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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33
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5answers
13k views

How does a fan differ from a propeller?

Why is the fan in a turbofan different than a propeller in a small airplane? Why do propellers typically have 2 or 3 blades, but the fan has a lot more? And why is the fan shrouded but the propeller ...
29
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4answers
7k views

In a turbofan what holds the spinning axis?

When the turbofan is spinning inside the housing, what holds the axis? All I know is that the axis holds the fan blades.
10
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5answers
10k views

What is the bypass air in a turbofan engine actually for?

I'm planning on building a small model turbofan engine for a bit of fun but I thought I'd better get a better understanding of how they work first. I understand the majority of it at the moment but I'...
23
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2answers
11k views

Where is the generator in a large turbofan of a commercial airliner?

So, where do you put the electrical generator? If it's gonna be coaxial, the only place is the rear (it will be burnt) or the front (it will get in the way of intake). If it's gonna be coupled to a ...
26
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1answer
21k views

What provides the greatest thrust in a high-bypass turbofan engine?

I'll try to make as much sense as I can with this question. I've been flying quite often in 2015, and I have recently wondered this question regarding high-bypass turbofan engines. I know that there ...
19
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2answers
2k 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—...
16
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1answer
3k views

How much power is drawn by a turbofan to power its own compressor?

In a modern commercial airliner how much percentage of its engine power is used to power its own compressor, the ducted fan and other ancillaries like the airconditioning etc? Maybe it can't be ...
9
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1answer
2k views

Why do some turbofan blade have forward swept tips?

I notice that in Trent700 engine fan blade there is no curve extension at the tip unlike in other engine's fan blades such as the GE90 ,T900 etc. What are the purpose of it? Trent 700 without ...
17
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2answers
21k views

Why do military turbofan engines use a low bypass ratio?

I know that the most civilian engines use a high bypass ratio which is good for fuel economy and noise reduction. What prevents military engines from using the same technology instead of opting for ...
25
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3answers
3k views

Why are turbofan inlets leaned/angled forward?

(Image Source: Wikipedia) Seeing that everything is radially symmetric (apart from the nacelle mount, naturally), I wonder why the inlet (the front part of the nacelle) is usually skewed?
18
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7answers
43k views

Why does an aircraft as big as the Airbus A400M use turboprops?

Why is it that a plane as big as the C-17 (the A400M is slightly smaller though) use turboprops instead of turbofans? Both aircraft seem to have the same purpose and are both capable of landing at ...
10
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2answers
6k views

What are the limitations in adoptions of GTF (Geared Turbofan) technology?

The only recent engine using GTF technology is the PW1000G, however some old designs like ALF502 or TFE731 use this technology. I understand the basic concept of the benefit obtained by the engine ...
19
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2answers
15k views

How does this vortex form inside a jet engine?

I have seen this in a picture once online and thought it was very strange and wondered about the formation of this vortex and how could it happen. Source Not everyday do you see this happening. So ...
9
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1answer
1k views

How does the efficiency of a turbofan compare between take off speeds and optimal conditions?

I know turbofans are less efficient than propellers due to accelerating a smaller mass of air faster. So my question here is not comparing turbofans vs other engines, but compare how inefficient is a ...
4
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2answers
2k views

Why are turbofan inlets circular- or oval-shaped instead of square-shaped?

Source: materialsengineeringconsultant.com and initious.blogspot.com. Most of the engines are circular except for some that are oval. The oval shape provides a better ground clearance. Why aren't ...
10
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2answers
4k views

Why is there a maximum altitude to restart a jet engine?

On all the turbojets that I have flown the maximum altitude a pilot can attempt a restart is 30,000 FT MSL. What factors go in to deciding what the maximum altitude is for an engine restart / relight?...
6
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1answer
22k views

Which are typical rpm values for aeronautical turbines?

