• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

Flight Literacy

Flight Training Educational Materials

  • Home
  • Basic Flight Training
    • Basic Aircraft Flight
    • Aeronautical Knowledge
    • Airplane Ownership – General Aviation Information
  • Advanced Flight Training
    • Instrument Flight Rules
    • Instrument Procedures
    • Flight Navigation
    • Aircraft Weight and Balance
    • Advanced Avionics
    • Risk Management
    • Aviation Instructor Training
    • Glider Flying
    • Weight-Shift Control Aircraft Flight
    • Helicopter Flight Training
    • Advisory Circulars
  • Training Aids
  • Tip Jar
You are here: Home / Basic Aircraft Flight / Transition to Jet-Powered Airplanes / Jet Engine Basics

Jet Engine Basics

Filed Under: Transition to Jet-Powered Airplanes

A jet engine is a gas turbine engine. A jet engine develops thrust by accelerating a relatively small mass of air to very high velocity, as opposed to a propeller, which develops thrust by accelerating a much larger mass of air to a much slower velocity.

Piston and gas turbine engines are internal combustion engines and have a similar basic cycle of operation; that is, induction, compression, combustion, expansion, and exhaust. Air is taken in and compressed, and fuel is injected and burned. The hot gases then expand and supply a surplus of power over that required for compression and are finally exhausted. In both piston and jet engines, the efficiency of the cycle is improved by increasing the volume of air taken in and the compression ratio.

How to Fly an AirplaneFlight Literacy Recommends

Rod Machado's How to Fly an Airplane Handbook – Learn the basic fundamentals of flying any airplane. Make flight training easier, less expensive, and more enjoyable. Master all the checkride maneuvers. Learn the "stick and rudder" philosophy of flying. Prevent an airplane from accidentally stalling or spinning. Land a plane quickly and enjoyably.

Part of the expansion of the burned gases takes place in the turbine section of the jet engine providing the necessary power to drive the compressor, while the remainder of the expansion takes place in the nozzle of the tail pipe in order to accelerate the gas to a high velocity jet thereby producing thrust. [Figure 15-1]

Figure 15-1. Basic turbojet engine.
Figure 15-1. Basic turbojet engine.

In theory, the jet engine is simpler and more directly converts thermal energy (the burning and expansion of gases) into mechanical energy (thrust). The piston or reciprocating engine, with all of its moving parts, must convert the thermal energy into mechanical energy and then finally into thrust by rotating a propeller.

One of the advantages of the jet engine over the piston engine is the jet engine’s capability of producing much greater amounts of thrust horsepower at the high altitudes and high speeds. In fact, turbojet engine efficiency increases with altitude and speed.

 

Although the propeller-driven airplane is not nearly as efficient as the jet, particularly at the higher altitudes and cruising speeds required in modern aviation, one of the few advantages the propeller-driven airplane has over the jet is that maximum thrust is available almost at the start of the takeoff roll. Initial thrust output of the jet engine on takeoff is relatively lower and does not reach peak efficiency until the higher speeds. The fanjet or turbofan engine was developed to help compensate for this problem and is, in effect, a compromise between the pure jet engine (turbojet) and the propeller engine.

Like other gas turbine engines, the heart of the turbofan engine is the gas generator—the part of the engine that produces the hot, high-velocity gases. Similar to turboprops, turbofans have a low-pressure turbine section that uses most of the energy produced by the gas generator. The low pressure turbine is mounted on a concentric shaft that passes through the hollow shaft of the gas generator, connecting it to a ducted fan at the front of the engine. [Figure 15-2]

Figure 15-2. Turbofan engine.
Figure 15-2. Turbofan engine. [click image to enlarge]
Air enters the engine, passes through the fan, and splits into two separate paths. Some of it flows around—bypasses the engine core, hence its name, bypass air. The air drawn into the engine for the gas generator is the core airflow. The amount of air that bypasses the core compared to the amount drawn into the gas generator determines a turbofan’s bypass ratio. Turbofans efficiently convert fuel into thrust because they produce low-pressure energy spread over a large fan disk area. While a turbojet engine uses the entire gas generator’s output to produce thrust in the form of a high-velocity exhaust gas jet, cool, low-velocity bypass air produces between 30 percent and 70 percent of the thrust produced by a turbofan engine.

The fan-jet concept increases the total thrust of the jet engine, particularly at the lower speeds and altitudes. Although efficiency at the higher altitudes is lost (turbofan engines are subject to a large lapse in thrust with increasing altitude), the turbofan engine increases acceleration, decreases the takeoff roll, improves initial climb performance, and often has the effect of decreasing specific fuel consumption. Specific fuel consumption is a ratio of the fuel used by an engine and the amount of thrust it produces.

Flight Literacy Recommends

Rod Machado's Private Pilot Handbook -Flight Literacy recommends Rod Machado's products because he takes what is normally dry and tedious and transforms it with his characteristic humor, helping to keep you engaged and to retain the information longer. (see all of Rod Machado's Products).

Primary Sidebar

SEARCH FLIGHT LITERACY

Basic Flight Training

Basic Aircraft Flight
Aeronautical Knowledge
Airplane Ownership - General Aviation
Training Aids

Advanced Flight Training

Instrument Flight Rules
Instrument Procedures
Flight Navigation
Aircraft Weight and Balance
Advanced Avionics
Risk Management
Aviation Instructor Training
Glider Flying
Weight-Shift-Control Aircraft
Helicopter Flight Training
Aircraft Mechanic (flight-mechanic.com)
Become a Patron!

Contact Us | Privacy Policy | Terms of Use
Easy Campfire Recipes | Recipe Workbook


Please help support our work
HIT THE TIP JAR

Copyright © 2021 FlightLiteracy.com




.