I.  Introduction to Propulsion

A. Goal:  Create a Force to Propel a Vehicle

Two options:

  1. Take mass stored in a vehicle and throw it backwards (rocket propulsion). Use the reaction force to propel the vehicle.
Propellant ---> burn ---> expand through nozzle
(chem. energy)   (thermal energy)   (kinetic energy & momentum)

Rocket Engine          Rocket Engine Schematic

Figure 1.1 Typical liquid propellant rocket motor (Hill and Peterson, 1992).

  1. Seize mass from the surroundings and set the mass in motion backwards. Use the reaction force to propel vehicle (air-breathing propulsion).
Continuously: a) Draw in air.
  b) Compress it.
  c) Add fuel and burn (convert chemical energy to thermal energy).
  d) Expand through a turbine to drive compressor (extract work).
  e.1) Then expand in a nozzle to convert thermal energy to kinetic energy & momentum (turbojet).
  e.2) Or expand in a second turbine (extract work), use this to drive a shaft for a fan (turbofan), or a propeller (turboshaft). The fan or propeller impart k.e. & mom. to the air.



Overall goal:  take  at Vo (flight speed), throw it out at Vo + DV

Gas Turbine Engine Schematic
Gas Turbine Engine

Figure 1.2 Schematics of typical military gas turbine engines.  Top: turbojet with afterburning, bottom: GE F404 low bypass ratio turbofan with afterburning (Hill and Peterson, 1992).


Turboprop Schematic
Turboprop Engine
Figure 1.3 Schematics of a PW PT6A-65, a typical turboprop (Hill and Peterson, 1992).
Turboprop Engine
Turboprop Engine

Figure 1.4 The RB211-535E4, a typical high bypass-ratio turbofan (Hill and Peterson, 1992).


B. Performance Parameters

The two performance parameters of greatest interest for a propulsion system are the force it produces (thrust, T), and the overall efficiency with which it uses energy to produce this force (hoverall).  We will begin by looking at the production of thrust using the integral form of the momentum theorem.  In the second lecture we will discuss the efficiency of propulsion systems.


C.   Propulsion is a systems endeavor

There are a multitude of other factors which a propulsion engineer must take into account when designing a device including weight, cost, manufacturability, safety, environmental effects, etc.  Thus propulsion is truly a systems endeavor, requiring knowledge of a variety of disciplines:
Fluids  +  thermo  + structures  +  dynamics  +  controls  +  chemistry  +  acoustics + …

We will focus mostly on these two disciplines in the Unified propulsion lectures.


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