Questions tagged [jet-engine]

Engines which propel aircraft via "jet propulsion", i.e. by expelling high-velocity gasses (usually primarily air) through propelling nozzles.

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67 views

Why does a jet's combustion energy propel the engine forwards rather than acting equally in all directions to create zero thrust? [duplicate]

I'm a novice. I have high school physics and I've seen many explanations of how a jet engine works. To paraphrase: Fans compress air into a chamber where combustion energy is created, which spews ...
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What is the speed of gas in the core of a jet engine?

Coming from a slightly related question, I want to know what is the speed of the gas in the core of a jet engine, after combustion but before the first turbine stage. I'll just pick a random example: ...
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What is the fan pressure ratio in a turbofan?

What is it and how does it affect efficiency and thrust?
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Why is the air:fuel ratio of a turbojet engine typically around ~1:4 - 1:3 and not around ~1:15 (the stoichiometric ratio)?

Also, what is the maximum fuel:air ratio possible in a combustion chamber of a jet engine?
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Why do jet engine igniters require huge voltages?

Wikipedia's Components of Jet Engines has this to say on the igniters: A high voltage spark is used to ignite the gases. The voltage is stored up from a low voltage (usually 28 V DC) supply provided ...
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What were/are the military designations of the JT8D and PW4000?

Turbine engines on U.S. military aircraft, in addition to their manufacturer-given names, receive separate designations (consisting of J [for turbojets], F [for turbofans; formerly TF], or T [for ...
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Why would changes in jet-engine power settings not result in changes in engine loudness?

My casual AAR reading has dredged up another counterintuitive detail of aircraft behaviour, this time regarding the relationship between engine power and engine loudness: 1.16.7.3 Sound Similar to ...
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Are centrifugal compressors/turbines less efficient internally, and if so, why?

From my related question which found a good example of a centrifugal turbine jet engine, the Henkel Hes 3. Picture Source Website (it's in Czech). Thanks to Jan Hudec for finding it. My understanding ...
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What turbine temp. would result from burning pure stoichiometrically?

I've heard that jet engine efficiency is limited by turbine temperatures---that is, the max temp. that the turbine blade alloy can withstand before weakening too much. So jet engines are run fuel-lean....
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Does airspeed impact fuel flow?

Let's say an F-104 Starfighter is flying at sea level at 600 KIAS with throttle at 100% RPM. Then, let's say the F-104 is still flying at sea level, but the pilot reduces throttle and airspeed falls ...
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Why is the F-104 Starfighter’s afterburner thrust not greatly impacted by altitude?

Here is a page from the F-104 flight manual. It shows the flight envelope for the F-104 Starfighter with the powerful J79-GE-19 turbojet engine: I have a question regarding the shape of the ...
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In general, what are the RPM ranges/differences between the various compression stages on a 2 or 3 spool (LP,IP,HP) turbojet/fan engine?

I have a general interest in jet engines and am pretty new to the topic so I wanted to toss this question into the wind as I don't have any previous experience or knowledge to pull from and haven't ...
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Is there any theoretical problem powering the fan with an electric motor [duplicate]

A question that I have been wondering about lately is whether it would be possible to power the fan in a modern hi-bypass turbofan with an electric motor and achieve performance comparable to the ...
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1answer
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What's the name of this part of combustion chamber and what is it for?

There are two "excrescences" Near the end of diffuser of some combustion chambers. e.g. CFM56 and F101 What's the name of this part of combustion chamber and what is it for?
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What's this outlet of IAE V2500 for? [duplicate]

Anybody knows what is this outlet for and why it is designed in such way? Edit: On MD-90 didn't see such thingy
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What are these painted lines on the fan blades of Rolls Royce Pearl 15?

I'm not sure that they are painted lines but it looks they are. What are they for? More images:
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What kind of test is going on in this image?

Some times we see images of jet engines on the net that have strange colors. For example take a look at the bellow image. What the operator is doing? Why the color of blades are white with red on its ...
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Are variable area exhaust nozzles or variable area throats more impactful?

I was reading this NACA research paper where, while discussing an adjustable plug-type nozzle, they state: Although this nozzle did not have independently variable area throat and exit areas, as ...
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Is everything OK with engine placement depicted in Flight Simulator poster?

Does the Airbus A320neo depicted in Microsoft Flight Simulator 2020 box cover photo has the right engine in all the wrong place? Here is the snapshot: Is it only me, who clearly sees that it is way ...
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Why does the LEAP 1A HPT run at such a high RPM?

I've watched the N2 on the LEAP sit at 100% at cruise and fluctuate as high as 101%. Why does the HPT run at such a high RPM?
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What does unmixed mean?

For a unmixed turbofan engine what does ‘unmixed’ mean in regards to the flow of air? How does this differ from ‘mixed’ also in terms of air flow ?
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Does the flow in an afterburner have to be subsonic?

This question is prompted by the problem on page 350 of the fluid mechanics book by Landau and Lifshitz. The problem states, "A small amount of heat is supplied over a short segment of a tube in ...
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Do pilots turn off the engines during de-icing?

During winter operations and de-icing are the engines (jet engines) usually in operation? If not, what is the reason for that? Also I was wondering if the engine nacelles require de-icing since I have ...
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Why are Stratolaunch's engines so far forward?

Stratolaunch's engines hang from pylons, not under the wing, but entirely forward of the wing's leading edge. (Even farther forward than, say, the 747's.) What benefit does this have, to compensate ...
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Why do new engines have a case with a triangular tiling pattern?

Take a look at the case of new engines such as the F-135: or the F-119: Why do they have a case with a triangular tiling pattern? Is this a new technology? A new material?
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How does afterburner efficiency vary with thrust?

