Jet Propulsion and Newton's Third Law

Jet Propulsion

• Jet propulsion started during World War 2
• Offered several advantages over piston engines including higher speed, increased reliability, and greater efficiency.
• It also required less maintenance at high altitudes.
• Jet engines have commercial applications in power generation and shipping industries, as well as in modern vehicles.

Applying Newton's Third Law

• For every action, there is an equal and opposite reaction.
• Acceleration is the action, and forward movement is the reaction.
• An example of this is a squid expelling water to propel itself forward, and a balloon propelling itself forward when the opening is released.

Turbine Engine History of Jet Propulsion

• Hero of Alexandria (250 B.C.) created the aeolipile, a toy that demonstrated the principle of reaction propulsion.
• Dr. Sanford Moss's research applied concepts to turbo-supercharger development.
• Frank Whittle created the first successful turbojet engine in 1930.
• His patent application was granted in 1930, and the engine completed its first successful flight in a Gloster model E28/29 aircraft in 1939.
• The aircraft produced 1000 pounds of thrust.
• Hans Von Ohain, a German engineer built a jet engine installed in Heinkel He-178 aircraft, and made a successful flight in August 27, 1939, producing 1,100 pounds of thrust.

Jet Propulsion Today

• Modern commercial aircraft fly at 600 mph and can carry over 400 passengers and several tons of cargo.
• Commercial and military aviation use jet propulsion to propel aircraft faster than the speed of sound.
• The SR-71 Blackbird aircraft can fly at Mach 5.
• Concorde aircraft could fly at 2.2 times the speed of sound.
• Jet Propulsion is used in both military and commercial aviation today.

Types of Jet Propulsion: Rockets

• Rockets are non-airbreathing engines carrying their own fuel and oxygen for combustion.
• Two main types are solid-propellant and liquid-propellant rockets.

Types of Jet Propulsion: Solid-propellant Rockets

• Use a solid fuel mixed with an oxidizer.
• The fuel is formed into a specific shape to promote optimum burning rate.
• These rockets are commonly used to propel military weapons and provide additional thrust for takeoff of heavily loaded aircraft.

Types of Jet Propulsion: Liquid-propellant Rockets

• Use fuel and an oxidizer, such as liquid oxygen
• The resulting high-velocity gas jet behind the rocket provides enough thrust to propel an object.
• Space shuttles utilize liquid-fuel rockets.

Types of Jet Propulsion: Ramjet

• An aerodynamic duct engine.
• No moving parts.
• To produce thrust, a ramjet must be moving at high velocity.
• In operation, fuel is injected into the engine and ignited, accelerating the air and creating thrust.
• Used in some military weapons delivery systems.

Types of Jet Propulsion: Pulsejet

• Similar to ramjets but features spring-loaded shutter valves in the air intake duct.
• In operation, air enters the engine, fuel is injected and ignited, accelerating the air. The expanding air forces the shutter valves closed, producing thrust.

Types of Jet Propulsion: Gas Turbine Engine

• The most practical form of jet engine currently in use for commercial, business, and military aircraft.
• Four types: turbojet, turboprop, turboprop, and turbofan.

Types of Jet Propulsion and Components(Turbojet Engine)

• Air enters the inlet duct and is compressed by the compressor.
• The compressed air goes to the combustion section where fuel is added and ignited.
• The heat generates expansion, which rotates the turbine.
• The turbine's energy is transferred to the compressor via a common shaft.
• The high-velocity exhaust gases generate thrust.
• EPR measures engine pressure ratio and is used in setting the power according to given situation.

Types of Jet Propulsion and Components(Turboprop Engine)

• A gas turbine engine delivering power to a propeller
• Similar design to a turbojet.
• The power is transferred to the propeller through a reduction gearbox.
• This type is popular in business and commuter aircraft.

Types of Jet Propulsion and Components(Turbofan Engine)

• Compromises the best features of turbojet and turboprop.
• Includes a multi-bladed fan mounted in front of the compressor.
• A portion of the intake air bypasses the core engine to increase thrust, enhance cooling, and reduce noise.
• Forward- and aft-fan designs are distinguished by fan location relative to the compressor.

Types of Jet Propulsion and Components(Turboshaft Engine)

• A gas turbine specifically designed to deliver power to a shaft, not for producing thrust.
• This power is used to drive a propeller or other machinery.
• Used in helicopters and industrial applications like electrical generator systems.

