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 the fan) for obtaining thrust.

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2answers
96 views

Can an S-duct fit a turbofan exhaust instead of the intake?

Can an S-duct fit a turbofan exhaust instead of the intake? The idea here is to merge 2 exhausts into one at the exact center of the tail. This would be for twin-engine aircraft that have both engines ...
0
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1answer
145 views

Why is the intake of the 757 (RR) engine slanted? [duplicate]

I'm sitting looking at a 757 with Rolls-Royce engines and just noticed that the intake is slanted forward by 5-10 degrees. Anyone know why? (wikimedia.org)
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4answers
407 views

How does an operator change the engine thrust rating?

If, for example, an operator has a Boeing 737-800 with CFM56-7B engines set at a 22K thrust rating, but the next operator wanted to operate the engines at 24K thrust rating, what would they need to ...
2
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1answer
101 views

Why can’t electric motors be used in aviation [duplicate]

Why can’t electric motors be used in aviation? Is it a problem with batteries, torque, or what? From what I’m aware motors at high torque are expensive and need a massive footprint, than a high rpm ...
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0answers
117 views

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 ...
2
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2answers
119 views

What do compressor/turbine stages mean, and why we need a different number of stages?

I am new to aviation. I realize that LP (Low Pressure) and HP (High Pressure) compressors/turbines have a various number of stages. What do stages mean? What is the reason to have a different number ...
6
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1answer
201 views

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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1answer
95 views

Why can't turbojets or turbofans be overtemped or overtorqued the way turboprops can?

Turboprops that aren't FADEC controlled can be overtorqued or overtemped if the power lever is moved too far forward yet I have never heard of a jet that can't be "firewalled", FADEC or not. Why is ...
4
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1answer
114 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 $$ m_\mathrm{Fan} = 0.1 \times m_\mathrm{Turbine} $$ ...
1
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1answer
118 views

Can the maximum thrust of a turbofan engine be estimated by its intake diameter?

I have no clue in aeronautics. How to estimate maximum thrust (at any rated condition, such as altitude, speed, rotation velocity- any given condition) by intake diameter?
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0answers
43 views

Oultlet vane guides

I have looked around the web and I could not fine this information. How many vanes are there for the CF6-80 and the CFM-56? Is the count dependant on anything particular, such as fan diameter?
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1answer
118 views

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 ...
3
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0answers
143 views

Is the combustion process in turbofans and turboshafts different?

According to a journal paper, for a Gnome turboshaft engine, fuel-air equivalence ratio decreases as power output increases. However, for a CFM56 turbofan engine, the opposite trend is true, and ...
34
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3answers
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'...
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3answers
108 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 ...
3
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1answer
344 views

Does the P&W F100 turbofan engine of the F-16 really produce this much power?

I've been trying to calculate the power a P&W F100 engine on a F-16 is producing using some of the available data on thrust and velocity and I ended up with a number that I want to confirm. Here's ...
7
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2answers
1k views

Gear reduction on large turbofans

Do engines like the GE90 and Trent 1000 use transmissions (planetary gears?) for RPM reduction on the fans, or are they welded directly to the same shaft as the low pressure turbine?
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2answers
1k 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 ...
1
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1answer
54 views

Proportionally, what is more affected by a hot and high takeoff - a electrically driven propeller or a turbofan?

My assumption would be the electrically driven propeller would be less affected compared to turbofans at high altitudes and take off as although the air would be less dense at these ambient conditions,...
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2answers
176 views

Why Engine Exhaust Nozzle can not be totally buried in aircraft fuselage? [closed]

Why The CD nozzles of the fighter aircraft are always outside the fuselage, Why the whole engine is not buried in the fuselage?? If engine shroud also can be made variable area and varies with CD ...
4
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2answers
279 views

Why was the DC-8-70 successful, but not the 707-700?

The first high-bypass turbofan small enough to use on a narrowbody jetliner was the GE/SNECMA CFM56, which entered service in the late 1970s as an upgrade engine for the KC-135 tanker; Boeing almost ...
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2answers
447 views

Turboprop vs turbofan (in regional aircraft)

I'm trying to figure out WHY turboprops are more efficient at lower altitudes and airspeed, while turbofans are better at faster speeds and higher altitude. Simplistically, my explanation is the ...
4
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1answer
83 views

Are low pressure (LP) compressors and booster compressors the same thing?

Based on the above picture, are "LP compressor" and "Booster compressor" different names for the same thing or are they actually different things?
2
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1answer
118 views

Turbofan engine 2 spool - Turbine drives the compressor or Starter drives the compressor [duplicate]

I have read somewhere regarding turbofan engine 2 spool that says "LP or HP turbine will drive the LP or HP compressor" "During engine starting, the starter will drive the HP compressor via the ...
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2answers
238 views

Did Boeing or Lockheed ever seriously consider releasing a widebody airliner powered by low-bypass engines?

During the 1960s race to build the first widebody jetliner, each of the three major engine manufacturers was racing to put out a high-bypass engine for one of those jumbo jets: Boeing went with Pratt ...
3
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2answers
259 views

Do any propellers/propfans use stator vanes? Why is this not a commonplace feature?

I understand that axial-flow turbine engines generally include stator vanes behind every(?) compressor and turbine stage. This makes quite intuitively sense, because without them the rotating blades ...
3
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3answers
384 views

Can a turbofan run without the fan to provide power without thrust?

