module 17a-02 pr opelle r

Sky Exams: PART 66 courseware Category A B1 B2 B3
Level 1 2 3
17A –Propeller 02–Propeller construction
Mo d u l e 1 7A-02 Prope l l e r
Propeller Construction
Level 1 2 3
Table of contents
I. BLADE STATION, BLADE FACE, BLADE SHANK AND HUB ASSEMBLY ................................................................................................................................... 3 1. TERMINOLOGY ........................................................................................................................................................................................................................................ 3 1.1. Hub assembly ....................................................................................................................................................................................................................................... 4 1.2. Three blade, constant speed propeller hub assembly .................................................................................................................................................................... 5
II. CONSTRUCTION METHODS AND MATERIALS USED IN WOODEN, COMPOSITE AND METAL PROPELLER.................................................................... 7 1. WOODEN PROPELLERS: ...................................................................................................................................................................................................................... 7 2. COMPOSITE PROPELLERS: ................................................................................................................................................................................................................ 8 2.1. Types of composite propellers: .......................................................................................................................................................................................................... 8 2.2. Properties of composite propellers .................................................................................................................................................................................................... 8
3. METAL PROPELLERS: ........................................................................................................................................................................................................................... 8 III. FIXED PITCH, CONTROLABLE PITCH, CONSTANT SPEEDING PROPELLER ......................................................................................................................... 10
1. FIXED PITCH PROPELLER: ................................................................................................................................................................................................................ 10 2. GROUND ADJUSTABLE PROPELLER: ........................................................................................................................................................................................... 12 3. CONSTANT SPEED OR AUTOMATIC PROPELLER: .................................................................................................................................................................... 13
IV. PROPELLER/SPINNER INSTALLATION ............................................................................................................................................................................................. 16
Level 1 2 3
I. BLADE STATION, BLADE FACE, BLADE SHANK AND HUB ASSEMBLY
1. TERMINOLOGY:
Parts of propeller blades
The typical propeller blade can be described as a twisted aerofoil of irregular planform. For purposes of analysis, a blade can be divided into segments, which are located by station numbers in inches from the centre of the blade hub.
The blade shank is the thick, rounded portion of the propeller blade near the hub, which is designed to give strength to the blade.
The blade butt, also called the blade base or root, is the end of the blade which fits in the propeller hub.
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The blade tip is that part of the propeller blade farthest from the hub, generally defined as the last 6 inches of the blade. This section or blade element is an airfoil comparable to a cross section of an aircraft wing.
The blade back (or cambered side) is the cambered or curved side of the blade, similar to the upper surface of an aircraft wing.
The blade face (or flat side) is the flat side of the propeller blade.
The chord line is an imaginary line drawn through the blade from the leading edge to the trailing, edge.
The leading edge is the thick edge of the blade that meets the air as the propeller rotates. The trailing edge is opposite.
Blade angle, usually measured in degrees, is the angle between the chord of the blade and the plane of rotation.
The chord of the propeller blade is determined in about the same manner as the chord of an airfoil. In fact, a propeller blade can be considered as being made up of an infinite number of thin blade elements, each of which is a miniature airfoil section whose chord is the width of the propeller blade at that section.
Because most propellers have a flat blade face, the chord line is often drawn along the face of the propeller blade.
Note:
Pitch is not the same as blade angle, but, because pitch is largely determined by blade angle, the two terms are often used interchangeably.
An increase or decrease in one is usually associated with an increase
1.1. Hub assembly:
The propeller assembly process also involves static balance of the individual propeller blades as a set.
Each blade is balanced to determine the heaviest blade in the set. Weight in the form of lead wool is then added (compressed in place, inside blade balance tube), in the lighter blade (s)making up the set, to bring the set of blades into balance.
Negligible unbalance or blade twist variation is measured as a result of the precise blade moulding process.
The assembling proceeds with the blades assembled in the constant speed hub together with the detail hub parts (e.g. links, bearings, cylinder, piston). Blade low pitch and high pitch stop angles are measured at each blade's reference station and adjusted, as required, where all critical assembly data/dimensions is recorded.
The propeller pitch change mechanism is then activated pneumatically on the assembly stand to confirm proper pitch change actuation. The propeller is then statically balanced as an assembly with fasteners safety-wired in place.
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The propeller assembly is then given a final inspection, paperwork is checked for completeness and compliance with customer/propeller build requirements, and the propeller is then packaged in a specially fabricated and sturdy wooden shipping container in preparation for shipment to the customer.
