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Questions tagged [jet-engine]

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

13
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1answer
3k views

What is this aircraft that has both piston and jet engines?

A friend sent me this picture of a trimotor aircraft with what looks like two radial engines and a jet in the middle. He didn't know what is was and neither do I. Anyone recognize it?
2
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2answers
601 views

Can current fighter jets perform a deadstick landing?

If a current modern day fighter were to have a total engine failure over a suitable landing site or airport, can the pilot safely perform a dead stick landing? If so, are they routinely given training ...
6
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2answers
198 views

How do engine manufacturers derive varying amounts of thrust from a single engine model?

What changes do manufacturers make to an engine to vary the amount of thrust it produces for different applications? Take the GE CF34 for example where there is a 10780lb difference between the thrust ...
3
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1answer
151 views

How can you explicate the efficiency of a turbofan engine with Carnot's theorem?

From Carnot's theorem, we know that efficiency is $$ \eta = 1-\dfrac{T_c}{T_h}$$ where $T_c$ is the temperature of the cold reservoir and $T_h$ the temperature of the hot reservoir. But what do we ...
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1answer
688 views

How much air does a GE90 ingest at sea level and at cruise level per meter?

I just wanted to know how much air PER METER a GE90 turbofan engine sucks in considering the same thrust output at different altitudes to better understand how the engine can travel further while ...
4
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2answers
404 views

Why do compressors constrict flow if this decreases pressure?

An axial compressor (and a ramjet intake, for that matter) is commonly depicted as decreasing the volume of air travelling through as we move closer to the combustion chamber. In axial compressors, ...
3
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1answer
391 views

Why are jet engine nacelles, used on the same plane, so different? [duplicate]

One thing that is plainly obvious about the design and configuration of jet airliners is how little they tend to differ. It's surprising then that even on the same airliner, you will see two quite ...
3
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1answer
273 views

Why are most turbofans tractors, but most propfans pushers?

Turbofans and propfans are, in concept, quite similar: both have a turbojet core, plus one or more additional turbine stages that drive a fan(s) which blows air around the core (this is known as ...
1
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1answer
300 views

What prevents DC-9 series aircraft from being reengined with more-efficient engines?

All DC-9s except for the MD-90\B717 series use old, inefficient Pratt & Whitney JT8D series low-bypass turbofans, even the best of which have a paltry 1.74:1 bypass ratio. We know that a DC-9 can ...
3
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3answers
591 views

How does the nozzle diameter affect the thrust of a ducted propeller?

I currently do some experiments with ducted propellers in which I try to figure out which effect a nozzle has on the thrust produced. My theory goes like this: If I reduce the exit diameter of the ...
5
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3answers
434 views

What is this tab above the DC-10's #2 engine? [duplicate]

What is this big rectangular tab (?) thingy extending backwards just above the DC-10's #2 engine? What does it do? (wikimedia.org, picture modified to point out the tab thingy)
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2answers
939 views

Could two GE9x engines power a 747? [duplicate]

These new GE9x engines are huge and extremely powerful, but could two of them power a B747–8? It is possible for some engines to power the original 741s but I am mainly interested in the B748.
4
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1answer
230 views

Is “laze” (lava + haze) as hazardous as volcanic ash to turbo engines?

Reading an article about Pahoa, I read that erupting Hawaiian volcanoes produce a combination of lava and haze - resulting in clouds that contain hydrochloric acid. Are these as dangerous as ...
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1answer
549 views

What happens during Engine Performance Restoration

What is the typical process during an Engine Performance Restoration? I am trying to find a resource that gives an overview of what happens but I have not been successful. Any help would be much ...
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4answers
262 views

How bad is the efficiency of jet engines under low loads?

VTOL operations need 4-5 times more thrust than a conventional take-off of an aircraft. If you don't want to install additional lift-engines into a hypothetical aircraft and use thrust vectoring to ...
0
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1answer
407 views

Why does an Exhaust Gas Temperature (EGT) gauge require a power source?

Why does the EGT gauge on jet engines require bus power if thermoelectric voltages generated by thermocouples are sufficient to move the needles?
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3answers
376 views

Why should pilots keep the engines running so they are hot or warm immediately after landing?

