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Module 17 –PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
MODULE 17 SUB MODULE 17.2 PROPELLER CONSTRUCTION
Rev. 00 Oct 2006
17.2 For Training Purposes Only
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Contents
Page
Propeller Materials And Construction ..........................................2 Metal Propellers ............................................................................2 Composite Propeller Blades..........................................................4 Hartzell Blade Construction..........................................................4 Hamilton-Standard Blade Construction ........................................6 Dowty Rotol Blade Construction ..................................................6 Propeller Shafts .............................................................................8 Propeller Spinners .......................................................................10
Rev. 00 Oct 2006
i For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
“The training notes and diagrams are compiled by SriLankan Technical Training and although comprehensive in detail, they are intended for use only with a Course of instruction. When compiled, they are as up to date as possible, and amendments to the training notes and diagrams will NOT be issued”.
Rev. 00 Oct 2006
1 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL PROPELLER MATERIALS AND CONSTRUCTION
METAL PROPELLERS
For decades, propellers used on low-powered engines were made of laminated hardwood and had a fixed pitch. When more power had to be absorbed, propellers made of metal became widely used, with forged aluminium alloy being the most popular metal.
Improvements in metallurgy and manufacturing techniques have enabled metal propellers to replace wood propellers for modern commercially manufactured aircraft. Figure 17.24 shows a metal construction propeller blade. Metal propellers are forged from high-strength aluminium alloy, and after being ground to their finished dimensions and pitch, are anodised to protect them from corrosion. Metal propellers cost more than wood for the same engine and aeroplane, but their increased durability, resistance to weathering, and ability to be straightened after minor damage have made them more cost effective in the long term.
Some of the most modern blades are made of composite materials. Composite blades are much lighter than metal blades and capable of absorbing the same amount of power. The lighter blades impose less centrifugal loading on the hub, allowing it to be made lighter. They have a very low notch sensitivity, and their foam cores absorb much of the vibration that would damage metal propellers. While composite blades currently cost more than metal blades, their greater efficiency and longer life make them much more cost effective.
Rev. 00 Oct 2006
Some propellers have blades made of steel with the blade halves stamped of thin sheet steel and brazed together along the leading and trailing edges. The blade shell is then installed over a tubular steel shank. A few propellers with hollow steel blades are still flying, but these are usually found only on specialpurpose aeroplanes.
2 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.24
Rev. 00 Oct 2006
3 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL COMPOSITE PROPELLER BLADES
HARTZELL BLADE CONSTRUCTION
Laminated wood, forged aluminium alloy, and brazed sheet steel propellers have been standard for decades. But the powerful turboprop engines and the demands for higher-speed flight and quieter operation have caused propeller manufacturers to exploit the advantages of modern advanced composite materials.
The typical Hartzell composite propeller, like that in Figures 17.25 and 17.26, has a machined aluminium alloy shank, and moulded into this shank is a low density foam core. Slots are cut into the foam core and unidirectional Kevlar shear webs are inserted. The leading and trailing edges are solid sections made of unidirectional Kevlar and laminations of pre-impregnated material are cut and laid up over the core foundation to provide the correct blade thickness, aerofoil shape, pitch distribution, planform and ply orientation.
Composite materials used in the propeller manufacturing consist of two constituents: the fibres and the matrix. The fibres most generally used are glass, graphite and aramid (Kevlar), and the matrix is a thermosetting resin such as epoxy.
The outer shell is held in place on the aluminium alloy shank by Kevlar filaments impregnated with epoxy resin wound around the portion of the shell that grips the shank. Some Hartzell blades have a stainless steel mesh under the final layer of Kevlar to protect against abrasion, and a nickel leading edge erosion shield is bonded in place. The entire blade is put into a blade press and cured under computer-controlled heat and pressure.
The strength and stiffness of the blades are determined by the material, diameter and orientation of the fibres. The matrix material supports the fibres, holds them in place and completely encapsulates them for environmental protection. Because the fibres have strength only parallel to their length, they are arranged in such a way that they can sustain tensile loads.
Figure 17.27 shows the method of blade retention of a Hartzell composite propeller blade.