1.2. Three blade, constant speed propeller hub assembly:
The full illustration shows an example of the hub assembly, the spinner (the domed cover over the hub), the attaching parts of the spinner to the prop, and the attaching parts of the prop to the front flange of the engine.
The blade stake up most of the diameter and have been shortened in the image above since they are of little interest.
Below, the hub has been enlarged and the spinner has been removed to show the details of the blade roots, hub body and counterweights.
The propeller is held to the engine with 6 large bolts (not shown) which are wire-locked into place.
The 3 blades of the propeller can rotate about each one's own axis so that a coarser or finer pitch can be set; the coarser the pitch, the more thrust generated by the propeller and also the slower the engine runs.
The pitch of the propeller is set by a hand lever in the cockpit.
This type of propeller is a 'constant-speed propeller'.
In this illustration, the hub was generated by intersecting 3 cylinders at 120° to each other. The covers at the front of the hub are simple cylinders stacked with a bit of a chamfered detail or conic section.
The end-stop lock nuts were added to complete the front part.
The back plate is a conical section at the outer rim with a short cylinder at the centre. This combination gives the effect of the back plate appearing as if it's a circular disc where the edge has been rolled down into a flange. Captive nuts are then riveted onto the inside rim of the flange for screwing the spinner on.
The front plate is a cylindrical pipe section at the outer 1/4" rim.
Inside this is a narrower cylindrical section with 8 circular holes drilled through it to form the web of the front plate. And the central section is another cylindrical pipe section.
A circular tube is drawn around the circumference of the outer section tore present the rubber ring against which the spinner presses.
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Level 1 2 3
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Level 1 2 3
II. CONSTRUCTION METHODS AND MATERIALS USED IN WOODEN, COMPOSITE AND METAL PROPELLER
1. WOODEN PROPELLERS:
Wooden propellers are the lightest and present the smallest load to an engine assuming all else is equal (diameter, pitch and shape). They are capable of turning higher RPM than a heavier propeller.
Wooden propellers are also the most easily broken. Generally, wood propellers are the most efficient and best performing in the air.
Wooden propellers were used almost exclusively on personal and business aircraft.
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Level 1 2 3
A wood propeller is not cut from a solid block but is built up of a number of separate layers of carefully selected. Any types of wood have been used in making propellers, but the most satisfactory are yellow birch, sugarmable, black cherry, and black walnut.
The use of lamination of wood will reduce the tendency for propeller to warp.
For standard one-piece wood propellers, from five to nine separate wood laminations about 3/4in. thick is used.
2. COMPOSITE PROPELLERS:
2.1. Types of composite propellers:
Fibreglass-filled nylon propellers are the heaviest propellers and also the most durable. They are less efficient than wood or carbon fibre
propellers.
Carbon Fibre Propellers are light, but extremely expensive. The carbon fibre propellers are only used for large engines. They maybe available in smaller sizes in the future.
All of the above propeller materials maintain their shape well under load. Wood and carbon fibre are best.
Fibre glass-filled nylon propellers are the most flexible of propellers that are recommended, but not enough to cause significant problems.
Nylon propellers are so flexible that they twist in use which means they are constantly changing pitch. This flexing also creates a lot of
vibration. Nylon propellers are just bad. Don't use them.
2.2. Properties of composite propellers:
Light weight, composite material allows blades to be built with a special cross-section dimension, which increase stake-off and climb performance.
The capability of constructing multi-blade propellers with a smaller diameter eliminates high-speed drag and increases cruise speed. Wood and metal propeller blades built to these dimensions would be too heavy.
The reduction in diameter also reduces noise while increasing ground clearance.
A light weight propeller increases the useful load of the aircraft and also reduces the stress on the engine and crankshaft.
3. METAL PROPELLERS:
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Aluminium propellers have exceptional performances and along-life propeller. Industrial production is easy and, generally the costs are cheap. They can be 2, 3 bladed or more, fixed-pitch, ground adjustable pitch or controllable pitch.
Many metal propellers of the oldest models were machined in only one forged Duralumin part.
Compared with the propellers out of wooden material, they were lighter owing to the fact that they did not comprise a chucking device of the
blades. Their maintenance was more economic due to the fact that they were made of only one part.
They ensured a more effective cooling because of their useful pitch more brought closer to the hub; and, because there was no gasket between the blades and the hub, it was possible to modify the pitch in some limit by a light torsion of the blades.
The metal propellers with fixed pitch generally resemble the propellers out of wooden, with this close which they generally have a meaner section.
These propellers are very much used on many light models of aircraft.
