Reciprocating engines, Superchargers,Propellers

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Reciprocating engines, Superchargers,Propellers

• Lecture 9
• Chapter 4

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Reciprocating Engines

• Internal combustion recip. (piston) engine
• Four stroke cycle engine credited German
  Nickolaus Otto in 1876.
• Steam was not successful. Why?
• Figure 4-13 p. 94 Wright Brothers engine
• How did it work?

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Reciprocating Engines

• 1st reciprocating engines were liquid cooled.
• 1st airplanes were so slow that air cooled was
  not practical
• The rotary engine was cooled by air.
• The crankshaft of a rotary is mounted to the
  airframe cylinders revolve around it.
• The cylinders are air cooled even at low speeds.

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Air Cooled Engines

• Pro Cylinders placed radially around the
  crankshaft for equal cooling for many cylinders
• Con This arrangement allows for high drag with
  the large frontal area.
• Horizontally opposed configuration worked well
  with 2/4 cylinders
• Horizontally opposed recip. engines with as many
  as 8 cylinders producing up to 450 horsepower.

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Reciprocating EnginePerformance

• Horsepower- English unit
• One Horsepower 550 foot-pounds
• It would take one horsepower to move something
  requiring a force of 550 lbs over a distance of
  one foot every second
• Mean Effective Pressure- average pressure
  throughout a stroke force on the piston

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Power

• Power is the time rate at which work is done
• The number of power strokes per minute is ½ times
  the rpm because there is a power stroke every
  other revolution
• The power in one cylinder is proportional to
  average cylinder pressure times the length of the
  stroke times piston area times rpm.

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Terms

• Brake horsepower- horsepower delivered at the
  shaft
• Pony Brake- classical method of measuring power
  output.
• Shaft horsepower- power delivered to the
  propeller.
• Thrust horsepower- amount of power that actually
  gets converted into thrust.

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Terms

• Rated brake horsepower- the power output at a rpm
  at standard sea level density.
• Figure 4-15 p. 98 typical variation of brake
  horsepower with altitude
• Economy cruise- 55 power
• Performance cruise- 75 power
• Good compromise- 65 power

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Superchargers

• Superchargers utilize a small compressor in the
  intake manifold that compresses the air received
  from the atmosphere to a higher pressure.
• Turbosuperchargers are more efficient because
  they use exhaust gas pressure.

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Turbosuperchargers

• The exhaust drives the turbine, which is
  connected to the compressor in the intake (like
  the compressor turbine function in a turbojet)
• The effect of supercharging/turbocharging is that
  sea level, or rated, power can be maintained up
  to a certain altitude.

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Figure 4-16 p. 100

• This shows the effect of supercharging
• The dotted line represents the power available at
  a constant rpm with turbocharger.
• The solid line represents the original
  unsupercharged engine.

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Propellers

• Propeller (airscrew) is essentially a small wing
  rotated in a plane perpendicular to the path of
  flight developing thrust in the same way that a
  wing develops lift.
• Figures 4-18 4-25

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Propeller Efficiency

• The efficiency of the propeller is really how
  much brake horsepower it converts into thrust
  power-dependent on the ratio to forward speed to
  rotational speed.
• Figures 4-26- 4-28
• What are the different types of props?
• Pros/Cons?
• Figures 4-29 4-30

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Turboprop TurbojetPerformance

• Figure 4-31

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Quiz on Lecture 9Chapter 4

• Please take out a sheet of paper
• Include todays date your name

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Quiz on Lecture 9Chapter 4

• Compare and contrast superchargers and
  turbosuperchargers.