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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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5
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0answers
79 views

How will the Rolls Royce UltraFan provide reverse thrust?

When perusing the Wikipedia article on the upcoming Rolls Royce UltraFan engine, I noticed that it cited an interesting bit of information from an Aviation Week article: As the fan system is ...
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0answers
18 views

Specific Thrust and its effect on max speed?

I was reading this. How (and why) does engine thrust changes with airspeed? I understand how thrust is calculated from inlet and exit velocity. I understand the energy it takes to increase velocity ...
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10answers
13k views

Why do new jet engines cost billions to design?

This question might come off as crude because it involves people's salaries, but I do not understand why new designs of large turbofans cost many billions of dollars to design. For example, the Pratt &...
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4answers
270 views

How to start up a Lockwood-Hiller Valveless Pulse Jet?

So me and my group mates in university got a lockwood hiller valveless pulsejet manufactured, and there was one error in manufacture. We are having trouble with trying to start the engine as ...
2
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1answer
50 views

Is there an equation for jet engine efficiency as a function of turbine inlet temperature?

I know that there is a relation between the turbine inlet temperature and the engine's efficiency. But, can anyone provide an equation or efficiency as a function of just the turbine inlet temperature?...
2
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1answer
63 views

Turbine blade manufacturing/assembly process

I want to know the process for manufacturing turbine blades and the companies that are involved. Who makes the turbine blades? Who applies the thermal barrier coating? Who repairs the blades? Let's ...
8
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4answers
3k views

Do modern jet engines need igniters?

I've read that modern aircraft don't need spark plugs like conventional aircraft do, as the jet fuel autoignites once it's mixed with the hot air exiting from the compressors. Then why do aircraft ...
0
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1answer
107 views

How does a propfan work?

Could someone give me a simple working of a propfan? Also I've heard the 2 sets of blades in a propfan rotate in opposite directions. Is this true? And if so why?
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2answers
208 views

Do the compressors and turbine rotate at the same speed?

Since the turbine and the compressors are connected to each other via a common shaft, do they both rotate at the same speed. Because I've read that in some jet engines (single spool engines) they don'...
2
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2answers
111 views

Why does idling RPM increase with altitude in a jet engine? [duplicate]

The Snecma-Larzac 04-C6 idling RPM ranges from approximately 53% on the ground to 85% at high altitude. Why is that?
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1answer
100 views

Turbines in jet engines

I was reading this thread and in the answer, the person wrote "For example, the turbine blades are replaced after a set number of turbine cycles and/or after a set number of hours, which are lesser ...
2
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1answer
133 views

How often are turbine blades in jet engines replaced?

How often are the turbines in the hot section of the jet engines replaced due to deteriorated TBC? or just how often are they replaced? lets say for CFM56-7
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2answers
227 views

What would be the minimum number of engines required to climb in a 747?

There was a really good Air Crash Investigation by Nat Geo which showed the British Airways Speedbird 9 issue where volcanic ash swept over all four engines and through the air vents inside the cabin. ...
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40 views

Effect on pressure and/or volume of a real vs. ideal compressor

I'm looking at the Brayton cycle and trying to understand what happens when we move from the ideal cycle (isentropic compression/expansion) to the real world where we have adiabatic compression/...
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47 views

What is the air/fuel mixture ratio in a turbojet engine?

How does it relates to stoichiometry ? What are the possible extinction accidents related to air/fuel mixture ratio ?
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0answers
88 views

Does the angular momentum of a jet engine affect aircraft performance?

I am interested, do jet engines have angular momentum? And how does such momentum affect airplane stability?
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2answers
179 views

Could hydrazine be the jet fuel of the future?

It is true that hydrazine is highly toxic and explosive, but it has tremendous energy density. The decomposition of hyrazine into hydrogen and nitrogen gases AFAIK produces enough heat to ignite the ...
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0answers
93 views

Why do the 737-100's JT8Ds, and no others, have suck-in doors?

Of the various use cases of the Pratt & Whitney JT8D (the most-produced low-bypass turbofan in history, and the second-most-produced turbofan of any description1), those installed on the 737-100 ...
6
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1answer
264 views

Why does taxiing produce large lateral loads on the 747's engine pylons?

While reading through a bunch of old AARs recently, I found (in the context of a 1993 747 in-flight engine separation) this interesting tidbit: [...] Boeing engineers report that the modifications ...
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0answers
77 views

Can the assumed temperature be lower than the flat rated temperature?

I was playing with reduced takeoff thrust in a Boeing 737-800 simulator yesterday and was surprised that I could enter assumed temperatures below the flat rated temperature of the engines. The ...
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0answers
106 views

Was the speed trim system on the B737 Classic modified to counter increased thrust?

How much additional thrust did the 737 classic generate compared to the original 737? Was the speed trim system added to counter the additional thrust?
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0answers
81 views

Why does not jet engines have a metal grid in the front? [duplicate]

An aircraft engine can get destroyed if a large object - like birds - enters it while running. I'm probably naive, but this seems pretty easy to solve. Why not just have some kind of metal grid in ...
3
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1answer
168 views

Why are liquid ring compressors not used in a jet engine?

A question has been asked here before whether sliding vane compressors could be used in place of axial compressors on jet engines since they have a high compression ratio per stage (Why were rotary ...
2
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1answer
147 views

Are four-engined airplanes calibrated to put out the same thrust for both their inner and outer engines?

Is there a slight difference baked into the aircraft's throttle control systems or are they always pumping out the exact same thrust as each other?
2
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1answer
201 views

What “jet engine” is featured in this ad that Simone Giertz made for a phone?

