Jet Propulsion Theory and Applications

Jet Propulsion Theory

• Newton's Third Law of Motion: For every action, there is an equal and opposite reaction.
• Newton's Second Law of Motion: Thrust = Mass x Acceleration, or Thrust = Mass x change in Velocity, or Thrust = Mass x change in momentum.

Newton's First Law Applied to Airplanes

• An object in motion stays in motion unless acted upon by an outside force.
• Thrust and Drag: When Thrust equals Drag, airspeed is constant. Increasing Thrust increases airspeed, and Drag increases with airspeed. When Drag equals Thrust again, the aircraft no longer accelerates but holds a new, higher constant airspeed.

Pioneers and Early Development

• Key factors for jet engine efficiency improvements: pressure rise by the compressor, temperature of the gases entering the turbine and combustor efficiency.
• Early applications were military aircraft, primarily emphasizing speed.
• Key figures: Orville and Wilbur Wright, Maxime Guillaume, Dr. A. A. Griffith, Hans von Ohain, Frank Whittle, and Dr. Hanratty.

Aircraft Types and Manufacturers

• Aircraft examples: Gloster, Meteor, Me-262, Bell XP-59A, Tornado B-45, Canberra, B-707, DC-8.
• Engine manufacturers: CFM, PW, RR, GE, and International Aero.

The Concord Olympus Engine

• The Concorde Olympus engine: weighed seven times more than Whittle's first engine but achieved 25 times more thrust at three times the speed with a lower specific fuel consumption.

Propulsive Efficiency

• Propulsive efficiency varies with airspeed and engine type (turbojet, turboprop, high-bypass turbofan, low bypass turbofan).

Force and Momentum

• Force (F) = Thrust, Weight of air & fuel divided by gravity (M).
• Acceleration (a) = change in momentum of mass.
• In metrics, 4.45 Newtons = 1 lb.

Acceleration Calculation

• Acceleration = change in momentum.
• Velocity of the air exiting the engine (V₂ or V jet).
• Velocity of the air entering the engine (V₁ or V flight).
• Change in velocity (V₂ - V₁)

Gross vs. Net Thrust

• Gross thrust: total thrust generated by the engine.
• Net thrust: thrust available with forward engine speed.

Choked Nozzles

• A choked nozzle accelerates exhaust gases to the local speed of sound; no more, no less.

Atmospheric Pressure at Altitude

• A table of pressure (psi) at different altitudes (ft) is provided.

Common Conversions

• Conversion factors for knots, mph, feet per second, PSI, and inHg.

Turbofan Engine

• Calculation of thrust (Fn):
  Fn = Waf (V2 – V1) / g + Wac (V2 – V1) / g + Aj (Pj-Pam)

Turboprop Engine

• Engine rated in shaft horsepower(SHP) using dynamometer.
• Calculation of thrust (Fn) only applicable during flight, straight and level flight.
• The engine design combines turbojet and propeller characteristics, efficient at speeds between 220 and 350 knots and altitudes between 18,000 and 30,000 feet.
• At 375 mph, one pound of thrust equals one horsepower.

Specific Aircraft Examples

• Navy P-3 Orion: describes its flow direction.
• King Air 200: Specifications such as take-off weight, engine type, power (850 SHP), speed (260 KIAS), and torque (1369 ft-lbs) are mentioned, along with altitude(FL260), and prop efficiency(80%).

Practice Problems

• Problems on various calculations involving thrust, horsepower, altitude, and speed related to different aircraft types (e.g., turboprop, turbo-jet, turbofan engines) are noted.

Engine Comparison

• Comparison of CFM LEAP-1A and PW1100G engine parameters, including thrust, bypass ratio, architecture, and dimensions.

Geared Turbo Fan (GTF)

• Advanced high-pressure turbine (HPT) and 8-stage high-speed low-pressure compressor (LPC).