Podcast
Questions and Answers
What is the primary reason for allowing the layers of a wooden propeller to dry for approximately one week?
What is the primary reason for allowing the layers of a wooden propeller to dry for approximately one week?
Which type of wood is considered the most widely used in the construction of fixed-pitch wooden propellers?
Which type of wood is considered the most widely used in the construction of fixed-pitch wooden propellers?
What materials are typically used for the metal tipping on wooden propellers?
What materials are typically used for the metal tipping on wooden propellers?
What is the thickness of each layer used in the construction of a fixed-pitch wooden propeller?
What is the thickness of each layer used in the construction of a fixed-pitch wooden propeller?
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Which process is NOT part of the construction of fixed-pitch wooden propellers?
Which process is NOT part of the construction of fixed-pitch wooden propellers?
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What is the primary function of the mechanical linkages in constant-speed propellers?
What is the primary function of the mechanical linkages in constant-speed propellers?
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From where does the oil pressure for the hydraulic pitch-changing mechanism usually originate?
From where does the oil pressure for the hydraulic pitch-changing mechanism usually originate?
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What effect does an increase in engine RPM have on the propeller governor?
What effect does an increase in engine RPM have on the propeller governor?
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What is the approximate oil pressure required for quicker blade-angle changes in a constant-speed propeller?
What is the approximate oil pressure required for quicker blade-angle changes in a constant-speed propeller?
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How is the governor connected to the engine in constant-speed propellers?
How is the governor connected to the engine in constant-speed propellers?
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Which of the following best describes the role of the pitch-changing mechanism?
Which of the following best describes the role of the pitch-changing mechanism?
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When the governor detects a drop in RPM, what action does it trigger?
When the governor detects a drop in RPM, what action does it trigger?
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What is the significance of using a pump integral with the governor?
What is the significance of using a pump integral with the governor?
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What is the primary reason the shape of a propeller blade creates thrust?
What is the primary reason the shape of a propeller blade creates thrust?
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How is thrust mathematically defined in relation to air mass and velocity?
How is thrust mathematically defined in relation to air mass and velocity?
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What effect does increasing the blade angle have on the engine's load?
What effect does increasing the blade angle have on the engine's load?
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What is the role of the area of decreased pressure in front of a propeller?
What is the role of the area of decreased pressure in front of a propeller?
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Why is the blade angle an important factor in controlling an engine’s RPM?
Why is the blade angle an important factor in controlling an engine’s RPM?
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What is the result of a propeller being mounted vertically relative to air pressure?
What is the result of a propeller being mounted vertically relative to air pressure?
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Which factor does NOT impact the amount of air displaced by a propeller?
Which factor does NOT impact the amount of air displaced by a propeller?
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The thrust produced by a propeller can be influenced by which of the following?
The thrust produced by a propeller can be influenced by which of the following?
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What is the main function of the hydraulic cylinder in the Hartzell Constant-Speed, Non-feathering propeller?
What is the main function of the hydraulic cylinder in the Hartzell Constant-Speed, Non-feathering propeller?
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How much centrifugal force can the blades transmit to the hub spider?
How much centrifugal force can the blades transmit to the hub spider?
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What mechanism is used to attach the piston to the blade clamps in non-feathering models?
What mechanism is used to attach the piston to the blade clamps in non-feathering models?
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What opposes the oil pressure supplied by the governor for the piston actuation?
What opposes the oil pressure supplied by the governor for the piston actuation?
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Which component transmits the propeller thrust and engine torque from the blades?
Which component transmits the propeller thrust and engine torque from the blades?
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What is the common feature of both Hartzell and McCauley propellers for light aircraft?
What is the common feature of both Hartzell and McCauley propellers for light aircraft?
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Where should one look for information on specific models of Hartzell propellers?
Where should one look for information on specific models of Hartzell propellers?
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What type of pitch actuation system does the hydraulic piston use in feathering models?
What type of pitch actuation system does the hydraulic piston use in feathering models?
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What is the primary function of the feathering propeller's governing device?
What is the primary function of the feathering propeller's governing device?
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Which forces are present while the feathering propeller is operating?
Which forces are present while the feathering propeller is operating?
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How many blades does the constant-speed feathering propeller typically have?
How many blades does the constant-speed feathering propeller typically have?
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What is the role of the piston within the feathering propeller's hub?
What is the role of the piston within the feathering propeller's hub?
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Which of the following forces typically attempts to decrease the blade angle of the feathering propeller?
Which of the following forces typically attempts to decrease the blade angle of the feathering propeller?
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What material is primarily used in the hub of the constant-speed feathering propeller?
