Aircraft power plant type

Aircraft Engine Types

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.

Divided into groups or types depending upon:

The working fluid used.

The means of compression.

The Propulsive working fluid.

Types Of Heat Engines



Means of compression: Turbine-driven compressor

Engine working fluid: Fuel/air mixture

Propulsive working fluid: Fuel/air mixture



Means of compression: Turbine-driven compressor

Engine working fluid: Fuel/air mixture

Propulsive working fluid: Ambient Air



· Means of compression: Ram compression

· Engine working fluid: Fuel/air mixture

· Propulsive working fluid: Fuel/air mixture


      • Means of compression: Compression due to combustion
      • Engine working Fluid: Fuel/air mixture

· Propulsive working Fluid: Fuel/air mixture



Means of compression: Reciprocating action of pistons

Engine working fluid: Fuel/air mixture

Propulsive working fluid: Ambient air

Engine Requirements


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.

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.

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

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.


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

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.

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.

Proven to be very rugged and dependable.

High horsepower.



Used during World War I by all of the warring nations.

Cylinders mounted radially around a small crankcase and rotate with the propeller.

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.



The propeller is a rotating airfoil, subject to induced drag, stalls, and other aerodynamic principles that apply to any airfoil. It provides the necessary thrust to pull, or in some cases push, the airplane through the air.

The engine power is used to rotate the propeller, which in turn generates thrust very similar to the manner in which a wing produces lift. The amount of thrust produced depends on the shape of the airfoil, the angle of attack of the propeller blade, and the r.p.m. of the engine. The propeller itself is twisted so the blade angle changes from hub to tip. The greatest angle of incidence, or the highest pitch, is at the hub while the smallest pitch is at the tip.


Figure 3: Changes in propeller blade angle from hub to tip.

The reason for the twist is to produce uniform lift from the hub to the tip. As the blade rotates, there is a difference in the actual speed of the various portions of the blade. The tip of the blade travels faster than that part near the hub, because the tip travels a greater distance than the hub in the same length of time.

Changing the angle of incidence (pitch) from the hub to the tip to correspond with the speed produces uniform lift throughout the length of the blade. If the propeller blade was designed with the same angle of incidence throughout its entire length, it would be inefficient, because as airspeed increases in flight, the portion near the hub would have a negative angle of attack while the blade tip would be stalled.


Figure 4: Relationship of travel distance and speed of various portions of propeller blade.

Small airplanes are equipped with either one of two types of propellers. One is the fixed-pitch, and the other is the controllable-pitch.


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