Afterburners are much less efficient than turbine engines at converting fuel into thrust, so AFAIK no jet will engage afterburner unless it is already at full throttle on the turbine. But what if an ...
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What causes the horn-like noise during the start-up of some jet engines?

Here's the specific sound I'm talking about (it starts specifically 56 seconds into the video, as well as at 2:02 for the second engine): I've only really heard that ...
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How do power and thrust curves compare?

I would like to really understand why when talking about jets we care about thrust but when talking about propeller aircraft we care about power. (THRUST)="Just a force" (POWER)= work/time = ...
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What is this turbine engine panel that opens on landing?

Tonight I flew from Munich to Dortmund on an A319 and I happened to sit just above the wings and turbine on the right side. Upon landing, the turbine opened a window or panel which exposed some grid ...
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Is Flight Idle a constant?

Is "Flight Idle" for a jet engine a constant N1% value or does it vary with Altitude, and OAT?
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Can ramjets reach higher thermal efficiencies than gas turbines?

Since a ramjet isn't constrained by turbine inlet temperature like a gas turbine is, it seems to me that it should be able to achieve a higher thermal efficiency, given that it's operating at a speed ...
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Is this the relationship between rpm and thrust of a Turbofan? [duplicate]

In this graph from the FAA Airplane Handbook Chapter 15, page 5: It looks like it is talking about "jet engines" but is it engine type specific or it is for both turbojet/fan/prop/shaft? It ...
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Why would sea level static thrust have a takeoff and a maximum continuous value?

In the type certificate data sheet for a jet engine, there is this table static thrust is the thrust generated by the engine when the plane is at rest with respect to the Earth and the surrounding ...
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Why is thrust said to be constant over speed for a jet engine?

I'm just interested in some basic facts regarding flight. On reading the rather "low level" book "Understanding Flight, David F. Anderson, Scott Eberhardt), I recently came up to the ...
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Is the well known textbook-formula for net-thrust oversimplified or do I have a misinterpretation?

In order to understand how Jet-Engines works I came across the "famous" formula for net-thrust: https://en.wikipedia.org/wiki/Turbojet#Net_thrust $F_{thrust} = Q_{out} \cdot v_{out} - Q_{in}\...
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Why do some Turbofan engines have multi-stage fans?

I was wondering why some turbofan engine have multi-stage fans. e.g. F-119 engine: F100 Saturn AL-31
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Are large jet turbofans so easy to spin?

In this question, in the accepted answer, there is a comment by alephzero that says one can actually rotate a large turbofan's blades with one finger! Is that true, ...
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1answer
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Factors to be considered when re-engining aircraft

What parts of the aircraft need to be adjusted / refitted / added when fitting new (different type) of engines? Also what what kind of re-certification regarding airworthiness etc. will be necessary?
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Can you identify this engine?

I am studying Aircraft mechanics currently, and in our academy we have some aircraft engines and different types of them, and I need please your help to know the reference of one of them, and if it is ...
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What is the diameter of each stage of the PW800 engine compressor and turbine?

I am an Aerospace Engineering student working to analyze P&WC's PW800 engine family--specifically, the PW814GA, for a project and we need to know some hard-to-find data. Does anyone knows where I ...
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What is the meaning of “Maximum Radial Projection (at Drain Mast)”?

I am an Aerospace Engineering student working to analyze P&WC's PW800 engine family--specifically, the PW814GA, for a project and I am stuck by a term: "Maximum Radial Projection (at drain ...
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Why is tangential velocity a loss of kinetic energy in a turbine section?

While researching turbine engines I came across a statement The mass of airflow naturally does not change in the transfer of energy to the rotor system, but the velocity of mass flow being slowed ...
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Why don't turbofan engines have shrouds affixed to the fan blades?

For a turbofan to be efficient the gap between the blades and the shroud has to be extremely small. Why don't we just attach the shroud directly to the blades and let it spin as one? Would that ...
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1answer
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What valve would be the best for a model rocket with a hybrid engine? [closed]

I am planning on building a model rocket with a hybrid engine. I am trying to find the best valve that could be used for the MOV, main oxygen valve. I plan to use gaseous oxygen and would like the ...
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3answers
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What causes air to move to combustor?

I know the pressure is highest at end of compressor. But what forces air to move low to higher pressure? Am i missing out something? I have heard seals are used to prevent leakage of air from ...
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What is the purpose of a movable inlet on a jet engine?

I was reading that aircraft like the F15 and SR-71 have movable inelts. Whats the purpose of this? I was also reading aircraft like the F-22 doesn't have a movable inlet. Why?
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Which dust size causes most damage to turbine engines?

I'm conducting some research on my bachelor's thesis on predictive maintenance and I have so far not been able to find a solution to the following question: Which size of dust is more damaging to the ...
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What is the engine shell temperature?

What are the highest temperature locations in the outer shell on an aircraft engine? Particularly, modern turbofans like the Trent 900 for example. I'm interested in the temperature constraints of ...
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If Sweden wants to export JAS39 to a 3rd country, will they have to get permission from the US govt.?

Does Sweden manufacture its own jet engine for JAS Gripen, or does it purchase engines from the USA? JAS39 C/D uses Volvo RM12 JAS39 E/F uses Volvo RM16 I read on the internet that Gripen's engine ...
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What are the differences between turbojet and turbofan (low and high by-pass ratio) in the graph of thrust relative to speed?

What are the curves of thrust relative to velocity of the turbojet, low-bypass turbofan and high-bypass turbofan engines from static thrust to Mach 4 generally. Approximation is okay as long it has ...

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