Rev. 00 Oct 2006
4 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.25
Fig 17.26 Fig 17.27
Rev. 00 Oct 2006
5 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL HAMILTON-STANDARD BLADE CONSTRUCTION
DOWTY ROTOL BLADE CONSTRUCTION
The Hamilton-Standard blade has tremendous strength and fatigue resistance because of its solid aluminium alloy spar enclosed in a glass fibre shell (Figure 17.28). The spar is machined to its correct configuration and placed in a mould cavity, and the core foam is injected around it. The foam is cured and removed from the mould. Glass fibre cloth, with the correct number of plies and the proper ply orientation, is then laid over the cured core. The complete item is then placed in a second mould that has the shape of the finished blade. The resin matrix is injected to impregnate all the fibres, and is cured with heat and pressure.
The Dowty Rotol composite propeller blade has two carbon fibre spars that run the length of the blade on both the face and back and come smoothly together at the blade root (Figure 17.29). The carbon fibres and pre-impregnated glass fibre cloth are laid with the correct number of plies and the correct ply orientation and are placed in a mould. Polyurethane foam is injected into the inside of the blade, and the entire unit is cured under heat and pressure.
Rev. 00 Oct 2006
The Dowty Rotol blade is secured in the hub by expanding the carbon fibre spars with tapered glass fibre wedges and locking them between the inner and outer sleeves (Figure 17.30).
6 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.28
Fig 17.30 Fig 17.29
Rev. 00 Oct 2006
7 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
The inside of the propeller hub is splined to match the shaft and the hub is centred on the shaft with two cones (Figure 17.33). The rear cone is a single-piece split bronze cone, and is considered to be part of the engine. The front is a two piece hardened steel cone and is considered to be part of the propeller. The two halves are marked with the same serial number to ensure that only a matched set is used. Prior to attaching this type of propeller, a check is carried out to ensure correct contact of the cones.
PROPELLER SHAFTS Most modern engines, both reciprocating and turbine, have flanged propeller shafts. Some of these flanges have integral internally threaded bushings that fit into counterbores in the rear of the propeller hub around each bolt hole. Propellers with these bushings are attached to the shaft with long bolts that pass through the propeller. On others the flange has a ring of holes and bolts pass from the engine side into threads in the propeller. Some flanges have index pins in the propeller flange so the propeller can be installed in only one position relative to the shaft. See Figure 17.31. This is done for synchronising and/or synchrophasing.
Engineers blue is applied to the cones and the propeller is fitted and torque loaded. The propeller is then removed and visually inspected to ensure that there is an even contact of 80% as seen by the blue around the cone on the propeller. If 80% of contact is not in evidence then the cone can be ‘stoned’ to fit, or replaced.
The most popular type of propeller shaft on the larger turboprop engines is the splined shaft. The sizes of splined shafts are identified by an SAE (Society of Automotive Engineers) number, SAE 20 splines are used on engines in the 200-horsepowered range; SAE 30 splines are used in the 300- and 400horsepowered range, and SAE 40 in the 500- and 600horsepowered range. SAE 50 in the 1,000-horsepowered range and SAE 60 and 70 are used for larger engines. Splines are longitudinal grooves cut in the periphery of the shaft. The grooves and lands (the space between the grooves), as shown in Figure 17.32 are the same size, and one groove is either missing or has a screw in it to form a master spline. The purpose of the master spline is the same as the index pin.
Rev. 00 Oct 2006
8 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.31
Fig 17.33
Fig 17.32
Rev. 00 Oct 2006
9 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL PROPELLER SPINNERS All modern propeller-driven aircraft have spinners over their propeller hubs. These spinners have the dual aerodynamic function of streamlining the engine installation and directing cool air into the openings in the cowling. Figures 17.34 and 17.35 show a typical spinner installation over a constant speed propeller. The spinner bulkhead is installed on the propeller shaft flange and held in place by attaching bolts. The propeller is then installed so that the dowel pins in the propeller hub align with the holes in the flange. The propeller attaching nuts are installed and tightened to the torque value specified in the aircraft maintenance manual. If a spinner support is required, it is installed and the spinner is secured to the bulkhead with the correct fixing screws. The propeller spinner and bulkhead are critical components, and cracks in either one can be repaired only if they do not exceed the allowable limits. Repairs can be performed using the procedures in the aircraft maintenance manual, although special care must be taken not to add weight where it could cause vibration.
