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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Why does the torque curve of free shaft gas turbines keep gradually dropping as RPMs increase?

When i look at the output shaft torque curve of a free shaft gas turbine i can see that they are almost like an electric motor. It makes peak torque at very low rpm and then torque keeps gradually ...
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A very loud, short- lived howl

Within the last eighteen months, I'd say - commercial aircraft descending into Heathrow have started to emit a terrifying, short-lived but very loud whining howl when they pass over my house. They are ...
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Why do we monitor N2 speed rather than N1, when starting jet engine?

I've just heard that N2 is the limit when starting jet engine, But I have no idea why it is. I know that N1 is Low compressor speed, and N2 is high compressor speed. So what makes high compressor ...
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How did the MiG-25M prevent a flameout?

How do afterburning turbofan or turbojet planes prevent or minimize the risk of a flameout at nearspace altitudes such as Fedotov's Mig-25M that went higher than 115K ft (35 km) two times? At these ...
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How does the F-16 engine startup work?

So, the simplest way to start up an F-16s engine is to flip the power switch to "main power" and then set the "jet fuel" switch to "Start 1" or "Start 2". I ...
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10 votes
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Why does the X-3 have two oil pressure gauges per engine?

The X-3, as currently in the National Museum of the US Air Force, has two oil pressure gauges per engine, and one fuel pressure gauge per engine. One of the per-engine oil pressure gauges is labeled ...
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How a power assurance check works?

In a Bell 407 the power assurance check takes into account torque, pressure altitude and MGT (measured gas temperature aka TOT). The flight manual states that if MGT when tested is less than or equal ...
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FOD ingestion & engine damage - how does the crew know it happened?

A 737 I was supposed to fly on yesterday was grounded after, per the captain, it ingested a pebble on the taxiway causing damage to a fan blade. My question is: how did they know this happened? (Lucky ...
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4 votes
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Early turbojet RPM and thrust indicator

The flight operations handbook for the Douglas X-3 Stiletto (an experimental aircraft from the early 1950s) says that the instrument panel has instruments that indicate the thrust of the two ...
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How to determine engine CG in order to calculate moments acting on it?

The aircraft has four engines mounted in pods under the wing. I know the values for the location of engine nacelle front face from the fuselage nose (longitudinal) and distance between engine ...
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1 vote
1 answer
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What is the margin of difference between copying and developing new? [closed]

Iran Flaunts New Missile and Jet Engine Technology The above article says that Iran is able to make exact copies of American General Electric J85 and Williams FJ33/FJ44 jet engines. Does this mean ...
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6 votes
4 answers
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Why is China still heavily reliant on Russian turbofan engines?

According to Paul Schwartz, China is "still heavily reliant" on Russian turbofan engines: Beijing is still heavily reliant on Russian aircraft engines, however, due to the great difficulty ...
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From what distance can a man hear and see an airplane flying overhead, without any equipments?

Suppose I stand at p = (latitude,longitude) on earth. I want to manually check for any airplane flying overhead in my neighborhood with naked eye and without any ...
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16 votes
3 answers
15k views

Do the design and manufacturing of cruise missile engines and aircraft jet engines require the same amount of efforts?

Cruise missile engines are relatively smaller in size. However, they might need the same level of expertise e.g. metallurgy, single-crystal blades, etc. Do the design and manufacturing of cruise ...
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7 votes
2 answers
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Why do turboprops not have a thrust value in the specifications? [duplicate]

When looking through aircraft engine specifications, turbofans always provide a thrust value, e.g. in JT8D engine: https://prattwhitney.com/products-and-services/products/commercial-engines/jt8d In ...
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Why do some jet engines have fewer fan blades than others?

I have found out upon researching jet engine fan blades that they can vary from 16 to 34. Why do they vary, I mean, does decreasing or increasing the number of fan blades have any performance impact? ...
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From which jet engine is this blade?

