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

Used most commonly on smaller aircraft• They generally fly slower, and at lower altitudes

Piston Engines and Propellers

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 PropellantSolid-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 RocketsHollow Core

Solid Fuel

Rocket PropellantLiquid-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