# 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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### Would it take 7 to 10 times more energy to lift a turbofan-helicopter?

I want to figure out how much energy it would take to lift a turbofan-helicopter. For reference I started with a rotor helicopter and assumed $T=100\ \mathrm{kN}$ gross weight and $d = 16\ \mathrm m$ ...
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### What is the maximum speed of all the stages of a geared bypass tubojet engine?

What is the maximum speed of all the stages of a geared bypass tubojet engine before they start losing efficiency.
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### Can a turbofan maintain torque when spinning fast?

I assume turbofan fan rpm could be increased only when: Using most modern jet engines (Airbus A380 and the Boeing B747-800) Using a magnetic gearbox which can handle more torque dor the same weight ...
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### What is the drag induced by a high bypass jet engine on an airliner?

What is the drag induced by a turbo bypass jet engine in a typical most modern airliner like the 777, the Jumbo Jet (Boeing 747-8) and the Airbus A380? Given that the jet is travelling faster than ...
312 views

### Is there an engine database that would include information on number of HPT blades per engine?

I am attempting to compile information on the number of high-pressure turbine blades across a wide range of turbine engines. Currently, I have only been able to find this information through brut ...
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### Why aren't there any single turbofan airliner?

A configuration which looks like a DC-10, without engines mounted under the wings. Let's say 737 sized. Let's forget about redundancy security advantages of twin or quad engines, since they're ...
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### How much weight does a thrust reverser add?

How much weight does a thrust reverser add to an engine? Let's take the CFM Leap 1B as an example, which powers the new version of the Boeing 737. This engine can produce up to 130 kN of thrust for ...
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### Why do large turbofans generally have many more LP turbine stages than HP turbine stages?

In almost every large turbofan I see, the LP turbine stages outnumber the HP turbine stages by a factor of at least 2. Here's a photo of the RR Trent 900: The Trent 900 (like most Rolls-Royce ...
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### In a turbofan, why are there no stators behind the fan?

Why are there no stators behind the fan? At least, I've never seen any turbofan design that has stators right behind it. (Here is the latest turbofan I've looked at, the CFM56. Cutaway part starts ...
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### What is the clearance between a fan blade and the nacelle?

What is the distance between the tip of a fan blade and the inside of the nacelle for a turbofan like the Rolls Royce Trent 900? Does this distance change significantly during cruise due to thermal ...
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### How much electrical power does one generator produce on a large turbofan?

From my related question, now I want to know just how much power does the generator produce? In other words, what is the max rating of the generator? It looks so small and that surprised me, but since ...
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### What is the Fuel-Oxygen ratio for a large turbofan at cruise conditions?

What is the Fuel-Oxygen ratio (by mass) for a large turbofan at cruise conditions? In order to be concrete, I'll just pick an engine at random. I pick the GE90-115B. Okay it's not really random, it'...
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### Where is the generator in a large turbofan of a commercial airliner?

So, where do you put the electrical generator? If it's gonna be coaxial, the only place is the rear (it will be burnt) or the front (it will get in the way of intake). If it's gonna be coupled to a ...
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### Turbo-fan idle at high speeds, will air speed up fan speed?

If N1 idle is 30%, will flying idle at very high speeds force the fan to go higher than 30%? (for example idle while descending fast) And if no, why not?
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### Are there turbofan/turbojet analogues to a centrifugal-compressing jet engine?

Axial-compressor jet engines fall into two categories (and only two as far as I'm aware): turbofan and turbojet. I'm wondering if centrifugal-compressor jets also have such a distinction or something ...
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### Why do turbofan jets fly faster in cold weather?

Why do turbofan jets fly faster in cold weather at high altitudes? I read somewhere that prop planes do it due to cold weather means air is more dense, and the prop therefore produce more power. But ...
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### Why do many large turbofans have a gap (of turbine blades) between the LP turbine and HP turbine?

After browsing around a while, I noticed that many...I think almost all...large turbofans have this gap between the LP turbine and HP turbine. I took some screenshots and put a red circle around the ...
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### What prevents miltiary jets and turbo-props from being refitted with a turbofan?

What prevents military jets and turbo-props (such as P-3 Orion) from being refitted with a high bypass turbofan?
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### Why do jet engine fan blades have a twisted shape?

is this a good answer. the blades rotate, the tip moves faster than the hub. So to make the blades efficient, the blades are usually twisted. The angle of attack of the blades at the tip is lower than ...
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### Why is EGT decreasing on a jet engine when the generators cut in (take over)?

Is the EGT decrease related to the generators cutting in or is it related to the fact that the fan is now providing enough ventilation air for the engine? When I say cut in I mean that the engine ...
350 views

### How can you do preflight fan inspection when it's windy?

While sitting, bored to tears, intermittently scanning the 'Delayed' display next to my flight, I've looked out of the airport windows. Out on the stand, amongst the baggage and fuel truck activity, ...
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### How do aircraft engine manufacturers achieve a higher bypass ratio while still meeting the thrust requirements for a given aircraft?

