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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.

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2answers
115 views

Why Engine Exhaust Nozzle can not be totally buried in aircraft fuselage? [on hold]

Why The CD nozzles of the fighter aircraft are always outside the fuselage, Why the whole engine is not buried in the fuselage?? If engine shroud also can be made variable area and varies with CD ...
18
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3answers
3k views

How much water is produced in jet exhaust?

If a jet has typical combustion efficiency, what equivilent amount of liquid water will be created per gallon of jet or kerosene fuel. An acceptable answer can be a ratio in weight or volume to the ...
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2answers
58 views
54
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4answers
24k views

Why can't jet engines operate with supersonic air and how do they slow it down?

Typically jets cannot operate when intake airflow is supersonic relative to the engine. Why is this so? Also, why are scramjets able to use supersonic air? To slow down the air to subsonic speeds, ...
61
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10answers
69k views

Why do jet engines get better fuel efficiency at high altitudes?

I'm told that this is true, but I can't imagine why. It seems like the fact that there is less air would make the engines less efficient... But that probably just shows how little I know about jet ...
16
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3answers
2k views

How do pilots set the exact amount of thrust needed for a reduced power takeoff?

I know jet-powered airplanes very rarely use 100% available power for takeoff, and most often reduce power to increase engine life. How does a pilot set thrust to an exact level? The airplanes I'm ...
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1answer
122 views

Are turbofans compensated for gyro effect?

In a multi-spool design is the gyro effect canceled or mitigated by having the two or more spools spinning in different directions?
18
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2answers
1k views

How do turbofan nacelle lengths compare?

For example, compare the JT9D and the PW4000 below (both from Pratt & Whitney, both on a 747): (Left, Right) The PW4000 has a longer forward nacelle, and a covered exhaust cone. On the inside—...
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1answer
174 views

Why B-52 was not re-engined as a more efficient 4-engine? [duplicate]

Why B-52 was not re-engined as a more efficient (also for maintenance) 4-engine but is still an 8-engine aircraft? In history, almost all others models were re-engined with new engines also quite ...
4
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1answer
162 views

How difficult is it to design a high bypass turbofan given a military derived core?

Suppose one of the big-threes is given a military low-bypass turbofan core, how difficult would it be to produce a design centered around this core that matches the competitive performance of a ...
7
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3answers
1k views

How is a turbine engine rotated for starting and inspections?

I'm doing an assignment for my Level 3 Aeronautical Engineering course and stumbled on this question and I can't seem to answer it (we have had no teacher for 4 months and therefore we have to learn ...
3
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1answer
151 views

Can a turbofan engine have less noise so that it doesn't disturb our ears?

A few years back I have seen that Pratt and Whitney 's Geared Turbofan Engine(GTF) has reduced it's noise levels to about 50%. But recently I was having a discussion with a friend and he told me that ...
25
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3answers
60k views

What material is used to make the hot sections of jet engines?

What metal alloy is used for the hot section of a jet engine? Specifically the exhaust nozzle? I have found mention of a titanium alloy and nickel alloy but nothing with that much detail. What sort of ...
16
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2answers
1k views

What is that CFM56 with a toothed exhaust on an A321?

I stumbled upon a wikimedia picture and I saw something that I have not seen before: a CFM56 with a toothed engine exhaust. Can someone explain to me what engine variant that is? Source Author: ...
1
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3answers
216 views

Is there a practical carbon-free jet fuel?

For example, when I want to use a small turbojet or low bypass turbofan as both the APU and bleed air supplier for blown flaps, ailerons, elevators, (like the ShinMaywa US-2 amphibious plane) and ...
11
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2answers
755 views

Are centrifugal turbojets easier to make than axial ones?

Looking at the history of jet engines, I noticed that the British first made centrifugal-types, but the Germans went straight into axial-types. Which type is easier, if any? By that I mean, which ...
15
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2answers
5k views

Why do jet engines sometimes spit out flames after ingesting birds?

After seeing this video of a 757's engine catching fire because of a bird, I wonder: What happens to the engine? Why does it periodically exhaust fire? Is this some safety feature?
2
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1answer
98 views

What is the aircraft in the 'Be Altitude' album cover?