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III. FIXED PITCH, CONTROLABLE PITCH, CONSTANT SPEEDING PROPELLER
There are several types of propellers, of which simplest are the propellers with fixed pitch, and the ground adjustable propellers. From these very simple forms to the complex automatic systems with adjustable pitch, the propellers become increasingly intricate.
In the paragraphs, which will follow, we will review the various characteristics of several types of propellers, but without claiming to examine them all.
1. FIXED PITCH PROPELLER:
As its name indicates, a fixed pitch propeller has a pitch, or angle of attack, given once during manufacture.
Once the completed propeller, one cannot its change the angle of attack anymore. This type of propeller is generally out of wood or alloy of aluminium and carried out of only one part.
Fixed pitch propeller
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Two-blade fixed-pitch propeller
A fixed pitch propeller has the blade pitch (blade angle) built into the propeller. For that reason the pitch angle cannot be changed by the pilot, as it can on controllable pitch propellers.
Generally, this type of propeller is constructed of wood or aluminum alloy.
The propellers with fixed pitch are built to have an ideal efficiency corresponding to a rotational speed and a given rate of advance.
They are built to adapt to a whole of inherent conditions at the same time at the speed of the engine and that of the aircraft, so that any variation of these conditions will led to a fall of the output.
The fixed pitch propellers are used on low power, low speed, and low range aircrafts.
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2. GROUND ADJUSTABLE PROPELLER:
In automatically controllable pitch propeller systems, a control device adjusts the blade angle to maintain a specific preset engine RPM without constant attention by the pilot.
Two-blade-ground-adjustable propeller
Level 1 2 3
For example, if engine RPM increases as the result of a decreased load on the engine, the system automatically increase the propeller's blade angle (increasing the air load) until the RPM has returned to the preset speed.
Three-blade-ground-adjustable propeller
3. CONSTANTSPEEDORAUTOMATICPROPELLER:
In an automatic system, the pitch regulates, without pilot control, to maintain the rotation of the engine at a desired given speed. For example, if the speed of the engine has suddenly increased, the control device automatically increases the angle of attack until desired speed is restored.
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Adjustable speed propeller
A good automatic control device will have o answer small variations rotational speed such as, in the cases, which can arise in practice, a rotational speed constant is maintained. The propellers with automatic control are called "constant speed propellers".
Additional improvements, such as reverse and flag setting, are fitted into the propellers in order to improve their operational characteristics.
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Aircraft 610 Lycoming adjustable propeller system
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IV. PROPELLER/SPINNER INSTALLATION
The propeller engine has a provision in the crankcase, ahead of the number one cylinder, for a hydraulic propeller installation. Also, the chromemoly- crankshaft on some models is fitted with a pair of small propeller flange bushings which allow this shaft to accommodate a controllable-pitch (constant- speed) propeller.
But crankshafts intended for constant speed propellers may not be substituted for shafts in fixed pitch installations unless the plug, in the rear of the hollow front section of the shaft, is installed.
The plug would be removed when switching back from fixed-pitch to controllable pitch.
Cylinders:
A propeller engine in the used market may or may not have chromed cylinder barrels. Never put chromed piston rings into a chromed cylinder barrel be cause some thing has to give and chrome against chrome makes this impossible.
Lubrication:
The mains, connecting rods, camshaft bearings, tappets, and push rods are pressure lubricated. Oil collectors and spray lubricate the piston pins, cylinder walls, and gears.
Governor:
Generally, a propeller governor drive furnished with the propeller allows installation of a constant speed governor and a single-acting controllable pitch propeller.
High pressure oil is carried from the governor, which is mounted on the accessory housing, to the front of the crankcase by way of an external oil line.
The oil then flows into the hollow front section of the crankshaft through indexing holes in the crankcase, front main bearing, and crankshaft.
Example: Lycoming chromes the cylinder barrels of its higher power engines in manufacture, while Continental prefers to use chrome rings.
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Lycoming propeller system
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I. BLADE STATION, BLADE FACE, BLADE SHANK AND HUB ASSEMBLY
1. TERMINOLOGY:
1.2. Three blade, constant speed propeller hub assembly:
II. CONSTRUCTION METHODS AND MATERIALS USED IN WOODEN, COMPOSITE AND METAL PROPELLER
1. WOODEN PROPELLERS:
2. COMPOSITE PROPELLERS:
3. METAL PROPELLERS:
1. FIXED PITCH PROPELLER:
IV. PROPELLER/SPINNER INSTALLATION

module 17a-02 pr opelle r

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