fixed pitch propellers 2022-08-24 B1-17 Propeller Page 67 of 228 CASA Part 66 - Training Materials Only  Ground-Adjustable The earliest adjustable propellers operated as fixed-pitch propellers. The pitch could be altered only when the propeller was not turning. This was achieved by loosening the retaining clamps or bolts securing each blade in place. With the clamps or bolts loosened, the blades could be adjusted to their required angle with the aid of a protractor. After the clamps have been tightened, the pitch of the blades cannot be changed in flight to meet varying flight conditions. The retaining clamps on a ground-adjustable propeller are shown. Ground Clamp Installation 2022-08-24 B1-17 Propeller Page 68 of 228 CASA Part 66 - Training Materials Only  Controllable-Pitch A controllable-pitch propeller allows blade angle to be changed while the propeller is rotating. These propellers can vary from a two-position propeller to one that can be altered to any angle between minimum and maximum settings. This permits the propeller blade angle (pitch) to be changed to give the best performance for different flight conditions. Early controllable pitch propeller 2022-08-24 B1-17 Propeller Page 69 of 228 CASA Part 66 - Training Materials Only  Constant-Speed A controllable-pitch propeller fitted to an aircraft can be turned into a constant-speed propeller by the addition of a speed-sensitive governor. This allows a selected engine speed (on directly coupled engine propeller units) or propeller speed to be maintained (on a free turbine engine propeller combination). If the engine rpm varies, the propeller blade angle is changed by the governor to bring the rpm back to the selected speed. This type of system produces the most efficient operating propeller under all conditions, reduces pilot workload and protects the engine from large rpm fluctuations. These effects will be covered in detail in the next section. © Aviation Australia Constant speeding propeller (Governor) 2022-08-24 B1-17 Propeller Page 70 of 228 CASA Part 66 - Training Materials Only  Contra-Rotating Contra-rotating propellers are two separate propellers mounted in line on two concentric shafts which rotate in opposite directions. The primary reason for fitment of contra-rotating propellers is to absorb (and therefore efficiently use) the output of high-powered engines. An advantage of this type of propeller is the cancellation of torque reaction and a reduction of the spiralling slipstream (i.e. much straighter airflow). Contra rotating type propellers 2022-08-24 B1-17 Propeller Page 71 of 228 CASA Part 66 - Training Materials Only  Counter-Rotating Counter-rotating propellers should not be confused with contra-rotating applications. The term counter-rotating refers to a twin-engine application in which the propellers on each engine turn in opposite directions of rotation to counteract torque reaction and gyroscopic effects. Counter rotating type propellers 2022-08-24 B1-17 Propeller Page 72 of 228 CASA Part 66 - Training Materials Only  Feathering A feathered propeller is of the controllable-pitch propeller type. On multi-engine aircraft, feathering capabilities must be utilised to allow the pilot to maintain single-engine performance and controllability of the aircraft. The failed engine, if not feathered, will produce excessive drag on the failed engine side due to windmilling of the propeller. Feathering also prevents further damage or destruction of a failed engine. These propellers have a mechanism to change the blade angle to such a position that propeller rotation stops, i.e. the blade chord (at a set distance from the hub) is parallel to the direction of flight. The leading edge of the propeller faces the same direction the aircraft is flying, preventing the propeller from windmilling. Feathered blade angle comparisons 2022-08-24 B1-17 Propeller Page 73 of 228 CASA Part 66 - Training Materials Only  Reversing Reversing permits an aircraft to reduce: Landing runs Brake wear Tyre wear. Reverse is used to slow the aircraft down upon landing and therefore shorten the landing roll. Reversing also assists in ground handling by allowing the aircraft to be taxied backwards. When reverse has been selected in the cockpit, the propeller blades rotate from a positive angle that will maintain flight (airflow rearward – forward thrust) to a negative angle in which thrust is now being produced rearwards (airflow forward – rearward/negative thrust). A comparison between negative/reverse angle and positive/forward angle is shown. Positive pitch angle 2022-08-24 B1-17 Propeller Page 74 of 228 CASA Part 66 - Training Materials Only  Negative pitch angle 2022-08-24 B1-17 Propeller Page 75 of 228 CASA Part 66 - Training Materials Only  Propeller Effects on Operation Propeller Selection Some factors to consider when selecting a propeller are: Engine power – the propeller needs to be able to absorb the available engine torque. Engine type – the method of propeller attachment to the engine, i.e. pusher/tractor type, splined/tapered propeller shaft, reciprocating/gas turbine, etc. Aircraft design – clearances between the ground, fuselage, tailplane and engine nacelle all need to be considered as well as the effect of the airflow over the wings, tailplane, control surfaces, etc. Aircraft performance – aircraft operating altitude, cruising speed, landing, take-off roll, etc. These factors and others, such