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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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3answers
7k views

Why did the turbojet replace the piston engine?

Many people say that this was because aircraft powered by turbojet engines were faster during WWII. However the Grumman F7F-4N Tigercat, a fighter powered by a piston engine, flew at a maximum speed ...
6
votes
1answer
273 views

(B737s) Why is the automatic activation range of the AUTO mode in flight limited to “between idle and 5%”?

This is the explanation on the Engine Start Switch in the 737 series FCOM. What might be the reason why the automatic activation range of the AUTO (or OFF) mode in flight limited to "between idle and ...
4
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2answers
792 views

What causes the “growl” of some large turbofans at takeoff thrust?

There are some (all?) large turbofans which emit a distinct "growl" (some people call it a "buzzsaw" sound) at takeoff thrust. What causes it? I've seen it explained (as in this question) as the fan ...
4
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0answers
152 views

What different intake designs are there, and what are their pros and cons?

I noticed that over the years (on fighter jets specifically) there have been many different methods of directing air into the engines. Primarily, the nose-intake, side intake, and underbody intakes ...
3
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1answer
415 views

What does it mean for N1/N2 to float?

The logic of ECU to hold N1 with fuel flow follow the logic: Idle N2------------N2 set ,N1 floats min ps3 schedule -----------N1 and N2 float So what does this ...
5
votes
2answers
369 views

How can a modified ramjet produce static thrust without a turbine?

A big selling point of the ramjet is its absence of moving parts (hence why it can be translated as "statojet" from other languages). However, an even bigger drawback is that a ramjet cannot produce ...
5
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2answers
2k views

What is meant by a “cold soak" of an APU?

What is the exact meaning of "cold soak" of an Auxiliary Power Unit (APU)? Is it to do with long flights at high altitude and the fuel getting cold? Will it affect the ignition of the APU? Can anyone ...
31
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4answers
7k views

How hazardous is it if an engine cowl falls off?

There was recently an incident where the engine cowl of the starboard engine of a United Airline's Boeing 777 fell off during flight: 'Scariest Flight of My Life.' United Airlines Made an Emergency ...
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0answers
68 views

At what operating temperatures would the Trent 900 need to operate, to equate to the efficiency of current geared turbofans?

What is the minimum optimum operating temperature (in degrees Celsius) that would be required for the Trent 900 to operate at, for it to attain the level of fuel efficiency of current geared turbo ...
20
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2answers
6k views

Why is a (jet) engine in flight shutdown so critical?

EASA just announced an Emergency Airworthiness Directive grounding all A320neo planes with a certain type of engine. Reason is, that they have apparently the tendency to shut down in flight more often ...
0
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0answers
67 views

Would it be possible to build an engine twice the size of the Trent 900? [duplicate]

Would it be possible to build an engine twice the size of the Trent 900 in terms of physical size, i.e. doubling the diameter? Let's assume that it's feasible to build an aircraft tall enough to ...
4
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2answers
275 views

Would tubofan aircraft benefit from adjustable fan blades?

Would turbofan aircraft benefit from adjustable fan blades as do turboprops? Propeller aircraft adjust their propeller size, i.e. shorter propeller for cruising at maximum design altitudes where the ...
0
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1answer
515 views

Would installing 6 engines on an Airbus A380 and or Boeing 747-800 achieve a shorter take off distance?

Would installing 6 engines on an Airbus A380 and or Boeing 747-800 achieve a shorter take off distance? Would that result in excessive acceleration and harmful or uncomfortable G-forces? Would the ...
8
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2answers
376 views

How big can a pulsejet be?

Pulsejets are mostly known for propelling the V-1 flying bomb, and have some use as small remote-controlled plane engines. In either case, the pulsejets aren't particularly big, as far as jet engines ...
3
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4answers
1k views

Do fighter jets have an auxiliary power unit?

Do fighter jets have an auxiliary power unit? If they don't, then how does the propulsion/ignition process start in the engine?
4
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3answers
987 views

Why does the Trent XWB have intermediate compressor stages?

I realized that the Rolls-Royce Trent XWB on the Airbus A350 has intermediate compressor stages. Why is that? Other engines like the CFM56 or IAE V2500 that power most of the A320-family have low ...
2
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1answer
136 views

How to find out what engine a plane had in the past?

I want to find out what engine a specific airplane had in the past. For example for the Airbus A320. The sources which I've found tell me there were different engines. CFM56-5A, CFM56-5B, IAE V2500 ...
2
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1answer
82 views

What type of engines are used on the RNLAF KDC-10 and KC-10's?

Does anyone know what type of engines are used on the Royal Netherlands Air Force's KC-10's/KDC-10's? I did some research and found out that they are GE CF6-50 engines, but what comes after the "50"? ...
3
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1answer
538 views

What were the J47's turbine blades made of?

What materials were used to make the General Electric J47 turbine blades in the 1960's?
8
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1answer
2k views

How do contemporary Russian jet engines compare to Western ones?

How do contemporary Russian aircraft engines like the PS-90A1 and PD-14 compare to similar engines from GE, PW, Rolls Royce and CFM International? How many years/generations they are behind their ...
3
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3answers
415 views

Would removing heat from the compressor and adding heat to the turbine increase a gas turbine's efficiency?

Since a compressor compresses air, the air temperature increases due to P1/T1=P2/T2. When the temperature is increased it would be harder to compress - so would removing the heat from the air inside ...
7
votes
1answer
204 views

Why weren't the rotor tips of the Djinn directly fed from the turbine's exhaust?

The Sud-Ouest Djinn seems to be pretty much the only tip-jet helicopter to have any sort of commercial success. It used a turbine to drive a compressor, which itself fed slightly warm air to pipes in ...
2
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2answers
724 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
votes
1answer
916 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
votes
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
91 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 ...
0
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1answer
138 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
vote
1answer
250 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
votes
1answer
160 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
votes
1answer
793 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
1k 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
108 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.
2
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2answers
302 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 ...
21
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3answers
6k 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
votes
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 ...
1
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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
votes
2answers
218 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
votes
1answer
151 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 ...
1
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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
votes
1answer
555 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
votes
1answer
357 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
525 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 ...
0
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0answers
65 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.
31
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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
109 views

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

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