Some years ago I bought a compressor blade on ebay but I don't know which jet engine it's from. It's quite light. I tried to determine the density by the help of my kitchen equipment and it's most ...
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Would blade-less (Dyson style) jet engines work? [duplicate]

Is it possible to design an aircraft with blade-less (same concept as Dyson) design to generate thrust? What are some of the key benefits, drawbacks and examples of attempts (if any) at this kind of ...
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Why do white marks on the spinners in front of engines have different patterns? Not Yellow? Omitted for some models?

In aeroailas' answer I understand that the cones in front of the props/fans are called spinners. In Farhan's answer I understand that the ehite marks painted onto the spinners act less as scarecrows ...
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4 votes
1 answer
175 views

Thrust varaition of a Turbofan engine with altitude and mach number [duplicate]

my classmates and I are trying to find a mathematical model for a low bypass turbofan engine, we ended up finding a model given by Snorri on "General Aviation Aircraft Design", but the ...
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2 votes
0 answers
126 views

What are these holes on the intake of Progress D-18T which are mounted on AN-225?

I was seeing a Progress D-18T of AN-225 and saw these holes on the intake of them. What are they for?
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Airflow through axial flow compressor

So I'm reading the Gas Turbine Engine Fundamental, and suddenly come across the airflow passes through one axial compressor stage. I wonder why the Resultant Rotor Inlet Velocity is pointing downward,...
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264 views

Do jet nozzles reset after the engine is off for a while?

I have seen jet engines with nozzles being able to dilate to adjust for throttle and things of the sort, but the question I have is, if the engine is turned off, does the nozzle "reset" to a ...
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What inspired the unique design of the F-105 Thunderchief intakes?

The horizontally forward-swept intakes of the Republic F-105 Thunderchief is not a design emulated in other production aircraft of the time, or I think at any time. If viewed as a more typical intake ...
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What’s the NCVA at the end of the F135 engine?

What’s NCVA at the end of the F135 engine? And what does it do?
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What is the speed the fan blade would go if it would separate from the shaft with the engine at full throttle?

I'm making a simulation of a blade separating from the shaft to test the case of the engine, but i don't know what speed should i put on the blade to go outwards the case, anyone has any idea how to ...
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7 votes
3 answers
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Is this image of Compressor aerodynamics correct?

Image Source: Air Gas Turbine Technology by Treager, Chapter 5 The rotation direction of rotor shown seems opposite. If it is correct, these are the questions I would like to ask: Why the Y vector is ...
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3 votes
2 answers
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Why do the replacements for craft like the C2 Greyhound and E2 Hawkeye still use turboprops?

These two airplanes are some of the classics in naval history, but replacements for them exist. When taking a look at them, they do have some improvements, but I still have one question. Why do they ...
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1 answer
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How to determine the length of the CD nozzle?

I am designing a convergent nozzle as well as a CD(Converging-Diverging) nozzle. How do I find out the length of those nozzles? If the throat of the CD nozzle has 0 length then what should be the the ...
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1 vote
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Why pressure and temperature decreases along the length of a convergent nozzle?

I know that the pressure and temperature follows stagnation relations of pressure and temperature as well as area mach relation inside a convergent nozzle along the length. And according to that ...
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3 votes
3 answers
3k views

Why does a rocket engine increase power with speed if the burn rate is constant?

A rocket produces constant thrust with speed, and that means increasing power with speed. Where does this increase in power come from if the fuel burn rate is constant? How can we explain this in the ...
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What type of bearings are used to support the shafts in jet engines? [duplicate]

I would like to know which types of bearings are commonly used to support the shafts in jet engines and why. I also read something about hydrodynamic bearings, how common are they?
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Can anyone help identify this turbine blade?

At the local army/navy surplus store and found this in a "junk" box. Got it for $1. Would live to know what airframe this came off of. Im new to this so compressor blade? Compressor turbine? ...
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Does the nacelle strut experience reaction forces due to lift, drag, thrust, weight of engine during cruise flight?