as cost and availability, need to be considered when selecting a suitable propeller for specific applications. © Aviation Australia Propeller selection for engine type and power 2022-08-24 B1-17 Propeller Page 76 of 228 CASA Part 66 - Training Materials Only  Engine Power Requirements and Performance Factors The propeller must be able to absorb the power provided to it by the engine; otherwise, the propeller will race (speed up) and both propeller and engine will become inefficient. The following four factors need to be considered when a propeller is to be chosen for an engine with known power output: Propeller diameter Number of blades (on the propeller) Propeller blade shape and section Propeller mass (solidity). © Aviation Australia Various aircraft propellers 2022-08-24 B1-17 Propeller Page 77 of 228 CASA Part 66 - Training Materials Only  Propeller Diameter As mentioned earlier, as power increased, so did propeller diameter. The diameter of propellers had to be limited due to the tips reaching the speed of sound. This limitation was overcome by either using contra-rotating propellers or increasing the number of blades fitted to the propeller. Fitting of contra-rotating propellers to an engine is in effect putting two propellers onto the one engine, thereby allowing the diameter of the propeller to be reduced. © Aviation Australia Propeller diameter 2022-08-24 B1-17 Propeller Page 78 of 228 CASA Part 66 - Training Materials Only  Number of Blades To reduce the overall size of a propeller, one method used is to increase the number of blades fitted to it. This allows engine power to be absorbed without increasing the propeller diameter. Of the four factors, increasing the number of blades is the most efficient method of absorbing increasing engine power. Propeller blade configurations 2022-08-24 B1-17 Propeller Page 79 of 228 CASA Part 66 - Training Materials Only  Blade Shape and Section Another method used to absorb power from an engine is to alter the shape or camber of the propeller blade; this effectively increases the thrust of a propeller. However, if camber is increased to produce extra lift, then drag is also increased. To achieve a balance, a compromise must be made in relation to the propeller’s shape and size. Adding to the increased drag is the extra weight that each propeller blade would incur. Any advantage in lift would therefore be lost by the penalty of the increase in drag and added weight of each blade. A blade with an increase in camber, showing the proportional increase in size and therefore an increase in weight, is shown. Blade Shape 2022-08-24 B1-17 Propeller Page 80 of 228 CASA Part 66 - Training Materials Only  Propeller Solidity The solidity of a propeller is determined by the area between the part of the propeller disc which is solid when viewed from the front (blades, dome, etc.), and the part which is air. The propeller area may be 10% of the total area of the disc; therefore, its solidity is 1:10. In real terms, it would be impractical to calculate the area of the blade and the area of the propeller disc because each blade surface is an irregular shape, making area calculation difficult. The same result can be easily obtained by using a ratio comparison. This ratio is measured by adding up all the blade chord lengths at a certain blade station (usually the master station) and dividing this sum by the circumference of that radius. The greater the solidity, the greater the power that can be absorbed. Propeller Solidity To increase a propeller’s solidity: Increase the number of blades (considering propeller diameter) Increase the blade’s chord length (width) Fitment of contra-rotating propellers. This will increase the prop’s solidity and therefore thrust. 2022-08-24 B1-17 Propeller Page 81 of 228 CASA Part 66 - Training Materials Only  Spinner Installation Propeller Spinner Types The spinner assembly is a cone-shaped configuration which mounts on the propeller and encloses the dome and barrel to reduce drag. A skull cap spinner is fitted to small aircraft as an aerodynamic fairing. Skull cap spinner When a skull cap spinner is used, a mounting bracket is installed behind two of the propeller’s mounting bolts. Once the mounting bracket is installed, the skull cap is attached to the bracket with a bolt and washer. If a full spinner is used, a rear bulkhead is slipped on the flange before the propeller is installed. 2022-08-24 B1-17 Propeller Page 82 of 228 CASA Part 66 - Training Materials Only  Full spinner After the propeller is mounted, a front bulkhead is placed on the front of the hub boss before the bolts are inserted. After the bolts are tightened and safetied, the spinner is installed with machine screws. The machine screws are inserted through the spinner into nut plates on the bulkheads. If the spinner is indexed, line up the index marks during installation to avoid vibration. Large aircraft have a full spinner mounted to a forward hub bulkhead. 2022-08-24 B1-17 Propeller Page 83 of 228 CASA Part 66 - Training Materials Only  Aviation Australia Large propeller assembly The spinner has two sections made up of the front spinner and rear spinner sections. Blade cuffs are normally fitted to streamline the shanks and transform the round shank into an aerofoil section on large propellers. These blade cuffs can be made of composite material or metal. 