Rev. 00 Oct 2006
10 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.35 Fig 17.34
Rev. 00 Oct 2006
11 For Training Purposes Only
17.2
CATEGORY B1– MECHANICAL
MODULE 17 SUB MODULE 17.2 PROPELLER CONSTRUCTION
Rev. 00 Oct 2006
17.2 For Training Purposes Only
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Contents
Page
Propeller Materials And Construction ..........................................2 Metal Propellers ............................................................................2 Composite Propeller Blades..........................................................4 Hartzell Blade Construction..........................................................4 Hamilton-Standard Blade Construction ........................................6 Dowty Rotol Blade Construction ..................................................6 Propeller Shafts .............................................................................8 Propeller Spinners .......................................................................10
Rev. 00 Oct 2006
i For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
“The training notes and diagrams are compiled by SriLankan Technical Training and although comprehensive in detail, they are intended for use only with a Course of instruction. When compiled, they are as up to date as possible, and amendments to the training notes and diagrams will NOT be issued”.
Rev. 00 Oct 2006
1 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL PROPELLER MATERIALS AND CONSTRUCTION
METAL PROPELLERS
For decades, propellers used on low-powered engines were made of laminated hardwood and had a fixed pitch. When more power had to be absorbed, propellers made of metal became widely used, with forged aluminium alloy being the most popular metal.
Improvements in metallurgy and manufacturing techniques have enabled metal propellers to replace wood propellers for modern commercially manufactured aircraft. Figure 17.24 shows a metal construction propeller blade. Metal propellers are forged from high-strength aluminium alloy, and after being ground to their finished dimensions and pitch, are anodised to protect them from corrosion. Metal propellers cost more than wood for the same engine and aeroplane, but their increased durability, resistance to weathering, and ability to be straightened after minor damage have made them more cost effective in the long term.
Some of the most modern blades are made of composite materials. Composite blades are much lighter than metal blades and capable of absorbing the same amount of power. The lighter blades impose less centrifugal loading on the hub, allowing it to be made lighter. They have a very low notch sensitivity, and their foam cores absorb much of the vibration that would damage metal propellers. While composite blades currently cost more than metal blades, their greater efficiency and longer life make them much more cost effective.
Rev. 00 Oct 2006
Some propellers have blades made of steel with the blade halves stamped of thin sheet steel and brazed together along the leading and trailing edges. The blade shell is then installed over a tubular steel shank. A few propellers with hollow steel blades are still flying, but these are usually found only on specialpurpose aeroplanes.
2 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.24
Rev. 00 Oct 2006
3 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL COMPOSITE PROPELLER BLADES
HARTZELL BLADE CONSTRUCTION
Laminated wood, forged aluminium alloy, and brazed sheet steel propellers have been standard for decades. But the powerful turboprop engines and the demands for higher-speed flight and quieter operation have caused propeller manufacturers to exploit the advantages of modern advanced composite materials.
The typical Hartzell composite propeller, like that in Figures 17.25 and 17.26, has a machined aluminium alloy shank, and moulded into this shank is a low density foam core. Slots are cut into the foam core and unidirectional Kevlar shear webs are inserted. The leading and trailing edges are solid sections made of unidirectional Kevlar and laminations of pre-impregnated material are cut and laid up over the core foundation to provide the correct blade thickness, aerofoil shape, pitch distribution, planform and ply orientation.
Composite materials used in the propeller manufacturing consist of two constituents: the fibres and the matrix. The fibres most generally used are glass, graphite and aramid (Kevlar), and the matrix is a thermosetting resin such as epoxy.
The outer shell is held in place on the aluminium alloy shank by Kevlar filaments impregnated with epoxy resin wound around the portion of the shell that grips the shank. Some Hartzell blades have a stainless steel mesh under the final layer of Kevlar to protect against abrasion, and a nickel leading edge erosion shield is bonded in place. The entire blade is put into a blade press and cured under computer-controlled heat and pressure.
The strength and stiffness of the blades are determined by the material, diameter and orientation of the fibres. The matrix material supports the fibres, holds them in place and completely encapsulates them for environmental protection. Because the fibres have strength only parallel to their length, they are arranged in such a way that they can sustain tensile loads.
Figure 17.27 shows the method of blade retention of a Hartzell composite propeller blade.
