What is Jet engine: Definition and 74 Discussions

A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. While this broad definition can include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion airbreathing jet engine such as a turbojet, turbofan, ramjet, or pulse jet. In general, jet engines are internal combustion engines.
Airbreathing jet engines typically feature a rotating air compressor powered by a turbine, with the leftover power providing thrust through the propelling nozzle—this process is known as the Brayton thermodynamic cycle. Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines that were relatively inefficient for subsonic flight. Most modern subsonic jet aircraft use more complex high-bypass turbofan engines. They give higher speed and greater fuel efficiency than piston and propeller aeroengines over long distances. A few air-breathing engines made for high speed applications (ramjets and scramjets) use the ram effect of the vehicle's speed instead of a mechanical compressor.
The thrust of a typical jetliner engine went from 5,000 lbf (22,000 N) (de Havilland Ghost turbojet) in the 1950s to 115,000 lbf (510,000 N) (General Electric GE90 turbofan) in the 1990s, and their reliability went from 40 in-flight shutdowns per 100,000 engine flight hours to less than 1 per 100,000 in the late 1990s. This, combined with greatly decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century, where previously a similar journey would have required multiple fuel stops.

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  1. Astronuc

    J58 jet engine and supersonic flight

    We've had several threads on the SR-71 (and related craft) and the J58 propulsion system. https://www.physicsforums.com/threads/sr-71-blackbird-supersonic-aircraft.68694/ https://www.physicsforums.com/threads/j-58-engine-inlet-spike.413262/...
  2. R

    How difficult will it be to build a 'hybrid' Jet engine?

    Hi, Here is a question - somewhat futuristic and at the moment, hypothetical. How difficult will it be to build a 'hybrid' Jet (turbofan) engine? The engine should be able to handle both Kerosene and (gaseous) Hydrogen as fuel. After burning the kerosene for a while, Hydrogen will take over as...
  3. JD_PM

    I Understanding the thrust generated by a typical jet engine

    I was reading propulsion chapter 9 of Anderson's Flight book ( J.D. Introduction to flight (8ed., MGH, 2016)(ISBN 9780078027673)(O)(929s) EAs .pdf) and came to Figure 9.18 b) & c), Figure 9.19 (I cannot post the image here due to...
  4. mopit_011

    Force on three Bolts holding up a Jet Engine

    My solution was that there would be a force of 0 Newtons on the bolt as the bolt is not moving. But this answer is wrong. Where am I going wrong?
  5. berkeman

    GE initiates testing on second XA100 "adaptive cycle" fighter jet engine

    This is pretty interesting. It sounds like GE and the Air Force have been able to make some good improvements recently...
  6. S

    Piston Engine versus Jet Engine Power

    Hello All The power output of piston engines fitted to aircraft were (and still are?) specified in terms of their HP rating, whereas jet engines are typically rated in terms of their trust. For example, a Mosquito two engined fighter/bomber was equipped with two Merlins, each producing...
  7. VTOL147

    VTOL Jet Engine Aircraft and VTOL Jet Engine

    I am thinking about VTOL jet engine aircrafts like the following example (an ambulance). To be able to buid that kind of aircraft VTOL jet engines are needed. At the moment there are no VTOL jet engines available, but I have my own proposal: I have questions to jet engine experts. Is my...
  8. P

    Can a Jet Engine Remove drag from the Hyperloop tunnel?

    [Moderator: link removed] Can a jet engine the size of the tunnel mean that you can have an effectively have drag-free vehicle? Any lorry tethered to the jet engine would be basically be drag free? Is this correct? Thanks
  9. FreeBob

    Calculating equivalent horsepower for a jet engine

    Trying to remember some basics. I know the thrust of a jet engine. I'm thinking about equivalent HP. I can establish HP at a given speed, but what about while accelerating? I will display my ignorance here :( Power for static, non accelerating flight: Power = [Thrust x Airspeed] Thrust...
  10. FreeBob

    What is the Career of a Retired Chief Technologist in Servo/Mech R&D?