2022-08-24 B1-17 Propeller Page 84 of 228 CASA Part 66 - Training Materials Only  Propeller Pitch Control I (17.3) Learning Objectives 17.3.1.1 Explain speed control and pitch change methods (Level 2). 17.3.1.2 Explain mechanical, electrical and electronic feathering (Level 2). 2022-08-24 B1-17 Propeller Page 85 of 228 CASA Part 66 - Training Materials Only  Pitch Change Mechanisms Variable Pitch Propeller Applications Many various types of aircraft operate in different flying conditions; no one propeller will suit all aircraft and conditions. These include variable-pitch propellers fitted to: Piston Engines Turboprop engines with a direct-drive propeller Turboprop engines with a free-turbine drive propeller. Therefore, different pitch changing mechanisms and systems were developed to vary the propeller blade pitch to suit a particular aircraft and operating condition. These systems include: Manual Mechanical Electrical and electronic Counterweight and hydraulic Hydromatic. Aviation Australia Propellers on piston and turboprop engines 2022-08-24 B1-17 Propeller Page 86 of 228 CASA Part 66 - Training Materials Only  Manual Pitch Change The earliest manual pitch change developed was the ground-adjustable propeller as discussed previously in the Propeller Construction section. The blade angle was changed, with the engine not turning and the clamps holding the blades in their position, loosened to adjust the blade angle to suit a cruise, climb or standard blade angle and re-tightening the clamps after adjustment. Aviation Australia Manual Pitch change 2022-08-24 B1-17 Propeller Page 87 of 228 CASA Part 66 - Training Materials Only  Mechanical Mechanical controls are not a new concept, having been used on aircraft as early as 1917. Mechanical pitch change An example of a mechanical controllable-pitch design is the Beech Roby, for light aircraft which only need a small pitch range. This propeller is controllable from the cockpit, allowing the pilot to set the best blade angle for varying flight conditions. There is a small crank handle on the instrument panel. When it is rotated, a connecting flexible cable rotates a pinion drive gear. This meshes with a large driven gear which is located around the crankshaft and mounted on the engine crankcase/nose section. Cockpit propeller pitch control handle 2022-08-24 B1-17 Propeller Page 88 of 228 CASA Part 66 - Training Materials Only  Mechanical pitch change mechanism hub Rotary motion of the driven gear is translated into axial pitch changing via helical slots in the driven gear flange. Lug pins in the actuator flange slide in the slots. The two arms of the actuator extend forward into the prop hub and connect to an actuating pin in each blade base. Thus, axial movement of the actuator causes the blade angle to change. A cockpit gauge displays the blade angle. It is not a constant speeding prop There is no rpm governor. One variation is to use an electric motor to drive the pinion gear. A pair of microswitches is used to stop the motor at the high and low blade angle positions. This operation is described under the Electric System heading. 2022-08-24 B1-17 Propeller Page 89 of 228 CASA Part 66 - Training Materials Only  Electric The electric pitch-changing mechanism enables light aircraft, of as little as 25 horsepower, to be fitted with controllable-pitch propellers. This system was used because it was less expensive and complex than a constant speed system. The control for an electric motor is managed by the pilot via a three-position toggle switch with the settings of: Increase rpm Decrease rpm Off. The electric motor is mounted near the rear of the propeller onto a fixed sleeve. This motor drives a large outer-toothed ring gear, the same as in the previously described mechanical system. As this ring gear is rotated by the electric motor, microswitches limit the end of travel by switching off electrical power. Simple electric pitch changing mechanism On more complex electric pitch-control mechanisms, the electric pitch change is an electric motor located in the hub of the propeller, with slip rings providing the flow of electrical power to the pitch change mechanism. Electrical sensors within the hub provide all the control, including constant speeding and feathering. 2022-08-24 B1-17 Propeller Page 90 of 228 CASA Part 66 - Training Materials Only  The Curtiss Electric Propeller. Curtis-Wright publication 1943 Advanced electric pitch changing Mechanism Propeller Electronic Control (PEC) PEC System Description The primary components of the PEC system are the Pitch Control Unit (PCU), the feathering pump, the overspeed governor and the beta tubes. The system gets inputs from: Cockpit controls Condition lever Power lever Feather/unfeather switches Propeller speed probe Auto-thrust system Full Authority Digital Engine Control (FADEC) system. During the engine start sequence, when the condition lever is set to RUN (and the aircraft is on the ground), the FADEC sets the system to Beta mode. In Beta mode, the system changes the pitch of the propeller as a function of the power lever angle. The Beta feedback transducer sends data about the position of the Beta tubes (and thus the pitch of the propeller) to the FADEC. When the aircraft is in flight (with the power lever between Flight Idle and MAX), the system controls the propeller in constant speed Alpha mode. 2022-08-24 B1-17 Propeller Page 91 of 228 CASA Part 66 - Training Materials Only  When Auto-Feather mode