Rev. 00 Oct 2006
4 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.25
Fig 17.26 Fig 17.27
Rev. 00 Oct 2006
5 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL HAMILTON-STANDARD BLADE CONSTRUCTION
DOWTY ROTOL BLADE CONSTRUCTION
The Hamilton-Standard blade has tremendous strength and fatigue resistance because of its solid aluminium alloy spar enclosed in a glass fibre shell (Figure 17.28). The spar is machined to its correct configuration and placed in a mould cavity, and the core foam is injected around it. The foam is cured and removed from the mould. Glass fibre cloth, with the correct number of plies and the proper ply orientation, is then laid over the cured core. The complete item is then placed in a second mould that has the shape of the finished blade. The resin matrix is injected to impregnate all the fibres, and is cured with heat and pressure.
The Dowty Rotol composite propeller blade has two carbon fibre spars that run the length of the blade on both the face and back and come smoothly together at the blade root (Figure 17.29). The carbon fibres and pre-impregnated glass fibre cloth are laid with the correct number of plies and the correct ply orientation and are placed in a mould. Polyurethane foam is injected into the inside of the blade, and the entire unit is cured under heat and pressure.
Rev. 00 Oct 2006
The Dowty Rotol blade is secured in the hub by expanding the carbon fibre spars with tapered glass fibre wedges and locking them between the inner and outer sleeves (Figure 17.30).
6 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.28
Fig 17.30 Fig 17.29
Rev. 00 Oct 2006
7 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
The inside of the propeller hub is splined to match the shaft and the hub is centred on the shaft with two cones (Figure 17.33). The rear cone is a single-piece split bronze cone, and is considered to be part of the engine. The front is a two piece hardened steel cone and is considered to be part of the propeller. The two halves are marked with the same serial number to ensure that only a matched set is used. Prior to attaching this type of propeller, a check is carried out to ensure correct contact of the cones.
PROPELLER SHAFTS Most modern engines, both reciprocating and turbine, have flanged propeller shafts. Some of these flanges have integral internally threaded bushings that fit into counterbores in the rear of the propeller hub around each bolt hole. Propellers with these bushings are attached to the shaft with long bolts that pass through the propeller. On others the flange has a ring of holes and bolts pass from the engine side into threads in the propeller. Some flanges have index pins in the propeller flange so the propeller can be installed in only one position relative to the shaft. See Figure 17.31. This is done for synchronising and/or synchrophasing.
Engineers blue is applied to the cones and the propeller is fitted and torque loaded. The propeller is then removed and visually inspected to ensure that there is an even contact of 80% as seen by the blue around the cone on the propeller. If 80% of contact is not in evidence then the cone can be ‘stoned’ to fit, or replaced.
The most popular type of propeller shaft on the larger turboprop engines is the splined shaft. The sizes of splined shafts are identified by an SAE (Society of Automotive Engineers) number, SAE 20 splines are used on engines in the 200-horsepowered range; SAE 30 splines are used in the 300- and 400horsepowered range, and SAE 40 in the 500- and 600horsepowered range. SAE 50 in the 1,000-horsepowered range and SAE 60 and 70 are used for larger engines. Splines are longitudinal grooves cut in the periphery of the shaft. The grooves and lands (the space between the grooves), as shown in Figure 17.32 are the same size, and one groove is either missing or has a screw in it to form a master spline. The purpose of the master spline is the same as the index pin.
Rev. 00 Oct 2006
8 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.31
Fig 17.33
Fig 17.32
Rev. 00 Oct 2006
9 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL PROPELLER SPINNERS All modern propeller-driven aircraft have spinners over their propeller hubs. These spinners have the dual aerodynamic function of streamlining the engine installation and directing cool air into the openings in the cowling. Figures 17.34 and 17.35 show a typical spinner installation over a constant speed propeller. The spinner bulkhead is installed on the propeller shaft flange and held in place by attaching bolts. The propeller is then installed so that the dowel pins in the propeller hub align with the holes in the flange. The propeller attaching nuts are installed and tightened to the torque value specified in the aircraft maintenance manual. If a spinner support is required, it is installed and the spinner is secured to the bulkhead with the correct fixing screws. The propeller spinner and bulkhead are critical components, and cracks in either one can be repaired only if they do not exceed the allowable limits. Repairs can be performed using the procedures in the aircraft maintenance manual, although special care must be taken not to add weight where it could cause vibration.
Rev. 00 Oct 2006
10 For Training Purposes Only
17.2
Module 17 – PROPELLER Sub Module 17.2 – PROPELLER CONSTRUCTION
CATEGORY B1– MECHANICAL
Fig 17.35 Fig 17.34
Rev. 00 Oct 2006
11 For Training Purposes Only
17.2
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