    BSME Missouri University of Science and Technology (was University of MO at Rolla) '78 Retired after 32 year career in disk drives Chief Technologist managed about 150 electrical, mechanical and computer science engineers developing servo mechanics for hard disk drives Two boys, one graduating...
  11. S

    Calculating suction area around the intake of a jet engine

    I am looking to calculate the area around the engine where, if an object enters this area, it would be "ingested" by the engine (subsonic flight). In other words, I am looking to draw the shape around the engine, where the air within that shape is disturbed air (being ingested by the engine)...
  12. E

    B Exploring the Possibility of a Warp Jet: A Theoretical Approach

    I was looking at videos on how a warp drive theoretically could work: by compressing space in front and expanding space in the back. This reminded me of a jet engine compressing air and blasting it out of a nozzle. My question is, could you build a sort of warp jet that would compress space...
  13. orb_yt

    How are/were computers used in jet engine design?

    Hello all, I have been tasked with writing a very short article regarding the use of computers and software in early jet engine design up to modern times. I've been having a relatively hard time finding reading material through Google. I understand that modern jet engine designers use CAD...
  14. T

    Thermodynamics: The Jet Engine

    Good evening everyone,I had several questions regarding basic thermodynamics. After going to Paris Airshow (Le Bourget), lot's of questions came to my mind after looking at those beautiful Jet engines...I have always had a very basic understanding on these engines: a fan, a compressor (High and...
  15. T

    Fuel with Static Air in a Jet engine

    Good evening, Today's planes' need bleed air to start. Above a certain speed, igniters fire up and we inject fuel inside the combustor chamber. Why do we need to have the engine running to inject fuel (around 20%N2)? Can we simply not inject fuel with static air (i.e. when engine is not...
  16. A

    Could you create thrust with water vapor?

    Whilst I was thinking of hydrogen combustion jet engines. I thought of a little idea... What if you could create thrust with water vapor the same way you could with the exhaust gas of a jet engine. (NOTE: I have no experience in engineering and I only have a mild interest in it). If this is...
  17. BoeingJet

    Can a Railgun-Powered Ramjet Solve the Challenges of High-Speed Travel?

    Recently, I designed (in my head) a Hypervelocity Passenger Vehicle (just a cool name for really high speed transports). I immediately ran into engine design problems ( I like designing everything stand-alone), since regular jet engines can't get to Mach 8.8 without burning up into flames, and...
  18. Maximilian Popelier

    What is the force of a jet engine and how can I calculate it?

    Hi Does someone know realistic numbers that i can put in this equation so i can calculate the force? Ty maximilian Popelier
  19. Maximilian Popelier

    Mechanical parts of a jet engine

    Hi guys I'm making a project about jet engine. I need to write 10 pages of the mechanical part of a jet engine. I already did it for physics. What can i talk about. I need formules en stuff in the 10 pages Ty for the help guys! Max
  20. O

    Can a Hybrid Lightning Jet Engine Outperform a Traditional Jet Engine?

    Does lightning heat air 5 times more the the suns surface? If so can a hybrid lightning jet engine work, as lightning heats up air, more then fuel can? Americas 5th gen jet fighter can travel 3* more then enemy jet's. That means it's a hybrid engine right? Compressed air heated sees the air...
  21. A

    Why do Jet fighter pilots experience a greater G-force?

    Hi! I'm a high school student, aspiring to pursue a career in Astronautical Engineering. I always try and ponder on questions about everyday aerodynamics and physics. So, here's a question from you from an aspiring scholar. It is known that, at high velocities, pilots in super-sonic jet...
  22. H

    This futuristic jet engine is very real

  23. G

    Practical measurements of ramjet engine

    Hello everyone I am trying to design a ramjet engine. For that I need measurements of its parts. Does anyone know how to calculate them or have a link to a website where I could find more information?
  24. J

