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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3answers
419 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 ...
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7answers
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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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3answers
625 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 ...
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1answer
8k 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 ...
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1answer
388 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,...
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2answers
188 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?
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2answers
470 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?
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1answer
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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 ...
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1answer
255 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 ...
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3answers
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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?
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1answer
2k 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 (...
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0answers
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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 ...
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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 ...
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1answer
443 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 ...
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7answers
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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 ...
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2answers
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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?
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1answer
283 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.
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1answer
482 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
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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?
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2answers
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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
257 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 ...
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3answers
3k 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 ...
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309 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 ...
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1answer
504 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
1k 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
132 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
160 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 ...
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3answers
219 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?
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1answer
314 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 ...
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2answers
940 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 ...
7
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1answer
270 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 ...
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1answer
818 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 ...
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3answers
8k views

Why did the turbojet replace the piston engine?

Many people say that this was because aircraft powered by turbojet engines were faster during WWII. However the Grumman F7F-4N Tigercat, a fighter powered by a piston engine, flew at a maximum speed ...
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1answer
304 views

(B737s) Why is the automatic activation range of the AUTO mode in flight limited to “between idle and 5%”?

This is the explanation on the Engine Start Switch in the 737 series FCOM. What might be the reason why the automatic activation range of the AUTO (or OFF) mode in flight limited to "between idle and ...
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2answers
1k views

What causes the “growl” of some large turbofans at takeoff thrust?

There are some (all?) large turbofans which emit a distinct "growl" (some people call it a "buzzsaw" sound) at takeoff thrust. What causes it? I've seen it explained (as in this question) as the fan ...
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0answers
167 views

What different intake designs are there, and what are their pros and cons?

I noticed that over the years (on fighter jets specifically) there have been many different methods of directing air into the engines. Primarily, the nose-intake, side intake, and underbody intakes ...
3
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1answer
436 views

What does it mean for N1/N2 to float?

The logic of ECU to hold N1 with fuel flow follow the logic: Idle N2------------N2 set ,N1 floats min ps3 schedule -----------N1 and N2 float So what does this ...
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2answers
427 views

How can a modified ramjet produce static thrust without a turbine?

A big selling point of the ramjet is its absence of moving parts (hence why it can be translated as "statojet" from other languages). However, an even bigger drawback is that a ramjet cannot produce ...
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2answers
3k views

What is meant by a “cold soak" of an APU?

What is the exact meaning of "cold soak" of an Auxiliary Power Unit (APU)? Is it to do with long flights at high altitude and the fuel getting cold? Will it affect the ignition of the APU? Can anyone ...
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4answers
7k views

How hazardous is it if an engine cowl falls off?

There was recently an incident where the engine cowl of the starboard engine of a United Airline's Boeing 777 fell off during flight: 'Scariest Flight of My Life.' United Airlines Made an Emergency ...
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At what operating temperatures would the Trent 900 need to operate, to equate to the efficiency of current geared turbofans?

What is the minimum optimum operating temperature (in degrees Celsius) that would be required for the Trent 900 to operate at, for it to attain the level of fuel efficiency of current geared turbo ...
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2answers
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Why is a (jet) engine in flight shutdown so critical?

EASA just announced an Emergency Airworthiness Directive grounding all A320neo planes with a certain type of engine. Reason is, that they have apparently the tendency to shut down in flight more often ...
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0answers
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Would it be possible to build an engine twice the size of the Trent 900? [duplicate]

Would it be possible to build an engine twice the size of the Trent 900 in terms of physical size, i.e. doubling the diameter? Let's assume that it's feasible to build an aircraft tall enough to ...
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2answers
323 views

Would tubofan aircraft benefit from adjustable fan blades?

Would turbofan aircraft benefit from adjustable fan blades as do turboprops? Propeller aircraft adjust their propeller size, i.e. shorter propeller for cruising at maximum design altitudes where the ...
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1answer
655 views

Would installing 6 engines on an Airbus A380 and or Boeing 747-800 achieve a shorter take off distance?

Would installing 6 engines on an Airbus A380 and or Boeing 747-800 achieve a shorter take off distance? Would that result in excessive acceleration and harmful or uncomfortable G-forces? Would the ...
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2answers
447 views

How big can a pulsejet be?

Pulsejets are mostly known for propelling the V-1 flying bomb, and have some use as small remote-controlled plane engines. In either case, the pulsejets aren't particularly big, as far as jet engines ...
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4answers
2k views

Do fighter jets have an auxiliary power unit?

Do fighter jets have an auxiliary power unit? If they don't, then how does the propulsion/ignition process start in the engine?
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3answers
1k views

Why does the Trent XWB have intermediate compressor stages?

I realized that the Rolls-Royce Trent XWB on the Airbus A350 has intermediate compressor stages. Why is that? Other engines like the CFM56 or IAE V2500 that power most of the A320-family have low ...
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1answer
136 views

How to find out what engine a plane had in the past?

I want to find out what engine a specific airplane had in the past. For example for the Airbus A320. The sources which I've found tell me there were different engines. CFM56-5A, CFM56-5B, IAE V2500 ...