Propellers and Engine Instruments 4 7 . 5 Propellers and Engine Instruments

The Propeller The function of the propeller is to convert the torque, or turning movement, of the crankshaft into thrust, or forward, speed. Designed that, as it rotates, it moves forward along a corkscrew or helical path. It pushes air backward with the objective of causing a reaction, or thrust, in the forward direction. Regional Gliding School

The Propeller The jet engine moves a small mass of air backward at a relatively high speed. The propeller, on the other hand, moves a large mass of air backward at a relatively slow speed. The propeller blade is an airfoil section, similar to the airfoil section of a wing. Regional Gliding School

The Propeller It meets the air at an angle of attack as it rotates. It produces lift and drag. In the case of the propeller, the forces are designated as thrust and torque. Regional Gliding School

The Propeller Those attached forward of the engine and pull are called tractors. Those which are attached aft of the engine and push from behind are called pushers. Regional Gliding School

Pitch The distance in feet a propeller travels forward in one revolution. The angle at which the blade is set governs the pitch. There is a Coarse Pitch meaning the blade is set at a larger angle. There is a Fine Pitch meaning the blade is set at a small angle. Regional Gliding School

Coarse Pitch Travels forward a greater distance with each revolution. The airplane will move forward at greater speed for a given RPM. Like high gear in a car. Best suited for high speed cruise and for high altitude flight. Regional Gliding School

Fine Pitch Less torque, or drag. Revolves at a higher speed around its own axis. Enables the engine to develop greater power. Like low gear in a car. Gives best performance during take-off and climb. Regional Gliding School

Types of Propellers Fixed Pitch: Controllable Pitch: Constant Speed: constant blade angle, blades are at an angle in between fine and course pitch to give the best overall performance possible for all flight conditions. Controllable Pitch: blade angle can be adjusted by the pilot to various angles during flight. Constant Speed: blades automatically adjust themselves to maintain a constant RPM as set by the pilot. Adjustable Pitch: blade angle may be adjusted on the ground. Regional Gliding School

Propeller Control Systems: the mechanism for varying the pitch of the propeller may be: mechanical - hand controlled by linkages hydraulic - a fluid under pressure pushes or pulls on a cam that uses gears to turn the blades of the propellers electrical - operated by an electric motor. Feathering: turning the propeller blades to an extreme coarse pitch, used in the event of an engine failure to stop the propeller from “wind milling”. It will reduce drag of the failed engine or propeller. Regional Gliding School

Thrust Reversing: changing the pitch below the idle position (full fine pitch) into the reverse range or negative pitch, thrust now works in the reverse direction, used to slow down the aircraft after it has landed and to manoeuvre the aircraft on the ground. Regional Gliding School

NOTE: You must use the buttons in the Confirmation Stage

Aero Engines The Propeller and Engine Instruments Let's try a few review questions on Aero Engines: Question #1 - Name a type of pitch? Mechanical A B Adjustable C Fine D Constant Regional Gliding School

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Aero Engines The Propeller and Engine Instruments Let's try a few review questions on Aero Engines: Question #2 - Changing the pitch below the idle position (full fine pitch) into negative pitch is known as what? Feathering A B Air braking C Thrust reversing D Hydraulic positioning Regional Gliding School

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Basic Engine Instruments Although an aircraft has many complex instruments, the basic engine instruments are perhaps the most important. These gauges monitor essential components of the engine. Can indicate early warning signs of potential problems and possible engine failure. Regional Gliding School

Colour Coding Colour code ranges from green, to yellow to red, indicating normal, caution and danger operating settings respectively. Regional Gliding School

Oil Pressure Gauge Monitors oil pressure supplied by oil pump. High pressure can force oil into the combustion chamber where it will burn. Low pressure leads to poor lubrication. Regional Gliding School

Oil Temperature Gauge Monitors temperature of oil. Regional Gliding School

Carburetor Air Temperature Gauge Enables pilot to monitor the temperature of intake air or air/fuel mixture into the carburetor. If icing exists, the carburetor heat control unit can be activated by the pilot. Regional Gliding School

Tachometer (RPM Indicator) Monitors the number of revolutions per minute the engine crankshaft is turning. On aircraft with fixed or controlled pitch propellers, RPM is controlled by the throttle. Regional Gliding School

Cylinder Head Temperature Gauge Records the temperature of one or more of the engine cylinder heads. Extremely high cylinder head temperatures are immediate signs of engine overloading. Regional Gliding School

Manifold Pressure Gauge Usually located beside the tachometer because both indicate engine power output. A drop in manifold pressure usually indicates carburetor icing. Regional Gliding School

NOTE: You must use the buttons in the Confirmation Stage

Aero Engines The Propeller and Engine Instruments Let's try a few review questions on Aero Engines: Question #3 - What does the tachometer monitor? Crankshaft revolutions A B Camshaft revolutions C Engine power control D All the above Regional Gliding School

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Aero Engines The Propeller and Engine Instruments Let's try a few review questions on Aero Engines: Question #4 - What instrument indicates engine power output? Tachometer A B Cylinder Head Temperature Gauge C Manifold Pressure Gauge D Both A and C Regional Gliding School

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Aero Engines The Propeller and Engine Instruments Congratulations!! You have now completed the Propeller and Engine Instruments lesson of the Aero Engines Module. Of course, this lesson is always available to you for future reference if required. You are now ready to move along to the next module you have not completed or to any other module you wish. You can advance to the Self Test Module if you feel ready to challenge the final exam. Good Luck! Regional Gliding School