Lesson 2: Aircraft Engine Types And Construction
The Heat Engine
• Converts chemical energy (fuel) into heat energy.
• Heat energy is then converted into mechanical energy.
• The heat energy is released at a point in the cycle where the pressure is high, relative to atmospheric.
The Heat Engine
• Divided into groups or types depending upon:
• The working fluid used.
• The means of compression.
• The Propulsive working fluid.
Types Of Heat Engines
Types Of Heat Engines
• Turbojet
• Means of compression: Turbine-driven compressor• Engine working fluid: Fuel/air mixture• Propulsive working fluid: Fuel/air mixture
Types Of Heat Engines
• Turboprop
• Means of compression: Turbine-driven compressor• Engine working fluid: Fuel/air mixture• Propulsive working fluid: Ambient Air
Types Of Heat Engines
• Ramjet
Means of compression: Ram compression Engine working fluid: Fuel/air mixturePropulsive working fluid: Fuel/air mixture
Types Of Heat Engines
• Pulse-Jet
• Means of compression: Compression due to combustion
• Engine working Fluid: Fuel/air mixture• Propulsive working Fluid: Fuel/air mixture
Types Of Heat Engines
• Rocket
• Means of compression: Compression due to combustion
• Engine working fluid: Oxidizer/fuel mixture• Propulsive working fluid: Oxidizer/fuel mixture
Types Of Heat Engines
• Reciprocating
• Means of compression: Reciprocating action of pistons
• Engine working fluid: Fuel/air mixture• Propulsive working fluid: Ambient air
Engine Requirements
Engine Requirements
• Efficiency
• Power and Weight: If the specific weight of an engine is decreased, the performance of the aircraft will increase.
• Reciprocating engines produce approximately 1 HP for each pound of weight.
Engine Requirements
• Fuel Economy
• The basic parameter for describing the fuel economy of aircraft engines is specific fuel consumption.
• Specific fuel consumption for reciprocating engines is the fuel flow (lbs/hr) divided by brake horsepower.
Engine Requirements
• Durability and Reliability
• Durability is the amount of engine life obtained while maintaining the desired reliability.
• Reliability and durability are built into the engine by the manufacture.
• Continued reliability is determined by the maintenance, overhaul, and operating personnel
Engine Requirements
• Operating Flexibility
• The ability of an engine to run smoothly and give desired performance at all speeds from idling to full-power.
• The engine must also function efficiently through all variations in atmospheric conditions.
Engine Requirements
• Compactness
• To effect proper streamlining and balancing of an aircraft, the shape and size of the engine must be compact.
• In a single engine aircraft, the shape and size of the engine will affect the view of the pilot.
Engine Requirements
• Powerplant Selection
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Reciprocating Engine
• For aircraft whose cruising speeds will not exceed 250 MPH the reciprocating engine is the usual choice.
• Chosen for its excellent efficiency.
• Turbocharged or supercharged for high
altitude use.
-- Turbo-use exhaust
-- Super-use accessory drive
Turboprop Engine
• For cruising speeds from 180 to 350 MPH the turboprop engine performs better.
• Develops more power per pound then reciprocating.
• Operate most economically
at high altitudes.
Turbojet/Turbofan Engines
• Intended to cruise from high subsonic speeds up to Mach 2.0.
• Operates most efficiently at high altitudes.
• Less instrumentation and
controls required.
Types Of Reciprocating Engines
In-Line Engines
• Generally has even number of cylinders.
• Liquid or air cooled.
• Has only one crankshaft.
In-Line Engines
• Small Frontal area, better adapted to streamlining.
• When mounted inverted, it offers the added advantages of a shorter landing gear.
• High weight to horsepower ratio.
V-type Engines
• Cylinders are arranged in two in-line banks generally set 30-60° apart.
• Even number of cylinders and are liquid or air cooled.
Radial Engines
• Consists of a row, or rows, of cylinders arranged radially about a center crankcase.
• The number of cylinders composing a row may be either three, five, seven, or nine.
Radial Engines
• Proven to be very rugged and dependable.
• High horsepower.
Rotary-Radial
• Used during World War I by all of the warring nations.
• Cylinders mounted radially around a small crankcase and rotate with the propeller.
Rotary-Radial
• Torque and gyro effect made aircraft difficult to control.
• Problems with carburetion, lubrication, and exhaust.
Opposed Or O-type Engines
• Two banks of cylinders opposite each other with crankshaft in the center.
• Liquid or air cooled, air cooled version used predominantly in aviation.
Opposed Or O-type Engines
• Has low weight-to-horsepower ratio.
• Its narrow silhouette makes it ideal for installation on wings.
• Little vibration.
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