In 1972, the Staple Singers released the "Be Altitude" album, which has them posing in a jet engine's intake. My question is what aircraft does that engine belong to? And why would someone let them ...
3
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2answers
138 views

What are the issues involved in converting a quadjet into a twinjet?

As you are probably all aware already, the fewer engines you have, the better your fuel efficiency; that’s why the airlines are selling off their (quadjet) 747s and buying (twinjet) 777s, why they’ve ...
3
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2answers
153 views

Why aren’t any JP-1-type (extreme-narrow-cut) fuels in use today?

JP-1 was the first U.S. military standard jet fuel (hence the 1 in the designation), with its specifications issued in 1944; it was an extremely narrow-cut, high-alkane kerosene, not far from what ...
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2answers
7k views

Can a Boeing 767-200 fly at 510 knots at a height of 400 metres?

Can a Boeing 767-200 physically fly at 510 knots at around 400 metres altitude? If it did manage that speed, how likely would a structure failure be? Also, if those measurements were achieved, how ...
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0answers
57 views

What is the minimum size of a ramjet?

Having recently learned that 155 mm ramjet artillery shells are now a thing, I wonder how much ramjet engines can be miniaturized. Could we see ramjet tank shells? Man-portable recoilless guns? ...
2
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2answers
195 views

How do bearings in a jet engine keep water out when it's been cleaned?

When a jet engine is running, it's generally immune to any liquid in the incoming air as the liquid would have been evaporated in the compressor. However, when the engine is being cleaned for carbon ...
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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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1answer
5k views

What are the reliability statistics for modern jet engines?

What is the actual numerical reliability statistics of the modern, large-aircraft, commercial turbofan engines available today? e.g. How many running hours can we expect a failure after? Are there ...
45
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2answers
8k views

How can the landing gear fit in the small room in the engine bay on the Tupolev Tu-144?

I recently went to the museum in Sinsheim, Germany, where a Tupolev Tu-144 is on display. I noticed that the landing gear of this plane is actually way wider than the space it has available when ...
26
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4answers
13k views

Why didn’t the Captain of Cathay Pacific flight 780 shut down engine 1 and land with a more reasonable speed?

In the approach phase, engine 1 of Cathay Pacific flight 780 got stuck at about 70% N1 and it forced the crew to do an overspeed landing (230knots). Why didn't they shut it off by turning the fuel ...
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1answer
135 views

Why does the Convair 990 produce this howling sound during landing?

Watching this video of a landing Convair 990, one can hear a whooshing howl at about 0:11-0:12, as it flares just prior to touchdown (not to be confused with the run-of-the-mill howling that you can ...
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1answer
143 views

Who should design the nozzle of jet engines on aircraft?

There is a question in my mind that which company should design the nozzle of jet engine - the aircraft designer or the engine designer? If you watch this documentary: BBC Documentary Rolls Royce ...
41
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3answers
104k views

What are N1 and N2?

When I'm reading something about jet engines, it's common to see references to N1 and N2. I've never fully understood what N1 and N2 are on engine instruments and how they relate to thrust and the ...
5
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1answer
350 views

Why Western fighters' afterburner glow is reddish orange while Eastern Bloc fighters' is blue?

Recalling what little physics I know, this could be explained by two factors: The blue color is given by the characteristic EM radiation of C-H bond breaking, C- and H- radicals forming and ...
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5answers
7k views

Why do most military aircraft use different engines than commercial aircraft?

Why do most military aircraft and helicopters use different engine technology (fighters, B52, U2, etc) than most commercial aircraft? [I removed the use of axial terminology]
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1answer
136 views

Increase to Flight idle during start-up?

Ground idle takes about 5% of the total rpm, flight idle takes about 85% of the total rpm. Why is so much of the engine power wasted before it gets to flight idle?
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1answer
143 views

What percentage or airplanes have engines [closed]

I heard that some airplanes don't have engines. how many airplanes in the world have engines?
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4answers
191 views

How is vertical speed managed in Airliners? [duplicate]

When an Airplane starts to take off, the Horizontal velocity would generate it the necessary lift, and then Airplane pitches up to further increase the lift. As the Airplane is climbing up, the net ...
14
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4answers
8k views

What are the pros and cons of a pulsejet?