Simone Giertz's video "Having Dinner With a Jet Engine/Leaf Blower" has a number of views of the turbine, on a cart, with a ducted fan attached. This side view is the best view, in my opinion. I put ...
2
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1answer
72 views

Are compressor maps for multistage compressors drawn for one blade row or the whole compressor?

Apologies if this is a stupid question. I am a little confused about compressor maps. Are compressor maps such as this one, drawn for one blade row only or the whole compressor? (source: Wikimedia) ...
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1answer
150 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 ...
10
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1answer
248 views

How does the Harrier avoid engine damage when operating from dirt fields?

The Harrier V/STOVL jet was designed in order for its users to be able to retain a functional air force even with all conventional airports destroyed; to this end, it can take off from, and land in, ...
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2answers
196 views

What is a jet engine's fuel flow at constant IAS?

Here is my assumption: In straight and level flight of a jet turbine engine: One IAS = One drag = One thrust = One fuel flow Therefore, the fuel flow will be approximately the same for a ...
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0answers
42 views

Is there a way to determine maximum rpm for axial compressor due to material limitations?

I'm looking for RPM to Stress relation to determine maximum rotational speed that compressor/turbine blades can have without undergoing deformation due to centrifugal tensile stress. I've come come ...
25
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2answers
4k views

Do multi-engine jets need all engines with equal age to reduce asymmetry in thrust and fuel consumption arising out of deterioration?

Let's assume, one of the engines on a twin-jet needs replacement and the jet is is fitted with an old engine and a newer engine after the due replacement, the older engine would tend to produce less ...
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1answer
233 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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4answers
170 views

On a bypass engine does the bypass air travel faster or slower than core air?

Using the convergent /divergent duct theory the low pressure cold stream bypass air would travel faster but I read on a web page that the bypass air travels much slower than core air. But again using ...
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40 views

Non-dimensional variables choked nozzle

I understand that a choked nozzle removes the dependance on the static pressure $p_a$ because if M>1 in a choked nozzle then waves cannot travel upstream in the nozzle (as explained in the paragraph ...
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1answer
174 views

How are compressor blades connected to the shaft in turbojet engines?

The below figure is about rotor and stator blades of compressor . How these are connected to the compressor shaft in jet engines ?
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2answers
4k views

Why don't modern jet engines use forced exhaust mixing?

Jet engines are noisy[citation needed] - even a modern high-bypass turbofan is still deafeningly loud compared to pretty much anything except the even-louder low-bypass turbofans or a turbojet (much ...
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5answers
1k views

Are any jet engines used in combat aircraft water cooled?

Are any jet engines used in combat aircraft water cooled? If they are not, and instead are air cooled, how can the engine ensure consistent cooling? Wouldn't the airflow passing through whatever ...
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3answers
144 views

Efficiency of Flyboard engine

From what I understand (not much), you need good specific impulse to travel long distances with, say, flyboard. I know that RP1 has good specific impulse. I wonder if he used it, and what type of ...
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0answers
24 views

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
385 views

How does an engine work when an airplane has $v=0$ on the ground?

I mean, for a turbofan: $$ T= \dot m_{air,h} (1+f) v_{e,h}+ \dot m_{air,c} v_{e,c}- (\dot m_{air,h}+ \dot m_{air,c} ) v_0+ (P_{e,h}-P_{amb} ) A_{e,h}+ (P_{e,c}-P_{amb} ) A_{e,c} $$ but $$ \dot m_{air}...
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2answers
178 views

Can we trade some efficiency to curb high-altitude emissions?

Considering our problematic issues, Emissions at high altitude Contrails ~10,000 premature deaths per year from airline emissions This is an area of concern where it's worth asking some stupid ...
3
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2answers
225 views

From which stages is the bleed air from a GE90?

I'm doing a university project on the GE90-115b engine and I'm having a hard time understanding this EASA type-certificate data sheet. In particular I can't figure out the air bleed extraction section ...
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1answer
293 views

Is this plane safe to fly on? The turbine blades look damaged [closed]

While waiting for a recent flight, I observed this aircraft with what appear to be rather worn turbine blades. Is this close to being a safety issue or is it purely cosmetic?
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4answers
428 views

What would be the impact of replacing the engines on the 737 MAX, not just reworking MCAS?

There has obviously been a lot of focus on the MCAS failure following from the 737 MAX crashes. However, the MCAS appears to be a compensating control for design decisions, specifically the ...
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0answers
109 views

Do rotating deflagration engines exist?

Pulsejets (which could have been called pulse deflagration engines) rely on pulsed deflagration to generate energy and thrust. Their pulsed mode makes them hideously loud and rather inefficient, but ...
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2answers
60 views

Engine Oil Consumption limits part of certification?

Does anyone knows if Engine Oil Consumption limits are part of the engine certification requirements?
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3answers
267 views

Can a gas turbine be able to switch from torque to thrust?

Can a turbine engine be switched from providing torque (like a helicopter) to the rotor to transfer power to provide exhaust thrust (like a jet plane)? Related: BV-347 upgrade this way?
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2answers
230 views

When are more engines better than not on a plane?

A model of this airplane was used to carry a space shuttle. In this picture below the airplane had a few extra engines added since then. How is the number of engines decided on an airplane? Why not ...
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3answers
221 views

Is it better to have the engines center or apart on a plane?

Are there any advantages or disadvantages to having the engines closer or farther to the center of the plane? How is the ideal engine spacing determined length or span wise for performance? Related: ...
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2answers
222 views

Why can’t the CF34 use wide-cut fuels?

The General Electric CF34 high-bypass turbofan (used primarily on the Bombardier CRJ and Embraer E-Jet regional jets), unlike the vast majority of jet engines (both civil and military), is not ...