AERO ENGINE MAINTENANCE AND REPAIR AE1009

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AERO ENGINE MAINTENANCE AND REPAIR (AE1009)

• By
• Yogesh Kumar Sinha
• Rajalakshmi Engineering College

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General Requirement of Aircraft Engine

• An aircraft engine must be
• reliable, as losing power in an airplane is a
  substantially greater problem than an automobile
  engine seizing. Aircraft engines operate at
  temperature, pressure, and speed extremes, and
  therefore need to operate reliably and safely
  under all these conditions.
• Durable It is the amount of engine life obtained
  while maintaining the desired reliability
• lightweight, as a heavy engine increases the
  empty weight of the aircraft reduces its
  payload.
• powerful, to overcome the weight and drag of the
  aircraft.
• small and easily streamlined large engines with
  substantial surface area, when installed, create
  too much drag, wasting fuel and reducing power
  output.
• repairable, to keep the cost of replacement down.
  Minor repairs should be relatively inexpensive.
• fuel efficient to give the aircraft the range the
  design requires.
• capable of operating at sufficient altitude for
  the aircraft

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Powerplant Selection
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Types of reciprocating Engine
Inverted inline engine

• Inline Engine
• This type of engine has cylinders lined up in one
  row. It typically has an even number of
  cylinders.
• The biggest advantage of an inline engine is that
  it allows the aircraft to be designed with a
  narrow frontal area for low drag.
• The disadvantages of an inline engine include a
  poor power-to-weight ratio, because the crankcase
  and crankshaft are long and thus heavy.
• An in-line engine may be either air cooled or
  liquid cooled, but liquid-cooling is more common
  because it is difficult to get enough air-flow to
  cool the rear cylinders directly
• Example Wright Flyer

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Opposed or O-type Engine

• An opposed-type engine has two banks of cylinders
  on opposite sides of a centrally located
  crankcase. The engine is either air cooled or
  liquid cooled
• Due to the cylinder layout, reciprocating forces
  tend to cancel, resulting in a smooth running
  engine free from vibration.
• Low weight to power ratio

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V-Type engine

• Cylinders in this engine are arranged in two
  in-line banks, tilted 30-60 degrees apart from
  each other
• The vast majority of V engines are water-cooled.
• The V design provides a higher power-to-weight
  ratio than an inline engine, while still
  providing a small frontal area.

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Rotary Engine

• Rotary engines have all the cylinders in a circle
  around the crankcase like a radial engine (see
  below), but the difference is that the crankshaft
  is bolted to the airframe, and the propeller is
  bolted to the engine case.
• The entire engine rotates with the propeller,
  providing plenty of airflow for cooling
  regardless of the aircraft's forward speed.
• Unfortunately, the severe gyroscopic effects from
  the heavy rotating engine made the aircraft very
  difficult to fly.

Le Rhone 9C rotary aircraft engine
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Radial Engine

• This type of engine has one or more rows of
  cylinders arranged in a circle around a
  centrally-located crankcase. Each row must have
  an odd number of cylinders in order to produce
  smooth operation
• A radial engine has only one crank throw per row
  and a relatively small crankcase, resulting in a
  favorable power to weight ratio.
• The lower cylinders, which are under the
  crankcase, may collect oil when the engine has
  been stopped for an extended period causing
  serious damage due to hydrostatic lock
• In military aircraft designs, the large frontal
  area of the engine acted as an extra layer of
  armor for the pilot. However, the large frontal
  area also resulted in an aircraft with a blunt
  and aerodynamically inefficient profile.
• The power output varies from 100 to 3800 hp

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Principles of Operation
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Reciprocating Engine Power and Efficiencies

• Piston displacement The volume displace by the
  piston is known as piston displacement
• Compression Ratio In a piston engine it is the
  ratio between the volume of the cylinder and
  combustion chamber when the piston is at the
  bottom of its stroke, and the volume of the
  combustion chamber when the piston is at the top
  of its stroke.
• The compression ratio is defined as (Swept
  Volume Clearance Volume) / Clearance Volume

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• Indicator Horse Power
• Indicated mean effective pressure is an average
  pressure value that theoretically must be present
  in a cylinder of an engine during the power
  stroke to generate the maximum horsepower
  possible, given the pressures recorded within the
  cylinder during a dynamometer test.
• IHP PLANK/33,000
• P - indicated mean effective pressure
• L - length of stroke
• A - area of piston head in square inches
• N - number of power strokes per minute
• K - number of cylinders

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• Brake Horsepower
• The power developed to the propeller for useful
  work is called brake horsepower

Prony brake dynamometer
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• Friction Horsepower
• FRICTION HORSEPOWER is the difference between
  indicated horsepower and brake horse- power
• Thrust Horsepower
• Propeller efficiency refers to the percentage of
  Brake Horsepower (BHP) which gets converted into
  useful Thrust Horsepower (THP) by the propeller.
  The propeller is never 100 efficient. Therefore
  the propeller efficiency is always a number less
  than one.
• Neta is propeller efficiency.

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• Propeller Efficiency

where J is Advance ratio, n is rpm and D is
propeller diameter, V is TAS
The most efficient J depends upon the propeller
blade angle. Course propellers (large blade
angles) will be more efficient at larger advance
ratios. Fine pitch propellers will be more
efficient at small advance ratios.
When choosing a fixed pitch propeller an
aeronautical engineer usually chooses one, which
is optimum for cruise.
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• Efficiencies
• Thermal Efficiencies
• The ratio of useful work done by an engine to
  the energy of the fuel it uses is called thermal
  efficiencies
• 25 to 30 useful power
• 15 to 20 lost in cooling
• 5 to 10 lost in overcoming friction
• 40 to 45 lost through exhaust
• Useful power can be increased by increasing the
  compression ratio
• Indicated thermal efficiencies
• i.h.p 33000
• wt of fuel burned/min heat value 778

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• Mechanical Efficiencies
• In an engine it is the ratio of brake horsepower
  to indicated horsepower.
• The factor greatest effect mechanical effect is
  the friction within the engine. Mechanical
  efficiency is high when the engine is running at
  the rpm at which max b.h.p is developed.
• Note Friction remain practically constant for an
  engine

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• Volumetric Efficiency
• It is a comparison of the volume of fuel/air
  charge conducted into the cylinders to the total
  piston displacement of the engine
• Factors decrease volumetric efficiency
• Part throttle operation
• Long intake pipes of small diameter
• Sharpe bend in intake pipe
• Carburetor air temperature to high
• Cylinder head temperature to high
• Incomplete scavenging
• Improper valve timing

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• Propulsive efficiency
• It is the ratio of thrust horsepower to brake
  horsepower. Ranges to 80-85
• Loss is due to friction and slippage
• Controlling the blade angle is the best method to
  maximize propulsive efficiency
• During take off less blade angle
• During high speed or diving more blade angle

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