What material is primarily used in the hub of the constant-speed feathering propeller?
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What mechanism does the feathering spring and piston form part of in the feathering propeller?
What mechanism does the feathering spring and piston form part of in the feathering propeller?
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Which factor is least influential in determining the blade angle in a feathering propeller?
Which factor is least influential in determining the blade angle in a feathering propeller?
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What does pitch distribution in a propeller refer to?
What does pitch distribution in a propeller refer to?
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Which statement accurately describes fixed pitch propellers?
Which statement accurately describes fixed pitch propellers?
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What is the primary function of the propeller control in a constant-speed propeller?
What is the primary function of the propeller control in a constant-speed propeller?
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In terms of speed, how does the tip of a propeller blade compare to the inner portion?
In terms of speed, how does the tip of a propeller blade compare to the inner portion?
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Where is the control for a constant-speed propeller typically located?
Where is the control for a constant-speed propeller typically located?
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Which of the following is NOT a feature of constant-speed propellers?
Which of the following is NOT a feature of constant-speed propellers?
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What is the primary purpose of the pilot valve in propeller controls?
What is the primary purpose of the pilot valve in propeller controls?
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How is the propeller control's 'pull back' position intended to function?
How is the propeller control's 'pull back' position intended to function?
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Study Notes
Week 1 Complete
- AVIA-1052 course is complete for week 1
- Contact Matt C if any errors/improvements are needed
Week 1 of 1 Day 1
- First class of AVIA-1052
- Topics to be covered: propellers, general prop stuff, aircraft propeller theory, basic propeller controls
Previously On AVIA-1052
- Initial topics discussed: general prop stuff, aircraft propeller theory, and basic propeller controls
Today On AVIA-1052
- Topics for the day: propeller location, types of propellers, including fixed-pitch, test club, ground-adjustable, controllable-pitch, constant-speed, feathering, reverse-pitch, and propeller governor
Where are we?
- Powerplant (Volume 2), 7-2 to 7-6
- Starting at general, and stopping at propeller location
- FAA handbooks listed
Propellers
- The unit responsible for absorbing power from the engine
- Propeller development's progression
- Early propellers were fabric-covered sticks
- Designed to force air in a rearward direction
- Propellers started as simple, two-bladed wood propellers
- They have developed into sophisticated systems.
- Variable-pitch, constant-speed feathering, and reversing propeller system.
- This system allows for adjustments in engine RPM while maintaining efficiency.
- Constant speed systems consist of flyweight-equipped governor units to maintain consistent engine speeds.
- Different types of blade positions during various flight conditions.
- Different types of propeller configurations such as two-bladed, four-bladed, and six-bladed designs.
- Forces acting on a propeller during operation, such as centrifugal force.
- Excessive blade tip speed can lead to poor blade efficiency, vibration or fluttering.
- Propeller-driven aircraft have takeoff and landing advantages.
- Propeller systems are designed for specific aircraft and operating conditions.
- Basic nomenclature of simple fixed-pitch, two-blade wood propellers and aerodynamic cross-sections.
- Different parts of propellers such as blade tip, trailing edge, leading edge, chord line, etc.
Aircraft Propeller Theory
- Aircraft propeller consists of two or more blades.
- Each propeller blade is a rotating wing.
- Generates thrust needed for the aircraft to fly through the air.
- The power needed to rotate the blades is supplied by the engine.
- A central hub which attached to blades.
- Different types of engines (low horsepower and high horsepower) attached to propellers, how they work and difference in mounting configuration, propeller shaft on different types of engines.
Propeller Aerodynamic Process
- Airplane in flight produces drag force to resist its motion.
- Propeller thrust needs to overcome this drag to propel the airplane forward.
- The work by thrust is measured in terms of thrust horsepower, when measured in horsepower units.
- The engine supplies brake horsepower through a rotational shaft, which the propeller converts to thrust horsepower.
- Some power is lost during the conversion of brake to thrust horsepower.
- Propeller efficiency is the ratio of thrust horsepower to brake horsepower, and measured using the Greek letter, n (eta).
- Propeller efficiency varies widely from 50% to 87%.
- Pitch is not the same as blade angle.
- Pitch is largely determined by blade angle
- an increase or decrease in one is usually associated with an increase or decrease in the other.
- Geometric pitch is the distance a propeller should advance in one revolution with no slippage, usually expressed in pitch inches.
- Effective pitch is the distance a propeller advances in one revolution considering propeller slippage and calculated by using the formula: GP = 2 * πR * tangent of blade angle at 75% station.
- Important blade parts - chord line of a propeller blade, blade back, blade face
- Types of propellers - various designs for different uses.