    Rocket Specific Impulse vs Jet Engine Specific Impulse

    I really can't seem to wrap my head around why the specific impulse on a rocket is so much lower than that on a jet. I know a jet engine has a larger supply of oxygen, but I don't see why that has such a huge effect. I also know exhaust velocity plays a large part, but I would have thought that...
  25. G

    Mph jet engine reaches 2 atmosphere 29.4 psi

    As a jet engine travels through the sky and picks up speed ram air increases the air pressure at the air intalk of the engine. How many mph does the engine have to be going for ram air to 2 atmospheres = 29.4 psi? At what speed in mph = 3 atmospheres? 4 atmospheres? Is this a linear or...
  26. Y

    Exploring Jet Engine Position: Front or Back?

    Hello. Do you think the idea of placing the jet engine at the front is plausible? Why? Why not? Thanks Yrjosmiel
  27. N

    Rocket engine vs jet engine efficiency

    Which are more efficient, Rocket Engines or Jet engines, and why? It would make sense that rocket engines are more efficient because they aren't effected by air pressure but I have been told by some people that actually Jet engines are more efficient so I am confused. If you know of any link...
  28. N

    Can a Jet Engine be Created Using a Traffic Cone Design?

    Would it be possible to make a working jet engine by simply having a structure like two metal cones stuck tip to tip (traffic cone shaped)? The idea is to get it going fast, inject fuel in the middle, have the fuel auto ignite due to compression heating in the front cone, and than use the back...
  29. W

    Compressed oxygen for jet engine (?)

    as jet engines lose there productivity at altitude due to thining air/oxygen , why isn't injecting compressed air directly along side the fuel a good idea ? , is this already being done ? would /does this not increase ceiling height and allow sub orbit levels or possible leave atmosphere...
  30. Z

    Jet Engine performance in Cold Weather

    Hey guys. I was studying up jet-engines and their performances with varying ambient temperatures and found myself stuck on something that is probably very trivial. What I've read online and in my notes is all generally the same - that as temperature falls air density rises and as such more...
  31. F

    Could a jet engine be run on nuclear power?

    I know people have designed nuclear rocket engines, but is there any reason you couldn't have a nuclear thermal jet engine? Simply take a conventional jet and swap out the combustion area with a small reactor? Could the same idea work at higher speeds with a nuclear ramjet, or scramjet equivalent?
  32. M

    Several questions involving a homemade miniature jet engine.

    Hey guys. I am new to engineering and I came to this because I wanted to make my own miniature jet engine. I have a limited knowledge of physics but I wish to broaden it through this idea. Now I know that this was made before for RC models, but I want to actually make one so I understand how...
  33. M

    Achieving VTOL with jet engine instead of rocket engine

    Jetpack International's T-73 achieves vertical takeoff with an actual jet engine as opposed to the rocket engines used by the majority of jetpack models. This allows it to have longer flight time (9 minutes as opposed to 30 seconds). Some fighter planes also manage VTOL with a jet engine, the...
  34. B

    Testing a 100lbf Jet Engine: Blast Shields

    Hey guys. As the title reads, I am a part of a research project and we will soon be testing a 100lbf jet engine. We take safety very seriously and want to take all the proper precautions in order to ensure everybody involved will come out of the experimentafely in case something goes wrong...
  35. S

    A 1600 kg jet engine is fastened to the fuselage of a passenger jet

    Homework Statement A 1600 kg jet engine is fastened to the fuselage of a passenger jet by just three bolts (this is the usual practice). Assume that each bolt supports one-third of the load. (a) Calculate the force on each bolt as the plane waits in line for clearance to take off. (b) During...
  36. T

    Light amplification jet engine?