Understandably, airliner pilots - particularly those operating in extremely cold climates and airports - should preheat the engine at idle for 3 minutes or more so they do not apply full thrust and ...
30
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7answers
19k views

Why don't 747s use unreliable, but cheap, jet engines instead?

I'm a neophyte who was reading a little bit about jet engines, and the economics behind them. In particular, I was curious about what makes jet engines so expensive compared to piston engines. A ...
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0answers
38 views

What is a Compressor Stall and what is the main cause of it? [duplicate]

What is compressor stall when does it happen and what is the main cause of it is it dangerous ?
2
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3answers
525 views

What are the consequences of throttling up past 100% of N1?

The B737 is probably my favorite aircraft and I'm always sure to never throttle past 100% of N1. I was told the aircraft is pretty much totaled if you take N1 past 100% but you can eke out that extra ...
13
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1answer
6k views

Which jet engines have the highest thermal efficiency?

Some automakers (Mercedes-Benz, Toyota) have recently been making news about the improved thermal efficiency of their engines, stating that they reached the 50% mark. I was wondering if it was the ...
7
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1answer
373 views

Are engine casings expected to contain turbofan blade fragments?

On Southwest 1380, initial indications are that a fragment of the engine blade pierced the engine casing, which then hit the airplane window (or perhaps a part of the casing did). According to the BBC,...
2
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2answers
184 views

What were the make and model of the engine that failed in flight Southwest 1380?

Regarding the tragedy of Southwest 1380 flight on 2018-04-17 involving an engine failure, what company manufactured that engine, and what engine model/type was it?
8
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2answers
402 views

What is purpose of engine pylon airfoils on the Hondajet HA-420?

The engine pylons on the Hondajet are aerodynamically shaped so as to provide a lift force laterally and outwardly. Engine pylon as viewed from rear Engine pylon as viewed from front Are these for ...
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1answer
2k views

What are the advantages of 3 spool over 2 spool turbofan engines? [duplicate]

What are the advantages of 3 spool over 2 spool turbofan engines?
34
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1answer
8k views

What exactly happened in this bird strike incident?

This Boeing 737 was hit by a bird and continued all the way to its final destination, from Prague to Las Palmas. What actually happened here? Was the incident considered a bird strike or an engine ...
1
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1answer
187 views

What are “referred” speeds and “referred TET”?

i'm currently reading the Rolls Royce publication The Jet Engine. It makes reference to "referred speed", "referred TET" and "referred mass flow". Referred speed seems to be defined as N/sqrt(T). I ...
3
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3answers
2k views

What does RPM mean in a propellor aircraft, compared to a jet aircraft? [closed]

What is the practical significance of speed RPM in a propeller aircraft for a pilot? I am not able to correlate it with RPM in jet engines?
9
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1answer
1k views

How (and why) does engine thrust changes with airspeed?

I'm interested in how the thrust of a turbofan engine is affected at higher airspeeds (TAS). I know (I believed) that engine thrust(at constant N1) was relatively constant like in the following graph (...
1
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0answers
124 views

What could cause an engine shutdown on a Q400 with CDS codes 732, 907, 915 and 938?

A Bombardier Q400 displays error code 938 on the Central Diagnostics System(CDS), which is attributed to turbomachinery chip detector. An examination shows debris in the detector hitch which is ...
5
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3answers
3k views

Why don't most military transports use modern commercial engines?

Why don't most military transports use modern commercial engines? More specifically planes like C-17, the Antonov's use older less powerful engines while modern efficient and powerful engines are ...
0
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1answer
380 views

How are jet engine RPM cycles used to monitor LCF life?

Can someone please define what are N1 and N2 throttle cycles? These are used to keep track of the accumulated low cycle fatigue (LCF) life of rotating components. But I cannot find an exact definition ...
24
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7answers
16k views

Are German, Japanese, and Chinese companies not able to build aircraft jet engines on their own?

As far as I know, only 4 countries can build aircraft jet engines on their own: USA {GE, P&W} Russia {Klimov, NPO Saturn} France {Safran} UK {Rolls-Royce} All other countries use jet engines ...
3
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1answer
1k views

What is so special about new Russian jet engine called PD-14?