- Forces on a rotating propeller - centrifugal force tends to pull the blades out of the hub at high RPM, blade weight is vital to propeller design.
Basic Propeller Controls and Instruments
- Fixed-pitch propellers have no controls, and no adjustments are required.
- Constant-speed propellers have a control in the center pedestal, allowing for adjusting RPM.
- Two positions of the control: increasing or decreasing RPM (full forward or pulled aft)
- Propeller control is directly connected to the propeller governor, adjusting tension on governor speeder spring.
- Types of controls for constant-speed propellers: engine tachometer, manifold pressure gauge.
- Techniques for sensing speed - Tachometer generator measures RPM, generated alternating current (AC) is read by circuitry and displayed.
Propeller Controls and Instruments
- YouTube videos linked for more information about propeller controls and instruments.
Propeller Governor
- Engine rpm-sensing device high-pressure oil pump
- Responds to engine speed by using hydraulic systems to adjust blade angle.
- In a constant-speed propeller system, the change in oil volume in the hydraulic cylinder changes the blade angle.
- Governor maintains propeller system rpm.
- Specific rpm value is set by a cockpit propeller control which compresses or releases the governor speeder spring.
Governor Mechanism
- Constant-speed control consists of a gear pump that increases engine oil pressure and a pilot valve.
- Controlled by flyweights in the governor to control the flow of oil through the governor to and away from the propeller.
- The position of pilot valve, respective to the propeller/governor metering port, regulates the quantity of oil in flow.
- Regulates operating oil pressures in the governor.
Propeller Governor (continued)
- Centrifugal force acting on propeller blades that causes them to move into a low pitch.
- The opposing force of a spring called speeder spring, balances the governor flyweights ability to fly outward during turning.
- Unbalancing these forces can be caused by the aircraft changing attitude; this can be adjusted by using the propeller control.
Propeller Governor (continued)
- The governor maintains the necessary balance between control forces by metering or draining from the piston to maintain the correct blade angle for constant-speed operation.
Propeller Governor (continued)
- Underspeed condition
- The governor is operating in an under-speed condition when the engine is operating below the rpm set.
- The governor flyweights tilt inward in this condition.
Propeller Governor (continued)
- Overspeed condition
- The governor is operating in an over-speed condition when the engine is operating above the set rpm.
- The governor flyweights tilt outward in this condition.
Propeller Governor (continued)
- On-speed Condition
- The governor is operating at the set rpm; the centrifugal force on flyweights and the spring tension are balanced.
- The pilot valve does not directly deliver or collect oil from the propeller hydraulic cylinder.
Propeller Governor (continued)
- Governor System Operation
- If the engine speed decreases below the set rpm, the rotational force on the engine-driven governor flyweights decreases.
- The speeder spring moves the pilot valve downward allowing oil to flow to the propeller cylinder, which moves outward
Propeller Governor (continued)
- Governor System Operation (continued)
- Governor obtains oil from engine lubricating system for operation.
- Higher oil pressure, up to 300 psi, allows for quicker blade angle change.
- Governors direct pressurized oil for hydraulic pitch-changing mechanisms.
Propeller Governor (continued)
- If the engine speed increases above the set rpm, the flyweights move away enough to overcome the speeder spring tension, raising the pilot valve from their inward position.
- This action permits oil from the propeller, which causes higher propeller pitch and lowers the engine speed.
Propeller Governor (continued)
- the governor maintains the required balance between control forces by either metering to or draining from the propeller piston to control the exact quantity of oil necessary to maintain the proper blade angle for constant-speed operations.
Propeller Governor (continued)
- The mechanism used to adjust the pitch through hydraulic oil pressure
Propeller Auxiliary Systems
- Overview of auxiliary systems for aircraft propellers, particularly concerning ice control
Ice Control Systems
- Ice formation on propeller blade produces a distorted blade airfoil section, causing loss of efficiency and producing propeller unbalance, destructive vibration, and also increases the weight of the blade.
Anti-Icing Systems
- Fluid anti-ice system typically includes a tank, a pump, forces fluid to each propeller, and a control system.
- Different types of fluids, such as isopropyl alcohol.
Deicing Systems
- Electric propeller de-icing system and its components (electrical energy source, resistance heating element)
- System can be controlled and have auxiliary devices.
Propeller Synchronization and Synchrophasing
- Used on multiple-engine aircraft to control and synchronize engine RPM and thus reducing vibrations.
Autofeathering System
- An auto-feather system is used normally during takeoff, approach, and landing and feathers automatically when the engine power is lost.