I understand that a higher bypass ratio leads to greater efficiency as less air moves through the core, and therefore less fuel is burned. However, how is the thrust requirement for the same aircraft ...
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### Why does intake of turbofan engine have angle of attack? [duplicate]

As you can see the title of the question, intake of turbofan engine has an angle of attack. why? see:
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### Which engine type requires the shortest take-off run: a turboprop or a turbofan?

If two fixed-wing aircraft almost identical except for the engines, one turbofan and one turboprop, which one would need less runway to take off?
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### 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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### How do turbofan nacelle lengths compare?

For example, compare the JT9D and the PW4000 below (both from Pratt & Whitney, both on a 747): (Left, Right) The PW4000 has a longer forward nacelle, and a covered exhaust cone. On the inside—...
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### Can a turbofan have a fan driven electrically so as to run at optimal speed?

I just watched this pretty dumbed-down video about the idea of putting a gearbox in a turbofan so the fan can run at its optimum slower speed while the core runs at its optimum high speed. And I ...
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### Is it possible to have an afterburner in a turbofan with bypass ratio greater than 1:1?

Is it possible to have an afterburner in a turbofan with a bypass ratio greater than 1:1? At 1.05:1, say, can it have an afterburner?
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### What are the advantages of a geared contrarotating turbofan? [duplicate]

I read that this would be the holy grail of jet engines: Next Gen NB Engines : Contra Rotating Turbofan Fan Why is this so and what problems are stopping us from doing this?
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### Why do turbofan engines not have a contrarotating second fan?

Why aren't planetary gears used to have a fan in front of the fan in a turbo fan engine. Would this not lower energy consumption etc?
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### Why Planes Don't Fly Faster? [duplicate]

I recently Stumbled on this Why Planes Don't Fly Faster on youtube and it talked about how less speed is more economical for airlines and he also said something that plane above and below speed of ...
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### Why aren't compressor and turbine blades flat? [duplicate]

Why are the compressor and turbine blades of a jet engine shaped as airfoils? Why can't they be flat?
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### At what point is a turbine powered ducted propeller considered a turbofan?

Turboprop Propellers can be ducted for extra thrust. What are the criteria for determining that the engine is no longer a ducted propeller design, but a turbofan? Does there have to be a type of ...
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### What is the material that is used for turbine blades that has the highest melting point?

What is the material that is used for turbine blades that has the highest melting point ?
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### Why do some turbofan blade have forward swept tips?

I notice that in Trent700 engine fan blade there is no curve extension at the tip unlike in other engine's fan blades such as the GE90 ,T900 etc. What are the purpose of it? Trent 700 without ...
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### How do turbofans and piston-engines compare in terms of maintenance costs?

I want to compare piston engines and turbofans on a maintenance basis. Let's say both engines are capable of 100 kN of thrust. Let's say both engines fly for 10,000 hours. Over that time, what kind ...
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### What kind of liquid can be seen 'leaking' from the bottom of a Boeing 737-800 engine?

I was on holiday over the Christmas holidays, and was sat in the airport awaiting our plane back to England, looking out of the large window which over looked aircraft that have just landed and the ...
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### What is the function of variable inlet guide vanes in terms of pressure change?

Nowadays in the turbofan Variable Inlet Guide Vanes are more and more used. My question is: which is their function in terms of pressure change? The question is very specific: I know that they allow ...
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### What's the name of this component of the turbofan engines? [duplicate]

Almost many of turbofan engines that I've seen so far nowadays had a part like a small wing. what do you call them? here is some pictures of the thing I'm asking question about:
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### Could a turbofan have two adjacent fans?

Is there any a point where it becomes possible/ideal to run two large front fans (side by side) powered from a 'single' core? Otherwise shoot this to pieces and explain the ways this is a bad idea. ...
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### How much do the fan blades of a GE90-115b stretch when the engine is spinning at maximum RPM?

I've always wondered what kind of stresses and resulting deformations jet engines are subjected to when running.
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### What are the current principles for turbofan nacelle air path design?

The Wikipedia entry for 'turbofan' states: Some high bypass ratio civil turbofans use an extremely low area ratio (less than 1.01), convergent-divergent, nozzle on the bypass... But the article ...
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### Why is the bypass ratio of a turboprop higher than turbofan?

Whenever, I come across turboprop, the author always mentions that they have higher bypass ratio than turbofan but no one explains the reason for this. So, is the bypass ratio higher due to higher ...
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### Why is there a maximum altitude to restart a jet engine?

On all the turbojets that I have flown the maximum altitude a pilot can attempt a restart is 30,000 FT MSL. What factors go in to deciding what the maximum altitude is for an engine restart / relight?...
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### How does the efficiency of a turbofan compare between take off speeds and optimal conditions?

I know turbofans are less efficient than propellers due to accelerating a smaller mass of air faster. So my question here is not comparing turbofans vs other engines, but compare how inefficient is a ...
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### Why would a jet engine use cannular combustors if the annular design is superior?

Why are cannular type burners used in aircraft engines if annular type have more advantages over it?
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### 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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### Just how much power (as a percentage) is necessary to drive a compressor in a jet engine? [duplicate]

If i understand correctly this is the "back work ratio". I'd like to know how much % of the "gross" thrust is used by the turbine to drive the compressor in a typical turbofan.