I've heard pulsejet powered aircraft can fly at very fast speeds but are there any drawbacks to this type of engine? And are the disadvantages greater than the advantages or vice versa?
5
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2answers
309 views

How do I optimize a turbofan engine to fly lower and slower instead of higher and faster?

I was reading something about someone who was doing this and I'm intrigued, but I have no idea what you actually do to optimize the engine to be better at lower altitudes and lower speeds?
3
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3answers
108 views

Would there be a purpose for a set of compressors in an electric turbo fan?

This is actually a two part question. Would there be a purpose to a compressor in an electric turbofan where there is no need for a combustion chamber, and if not, is there then a purpose for a bypass ...
10
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5answers
3k views

Why didn't Boeing or Douglas make a jet airliner before the British DH Comet?

I was looking at the history of commercial aircraft and was wondering why UK-based De Havilland was the first to produce a jet powered airliner (the DH 106 Comet) when the US had a much bigger civil ...
0
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2answers
69 views

How to calculate power required to drive an isolated fan of a TurboFan engine?

If I isolate the fan from a TurboFan jet engine (specifically GE90) and power it electrically with a motor, how much power is required for the electrical source to drive the fan to give the same ...
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2answers
107 views

How do engines cope with various intake airflow speeds?

On a recent trip out of Washington Dulles to San Francisco, our B777 met with 200+ mph headwinds (as per the passenger entertainment system) at 35,000 ft for the first half of the route, before ...
15
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3answers
2k views

Why are modern regional jet designs shifting towards under wing engines?

Historically regional jets (eg, MD-95/B717, CRJ-700/900, ERJ-145, etc) have had their engines mounted near the rear of the fuselage. But, recently, regional jets are increasingly using an under wing ...
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2answers
168 views

How does fuel flow and altitude affect the compression ratio of jets?

Does the compression ratio of jet engines change with altitude and/or with the rate of fuel flow?
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2answers
368 views

What are the pros and cons of adding a gearbox to larger jet engines?

What are the merits and demerits of adding a gearbox to larger jet engines like the Trent 900. If its about torque, why not use a magnetic gearbox? What are the demerits of using magnetic gearboxes ...
3
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1answer
137 views

What is the purpose of the pressure relief door fitted on the PW1127G-JM engines of the A320NEO?

Hey guys many times during my exterior walkaround I noticed on the A320NEOs that they have this pressure relief door and our SOP for the exterior walkaround states to check that this door is closed. ...
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3answers
146 views

What are the advantages of using a ramjet in an air-to-surface missile?

Which are the advantages of using a ramjet compared to a rocket engine in an air-to-surface missile? I suppose the cost rises a lot, so why do some countries use ramjets as a way of propelling ASM ...
2
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1answer
134 views

Why is there a minimum altitude for at least some high-speed jet engine restarts?

While reading this other question about envelope constraints for jet-engine restarts, I noticed something odd in the graph provided (of the relight envelope for the Honeywell HTF7000 medium-bypass ...
15
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4answers
5k views

Why is the nacelle outlet of the tail engine of the L-1011 Tristar lower than the engine itself?

I've noticed that the nacelle outlet of the Lockheed Tristar is situated below the engine itself. It is at the end of the fuselage. The nacelle outlet of the tail engine of the DC-10 on the other hand,...
36
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3answers
52k views

How do aircraft keep fuel from freezing while in flight?

On aircraft which fly above 30,000 feet, the temperature can often can get to temperatures below Jet-A's freezing point. For example: at 36,000 feet the standard outside air temperature is -56.5°C (-...
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2answers
341 views

What position was this photo of a jet engine taken from?

From that aviation photographer, I saw that beauty: Having in mind the jet engine I would see, let's say as a normal passenger, I am not really able to understand from where I am looking at that ...