Engine Components

• Air inlet section: Recovers total pressure from the airstream.
• Compressor section: Forces air into the engine and increases pressure.
• Combustion section: Combines compressed air with fuel, ignites the mixture, and generates heat and energy.
• Turbine section: Extracts energy from the hot gases to drive the compressor and other components.
• Exhaust section: Channels and directs exhaust gases to produce thrust
• Accessory section/drive: Powers different engine and aircraft accessories such as generators, pumps.
• Cold section: Includes the air inlet, compressor, air supply to the cabin, etc.
• Hot section: Includes Combustion and gas turbine segment of the engine

Air Inlet Ducts

• Forms part of the airframe.
• Function: Recovers most total pressure from the free airstreams.
• Function: Delivers pressure to the engine compressor.
• Inlet shape raises pressure.
• Inlet duct has little drag to reduce wear from friction.
• Inlet cover protects the intake

Compressor Section components

• Component forces air into the engine
• Compressor effectiveness is measured by compressor pressure ratio
• Supportive function-support combustion; supplying bleed air for cooling purposes.
• The air compressor must increase the intake pressure.

Diffuser Section Components

• Divergent shape used to slow the leaving compressor velocity to support combustion
• Air pressure within the diffuser increases due to decrease in velocity

Combustion Section Components

• Made from corrosion resistant steel
• Four basic elements:
  • One or more combustion chamber(s)
  • A fuel injection system
  • Ignition source
  • Fuel drainage system
• Has a primary and secondary airflow segment

Turbine Section Components

• Extracts energy from hot gases post combustion
• Generates mechanical energy to drive the engine compressor accessories/gearbox.
• Approximately 60%to 80% of the total pressure energy from hot gasses are absorbed by the turbine

Exhaust Section Components

• The design of the turbojet exhaust section has a strong influence on engine performance.
• Exhaust segments: Exhaust cone, exhaust duct/ tailpipe, and the exhaust nozzle

Accessory Section Components

• Known as the accessory drive
• Provides power to different engine and aircraft accessories
• Examples: generators, pumps such as hydraulic, fuel, and oil pumps.

Cold and Hot Section Components

• Cold section: air inlet, compressor, and other pre-combustion segments
• Hot section: Combustion, turbine, and exhaust

Categories of Thrust Reversers

• Mechanical blockage type (clamshell)
• Aerodynamic blockage type (obstruction, or cascade vanes
• Various types of thrust reversers exist for various engines and situations.

Gearboxes

• Known as the accessory drive
• Engine's power shaft powers accessories using a set of bevel gears
• Power delivery from the gearboxes provides power to the different auxiliary power and accessory segments

Engine Mount

• Engine mount for different engine types may vary in construction and use different methods to support the engine

Bearings

• A combination of compressor and turbine rotors on a common shaft.
• Engine bearings are assigned in a critical function.
• Various types of bearings are used for different situations
• Special turbines engine(oil-dampened bearing) used for higher quality engines

Compressor Stall

• Described as an imbalance between inlet velocity and compressor rotational speed
• Occurs when compressor blade angle of attack exceeds critical angle, interrupting airflow and causing turbulence
• Indication on cockpit displays may vary depending on the type of stall.

Factors Cause Compressor Stall

• Flight in severe turbulent or abrupt maneuvers may cause stall
• Excessive fuel flow accompanied by incompatible engine RPM and airflow may cause stall
• Damage to compressor blades, stator vanes, or turbine components can cause stall

Combination Compressor

• A hybrid design that combines axial and centrifugal compressors

Auxiliary Power Unit (APU)

• Turbine-powered units supplying electricity, air conditioning, and other necessities when engines are off
• Used in aircraft which need extra power for situations such as passengers and engine maintenance, starting, and running ground operations

Flameout

• Causes of flameout: -Excessively high velocity airflow literally blows the flame out -Lean die out occurs at high altitudes when engine speed and fuel pressure are inadequate. -Rich blow out happens when rapid changes occur with a throttle movement that cause fuel temperature to fall below the combustion temperature range

Turbine Section

• Component that extracts the energy from the burned fuel and air for propelling
• Basic elements include Case, Stator, Shroud, and Rotor

Advantages of Turbojet Engine

• Simplicity and low manufacturing costs
• Low power required for initial operation
• High operating efficiency across a wide range of rotation speeds
• High compressor ratio (15:1)

Disadvantages of Turbojet Engine

• Large frontal area
• Limited stages

Advantages of Axial-flow Compressors

• Ability for higher compressor ratio via further stages
• Lower aerodynamic drag

Disadvantages of Axial-flow Compressors

• High weight.
• Low pressure rise per stage (1.25 :1)
• Expensive and difficult manufacturing

Types of Compressors

• Centrifugal flow compressor
• Axial flow compressor

Noise Suppressors

• Some released energy from combustion is converted to noise.

Older Design of Turbojet Engines

• Require additional noise suppression equipment which includes devices that break airflow behind the tail cone and additional soundproofing and insulating materials.
• Re-designing is required to meet more stringent new federal noise standards

Sound Intensity Measure

• Sound intensity of engine noise levels are measured in decibels (dB).
• A dB is the ratio of one sound to another.

Explore the fascinating history of jet propulsion, its advantages over traditional engines, and how Newton's Third Law applies to propulsion concepts. From Hero of Alexandria's early inventions to modern jet engines, this quiz covers key developments and principles in the field.