All Questions
Tagged with turbofan jet-engine
91 questions
0
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2
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145
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How do tubojets compare to afterburning turbofans in terms of efficiency?
Turbojets used to be more common in the 40's and 50's but once jet engine design matured they pretty much went extinct in favor of the more efficient turbofan. I know one advantage of the turbojets is ...
- 41
2
votes
1
answer
185
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Is it a good idea to increase exhaust duct length?
I am a big newbie in aviation but still, I have a question:
Let's assume a civil aircraft (Boeing 737 or Airbus 320), flying with those impossible real life hypothesis:
the exact SAME turbofan are ...
- 29
1
vote
1
answer
225
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Exhaust temperature of CFM56 engines range (Nozzle downstream temp)?
EGT is available but not the temp of the exhaust nozzle in the CFM56 series.
- 13
0
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1
answer
127
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Why do we take into consideration holes for pressure thrust in jet engine calculations?
In many sources related to jet engine thrust calculations such as https://www.jet-x.org/a8.html ,
pressure thrust of a module such as combustion chamber, nozzle or compressor, is calculated by front ...
- 244
1
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1
answer
455
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Do compressors and turbines in jet engines end with rotor or stator?
I am trying to understand compressor and turbine design principle based on stators and rotors.
I know that turbines and compressors both have a rotating and fixed section that constitute a stage.
For ...
- 244
1
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2
answers
470
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Why are inlet and outlet (exhaust) pressure considered to be the same in a turbojet engine?
Why do we take outlet/exhaust pressure (station 6) as the same as in inlet (station 1) ?
In T-S diagram, we see that outlet temperature is much higher than inlet temperature since flow in outlet has ...
- 244
6
votes
4
answers
6k
views
Can electricity be harvested from magnets in jet engines?
I was reading about bleedless-787 power system but found out it still requires a gearbox.
What if you put coils around the "tube" part of the jet and tiny magnets in the end of the fan/...
- 95
4
votes
2
answers
581
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Could a F-22's exhaust stall a highjacked Boeing 767's turbofan(s) and force it to land?
Would it be possible to use a F-22's exhaust to intentionally stall a hijacked Boeing 767's turbofan engines in order to force it to land instead of shooting it down?
The idea being that stalling one ...
- 41
1
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1
answer
551
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Why does the gas turbine recuperator hugely increase efficiency but slightly decrease the peak power?
I understand that the heated intake air will burn more efficiently with the fuel and that's why recuperators increase efficiency. The part I don't understand is that if efficiency is going up, why isn'...
- 159
5
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3
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4k
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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 turboprop powered 737 would be of any use really, but as ...
- 51
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4
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1k
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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 ...
7
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2
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3k
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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 ...
- 173
4
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3
answers
2k
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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? ...
4
votes
1
answer
1k
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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 ...
- 181
2
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0
answers
250
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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?
- 3,329
1
vote
1
answer
207
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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 ...
- 11
6
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2
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6k
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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.
- 181
2
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2
answers
2k
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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/...
- 886
3
votes
1
answer
2k
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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?
- 181
4
votes
1
answer
2k
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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 ...
- 3,329
2
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0
answers
293
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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?
- 1,567
2
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0
answers
222
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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 ...
- 761
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0
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6k
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What is the fan pressure ratio in a turbofan?
What is it and how does it affect efficiency and thrust?
2
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0
answers
127
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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
- 3,329
14
votes
2
answers
760
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:
- 3,329
1
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2
answers
291
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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 ...
- 3,329
2
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0
answers
242
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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?
- 21
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1
answer
3k
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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 ...
- 73
1
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2
answers
2k
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Why would sea level static thrust have a takeoff and a maximum continuous value?
In the type certificate data sheet for a jet engine, there is this table
static thrust is the thrust generated by the engine when the plane is at rest with respect to the Earth and the surrounding ...
- 323
3
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1
answer
2k
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Why do some Turbofan engines have multi-stage fans?
I was wondering why some turbofan engine have multi-stage fans.
e.g. F-119 engine:
F100
Saturn AL-31
- 3,329
29
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2
answers
6k
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Are large jet turbofans so easy to spin?
In this question, in the accepted answer, there is a comment by alephzero that says one can actually rotate a large turbofan's blades with one finger! Is that true, ...
