Questions tagged [turbofan]

A type of jet engine which uses two different airflow streams (one passing through the core and another blown past it by a fan) for obtaining thrust.

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How come a turboprop can't reach speeds as high as a turbofan?

I understand that turbofan powered aircraft can reach much faster speeds than turboprops like the C130 Hercules, and I can't imagine a turbofan powered 737 would be of any use really, but as to the ...
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Engine torque due to Turbofan engines and its effect on aircraft attitude

I know that for turbofan engines there will be Gyroscopic effects while pitching, rolling and yawing maneuvre. But if the aircraft is cruising at an altitude or is simply idling on the ground, what ...
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Why does adding more blades to a propeller/fan not show a decrease in efficiency?

According to this answer increasing blade solidity increases the blade area by either enlarging chord or increasing blade count both of which reduce efficiency via reducing the lift coefficient and ...
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1 vote
1 answer
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How is bleed air flow related to thrust level?

I read that the bleed flow negatively affects the thrust levels for a turbofan engine. However, I was wondering if vice-versa is true as well? Whenever the thrust levels for a turbofan are lowered at ...
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6 votes
4 answers
476 views

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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7 votes
2 answers
3k views

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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Is the U2's 74,000 ft the highest a turbofan plane ever has gone?

What is the altitude record for a turbofan? The (usually) turbofan-powered U2 has gone to 74,000 ft (22.6 km) MSL, but did any turbofan plane surpass that, in a zoom climb for instance and with ...
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4 votes
3 answers
407 views

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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4 votes
3 answers
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What is a spool in any jet engine, what is its funtion?

I am a student and I'm trying to determine how a spool works in an engine. What effect does it have depending on the number of spools on the performance of the engine? I tried to find it on Google but ...
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3 votes
0 answers
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Why is thrust (in a high bypass turbofan for e.g.) non-linear with respect to N1?

I've been studying jet engines for a short while now and I think I have a pretty decent understanding of how thrust is generated, but one thing I'm struggling a bit with is how thrust varies across ...
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8 votes
1 answer
364 views

What are these white drops on the exhaust plug of a CFM56-7B engine?

Does anybody know what those white dried-up drops are? I checked out another Boeing 737-800 on the ramp and it also had the same defect so I'm guessing this is a common issue, or is it? This shows up ...
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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
127 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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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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1 answer
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How to find the velocity of the working fluid through the fan in a turbofan engine?

Is there any formula for the velocity of the working fluid (air) through /the fan of a turbofan engine? If not, how can I find the velocity?
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4 votes
2 answers
212 views

How much extinguishing agent is needed for an engine fire?

I am quite interested in the firefighting fluid tank choices in turbofan-equipped aircraft. As seen in this picture: Although this is only the APU, but the fire extinguishing agent bottle looks quite ...
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0 votes
1 answer
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Why are there motive flows for the turbine pumps of Williams International FJ44-3A engine?

For my university project, I am designing the fuel supply of an aircraft using a Williams International FJ44-3A engine. Studying the related FAA TCDS, I read "Fuel from the motive flow port on ...
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1 vote
1 answer
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What are the fuel system pressure and temperature requirements of a Williams FJ44 engine?

For my university project, I am designing the fuel supply and control system of an aircraft that use Williams International FJ44-3A engine. However, after scouring through its type certificate ...
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1 vote
1 answer
100 views

Is axial bearing in turbo fan,turbo jet engines neutraly loaded?

Is axial bearing in turbo fan,turbo jet engines neutraly loaded,if yes then turbine/fan and compresor produce eqaul and opposite force? If yes ,where then thrust come from,at internal walls,must be ...
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2 votes
1 answer
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Do aircraft engines come with electric generators?

For turbojet/fan/prop engines, do they come with an electric generator when delivered to aircraft manufacturers, or it is something that the aircraft manufacturer has to find or make themselves? I am ...
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6 votes
2 answers
269 views

Do turbine engines contain engine oil and fire-extinguishing fluid?

When aircraft turbine engine companies sell their engines to aircraft manufacturers, does the product contain the tank and pipe for engine oil and fire extinguishing fluid in the same package? Or is ...
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6 votes
2 answers
2k views

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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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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5 votes
1 answer
330 views

Will N1 shaft turn at the same time as N2 shaft?

For Turbo Fan Engine CFM56-7, was wondering how come the Fan blades (N1 shaft) turns when I turn the N2 Shaft manually. I thought N1 shaft is connected to the fan and booster rotor and LPT rotor and ...
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3 votes
1 answer
415 views

How do variable bleed valves prevent surge?

All I know is that the valves open at low speed or when decelerating, and close at high speed or when accelerating. How do they prevent the compressor from stall or surge?
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3 votes
1 answer
352 views

What is this sound for when starting the engine of an F-15?

If I remember correctly, to start up old fighters such as F-4s, you need an ASU but it looks new fighters do not need an ASU. Today, I was watching this video. It's a so cool video to know how new ...
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What is that to and fro moving thing?

This video by AgentJayZ is the maintenance and repair of AI-25 turbofan. What is that thing moving due to applying certain pressure to that pipe? Can anyone describe its purpose and how it works?
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How are Fan pressure of and Static pressure in the turbofan engine related?