I think PD-14 engine is being promoted by Russians as something extraordinary. What is so special about PD-14 that the West doesn't have? Can you explain this in layman's terms?
3
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1answer
220 views

What does the last 'B' in 'GEnx-2B67B' stand for?

What does the last 'B' in GEnx-2B67B stand for? I guess it stands for Boeing, but the GEnx-1B series doesn't have it.
1
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1answer
379 views

Can an aircraft engine be started midair? [duplicate]

Can one start the aircraft's(commercial/fighters) engine midair at high altitudes especially turbojet or turbofan engines?
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2answers
2k views

What is the purpose of the 787 engines extending on landing? [duplicate]

As seen about 53 seconds into this video of the Qantas Dreamliner landing, the engine housings seem to extend upon landing. What specifically is the purpose of this? To balance? To help with air flow?
3
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2answers
2k views

How does the reverse thrust work while landing? [duplicate]

During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction to counter the aircraft's forward motion if I'm right So, my question here is "...
2
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1answer
212 views

At what Mach Number do variable cycle engines (VCEs) start showing benefits over turbofans?

Currently, most supersonic engines engines are low bypass turbofans. However turbofans start becoming infeasible as the mach number increases. Variable Cycle Engines, still have noise and weight ...
2
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3answers
2k views

Why B-52 engines produce lots of smoke only during take-off? [duplicate]

During the flight it seems there is no smoke, it's only during takeoff. Here is an example This question explains that smoke is caused by unburnt fuel but why is ...
0
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0answers
237 views

Does the safe taxi distance vary behind jet types for light aircraft?

It would seem a light aircraft taxiing behind a business jet could be closer than a B747. Perhaps there is a law (country or international) regulating power setting of a jet taxiing. One authors ...
6
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1answer
454 views

How does EEC/FADEC recognize/anticipate engine acceleration/deceleration?

So I'm wondering, when the engine runs at idle and the pilot sets a higher thrust level, what exactly happens, that the EEC/FADEC recognizes, that I want to accelerate? My professor said, it's ...
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2answers
782 views

Has a jet “engine” ever been made that only uses the thrust from the bypass air and doesn't have a combustion chamber?

I recently have been looking at different types of jet engines and came to this thread wherein they talk about how most of the thrust from airline turbofan engines (high bypass) comes from the bypass ...
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2answers
128 views

Can gas turbine engines be used for railways [closed]

Is it possible that gas turbine engines can be used for railways , even though it may posses some risk such as Foreign object damage , can it be efficient such as electric trains but it can act as ...
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1answer
158 views

Can compressor blades be made larger to increase thrust and efficiency? [closed]

Given the compressor section of the engine needs to move much faster and given the larger the blade, the larger the tip speed, would larger compressor blades produce more thrust and therefore better ...
0
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1answer
143 views

What is a “flare-out” and why does auto-thrust reduce thrust during flare-out?

The functions of auto-thrust include thrust reduction during a flare-out. What is flare out and why during flare out will the auto-thrust reduce thrust?
3
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1answer
244 views

Is my understanding of subsonic inlets correct?

For subsonic aircraft like commercial jets, the inlet has the job of making sure the correct airflow is coming into the engine. Correct airflow is important for keeping the engine's compressor stage ...
5
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2answers
736 views

How does a subsonic jet engine intake design ensure correct air intake?

I think I understand that inlets are there to slow down the airflow and increase the pressure to stop the compressors stalling?. If this is the case, I don't understand how the nacelle or intake ...
6
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1answer
233 views

Is there a rule of thumb for spacing between jet engines?

While viewing this week's press release for the taxi test of the Stratolaunch I noticed how closely the engines seemed to be spaced. It would seem the ideal position would be near the fuselage to ...
1
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1answer
575 views

What are the differences between single and double annular combustion chambers?

The combustion chamber of a jet engine may be can type or annular type. Annular type combustion chamber can be SAC (single annular combustion chamber) or DAC (double annular combustion chamber). What ...