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Questions tagged [jet-engine]

Engines which propel aircraft via "jet propulsion", i.e. by expelling high-velocity gasses (usually primarily air) through propelling nozzles.

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2answers
678 views

How will the Boom SST not require an afterburner?

The company Boom is developing a supersonic airliner (SST). In one of their blog-entries1 they state they would not need to use after-burners because they use modern turbo-fan engines. Does this ...
2
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1answer
761 views

What drives N1 during a jet engine start?

A typical jet engine start sequence that I understand is as follows: ENG Start Switch to Ground → Start Valve open → N2 increases → N1 increases → ENG Start lever to Idle (when N2 has reached a ...
4
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1answer
1k views

Why do the jet turbines spin while the engines are turned off?

Why do the jet turbines spin while the engines are turned off? Is this as a result of the wind? Or are the turbines deliberately spun using the APU? If so what is the reason behind this?
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0answers
88 views

Is the air bleeded from the engine to maintain cabin pressure for airlines heated or cooled [duplicate]

Is the air bleeded from the engine to maintain cabin pressure for airlines heated or cooled. If heated, what device is used, if cooled, what device is used and in both cases how much energy does it ...
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1answer
136 views

Is it possible to fully utilise excess heat from an aircraft to power other systems required for the aircraft to function?

Is it possible to fully utilize excess heat from an aircraft engines to power other systems required for the aircraft to function, using heat exchangers and other clever engineering tools and ...
1
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1answer
218 views

Are there any airliners and or aircraft that use bleed air and excess heat from the engine to prevent icing [duplicate]

are there any airliners and or aircraft that use bleed air and excess heat from the engine to prevent icing. Rather than use battery power or alternators, this would make sense from an energy ...
4
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1answer
138 views

Is it possible to build a jet engine that utilises all excess heat?

Is it possible to build a jet engine that utilises excess heat for thrust or does not produce any excess heat hence no need for cooling which is wasted energy
8
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1answer
672 views

Which commercial aircraft can perform a parallel engine start?

In various Youtube videos, e.g. this one, one can see that the Boeing 787 is capable of a parallel engine start (both engines are started at the same time). Are there any other commercial aircraft ...
15
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3answers
2k views

What fighters have both 1 & 2 engine versions?

Northrop originally built the F-5 "Freedom Fighter" (and T-38 "Talon") with two engines. Later it was re-fitted with a single F404 engine from the F/A-18, re-designating it the F-20 "Tigershark" to ...
7
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1answer
984 views

What is “Boost”/“Super Boost” in the PW127M/N?

This incident describes rejected take-off due to the "boost" being inoperable. The reason for the RTO is obvious: engine power lower than expected. But what is this ominous "boost" technology?
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0answers
106 views

Why are Jet Engine fan blades (and other turbomachinery blades) cantilevered rather than being connected together at their outer edges? [duplicate]

It seems to me that connecting the outside edges of each blade together would create a stiffer structure with lower stresses and a better fatigue life for a given operating condition.
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2answers
283 views

Can jet engine ingest (suck in) concrete from runway?

In the question Is there any emergency situation in which jet engines would not be shut down before passenger evacuation of a transport aircraft comment says: At full engine power, those vortices ...
20
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3answers
4k views

Are engines automatically stopped in an emergency landing?

This answer made me wonder if engines are stopped automatically after an emergency landing as soon as one of the exit doors are opened. (...) if the engine is still running, you're about to run ...
5
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1answer
1k views

What is the fan tip speed at maximum thrust?

What is the fan tip speed at maximum thrust? Is it any different for a Rolls-Royce Trent 900 (powers the Airbus A380) and Pratt & Whitney PW6000 (powers the Airbus A318)? Are they efficient at ...
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0answers
43 views

At what altitude after takeoff is thrust reduced for airliners? [duplicate]

When is thrust, after take off reduced for jumbos and smaller airliners? Is it any different for jumbos and smaller airliner aircraft?
7
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2answers
203 views

Can the mass flow rate for different power settings be determined?