    Using a series of focal reflectors, built in antenna strategically placed for proper phasing the EMF amplification system. Kinda like a space hyper engine. Possible? I can draw some blueprints I think.
  37. S

    Exploring Cyclic Symmetry: A Jet Engine Primer

    Hi, Please can anyone explian what is cyclic symmetry? I'm new to this term and have encountered this in jet engine example Vishal
  38. D

    Jet Engine Question Homework: Find Thrust w/ 100% Efficiency

    Homework Statement The major difference between a jet engine and a rocket engine is that a rocket carries its own oxidizer, usually in the form of liquid oxygen (LOX). A jet takes in air from the atmosphere as it moves, uses it to burn the fuel, and then ejects all the gases out the back...
  39. M

    Pressures in front and behind LP fan on jet engine

    My friends (all A&P Aircraft mechanics) say I'm nuts. A co-worker and I attended a Honneywell TFE731 jet engine maintenance school. During the class the instructor asked this question, "which side of the front fan on a TFE731 engine has the highest pressure?" His answer was the front. (we are...
  40. F

    Determine the power of the jet engine of an airplane

    Homework Statement The jet engine of an airplane takes in 130 kg of air per second, which is burned with 4.3 kg of fuel per second. The burned gases leave the plane at a speed of 600 m/s (relative to the plane). If the plane is traveling 260 m/s, determine the power (hp) delivered...
  41. N

    Finding required thrust power for jet engine aircraft.

    Homework Statement I need to find required thrust power for lockeed s3a. I know Thrust=Drag in horizontal flight. For take off, need to use the take off angle, split the Weight (G) into 2 components using the takeoff angle... Same for landing. Given: G=19278kg ---> 19278*9.81=189,1kN...
  42. M

    Building a Jet Engine - Step by Step Guide

    Hi guys... we are currently interested -in our clip of aerospace engineering in my uni.- to build a complete jet engine ... unfortunately.. we have not yet found any detailed explanation to each step in doing so .. if you have any link or uploaded book or even you remember some manuals...
  43. J

    What are the forces acting on a jet engine when encountering turbulence?

    Homework Statement A 1600kg jet engine is fastened to the fuselage of a passenger jet by just three bolts (this is the usual practice). Assume that each bolt supports one-third of the load. (b) During flight, the plane encounters turbulence, which suddenly imparts an upward vertical...
  44. V

    Thermodynamic cycle of jet engine

    How to choose thermodynamic cycle for designing new jet engine? While designing new jet engine what parameters are important for choosing thermodynamic cycle? what other parameters are important for jet engine designing?
  45. Phrak

    Could a Valveless Pulse Jet Engine Eliminate the Need for Moving Parts?

    A pulse jet has only one moving part. Nice. But what if it didn't need any moving parts? Stupid idea, right? Check out this stupid idea. They're all over the internet. http://www.youtube.com/watch?v=5U-grFuXZ9U&feature=related"
  46. M

    Note: This is not a real webpage, just a hypothetical title for the content.

    if i were to connect a central axis to the turbine in a small jet engine and down gear it using planetary gearing is there potential for jet a type engine to put out some "real" tourque is there a way i could figure this in foot lbs using the thrust? absolute pressure? thermal efficiency?
  47. V

    What are the Pros and Cons of High Bypass Ratio Jet Engines?

    low bypass ratio engine has low mas flow and high speed, high bypass ratio engine has high mass flow and low average speed. if the high bypass ratio engine has high mass flow and high average speed, what are the advantages and disadvantages of this jet engine?
  48. wolram

    Jet Engine Life Span: What to Know

    Does a jet engine have a life span?
  49. J

    Jet Engine Sound Intensity Calculation with Absorption Effects

    Homework Statement I=\frac{p_{ave}}{4\pi r^{2}} is derived on the assumption that the transmitting medium does not absorb energy. It is known that the absorption of sound in dry results in a decrease in energy of about 8 dB/km. The intensity of sound at a distance of 120 m from a jet engine is...
  50. D

    Power of a Jet Engine: 1.5 * 10^9 Nm/s

    A jet engine develops 1 * 10^5 n of thrust in moving the airplane forward at a speed of 900 km/h. What is the power developed by the engine? I thought I needed to convert 900 km/h to m/s, so I did and I got 15000 m/s. The only equation I see to use for this is: P = Fvcosθ When I...