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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60
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4answers
53k views

Why does the Boeing 787 engine nacelle exhaust have such an unusual shape?

Why does the Boeing 787 nacelle have this unique shape at the exhaust: I haven't seen it on any other airplanes, does it serve an aerodynamic purpose or help engine efficiency or is it just to look ...
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3answers
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What are the spiral marks in the center of the engines?

When I get a chance to peek inside an engine, I noticed that many have spiral marks painted in the center. What is the purpose of these? Pictures:
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2answers
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Jet engines: are they owned by the airline or just rented?

For commercial jets, the engines are complex parts of the aircraft, are the most expensive components, and must be carefully maintained. Source When a company buys an aircraft, do they also own the ...
31
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2answers
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Why does afterburner exhaust have “pulses”?

Instead of being consistently-dense, the afterburner exhaust looks "pulsed" in these pictures below. Is this a trick of the camera, a natural result of interaction with the air, or is there some ...
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5answers
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What are the differences between fuel types (comparing with vehicles)?

I find it funny that at gas stations, generally you can purchase "regular" gasoline (in various octane levels) or diesel. At airports, generally you can purchase 100LL avgas or Jet-A. Can you compare ...
26
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5answers
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Why do we use pylons to mount the engines on jetliners?

This question focus on jet airliners. The De Havilland Comet's engine were mounted inside the wing, the Concorde's engines were mounted underwing (as many jet engines) but without pylon. It seems jet ...
2
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2answers
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How does induction ice form in and affect jet engines?

Recently someone talked to me about the possibility of induction ice on the engine: He told me that because of conditions around fan and compressor blades (mainly because of pressure and temperature) ...
12
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2answers
3k views

What prevent jet engines design with bigger by-pass ratio?

In commercial aviation, it seems jet engines grow and by-pass ratio increase with newer engines. Here is some examples: 1963: by-pass ratio: 0.96 (P&W JT8D) 1970: by-pass ratio: 5.0 (P&W JT9D)...
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2answers
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Do any manufacturers have plans to use turbojets in future aircraft? What is the state-of-the-art in turbojet design?

Turbojets have largely been superseded by turbofans (or turboprops for low-speed flight). Are there any aircraft being planned that would use turbojets? I'm also interested whether there has been any ...
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3answers
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How is combustion flame maintained in the combustion chamber after igniters are switched off?

During start phase of a jet engine, igniters in the combustion chamber create sparks to initiate combustion. As far I know, when the engine reaches self sustaining speed, igniters get turned off (...
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1answer
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What is the difference between Jet Wash and Jet Blast?

I was reading about Wake Turbulence in Wikipedia and got to know about Jet Wash and Wing Vortex. According to Wikipedia, Jet Blast is the movement of air from the jet exhaust. Isn't this same as Jet ...
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3answers
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Are we at peak speed efficiency for jet airliners at Mach 0.85?

The cruising speed of large jet airliners has not increased in the past four decades. The 747 cruised at Mach 0.85 and the new Dreamliner 787 also cruises at Mach 0.85 even though it was designed 40 ...
35
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4answers
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Why do gases in the combustion chamber only flow one direction to the gas turbine in a jet engine?

As far as I know from the working principle of jets engines, compressed air in the combustion chamber (or combustion canister) is mixed with fuel. The ignited mixture expands backwards to turn the ...
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2answers
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Why do engine cowl lips appear larger and more blunt on the sides than on the top and bottom?

I was looking into engine nacelles. I was not able to understand the design shape of it Why is it that in most aircraft, the engine cowl lips on the side are bigger (more blunt) than on the top and ...
8
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1answer
821 views

What does aerodynamic noise of an airliner sound like in landing configuration?

I want to know what aerodynamic noise an airliner makes when flying with both engines shut down. Specifically, it is the sound made by air passing a plane which is in landing configuration, with gear ...
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3answers
13k views

What safety features prevent jets sucking in ground staff or equipment?

