Propulsion Systems
Propulsion System
• A machine that produces thrust to push an
object forward
• The amount of thrust depends on the
mass flow through the engine and the exit
velocity of the gas
Airplane Propulsion Systems
Propeller
Turbine (jet) engine
Ramjet or
Scramjet
Rocket Planes
Why Are There Different
Types of Engines?
Newton’s 1st Law
Objects in motion tend to stay in motion and
objects at rest tend to stay at rest unless
something pushes or pulls on the object.
Therefore:
1. Thrust from the propulsion system must
balance the drag when the airplane is cruising.
2. Thrust from the propulsion system must
exceed the drag for the airplane to accelerate.
Aircraft Motion
Propulsion System
Piston Engines and Propellers
Used most commonly on smaller aircraft
•They generally fly slower, and at lower
altitudes
Propulsion System
Piston Engines and Propellers
Airliners and Cargo Planes
• Spend most of the time in a cruise state
• High engine efficiency and low fuel usage
more important than excess thrust
• Turboprop and turbofan propulsion used
on airliners and cargo planes
Propulsion Systems
Jet propulsion is similar to the release of
an inflated balloon.
Propulsion Systems
• Turbojet
– First really useful jet engine built
Propulsion Systems
• Turbofan
– Adds a large set of fan blades at the front of
the inlet
• Turboprop
– The fan from turbofan is replaced with a
propeller
Fighter Planes and
Hypersonic Aircraft
• Require high excess thrust to accelerate
quickly and overcome high drag
associated with high speeds
• High thrust is more important than engine
efficiency
Rocket Powered Airplanes
• Uses a rocket
engine for
propulsion
• Has higher speeds
• Propels only for a
short period of time
• Unusual launch configurations
– From another plane
– Vertically – nose in the air and tail to
the ground
Rocket Propulsion
• Engine pushes itself forward or upward by
producing thrust
• A rocket engine uses only propellant
carried within it
• A rocket can operate in outer space, where
there is almost no air
3 – 2 – 1 Liftoff!
How Do Rocket Engines Work?
Newton’s 3rd Law:
For every action there is an
equal and opposite reaction.
1. Rocket engines generate thrust by
putting a gas under pressure.
2. The gas escaping the rocket is
called exhaust.
3. As the rocket pushes the exhaust
backward, the exhaust pushes the
rocket forward.
Rocket Propellant
Solid-Fuel Rockets
– Burn a solid material
called the grain
– Engineers design grains
with a hollow core
– Propellant burns from
the core outward
– Unburned propellant
shields the engine
casing from the heat of
combustion
Rocket Propellant
Solid-Fuel Rockets
Hollow Core
Solid Fuel
Rocket Propellant
Liquid-Fuel Rocket
– Carries fuel and
oxidizer in separate
tanks
– Fuel circulates through
cooling jacket before
entering combustion
chamber
– Circulation preheats the
fuel for combustion and
helps cool the rocket
Rocket Propellant
Ion (Electric)
– Coils are heated to
change a fuel, such as
xenon, into a vapor
– Hot platinum or
tungsten ionization grid
changes the flowing
vapor into a stream of
electrically charged
particles called ions
Rocket Propellant
Nuclear
– Uses heat from a
nuclear reactor to
change a liquid fuel
into a gas
– Some of the fuel,
heated by the
nozzle of the rocket,
flows through the
turbine
– Turbine drives the
fuel pump
What’s Next?
Our own experiments on jet propulsion!
Image Resources
Microsoft, Inc. (2008). Clip art. Retrieved September 10, 2008, from
http://office.microsoft.com/en-us/clipart/default.aspx
National Aeronautics and Space Administration (NASA). (2008). Beginner’s
guide to propulsion. Retrieved June 23, 2009, from
http://www.grc.nasa.gov/WWW/K-12/airplane/bgp.html
National Aeronautics and Space Administration (NASA). (2008). NASA TV
Video Gallery. Retrieved June 23, 2009, from
http://www.nasa.gov/multimedia/videogallery/index.html
National Aeronautics and Space Administration (NASA). (2008). NASA – A
closer look at the X-43 mission. Retrieved June 23, 2009, from
http://www.nasa.gov/missions/research/x43-image-feature.html
National Aeronautics and Space Administration (NASA). (2007). NASA –
Rocket. Retrieved June 23, 2009, from
http://www.nasa.gov/worldbook/rocket_worldbook.html