Is it possible to determine the mass flow rate for different power settings? Unfortunately I was unsuccessful in finding the engine specification for the PW2037 so I used the data from this source, ...
0
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1answer
135 views

Are there any calculations involved for designing pulse jets? [closed]

Are there any requirements for calculations to determine things like exhaust length, combustion chamber size, etc? Also, does the end of the combustion chamber need to be a semi-sphere, or can it be ...
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0answers
53 views

What max Mach number of the blade tips on Concorde's engines? [duplicate]

What was the maximum velocity and Mach speed of blade tips in Concorde's engines?
3
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1answer
518 views

Could the An-225 use Trent 500 engines?

Currently, the Antonov An-225 Mriya is being produced with Progress D-18T engines, rated at 229 kN each. However, I've looked at the A340 and I love its Trent 500 engines. But the Trent 556, rated at ...
5
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2answers
1k views

What is the transient bleed valve in a gas turbine engine?

What is a transient bleed valve and what's its purpose ? Also, can you explain the purpose of bleed valves in general?
6
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1answer
307 views

What effect would a afterburner have on the compressor if the nozzle outlet is not increased?

In order to operate an afterburner, it is necessary to adapt the nozzle outlet area. As far as I understand it is necessary to open up the nozzle when the afterburner is increasing its temperature or ...
17
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5answers
7k views

Why do most military aircraft use different engines than commercial aircraft?

Why do most military aircraft and helicopters use different engine technology (fighters, B52, U2, etc) than most commercial aircraft? [I removed the use of axial terminology]
6
votes
3answers
451 views

For any given modern turbofan engine, does bypass ratio stay approximately constant during a typical flight?

Bypass ratio is the quotient of mass flow rate through the bypass duct over mass flow rate through the engine core. Does it stay constant during the typical flight of an airliner? If it does not ...
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0answers
64 views

Do the spinning parts of the tail mounted jet engines produce yaw on pitch changes? [duplicate]

For example: on takeoff at rotation, would the clockwise rotation of the 2 engines have enough force to move the nose of the aircraft left? Precession would be the force, is it strong enough?
16
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2answers
3k views

Why isn´t TOGA thrust always 100% N1 or N2?

It makes sense to me, that under normal circumstances the engines shouldn´t be pushed to their maximum, to reduce wear and tear. But why isn´t TOGA thrust, which is the maximum selectable thrust ...
13
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1answer
2k views

What type is this aircraft and engine at Munich airport?

Please help me to identify the plane and engine.
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4answers
5k views

Why isn't the APU a standard diesel generator?

Why isn't the APU a standard diesel generator? Jet-A and diesel are interchangeable (with the addition of a lubricant). So why not use a cheaper piston engine as opposed to a jet turbine? V.S.
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1answer
104 views

What are Water Vapour Resistant (WVR) engine bags made from?

What specific material are Water Vapour Resistant (WVR) engine bags made from?
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1answer
225 views

What material is used to make engine covers for passenger airliners?

What material is used to make the engine shrouds for passenger airliners?
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1answer
188 views

Would it be feasible to use graphene in the gearbox of a large turbofan engine?

What is the possibility or are the drawbacks of substituting graphene for metal in a gearbox of a geared turbofan the size of a Trent 900, given its strength properties(graphene), harder than a ...
6
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1answer
714 views

Why does it take so much fuel to start a jet engine?

I just watched an Abrams tank documentary and it said something like it takes "1 liter of fuel for every mile but 39 liters for a startup." Is it true of turbine engines in general that they need a ...
1
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2answers
368 views

What are the pros and cons of adding a gearbox to larger jet engines?

What are the merits and demerits of adding a gearbox to larger jet engines like the Trent 900. If its about torque, why not use a magnetic gearbox? What are the demerits of using magnetic gearboxes ...
0
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1answer
144 views

Could adding a gearbox to the Trent 900 improve the efficiency of the A380?