Cruise flight indicates that total lift and weight of aircraft cancel and thrust forces generated cancels with total drag forces. However, I am looking closely at the nacelle instead of the whole ...
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3 votes
3 answers
331 views

How do jet engines cool the gas in the combustion zone?

The adiabatic flame temperature of kerosene in air is 2093 C (source). Modern jet engines have a turbine inlet temperature (TIT) of 1700 to 1800 C. This is the max acceptable temperature before the ...
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What does "military band" mean in this chart?

I'm reading the manual of J79 engine, and I just saw this chart: Does anybody know what "military band" means?
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Why does J79 have speed more than 100%? [duplicate]

In the maintenence manual of J79 saw this table: As you can see, there is speed more than 100% and it looks that the engine can handle it. Can't it? One more thing, days ago, watched this movie: ...
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7 votes
4 answers
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How does a jet engine burn fuel when it is not on an afterburner?

I understand the idea behind afterburner as fuel is added to the exhaust to increase the mass and expansion of gasses to increase the thrust, and that explains (in very obvious way) how the fuel is ...
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4 votes
2 answers
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What does "time at temperature" mean in the maintenance manual of the J79 engine?

I was reading the maintenance manual of the General Electric J79 and saw these two charts: and What does "time at temperature" mean?
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Why are jet engines still so noisy?

In general, jet engines on passenger aircraft make so much noise that in a long-duration flight it becomes really tiresome and uncomfortable. Nowadays, technology is much more advanced than before. ...
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2 votes
3 answers
211 views

Can you have a Hybrid Turboprop-Jet engine?

To start things off I am writing this to gain information for vehicles in a story, so I am more so looking for theoretical possibilities, unless there are real world examples. The background and my ...
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1 answer
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Why aren't air turborockets used in military fighters?

Why aren't air turborocket engines used in jet fighters? Few Third World countries have the capability to manufacture high quality turbine blades. Thus, why not use air turborocket engines for the ...
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10 votes
3 answers
937 views

What exactly is the pressure thrust component and why does it exist?

I'm teaching PowerPlants on a ATPL theory course and honestly have some trouble wrapping my head around this one: Most literature describes the term "pressure thrust" – as opposed to "...
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2 answers
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Why in a CFM56-3 is vibration measured in displacement for N1 and in velocity for N2?

N1 is measured in mils (thousandth of an inch) and N2 is measured in IPS (inches per second). Why are different methods used?
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6 votes
2 answers
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What does a High Pressure Turbine Clearance Control do?

In CFM56, I read that it is supposed to increase HPT performance but I don't know how it does that.
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4 votes
2 answers
327 views

Are turbine blisks common in jet engines?

This comes from a slightly related question about blisks. A blisk is a single component shaped like a disc with blades on it. This can be for compressors or turbines. I want to ask about the turbine ...
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7 votes
1 answer
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Why is turbine inlet temperature called "TET"?

I assume that at some point giggling engineering students caused their instructor to change "turbine inlet temperature" from TIT to TET, but I wonder if anyone knows the real reason and ...
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2 votes
2 answers
1k views

Do jet fighters use Turbojet engines, and do cargo/passenger aircraft use Turbofan engines? [duplicate]

I have a feeling that Turbofan engines are used in jet fighters and Turbojet engines are used in cargo or passenger aircraft. Is my perception correct? Do jet fighters use Turbojet engines? Do cargo/...
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0 votes
3 answers
196 views

How does bypass air work?

As far as I’m aware, high-bypass engines have far higher fuel efficiency than low-bypass engines, and as a result the effective specific impulse of the engine is increased. What I’m trying to figure ...
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3 votes
0 answers
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What is the highest operational ceiling for a nuclear scramjet?

A similar question is: What is the highest operational ceiling for an air-breathing jet engine? The answers point to scramjets. Cited reports focus on combustion kinetics. The Wikipedia Scramjet page: ...
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