I wonder which of these has higher or lower rotational speed: turboshaft turbofan turbojet turboprop Does anybody know the typical speeds for these kind of engines?
5
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1answer
930 views

What methods are used to make a turbofan engine spool up quicker? [closed]

In cases such as a low altitude stall the quick application of power might get a pilot out of a sticky situation, but turbofan engines are fairly sluggish in increasing thrust. If throttle is applied ...
31
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4answers
11k views

Why are the fan blades mounted loosely?

In this question it is mentioned that the fan, compressor and turbine blades are mounted loosely in the disc. This is well demonstrated by this video posted by RedGrittyBrick. What is the reason for ...
4
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3answers
2k 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 ...
4
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1answer
305 views

Why does the spool speed increase with altitude for a turbofan engine (single spool & double spool)?

So, I want to see the effect of altitude on the compressor characteristic of a single spool & double spool turbofan engine at constant flight speed and TIT (turbine inlet temp). I am aware that ...
20
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8answers
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What is the difference between turbojet and turbofan engines?

What is the difference between a turbojet engine and a turbofan engine? I know that both of them have a fan and have turbines but how to distinguish them?
16
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3answers
9k views

How much electrical power does one generator produce on a large turbofan?

From my related question, now I want to know just how much power does the generator produce? In other words, what is the max rating of the generator? It looks so small and that surprised me, but since ...
15
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1answer
13k 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 ...
12
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1answer
826 views

What drives and/or allows the move to higher-bypass turbofans on jetliners?

Note: I'm by no means an expert on any of this, I'm just curious. There seems to be a general trend toward higher and higher bypass ratios in commercial jetliner engines. (I'm thinking here of 737/...
9
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3answers
3k views

Is the bleed air passengers breathe tapped from the engines before or after it comes in contact with fuel? And why? Isn't this unhealthy?

Passengers are often surprised to hear that the air they breathe comes from inside the engines. This sounds unhealthy. Can you explain, why it is not ? Is bleed air tapped (for cabin pressurization) ...
9
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1answer
2k views

Why does the CF6/CFM56 Turbofan Fan Frame contain 12 circular holes between the primary and secondary flow?

This question is related to the answer I found on this particular thread, about the Frames in a Turbofan. In a turbofan what holds the spinning axis? I went on this thread after some research on ...
9
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3answers
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Why is thrust available constant with speed for turbojet engines, when it varies with speed for turboprop engines?

Similarly, why is power available (nearly) constant with speed for a propeller engine, while it varies for a jet engine?
8
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3answers
1k views

Why do turbofan engines not have a contrarotating second fan?

Why aren't planetary gears used to have a fan in front of the fan in a turbo fan engine. Would this not lower energy consumption etc?
7
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3answers
4k views

Is it possible to have an afterburner in a turbofan with bypass ratio greater than 1:1?

Is it possible to have an afterburner in a turbofan with a bypass ratio greater than 1:1? At 1.05:1, say, can it have an afterburner?
7
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4answers
3k views

Why aren't there any single turbofan airliner?

A configuration which looks like a DC-10, without engines mounted under the wings. Let's say 737 sized. Let's forget about redundancy security advantages of twin or quad engines, since they're ...
5
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1answer
371 views

Is it possible to power a B-52 bomber with four bypass turbofan engines?

Is it possible to power the B-52 Bomber with 4 bypass turbofan engines instead of the eight in its current configuration? They would have less noise and be a lot more fuel efficient.
1
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1answer
144 views

What is the temperature range of engine mounts connected to the pylon?

I want to know what is the temperature of the engine mounts in modern turbofan engines for example, Rolls Royce Trent 900. Also, what are the temperature considerations you need to make while ...
7
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2answers
9k views

Why do turbofan engines have low pressure compressors?

In my understanding turbofan engines usually have 2 stages of compressors: one low pressure compressor followed by a high pressure compressor But it looks like the high pressure compressor ...
5
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3answers
1k views

How much weight does a thrust reverser add?

How much weight does a thrust reverser add to an engine? Let's take the CFM Leap 1B as an example, which powers the new version of the Boeing 737. This engine can produce up to 130 kN of thrust for ...
1
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1answer
589 views

What is the drag induced by a high bypass jet engine on an airliner?