Is it possible for a turbofan jet - like on a 747 - to run without the fan, if for example you just want the thrust from the internal jet to use to heat up water, not to use as thrust?
3
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3answers
132 views

Would there be a purpose for a set of compressors in an electric turbo fan?

This is actually a two part question. Would there be a purpose to a compressor in an electric turbofan where there is no need for a combustion chamber, and if not, is there then a purpose for a bypass ...
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1answer
66 views

How to understand turbo machines?(compressors,fans,pumps,turbines,etc..)

From what I understood, the energy transfer between the blades and the fluid(fluid to blade or blade to fluid) occurs due to the curvature of the blade.Its because of this curvature the stream of the ...
3
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3answers
412 views

Why did narrowbody jetliners take so long to switch over to high-bypass engines?

High-bypass turbofans were introduced into the airliner market around 1970, when the first widebody jetliners were released (the 747 was first, followed in rapid succession by the DC-10, L-1011, and ...
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3answers
2k 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) ...
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2answers
114 views

How to calculate power required to drive an isolated fan of a TurboFan engine?

If I isolate the fan from a TurboFan jet engine (specifically GE90) and power it electrically with a motor, how much power is required for the electrical source to drive the fan to give the same ...
26
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7answers
3k 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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1answer
154 views

Turbofan design parameters [closed]

I am writing a model for LM Prepar3D to simulate the flight model of a commercial airliner. The specification I am following requires some parameters from the engine (CFM56). ...
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0answers
273 views

What will happen to a modern high bypass engine at 80 000 feet with cruise speed of 0.8 Mach?

While keeping the typical cruise speed of 0.8 Mach, will the engine shut down due to "air starvation" at such high altitude? Is it possible to design a turbofan engine, which is able to provide thrust,...
2
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1answer
108 views

Did turbofan engine explosions become more frequent in last years in commercial aviation?

There are many incidents with turbofan engine failures during last years. I can list: 2010-11-04 - Qantas_Flight_32 2015-09-08 - British Airways Flight 2276 2016-05-27 - Korean Air Flight 2708 2016-...
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0answers
149 views

What are the air mass flow rate and fan pressure ratio of the Trent XWB?

I have some basic questions regarding the Trent XWB: What's the air mass flow rate (or its range) of the Trent XWB engine? Is all of the air mass flow of the engine produced only by the 118" diameter ...
0
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1answer
247 views

How do you maximize an electric engines thrust?

I‘ve been recently looking for answers to this question on the internet but the jungle of propellers, fans and electric motors didn‘t quite get me an anwer. How would I have to design an electric ...
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0answers
110 views

How does a partially covered air intake affect the thrust of a propeller ?

does a partially covered air intake of a ducted propeller significantly affect its thrust? If so, will it be like 10 or rather 90 percent less thrust ? Thanks for your answers! Simon
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3answers
285 views

Does bypass air produce thrust?

How does bypass air exiting the bypass nozzle produce thrust in a turbofan engine? I thought that thrust was produced by air reacting with the fans. So if thrust happens when there is an action-...
3
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1answer
238 views

On a ducted propeller, how does duct length affect thrust?

So if we are looking at an aircraft with a ducted propeller (or a high bypass turbofan engine), does it matter how long the duct is? As an extreme example, would having a duct that extends 100 feet ...
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0answers
93 views

How turbofan engine efficiency increases over altitude or speed? [duplicate]

I am confused a lot about the efficiency and thrust relation with altitude and velocity of an aircraft. If thrust is related to air mass flow and velocity diffrence of bypassed air - exhaust gases ...
2
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2answers
334 views

Can a turbojet jet or turbofan powered aircraft land and take off from water?

Can a turbojet jet or turbofan powered aircraft land and take off from water? How much clearence from the water surface would it need for its engines so that it does not suck up water?
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2answers
186 views

How to compare two SFCs, one in thrust, the other in power (both turbofans)?

I want to compare some recent turbofan engines in terms of fuel efficiency, particularly the PW535A and FJ44-4. I found the SFC for the PW535A to be 0.44 lb/h/lbf. I couldn't find anything on the ...
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2answers
489 views

Why do compressors constrict flow if this decreases pressure?

An axial compressor (and a ramjet intake, for that matter) is commonly depicted as decreasing the volume of air travelling through as we move closer to the combustion chamber. In axial compressors, ...
3
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1answer
313 views

Why are most turbofans tractors, but most propfans pushers?

Turbofans and propfans are, in concept, quite similar: both have a turbojet core, plus one or more additional turbine stages that drive a fan(s) which blows air around the core (this is known as ...
13
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3answers
4k views

Why didn't early jetliners use turbofans?

For subsonic operation, high-bypass turbofans seem to have essentially only advantages for efficiency, noise and takeoff thrust, at least until they reach the size where ground clearance or LP/fan ...
8
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1answer
480 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 ...
2
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1answer
122 views

Is there a standard install direction of the abradable shroud honeycomb on a CF6-80c2 engine?

Is there a standard install direction of the honeycomb cells on the Fan Forward case on the CF6-80C2 abradable shroud section? I have seen engines that the honeycomb cells run point to point front ...
13
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1answer
7k 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 ...