- This system incorporates a solenoid valve and torque switches to quickly dump oil pressure from the propeller to feather the blades.
Propeller Inspection and Maintenance (continued)
- General inspection - Propellers are inspected often, using visual observation of blades, hubs, controls and accessories to check for defects.
- Specific inspections - visual inspection for cracks, dents, warpage, glue failure, delamination, and charring.
- In-flight inspections, checking for looseness and slipping, separation of soldered joints, loose screws, breaks, cracked sections and corrosion.
Propeller Vibration
- Propeller unbalance can cause vibration in aircraft. Static imbalance is when the center of gravity of the prop doesn't align with the rotation axis. Dynamic imbalance occurs when the center of gravity of propeller elements, like blades and counterweights, doesn't lie in the same plane with the rotational axis.
- Identifying the cause of the vibration by checking blade tracking and blade angle settings
- If the cause is not imbalance, the problem should be with the engine
- Inspecting for engine vibration to identify if the propeller vibration is related to the engine vibration or the propeller itself.
Blade Tracking
- Blades all should track one another in the same plane of rotation
- The difference in tracking points must not exceed the tolerance specified by the manufacturer
- Inspecting for separation between metal leading edge and the cap.
Checking and Adjusting Propeller Blade Angles
- Basic maintenance guidelines should be followed to address issues related to improper blade angles
- Follow the manufacturer's instructions to take the correct measurements and setting of propeller blade angles.
- Avoid using sharp metal instruments to mark the propeller blades because this can lead to cracks
Universal and Digital Propeller Protractor
- Universal propeller protractor and digital inclinometer used to check propeller blade angles when the propeller is on a balancing stand or installed on the aircraft engine.
- Digital inclinometers are used to check blade angles easily and accurately.
Propeller Balancing
- Propeller unbalance (static and dynamic) can cause vibration in the aircraft
- Static imbalance occurs when the center of gravity of the propeller does not coincide with the axis of rotation.
- Dynamic imbalance occurs when the center of gravity of similar propeller elements, such as blades or counterweights, does not follow in the same plane of rotation.
- Dynamic imbalance is negligible when the propeller assembly is short compared to its diameter, blades lie in the same plane perpendicular to the rotational axis, and the track tolerance requirements are met.
- Static balancing method to verify if the propeller is balanced.
- Determining if there is a definite tendency, this involves additional weights and removal of weights.
- Dynamic balancing to reduce vibration levels for better efficiency and operation.
- The procedure involves using an analyzer kit fitted to the engine near the propeller with a vibration sensor.
Propeller Removal and Installation (continued)
- Removing the propeller.
- Make sure that the propeller is supported in a sling.
- Removing and replacing the necessary nuts, bolts, studs, or washers (ensure that the components are not damaged during removal or reinstallation)
- Installing the propeller.
- Reinstalling and securing the propeller with corresponding holes on the engine mounting flange
- Positioning the propeller in the right orientations to avoid propeller imbalance.
Setting the Propeller Governor
- propeller governor incorporates an adjustable stop that limits the maximum speed of the engine.
- When takeoff rpm is reached, the propeller moves off the low pitch stop, maintaining the prescribed maximum engine speed.
- During ground run-up procedure, note the resultant RPM and manifold pressure.
- If RPM is above or below the prescribed maximum in the manufacturer's instructions, carefully adjusting the adjustable stop of the governor.
Servicing Propellers
- Servicing propellers includes cleaning, lubricating, and replenishing operating fluids for better preservation.
- Propeller blades should be cleaned using suitable cleaning solution and soft cloth/brushes.
- Avoiding the use of steel wool or acid/caustic materials and ensuring a high polish if required with commercial metal polish.
- Proper finishing of the process should include washing, rinsing, and drying.
Charging the Propeller Air Dome
- Propeller position must be checked for positioning using start locks and following the proper control procedure.
- Suitable air or nitrogen used to check the air chamber's correct pressure for proper operation.
- Checking the proper temperature to achieve the correct pressure needed to charge the hub air pressure.
Propeller Lubrication
- Lubrication of propeller, particularly for those with dissimilar metals, for better corrosion prevention and maintenance.
- Checking lubrication intervals against manufacturers' specifications.
- Proper cleaning and maintenance procedures.
Troubleshooting Propellers
- Basic troubleshooting steps, including reference to manufacturer's guides .Troubleshooting steps should be followed closely.
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Description
Test your knowledge on the construction and functioning of wooden propellers. This quiz covers materials used, drying processes, and the mechanisms involved in pitch adjustment. Perfect for aviation enthusiasts and students in aeronautical engineering.