There have been some gruesome deaths involving ground staff being sucked into jet engines, presumably because the engine thrust was set well above idle. Are there safety features (besides prudence on ...
22
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1answer
2k views

Does a jet engine keep running when it can no longer be controlled from the cockpit?

On the Qantas Flight 32 incident, the Airbus A380's number two engine suffered from an uncontained engine rotor failure and partially damaged the controls of number one engine as well. According to ...
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2answers
1k views

Is an engine surge classed as an engine fire?

Sometimes flames come out from the exhaust due to bearing distress or turbine blade fracture. Can such flames/fire be considered an engine fire?
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2answers
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Why are turbine blades not made out of titanium, only compressor blades?

According to this video on jet engine blades, titanium is never used for the turbine, because it "melts and burns at the temperature of the flame". Only the blades of the compressor are made of this ...
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1answer
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Using pure O2 for jet engine combustion [duplicate]

In addition to my previous question, I am mainly concerned with burning all the fuel. Why isn't the combustion process using all of the Oxygen in the air? Is it because other gases are in the way and ...
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4answers
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If jets carried pure O2 to use for combustion, would they be more efficient?

Air is around 21% Oxygen. The bulk of air is non-flammable Nitrogen. Wouldn't surrounding the jet fuel with only O2 create more efficient and clean combustion?
12
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1answer
939 views

Why is the combustor volume of a jet engine decided by altitude?

I have read that the combustor volume of a jet engine is decided by the maximum altitude up to which that aircraft will fly. I'm getting confused by that, because the maximum mass flow rate will occur ...
3
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1answer
1k views

How does pressure increase in a multistage compressor?

Given the overall pressure ratio of a multi-stage compressor, how can I calculate the increase in pressure at each stage? Does pressure increase linearly at every stage, or does it increase ...
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7answers
21k views

Why are adjustable area jet engine nozzles mostly limited to military use?

It seems that only jet engines with afterburners use adjustable area nozzles (this means adjusting the area of the nozzle but not necessarily the direction). This includes most fighter jets, as well ...
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6answers
21k views

What is the relationship between thrust and engine RPM in a turbojet?

I understand that, to increase the thrust of a turbojet engine in flight, it is necessary to increase fuel mass flow rate. This throttling then increases the exit velocity of air and gives increased ...
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2answers
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What is a “core lock” on an jet-engine?

This question came up while reading the Wikipedia article on core lock and Pinnacle Flight 3701. If my understanding is right then if for example inner parts of the jet engine heats up that so much ...
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1answer
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What is the purpose of the inlet doors of the Pratt & Whitney JT3D?

I have a question about the 707 Engine Inlet Doors, according to Wikipedia the Pratt & Whitney JT3D inlet doors purpose is to provide additional air. Is the thrust higher on more air intake? And ...
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3answers
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Is engine damage due to a fan blade failure irreparable?

I have a question related to this question and this video. The question says that sometimes a fan blade failure can occur. My question now is, if a fan blade separates or a malfunction occurs, is ...
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4answers
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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, ...
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1answer
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Why was there a rattling noise coming from the left engine of A319?

I recently flew on an Airbus A319. When boarding the aircraft from the front entrance we passed in front of the left engine. The fan blades were spinning and there was a rattling noise (like when a ...
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2answers
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Why is the compressed air (from engine compressors) taken from High Pressure (HP) stage instead of Low Pressure (LP) stage?

An aircraft that uses Turbofan or Turboprop engines would be taking the compressed air from 3rd stage and 6th stage (varies) and supplying it to the Pressurisation and Air Conditioning Kit (PACK). ...
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3answers
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What's that component between the engine and wing?

It's on most commercial aircraft and large aircraft with turbofan engines... Is there a specific name for it? Does it serve any other functions apart from attaching to the wing and feeding the engine ...
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2answers
10k views

Does the APU consume a lot of fuel compared to a jet engine?

