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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110 views

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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80 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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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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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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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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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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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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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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1answer
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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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1answer
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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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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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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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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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138 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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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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What is physically happening when you use a bypass nozzle on a turbofan?

I am having trouble understanding how a fan affects the flow of air through the bypass in a turbofan engine. Solving for the flow of air using thermodyanic states requires using a bypass nozzle to &...
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279 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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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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Why can’t the newest high-bypass turbofans run at their EPR, temperature, and RPM limits simultaneously at sea level?

The General Electric GE9X turbofan (used on the 777X), unlike the vast majority of turbofans before it, did not undergo the traditional triple-redline test (where the engine is run for a prolonged ...
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1answer
115 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 ...
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561 views

Do all single-engined aircraft experience torque that cause a turning tendency during the takeoff roll?

I've been flying the Cirrus Vision SF-50 for quite some time on my X-plane 11. Having a single turbofan engine mounted near the V-tail, I expected the requirement of at least a little right rudder. ...
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124 views

Why is the thrust-specific fuel consumption much worse for high bypass turbofans at cruise?

General Electric GE90 Takeoff: 0.278 lb/lbf/h (28.3 kg/kN/h) Cruise: 0.545 lb/lbf/h (55.6 kg/kN/h) Source: https://en.wikipedia.org/wiki/General_Electric_GE90#Specifications I assume this is typical ...
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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.
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Why is Active Flow Controlnot used in Fan And Compressor of aero engines?

Why active flow control is not used in the compressor and fan of aero engines even though they provide several advantages in terms of performance? what are the challenges of using active flow control ...
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What is the cost of electricity generated in the E175-E1?

I'm comparing two types of cabin illumination, and I'm having a difficult time to estimate the cost that will be saved by utilizing lights with a lower power consumption. What are the costs of ...
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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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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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3answers
167 views

Why do turbofans go faster than turboprops? [duplicate]

Can someone explain why turboprops are less effective in terms of thrust than turbofans? But at the same time, why turboprops burn less fuel? For example, the Bombardier Q400/De Havilland Dash 8 has a ...
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Effect of Exhaust Mixer on the temperature of Core Exhaust

After the core exhaust leaves the turbine section (having a temperature of about 900 C ), and it mixes with the by-pass air via the exhaust mixer , what will be the resulting temperature of the ...
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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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156 views

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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472 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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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
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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 ...
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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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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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409 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
226 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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171 views

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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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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