If the fan air is ducted to the rear, the total fan pressure must be higher than the static gas pressure in the primary engine's exhaust, or air will not flow. By the same token, the static fan ...
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2 votes
2 answers
365 views

Why do large civil airliners use cold rather than hot thrust reversers?

Is it because cold thrust reversers are best for turbofans and most civil airliners have turbofan engines?
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0 votes
1 answer
130 views

Turbo-electric engine vs high by-pass-ratio Turbo fan, which config. would seem more efficient? (Liquid Hydrogen Fuel)

Would be a turbo-electric config using 2 turbofans as generators for a 150 pax. aircraft more efficient than a very high bypass rationed Turbofan that burns hydrogen? If not, then why are all ...
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0 votes
1 answer
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Does aircraft nacelle length/shape/geometry affect the contrail formation?

This is coming from Question 1 and further down Question 2. I think the nacelle and exhaust cone do affect the contrail formation in some way, what is the relationship between them? Do the famous 787 ...
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3 votes
1 answer
2k views

What are variable stator vanes?

Most turbofans nowadays use "variable stator vanes"; what are these, what is their purpose, and how does it affect a gas turbine's performance?
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1 vote
1 answer
382 views

What is the relation between N1 and Wing anti-ice

When wing anti-ice is selected, the N1 or EPR limit is automatically reduced, and the idle N1 or EPR is automatically increased. What does this statement mean ???
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-1 votes
3 answers
214 views

What amount of electricity could we get from the Seebeck effect on a kerosene turbofan?

Edit: I rewrote my post. To downvoters, can you comment on your reasons? As a kind reminder: Downvote questions that don't show any research effort or don't contain enough information to be clear and ...
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2 votes
1 answer
233 views

Efficiency of the Kuznetsov NK-88 or NK-89 engine burning hydrogen

It's tough to find data about turbofan efficiency running on hydrogen. The Tupolev Tu-155 has been used as a test bed for exotic fuels right before the fall of the soviet union, without much follow-up....
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2 votes
0 answers
183 views

Why Not Just Replace All the Fan Blades?

It looks like operators will have to remove all their P&W powered B777s from service until they have checked the engines. Since the problem seems to be fatigue (which is a function of time) in a ...
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1 answer
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Why are jet engine fan blades painted?

I came across this extremely interesting article with details on a 2018 United Airlines Boeing 777 engine failure, which is also related to the more widely-publicized failure a few days ago: http://...
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6 votes
1 answer
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What are the engine-out implications of giant turbofans?

It seems that turbofans for civil airliners are improving fuel efficiency by building larger and larger fans that spin slower. For example, the RR Trent 800 introduced in 1993 had a diameter of 2.8m, ...
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What is the fan pressure ratio in a turbofan?

What is it and how does it affect efficiency and thrust?
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1 vote
0 answers
57 views

Texts on aero-engine structures

I have been scouring the web for resources on aero-engine structures and structural design (preferably civil turbofans) but unfortunately it seems like they are hard to come by. I would like dedicated ...
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0 answers
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What's this outlet of IAE V2500 for? [duplicate]

Anybody knows what is this outlet for and why it is designed in such way? Edit: On MD-90 didn't see such thingy
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4 votes
2 answers
308 views

The latest turbofan aircraft feature an exposed exhaust cone, does it come with some benefits? [duplicate]

Aircraft like Airbus A320neo/A330neo/A350 series have a visible exhaust cone, which is not visible in the older versions of Boeing 747, Airbus A330/A321/A319 etc. Why is this design preferred over the ...
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10 votes
1 answer
456 views

What are these painted lines on the fan blades of the Rolls-Royce Pearl 15?

I'm not sure that they are painted but it looks like they are. What are they for? More images:
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1 vote
2 answers
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What kind of test is going on in this image?

Some times we see images of jet engines on the net that have strange colors. For example take a look at the bellow image. What the operator is doing? Why the color of blades are white with red on its ...
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2 votes
0 answers
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Why does the LEAP 1A HPT run at such a high RPM?

I've watched the N2 on the LEAP sit at 100% at cruise and fluctuate as high as 101%. Why does the HPT run at such a high RPM?
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Would large, low aspect ratio fan/propeller blades be more efficient? Why not?

With reference to this answer We read in the above that accelerating a larger mass of air by a smaller amount is (theoretically) more efficient. This is an advantage of a larger propeller than is ...
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What is the purpose of air that passes through the engine core in a turbofan engine? Is it mainly to spin the fan rotor? [duplicate]

The majority of the air going through the bypass is producing most of the thrust and providing the air that cools the engine. Does is also provide the pressurization and cooling/heating for the cabins?...
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1 vote
1 answer
144 views

Why are high-bypass turbofans faster than turboprops?

The turboprop, and especially the high-blade-count propfan, differs from the high-bypass turbofan principally in throwing away the draggy outer ducting. This makes it easier to obtain a greater ...
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At what range does the turbofan start to become more economical than a turboprop? [duplicate]

By more economical I only mean 'burns less fuel'. I'm under the impression that at optimal cruise speed and altitude a turbofan will burn less fuel per mile per passenger than a turboprop, but I might ...
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7 votes
1 answer
620 views

What causes the horn-like noise during the start-up of some jet engines?

Here's the specific sound I'm talking about (it starts specifically 56 seconds into the video, as well as at 2:02 for the second engine): I've only really heard that ...
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