Could adding a gearbox to the Trent 900 improve the efficiency of the A380 so that it performs better than a smaller jet, i.e with economies of scale? Is the absence of a gearbox in the Trent 900 the ...
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3answers
265 views

Does a trent 900 engine have the ability to spin extra or more fans?

Given that the most modern geared turbo fans gear down spinning the fan, which essentially translates to requiring less torque or horse power to spin the fans. If the gearing down is in the magnitute ...
8
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3answers
424 views

How can engine positioning affect flutter tendency?

I understand that moving the engines towards the wingtips would increase flutter tendency, but are there any other positioning options which could affect flutter? How about moving the engine ...
13
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2answers
1k views

What engine are these fan blades from?

I bought these from a metal scrapper and paid about $30.00 total figuring they're worth more than that in cool factor. Problem is they aren't nearly as cool if I can't figure out what engine (and ...
5
votes
1answer
2k views

What throttle setting does an airliner use while cruising?

As a passenger, I have always felt like the engine are not kept at take-off thrust/full throttle a few (tens of) seconds after take-off, and so for obvious reasons as fuel efficiency, engine wear ...
4
votes
1answer
199 views

Is it possible for an airliner to cruise at engine full thrust?

What would happen if the pilot of a modern airliner like the boeing 747-800 or Airbus A380 left the throttle at full thrust at cruise altitude for an extended period of time e.g 4 hours if the ...
1
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1answer
148 views

What is the diameter of a Trent 900 engine?

What is the diameter of a Trent 900 engine, i.e the diameter of the fans, from one fan tip to the one that is directly opposite it? What is the radius of the fan or the the length of each fan blade?
4
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1answer
406 views

How much water is carried for jet engine water injection?

An answer on a related question stated that water injection was used on some of the early jet planes, for example Boeing 707 and Boeing 747-100/200. I presume the water is stored in some tank. How ...
4
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3answers
825 views

What is the purpose of blades on a compressor?

What is the point of having blades on a compressor. I heard on NASA that it alters the flow but how would this help. As the flow of a fluid increases, the pressure decreases, and vice versa. The ...
8
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1answer
432 views

How dangerous would it be to start a jet engine with coins inside?

With the multiple stories in the news of people throwing coins into a jet engine for good luck, I couldn't help but wonder how dangerous it would be if the act went unnoticed and the crew started up ...
0
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0answers
111 views

Why are there curved blades on jet engines? [duplicate]

On the fan and comssorssor and turbine for that matter there are blades and they are also curved. Im already confused beucase the fan has blades but wouldn't it blow out air not suck in air? Why are ...
3
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2answers
564 views

What materials are suitable for making a mini gas turbine engine?

What materials are suitable for a mini/model gas turbine engine, specifically the fan, compressor, combustion chamber and turbine?
0
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1answer
569 views

What is a TAPS combustor and how does it differ from any other annular combustor? [duplicate]

I found out that the GEnx engine uses a TAPS (Twin Annular Premixing Swirler) combustor. Is it a single or dual annular combustor ?
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2answers
352 views

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 ...
4
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1answer
337 views

Why use jet engines instead of propellers when designing new airplanes?

I'm looking at the 100 people project and I am looking at clean airplanes. Why did we stop using a clean source of lift, the propeller?
4
votes
1answer
847 views

What is the highest operational ceiling for an air breathing jet engine?

Air breathing jet engine can only operate at relatively low altitude where atmosphere is dense enough. But some jet aircrafts can operate at an altitude higher than 20 km (e.g. the SR-71). For really ...
6
votes
2answers
1k views

What is the origin of the term “military power”?

An engine producing 'dry' thrust is said to be at 'military power', a useful distinction from reheat / afterburner. It's always seemed an odd phrase to me. There's nothing particularly military about ...
3
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3answers
949 views

What is Engine Pressure Ratio?

I kind of know what it is but I don't fully understand it. Wikipedia says, the engine pressure ratio (EPR) is the total pressure ratio across a jet engine, measured as the ratio of the total ...