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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40 views

Why Turboprop engines are better than turbojet at low altitude and speed? [duplicate]

Please explain the Aerodynamic or engine considerations which makes turboprop more efficient at low altitude n low speed as compared to turbo jet.
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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 ...
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Why don't private jets use higher bypass turbofans?

Common private jet engines such as the Williams FJ44 has a bypass ratio of just 2.8:1. Installation requirements aside. From an engineering perspective is there much to gain in efficiency by going to ...
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2answers
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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 ...
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GE90-115b turbine 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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What integration of aircraft propulsion would be more efficient at sea level high speed flight? A turbofan, unducted fan or a turbojet?

For educational purposes I am designing a small single seat twin engine aircraft that will be as efficient as possible at sea level and at a variety of speeds 150-500+ mph. The goal is to be able to ...
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1answer
208 views

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 ...
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Do turbofan engine cowlings dilate during spool-up?

I was watching this Youtube video, portraying a Fokker 70 taking off. I wouldn't have noticed if it weren't for a comment, but during spool up (~ 3:24 in the video), it appears as if the engine ...
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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?
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109 views

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 ...
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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 ...
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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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151 views

Turboprop vs Turbofan: How to compare Specific Fuel Consumption

I understand that Turboprop engines have a lower Specific Fuel Consumption (SFC) than Turbofan engines, on average. I want to see this for myself by analysis, ideally by comparing values of SFC for ...
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How much N1 difference between two engines are acceptable?

While I was flying with 10+ year Airbus 320, IAE engine with EPR, I saw a constant difference between N1 parameters around 2%. I checked the Engine Hours and Engine Cycles that they are almost the ...
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1answer
127 views

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 ...
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Why are there no large turboprop passenger airliners? [duplicate]

If turboprop engines are more efficient than turbofan/jet engines at lower speeds, and have a lower specific fuel consumption, why are there no large passenger airliners that utilize the turboprop ...
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Why wasn't the 737 MAX's landing gear lengthened enough to mount the engines under the wings, rather than in front of them?

The reason Boeing originally added the MCAS to the 737 MAX was to compensate for a slight pitch-up moment generated by the engine nacelles at very high angles of attack. This pitch-up moment occurred ...
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Why was the DC-9-80/MD-80 so successful despite being obsolete almost from birth?

The McDonnell Douglas DC-9-80/MD-80 series of narrowbody jetliners was the second-to-last DC-9 major version produced (from 1979 through 1999), the second-largest, the most-produced (just under half ...
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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?
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Why does a turbofan shut off when rapidly retarding the thrust levers?

In a turbofan engine, when the thrust lever is at maximum and is then suddenly pulled back to idle, the engine will shut off and lose power. How can this be the case as the engine should be at idle ...
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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?
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1answer
134 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 can the effects of hot corrosion and salt deposits from sea water spray in gas turbine engines be negated/prevented?

In aircraft operating in a maritime environment, corrosive effects from salt water are common. Are there any specific coatings used in engines for such aircraft? If so, which are they? How frequently ...
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1answer
236 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 ...
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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 ...
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586 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 ...
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124 views

How is take-off power defined?

In a recent post it could be read that by definition, turbofans do not produce power in the static case (at velocity zero). The statement could be a bit confusing since turbofans and propeller engines ...
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Why did the 707 and DC-8 continue to use the JT3D even after the JT8D became available?

Pratt & Whitney’s first-generation turbofan was the JT3D (a derivative of the company’s first-generation turbojet, the JT3C), which entered service in March 1961, and, due to its greater power and ...
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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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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 ...
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2answers
202 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 ...
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1answer
183 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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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 ...
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1answer
195 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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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 ...
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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 ...
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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 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 ...
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138 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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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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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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137 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 ...
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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 ...
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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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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 ...
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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 ...
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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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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 ...
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1answer
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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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240 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 ...