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Reciprocating engines, Superchargers,Propellers

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1st reciprocating engines were liquid cooled. 1st airplanes were so slow that air cooled was not practical ... Pony Brake- classical method of measuring power output. ... – PowerPoint PPT presentation

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Title: Reciprocating engines, Superchargers,Propellers


1
Reciprocating engines, Superchargers,Propellers
  • Lecture 9
  • Chapter 4

2
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?

3
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.

4
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.

5
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

6
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.

7
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.

8
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

9
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.

10
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.

11
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.

12
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

13
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

14
Turboprop TurbojetPerformance
  • Figure 4-31

15
Quiz on Lecture 9Chapter 4
  • Please take out a sheet of paper
  • Include todays date your name

16
Quiz on Lecture 9Chapter 4
  • Compare and contrast superchargers and
    turbosuperchargers.
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