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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What factors cause a turbine aircraft to have decreasing fuel burn over time?

Consider a fictional aircraft with a fuel schedule similar to the following: ...
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Would mid-air refueling for an air-to-space vehicle that flies like a plane be a viable advantage if the tech was available? [closed]

Let's take the style of an F-22 Raptor (awesome!), build the fuselage, wings, etc to handle runway takeoff horizontally and then vertically (if needed) up to orbital space flight to reach the ISS in ...
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Short duct and long duct turbofan [duplicate]

Plss help me. I got a exam question about comparing the advantages and disavantages of short duct turbofan and long duct turbofan. Anyone knows the answer plss help me !!!
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Why doesn't a hot jet engine crack at 10,000 metres and -50 C air temperature?

I have seen videos of red hot jet engines being tested at sea level in a building. But even in a building the temperature difference between the engine and the room is large. Most materials would ...
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What other materials apart from conventional nickel and steel superalloys can be used as a first stage turbine blade material?

Steel and nickel chromium alloys have been prominent and most used as turbine blade material although there are other materials such as tantalum carbides, tungsten and many more which I have no ...
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Why does the CFM LEAP have so many LPT stages? [duplicate]

With the core power being similar, intuitively, the higher the number of turbine stages, the more energy is absorbed, the higher the RPM. But the PW1000G vs CFM LEAP (both engines have similar thrust ...
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Can I simply use multiple turbojet engines to fly supersonic?

the jet engine FJ33 produced by Williams International produces around 6 kN thrust (maximum, at sea level). Imagine: to fly supersonic, I need for my aircraft 9 kN of continious thrust. I am wondering ...
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Replacing or supplementing turbofan with electric fan [duplicate]

Could you replace 2 B747 engines with electric turbofans? Could the 2 standard turbofans produce enough power to allow electric cruise with jets used for take off?
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What are the “beta lines” of a gas turbine engine component?

For a compressor in particular, what do the beta lines represent? I know for a compressor map you have the lines of constant spool speed, and the contours of isentropic efficiency. I also understand ...
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Where is the fire suppression material injected into a jet engine?

This question is regarding the P&W 4000 engine that was involved in the recent incident on UAL 328, but it doesn’t have to be specific to that engine. From what I gather in this incident the fire ...
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What is the difference between RTOP, MTOP, and MCP?

I am currently learning how to fly the SD3-60 (Shorts) Aircraft, and I am trying to gain an understanding of RTOP (reserved take off power), MTOP (max take off power), and MCP (max continuous power). ...
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Why do thrust vectoring nozzles delay?

I saw a video demonstrating the SU-30's thrust vectoring nozzles and noticed that the horizontal stabilizers begin moving up/down before the nozzles do. It seems that the F-22 also has this delay. ...
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How does p-factor affect jet engines?

How does p-factor affect jet engines, if at all? If it doesn't, why?
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Is excess power always increasing with a decreasing altitude at iso-mach?

For an aircraft with a jet engine, let's say the power margin at M1.5 at an altitude Z1 is x. Is the power margin at a lower altitude Z1-H at M1.5 always greater than x ? From my point of view, there ...
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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 fuel:air ratio of a turbojet engine not around ~1:15 (the stoichiometric ratio)? [closed]

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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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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