Gas Turbine Engine: Force and Thrust

Forces and Work

• Force (F) can be calculated by multiplying pressure (P) and area (A): F = P × A
• Example: F = 6 psi × 300 in² = 1800 lb (force in pounds)
• The force mentioned is present in addition to reactive thrust in most gas turbine engine designs.

Work

• Work is done when a force acting on a body causes it to move through a distance.
• The formula for work is: W = F × d (where W is work in foot-pounds, F is force in pounds, and d is distance in feet)
• A force can act on an object:
  • Vertically (opposite the effect of gravity)
  • Horizontally (90° to the effect of gravity)
  • Anywhere in between the two

Power

• Power depends on three factors:
  • Force used
  • Distance the force moves
  • Time required to move the force
• Power is measured in foot-pounds per second, foot-pounds per minute, or mile-pounds per hour.
• Power is the rate at which work is performed.

Newton's Third Law

• Newton's Third Law of motion states: "For every action, there is an equal and opposite reaction."
• Example: a jet engine accelerating a mass of air backwards produces an equal amount of force that moves the aircraft forward.
• The law is best understood by observing a deflating balloon.

Bernoulli's Theorem

• Bernoulli's principle finds that if air is passed through a venturi:
  • As the air velocity increases, the pressure decreases
  • As the velocity decreases, the pressure increases

Gas Turbine Engines

• The history of propulsion began in 1930 with Frank Whittle's thesis advocating the use of the gas turbine engine.
• Whittle patented the first turbojet aircraft engine, which used a compressor impeller, driven by a turbine.
• The engine developed was a pure reaction turbojet, where the total thrust came from reaction to the hot gas stream emitted from a propelling nozzle.

The Gas Turbine Engine

• The aircraft gas turbine is a heat engine using air as a working fluid.
• It consists of a compressor, combustion chamber, and turbine for extracting energy from the high-velocity exhaust gases.
• The turbine-type jet and gas turbine engine is a family of engines based on the Whittle design.

Engine Constructional Configurations

• All gas turbine engines consist of seven basic components:
  • Air inlet
  • Compressor section
  • Combustion section
  • Turbine section
  • Exhaust section
  • Accessory section
  • Ancillary systems
• Ancillary systems are required for starting, lubrication, fuel supply, anti-icing, cooling, and pressurization.

Engine Performance Stations

• Engine performance stations are used to locate the position of temperature and pressure sensing.
• Station numbers are used to describe locations and functional data of the engine.
• Prefixes are used to show various parameters occurring at these stations within the engine, such as temperature (T) and pressure (P).