What is the drag induced by a turbo bypass jet engine in a typical most modern airliner like the 777, the Jumbo Jet (Boeing 747-8) and the Airbus A380? Given that the jet is travelling faster than ...
18
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6answers
6k views

Why do large turbofans generally have many more LP turbine stages than HP turbine stages?

In almost every large turbofan I see, the LP turbine stages outnumber the HP turbine stages by a factor of at least 2. Here's a photo of the RR Trent 900: The Trent 900 (like most Rolls-Royce ...
8
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3answers
3k views

How does the bypass air provide thrust?

To my knowledge, bypass air produces 80% of total thrust. But I don't understand to how it does that. By accelerating the air, by increasing the speed or increasing the pressure of the air? Is it ...
3
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3answers
293 views

How does the power distribution change for a turbofan engine from being stationary to going at full speed?

I have found out that a turbofan engine of say an F-16 is producing zero power when stationary since $Power = Thrust × Velocity$. But assuming that the engine is producing the same thrust, it appears ...
12
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2answers
3k views

Why is the bypass ratio of a turboprop higher than turbofan?

Whenever, I come across turboprop, the author always mentions that they have higher bypass ratio than turbofan but no one explains the reason for this. So, is the bypass ratio higher due to higher ...
10
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3answers
2k views

Why do many large turbofans have a gap (of turbine blades) between the LP turbine and HP turbine?

After browsing around a while, I noticed that many...I think almost all...large turbofans have this gap between the LP turbine and HP turbine. I took some screenshots and put a red circle around the ...
9
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2answers
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Why are the engines on the MAX and neo prone to bowing?

The engines of the 737 MAX$^1$ and Airbus A320neo family$^2$ are [more] prone to bowing (shafts deforming if no debow is applied during start – as I understand it, this happens in a turnaround while ...
4
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3answers
514 views

Electric Airplane - Hybrid / dual type engines how would that work?

If you have an airplane with electric propellers for take off and landing and you have a turbofan/jet to reach higher speeds for cruise. For example, electric propellers can go to 250mph and turbofan ...
16
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2answers
1k views

Are the A380 engines interchangeable (given they are not all equipped with reverse)?

I have noticed that the A380 only uses the two engines closest to the fuselage to reverse thrust to brake. Are all four engines the same (i.e.: could they theoretically swap engine 1 and engine 2) or ...
10
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1answer
1k views

If the efficiency of a turbofan engine is 35%, where does the rest of the fuel energy go?

There have been a couple of questions on this site about the efficiency and propulsive power of turbine engines (here, here, here). In a high bypass turbofan engine, what are the losses in the ...
10
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4answers
989 views

Could a turbofan have two adjacent fans?

Is there any a point where it becomes possible/ideal to run two large front fans (side by side) powered from a 'single' core? Otherwise shoot this to pieces and explain the ways this is a bad idea. ...
8
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1answer
972 views

Why does the CF6 have a lower bypass ratio than the TF39?

The General Electric TF39, which powered the original C-5 Galaxy, was the very first high-bypass turbofan brought into mass production, with a previously unheard-of 8:1 bypass ratio. Yet, when it ...
6
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1answer
2k views

In a turbofan, why are there no stators behind the fan?

Why are there no stators behind the fan? At least, I've never seen any turbofan design that has stators right behind it. (Here is the latest turbofan I've looked at, the CFM56. Cutaway part starts ...
6
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2answers
366 views

Why is a turbofan engine less efficient when air leaks over fan blade tips?

Image source I understand part of the reasoning for minimal clearance between the casing and the fan blades, is to have the larger fan blade possible, which generates a larger low pressure area to ...
5
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2answers
1k views

Are there turbofan/turbojet analogues to a centrifugal-compressing jet engine?

Axial-compressor jet engines fall into two categories (and only two as far as I'm aware): turbofan and turbojet. I'm wondering if centrifugal-compressor jets also have such a distinction or something ...