is armed, the FADEC system will immediately feather the propeller of the failed engine. Two different parameters are used to detect the failed engine. The engine speed sensor is used during low power, and the engine torquemeter signal is used at higher power settings. After landing, the FADEC sets the system to Beta mode when these two conditions are correct: The power lever is between Flight Idle and Ground Idle The FADEC gets an aircraft-on-ground signal. With the system in Beta mode, the pitch of the propeller is related to the power lever angle. When the power lever is set to Reverse, the system sets the propeller in the reverse pitch position. In this configuration, the system operates in the reverse governing mode and keeps the speed of the propeller between idle and minimum constant speed range rpm. The function to limit the speed of the propeller (directly coupled gas turbine engine or free power turbine) is as follows: The FADEC software adjusts the propeller blade angle through the PCU to control the propeller speed. A hydro-mechanical overspeed governor supplies the emergency protection if the propeller or free- turbine rotor overspeed condition occurs (power changes momentarily or failure occurs). If the propeller or free-turbine speed is more than the limit for the propeller governor, the FADEC software sends signals that decrease the fuel flow, and thus the engine power level. The FADEC has microprocessor-independent overspeed protection to stop the flow of fuel. This prevents an overspeed condition that can cause damage to the engine. On the latest generation of turboprop aircraft, the cockpit controls are reduced to one power lever for each engine, with all other selections being fully automated. This includes automatic synchronising and synchrophasing, which reduce engine and propeller vibration. These functions will be covered later in this topic. 2022-08-24 B1-17 Propeller Page 92 of 228 CASA Part 66 - Training Materials Only  Engine power levers incorporating automatic propeller control (no condition levers) Counterweight and Hydraulic Combination Before we continue with this subject, it will be beneficial to discuss the overall theory of variable- pitch propellers, which use a hydraulic medium to change the blade angle. The blades of a variable-pitch propeller, regardless of how sophisticated the control mechanism is, will only ever move the blades to increase or decrease pitch. The most convenient hydraulic force available in all engines is the supply of oil under pressure that is used to lubricate all the mechanical components. In its simplest form, this oil pressure is used to move the blade angle to fine pitch. This is convenient because on take-off, the engine is at its maximum rpm, therefore maximum oil pressure, and the blade angle desired for this is a fine pitch. The propeller manufacturer will decide what will be used to move the blades the other way, that is, to coarse pitch. This can be achieved with counterweights, springs, pneumatic pressure or hydraulic force, with consideration given to the forces of centrifugal and aerodynamic twisting moments which are always present. This knowledge is the beginning of understanding variable pitch propeller control systems. There are, however, many variations used by different manufacturers to control propellers. 2022-08-24 B1-17 Propeller Page 93 of 228 CASA Part 66 - Training Materials Only  Two-Position Propeller (Bracket Type) Two and three bladed bracket propellers The two-position propeller, or bracket-type propeller, is the most basic design which is not dependent upon an engine-driven governor. The propeller can be positioned in a fine or coarse position from the cockpit by a lever that controls engine oil pressure to the hub. Engine oil pressure overrides the counterweights and results in a full fine pitch. This pressure is dumped back to the engine crankcase on coarse selection, and the counterweights move the blades to a full coarse pitch. These systems use: Centrifugal Twisting Moment (CTM) to move to fine Centrifugal force (acting on the counterweights) to move to coarse Engine oil pressure to move to fine. These are the forces acting on a two-position propeller and their directions. Note: This system uses a stationary piston and a movable cylinder. It is the cylinder that extends and retracts to set blade angles. 2022-08-24 B1-17 Propeller Page 94 of 228 CASA Part 66 - Training Materials Only  Aviation Australia Forces on a two position propeller Fine Blade Angle The centrifugal forces acting on the counterweights are overcome by engine oil pressure acting to move the cylinder out, and by the CTM acting on the blades, thereby altering the blade angle to a finer pitch. Finer pitch angle 2022-08-24 B1-17 Propeller Page 95 of 228 CASA Part 66 - Training Materials Only  Coarse Blade Angle As the lever-operated control valve is repositioned, oil flows out of the cylinder. The counterweights are physically attached to each blade and the moveable cylinder. With the oil pressure dissipating from within the cylinder, centrifugal force acting on the counterweights is used to overcome the CTM acting on the blades and move the cylinder rearwards. The blades, attached to the counterweights, will alter to a coarser pitch. Coarser pitch angle To turn this two-position propeller into a constant speed unit, all that is required is the addition of a speed-sensitive governor t