Newton's Third Law of Motion

Newton's Third Law

• States: "For every action, there is an equal and opposite reaction."
• Applies to jet engines and propellers: accelerating a mass of air backwards produces an equal force that moves the aircraft forward.
• Example: a deflating balloon, where the air is accelerated out of the neck, causing an equal and opposite force to move the balloon.

Bernoulli's Theorem

• States: "The total energy of a particle in motion is constant at all points on its path at a steady flow."
• In a venturi, pressure is inversely proportional to velocity: if pressure increases, velocity decreases, and vice versa.
• Significance: a fundamental principle of operation of a jet engine.

Energy

• Types: potential and kinetic
• Potential energy: stored energy due to position, such as fuel or an aircraft in flight.
• Kinetic energy: energy possessed by a body due to its motion, dependent on mass and velocity.
• Formula: Kinetic Energy = 1/2 × Mass × Velocity^2
• Thrust of the engine is kinetic energy.

Conservation of Energy

• Law: "Energy can neither be created nor destroyed."
• Example: changes in pressure, velocity, and temperature during ground run-up.

Gas Turbine Engines

• History: Frank Whittle patented the first turbojet aircraft engine in 1930, using a compressor impeller, driven by a turbine.
• Design: a pure reaction turbojet, where the total thrust comes from the reaction to the hot gas stream emitted from a propelling nozzle.

Engine Performance

• Station numbers: used to locate positions on different engine types or by different manufacturers.
• Engine symbols: such as Pt and Tt, used in conjunction with station numbers to indicate temperature and pressure sensing.
• Examples: total temperature (Tt) and pressure ratio (EPR) are used to indicate thrust to the pilots.

Forces and Work

• Force (F) is measured in pounds, and can be calculated using the formula F = P × A, where P is pressure in pounds per square inch (psi) and A is area in square inches.
• Work is done when a force acting on a body causes it to move through a distance, and can be calculated using the formula 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 in different directions, including vertically, horizontally, or at an angle.

Power

• Power depends on three factors: force used, distance the force moves, and 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, and can be calculated using the formula P = F × d / t, where P is power, F is force, d is distance, and t is time.

Jet Propulsion Principles

• Jet engines and propellers develop thrust in accordance with Sir Isaac Newton's laws of motion.
• Thrust is defined as a forward force that imparts momentum to a mass of air behind it.
• Newton's First Law of motion states that a body at rest tends to remain at rest, and a body in motion tends to remain in motion in a straight line, unless acted upon by an external force.

Gas Turbine Engines

• Gas turbine engines are a family of engines based on the Whittle design, which include the turbojet, turboprop, turboshaft, and turbofan.
• The engine consists of seven basic sections: air inlet, compressor section, combustion section, turbine section, exhaust section, accessory section, and ancillary systems.
• Ancillary systems are required for starting, lubrication, fuel supply, anti-icing, cooling, and pressurisation.

Engine Constructional Configurations

• The hot section of a turbine engine includes the combustion, turbine, and exhaust sections.
• The cold section includes the air inlet duct and the compressor section.
• High-bypass engines and ducted fan engines produce more fan thrust than low-bypass engines due to reduced loss through skin friction and larger airflow mass.

Engine Stations

• Engine stations are numbered locations along the axis line of the engine, which follow the gas path and refer to basic locations such as the compressor inlet, compressor outlet, and turbine inlet and outlet.
• The number of designated stations varies according to engine complexity.