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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1answer
163 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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1answer
85 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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1answer
53 views

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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1answer
163 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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165 views

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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849 views

Why do propellers have less theoretical range (i.e. range ignoring impatient passengers wanting to go fast) than jets, despite greater efficiency?

I was playing around with the breguet range equation recently, and came across a suprising result, that propellers have less range than jets, despite having greater efficiency. The range equation for ...
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1answer
237 views

What mechanism did the turbine reversers of early high-bypass turbofans use?

Nearly all jetliners nowadays use fat, efficient high-bypass turbofans (turbofans with a bypass ratio greater than or equal to 5:1). As the vast majority of a high-bypass turbofan’s thrust comes from ...
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1answer
206 views

Why did the Mercure use cascade-type reversers?

There are three main types of jet-engine thrust reversers:1 Target-type reversers are seen on most civilian turbojets and low-bypass turbofans;2 they have the instantly-recognisable buckets that ...
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38 views

Bleed air examples and percentages [duplicate]

I'm doing an assignment in GSP where I've got to examine bleed air and it's effect on thrust and fuel consumption. I've got to simulate 1-10% bleed air and then answer whether the drop in performance ...
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1answer
96 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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3answers
178 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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1answer
106 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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175 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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1answer
952 views

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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1answer
184 views

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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Comparison of specific thrust vs. speed, for EDFs and propellers

I stumbled upon this graph showing the decrease in specific thrust (Thrust by Power) in relation to velocity, for a Schuebeler EDF: https://www.researchgate.net/figure/Specific-thrust-T-P-vs-airspeed-...
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Why does the takeoff N1 limit start to decrease below 30°C OAT?

It's easy to understand why the takeoff N1 limit decreases with an increase in the OAT in the chart above; the engines get less dense air at higher temperatures, and less dense air means less engine ...
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50 views

What is the fan pressure ratio in a turbofan?

What is it and how does it affect efficiency and thrust?
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55 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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89 views

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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2answers
250 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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2answers
254 views

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

I'm not sure that they are painted lines but it looks they are. What are they for? More images:
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14k 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 ...
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68 views

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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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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1answer
101 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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1answer
258 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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2answers
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What do these temperature data listed in the EASA Type Certificate Data Sheet mean?

Could you tell me what is the Maximum Permissible Indicated Turbine Temperature (ITT) and the ambient limit temperature for sea level static thrust?
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1answer
124 views

What gas turbines have the following configuration?

Is there any jet engines--with published data on the dimension of the turbines and compressors--that are of the configuration of 2 Low Pressure compressor, 8 High Pressure compressor, 2 High Pressure ...
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3answers
327 views

Do turbofan nacelles generate lift?

Since they are essentially an annular wing, how much do they contribute if at all to an aircraft's total lift? Would the effect of this lift be noticeable enough to help cancel out the drag they ...
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6k views

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, ...
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2answers
246 views

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 ...
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1answer
431 views

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
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2answers
392 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 ...
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1answer
219 views

What is the most recent turbofan engine that used steel for its bypass fan blades?

I haven't been able to locate any engines that use steel for the bypass fan. All sources suggest Ti and composites are used for blade construction. Apart from the weight steel could partially make up ...
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2answers
945 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 ...
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1answer
215 views

Why was a CFM56 conversion never offered for the short-body DC-8s?

A major part of why the DC-8 hung on well into the 21st century (albeit almost entirely in cargo service) was the late-1970s/1980s conversion of 110 DC-8-60s (out of a total of 262) into DC-8-70s; the ...
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How does the CFM LEAP-1B engine achieve the same efficiency as the LEAP-1A despite its lower bypass ratio?

The CFM LEAP engine comes in 3 variants (1A, 1B, 1C). The larger LEAP-1A and LEAP-1C variants have bypass ratios of 11:1, while the smaller LEAP-1B only has a bypass ratio of 9:1. For turbofan ...
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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 ...
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4answers
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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.
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8answers
5k 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?
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338 views

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 ...
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7answers
3k views

Why don't bypass ducts in jet engines narrow down the flow to accelerate it?

Since decreasing the flow area increases flow velocity, why don't turbofan bypass ducts narrow down to produce more thrust?
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1answer
166 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 ...
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120 views

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, ...
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1answer
232 views

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 $$ m_\mathrm{Fan} = 0.1 \times m_\mathrm{Turbine} $$ ...
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1answer
292 views

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 ...
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2answers
295 views

Is it true that high-bypass engines are inherently inefficient at higher speeds?

Power consumption=Kinetic energy=$1/2mv^2$. Thrust=momentum change=$mv$. I keep being told that aircraft engines are most efficient when their exhaust velocity closely matches the freestream. The ...

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