- 533
0
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1
answer
192
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Why is tangential velocity a loss of kinetic energy in a turbine section?
While researching turbine engines I came across a statement
The mass of airflow naturally does not change in the transfer of energy to the rotor system, but the velocity of mass flow being slowed ...
- 611
7
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3
answers
2k
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Why don't turbofan engines have shrouds affixed to the fan blades?
For a turbofan to be efficient the gap between the blades and the shroud has to be extremely small. Why don't we just attach the shroud directly to the blades and let it spin as one? Would that ...
- 2,544
1
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1
answer
455
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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 ...
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2
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0
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773
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How hot is the outer casing of a turbofan engine?
I am able to find temperatures inside different components of turbofan engines, but I can't seem to find what would be the temperature of the external casing/shell of the engine. For example, ...
- 41
3
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1
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416
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Why does turbofan exhaust appear to reverse direction?
Yesterday I was at the airport planespotting. I observed the exhaust of a couple of turbofan engines, and found it curious how the fluid seemed to behave as it was leaving the engine and gaining ...
- 443
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1
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2k
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What is the fuel/air ratio of the CFM56-5A1 engine (in the A320 model)?
I could find the fan-bypass ratio, which was 6:1 (on some models 5:1) but I was unable to find the fuel to air ratio used in this engine. For reference, it is a high-bypass turbofan engine.
- 11
6
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1
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345
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What factors contribute to the poor off design performance of turbofans?
I am looking to understand why turbofans have a higher specific fuel consumption when ran at lower power settings and what can be done to improve it.
How much does the rpm of the various spools and ...
3
votes
2
answers
541
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How do turbofan internals handle the load from the thrust?
To my understanding, turbofan engines get the majority of their thrust from the fan in front of the engine, up to around 70-80% while the core flow generates around 20-30%.
Forward movement is ...
- 443
3
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5
answers
7k
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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 ...
- 443
2
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1
answer
439
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Why was there no thrust from the engines in the TACA Flight 110 incident?
I have just watched Mayday episode 11, season 11, "Nowhere to Land" about TACA Flight 110 incident. Most key issues of the incident are clearly explained in the episode:
Why both engines turned ...
- 4,160
1
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1
answer
159
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Are high bypass turbo jet engines suitable for tail and body mounted engines
Are high bypass turbo jet engines suitable for tail and body mounted engines. If not what are the drawbacks, danger if so, are there any anycraft with any such setup?
- 8,567
1
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0
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How do the contrarotating turbines work in the F-119-PW-100?
I was reading about the F22 Raptor and found out that its powerplants use contrarotating turbines. How does this work
Also, if the spools and their connected compressors are rotating in opposite ...
- 11
2
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1
answer
1k
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How can I calculate turbofan efficiency as a function of turbine inlet temperature?
I know that increasing the turbine inlet temperature (TIT) increases the overall efficiency of the jet engine. So I wanted to find the overall efficiency as a function of TIT. I used the equations ...
- 113
40
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11
answers
19k
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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 &...
- 17.9k
10
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1
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4k
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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 ...
- 62.9k
1
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0
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38
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Why at increasing BPR the efflux area should be enlarged (at high BPR)?
I am working on a university project. I have to comment on this chart (that represents efflux area variation with the variation of the BPR).
Every other engine data are kept unchanged (turbine entry ...
- 53
1
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0
answers
544
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Why use turbofan engines for high altitude flight?
I noticed that a lot of high altitude aircraft have turbofans for engines. So I researched and figured out that turboprop engines are more efficient. But most high altitude aircraft like the Global ...
6
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1
answer
715
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How heavy are turbofan and turboprop propeller blades?
How heavy are the blades from
Turbofan (CFM56-5B, RRTrent800, PW4062A) and
Turboprop (PW127M)
engines?
Is there a general appromixation like
$$ m_\mathrm{Fan} = 0.1 \times m_\mathrm{Turbine} $$
...
- 61
1
vote
1
answer
230
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Which is better a push fan, a pull fan or both
intricate examination of modern by pass jet engines is despite where it is mounted, they use a pull fan configuration to generate thrust, which set up the most efficient, a pull fan or a combination ...
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