Skip to main content

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.

Filter by
Sorted by
Tagged with
37 votes
5 answers
21k 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 ...
Southbob's user avatar
  • 1,089
30 votes
4 answers
11k 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.
XTImpossible's user avatar
20 votes
2 answers
3k 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—...
user avatar
10 votes
5 answers
16k 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'...
mr-matt's user avatar
  • 457
58 votes
2 answers
237k 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 ...
David says Reinstate Monica's user avatar
24 votes
2 answers
15k 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 ...
DrZ214's user avatar
  • 17.8k
26 votes
1 answer
25k 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 ...
magicmq's user avatar
  • 363
20 votes
2 answers
26k 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 ...
Anarach's user avatar
  • 393
17 votes
1 answer
4k 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 ...
user avatar
9 votes
1 answer
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 ...
Ajas's user avatar
  • 101
26 votes
8 answers
56k views

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?
Alex Furnival Krauss's user avatar
19 votes
7 answers
58k 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 ...
Madhav Sudarshan's user avatar
9 votes
1 answer
4k 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 ...
Antoine Convert's user avatar
25 votes
3 answers
4k 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?
Pavel's user avatar
  • 909
13 votes
2 answers
5k views

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 ...
user avatar
10 votes
2 answers
7k 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 ...
Trebia Project.'s user avatar
6 votes
1 answer
33k 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?
Gianni Alessandro's user avatar
24 votes
2 answers
26k 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 ...
Ethan's user avatar
  • 9,349
16 votes
3 answers
12k 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 ...
DrZ214's user avatar
  • 17.8k
10 votes
2 answers
6k 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?...
wbeard52's user avatar
  • 12.7k
9 votes
3 answers
6k views

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?
Nirmal's user avatar
  • 319
9 votes
1 answer
2k 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 ...
Southbob's user avatar
  • 1,089
8 votes
1 answer
4k 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 ...
DrZ214's user avatar
  • 17.8k
7 votes
4 answers
4k 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 ...
user avatar
5 votes
1 answer
1k 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 ...
TomMcW's user avatar
  • 28.6k
4 votes
2 answers
4k 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 ...
Ethan's user avatar
  • 9,349
40 votes
11 answers
18k views

Why do new jet engines cost billions to design?

This question might come off as crude because it involves people's salaries, but I do not understand why new designs of large turbofans cost many billions of dollars to design. For example, the Pratt &...
DrZ214's user avatar
  • 17.8k
32 votes
4 answers
13k 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 ...
TomMcW's user avatar
  • 28.6k
28 votes
8 answers
7k views

Why do we refer to "power" for turboprop engines and "thrust" for turbojet/fan engines?

In jet engines, I read that thrust is related to the fuel flow rate, whereas in turboprop engines power produced is related to the fuel flow rate. What is the reason and brief math behind this?
user5349's user avatar
  • 514
24 votes
2 answers
5k views

Why are only some aircraft in this formation creating contrails?

The Republic Day celebrations at New Delhi, India had a series of flypasts by the Indian Air Force. What struck me the most was that in a formation with a C-17 in middle and two Su-30MKI flanking it, ...
Kanchu's user avatar
  • 927
19 votes
1 answer
20k 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 ...
clueless007's user avatar
12 votes
1 answer
1k 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/...
Flambino's user avatar
  • 747
10 votes
4 answers
4k 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) ...
summerrain's user avatar
  • 3,474
9 votes
3 answers
2k 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?
SRawes's user avatar
  • 1,211
8 votes
1 answer
2k 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 ...
Vikki's user avatar
  • 28.4k
8 votes
3 answers
7k 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?
Invariant's user avatar
  • 1,731
6 votes
2 answers
12k 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 ...
Eylan's user avatar
  • 61
6 votes
2 answers
3k 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 ...
Anthony X's user avatar
  • 3,400
5 votes
3 answers
3k 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 ...
Gary Zenger's user avatar
5 votes
1 answer
540 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.
securitydude5's user avatar
5 votes
3 answers
2k 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 ...
DrZ214's user avatar
  • 17.8k
4 votes
1 answer
822 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 ...
Topcatmki's user avatar
  • 163
3 votes
5 answers
6k views

What is the GE90-115b turbine power output in horsepower?

The GE90-115b is rated at 513 kN maximum thrust and is often said to have 110,000 shaft horsepower, but I have yet to find any document or specification that backs the claim on horsepower figure. A ...
Erik's user avatar
  • 443
2 votes
1 answer
2k views

Does jet engine exhaust velocity relative to itself remain constant despite speed changes?

Maybe this is a stupid question. I seem to have been told, the velocity of the exhaust leaving an airbreathing jet engine relative to the engine, is constant despite changes in airspeed. However, to ...
Abdullah is not an Amalekite's user avatar
1 vote
1 answer
915 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 ...
securitydude5's user avatar
0 votes
1 answer
501 views

What airfoil family does turbofan's fan blades use?

The thing is, I am trying to make turbofan blades in Solidworks for a possible undergraduate thesis. I want to know if there is any airfoil from the NACA series or any airfoil families plausible for ...
Paul P.'s user avatar
  • 21
34 votes
3 answers
7k views

How long to clear the 'suck zone' of a turbofan after start is initiated?

I recently found this (IMO funny) picture. All funny and all. But let's make this a real situation. Let's suppose I see my crush and his BF doing this, and I come with this 'genius' idea (alright, it'...
Hugo Woesthuis's user avatar
18 votes
6 answers
9k 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 ...
DrZ214's user avatar
  • 17.8k
17 votes
3 answers
6k views

Can high-bypass turbofans cruise at high altitude?

They have talked for years about re-engining the B-52 with something more modern than its TF33-P-3/JT3D turbofans, which are fairly low-bypass (1.42:1 for the JT3D). Modern engines are much higher ...
Harper - Reinstate Monica's user avatar
15 votes
2 answers
2k 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 ...
Sam Creamer's user avatar