I would like to know whether the APU of modern commercial airliners consumes more or less fuel than a jet engine. Of course, this will vary between aircraft types, so what comparisons in fuel usage ...
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5answers
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How are off-wing jet engines transported?

One of the optional services in Rolls-Royce TotalCare is "Engine Transportation" This service includes routine transportation of engines between the customer’s main base (or designated station) and ...
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5answers
1k views

What is the future of manufacturer independent jet engine maintenance repair and overhaul (MRO) services?

I have noticed that Air France KLM offer a Maintenence (MRO) service for aircraft and jet engines. This sounds like a potentially big threat to engine manufacturers like Rolls Royce who makes around ...
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3answers
4k views

How much would it cost for a large airline to switch engine manufacturer for their planes?

I am trying to understand how much of a hassle and cost it would be for a large civil airline, who already had lots of installed Rolls Royce engines on its fleet, to switch over to GE engines on new ...
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1answer
6k views

Why is engine No.2 started first, instead of No.1?

I realized that some Boeing manuals recommend that the engine number 2 must be started first, is there any special reason for this?
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1answer
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What is the buzzing noise generated by the engines in this 777 takeoff video?

I've flown a few times in my life, both in economy and executive class. Every time I fly in executive, during takeoff, there is a different noise from the engines. In economy class (behind the engines)...
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1answer
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Why is a higher bypass ratio more efficient at lower speeds?

Why is it that a larger volume of air moving slower is a more efficient means of propulsion than a smaller volume of air moving faster? (This is true up to a given speed, obviously, as supersonic ...
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3answers
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Why are the Boeing 737 nacelles odd shaped?

Why is a Boeing 737 NG engine not completely round in shape? It seems to be flat at the bottom and round at the top and sides. Earlier Boeing 737 versions (100 and 200) seem to have a more rounded ...
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4answers
19k views

Why do the engines seem to power down and then back up after take-off?

What is the phenomenon on a commercial airliner (say, a 737-800) where shortly after takeoff and before we reach 10,000 feet the engines feel like they slow down dramatically or even power off ...
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2answers
6k 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?
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3answers
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What is this molten metal coming from the engine of an Avro RJ 100? [closed]

Yesterday I flew in an Swiss Avro RJ100. As soon as we landed I was shocked to see some sort of molten metal which was incandescent and glowing red dripping down from the vent as indicated in the ...
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2answers
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What is this flange on the engine?

Flying home from the Denver ComiCon, on a 737, I saw an angled flange on the engine. Could you describe its purpose? Photos by CGCampbell licensed CC0
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2answers
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Do aircraft engine intakes require air filters?

I see helicopters which have air filters in their engine intakes, but jet fighters and commercial turbojet airliners don't seem to have any filters in their air intakes. Isn't it true that even tiny ...
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2answers
199k views

What is the difference between a turbofan and a turboprop engine?

I'm not an aircraft expert and I just realized that there are two different terms - turbofan and turboprop. I always had them combined in my head as a term for a large jet engine (like you would see ...
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3answers
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How does thrust reversal work on a jet engine, and when should it be used?

A two part question this time, though they are closely related enough that I figured I'd knock them out all at once. I figure the first question probably informs the second question anyway. Firstly, ...
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3answers
8k views

How do you start a jet engine if the start valve is stuck closed?

I was recently on a flight aboard an Airbus A380 where the flight was delayed 2 hours. The reason was claimed to be a start valve fault on engine #4, where it was stuck closed. According to the ...
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7answers
5k views

Can aircraft other than rockets go to space?

I always wondered if it was possible for planes and other aircraft to leave the Earth's atmosphere. Normal commercial transport airplanes can fly pretty high, but then they need air to get the speed ...
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1answer
2k views

How often does fan blade out happen?

Jet engines are designed to contain a fan blade failure, and the engines and airplanes are designed with this type of failure in mind. This is more critical in the modern high-bypass designs with ...