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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1answer
82 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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146 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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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
111 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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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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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
137 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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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
285 views

How does an engine works 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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170 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 ...
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2answers
124 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
278 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
268 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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106 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
55 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
253 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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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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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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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 ...
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Is this one of the engines from the 9/11 aircraft?

I ran across an interesting set of post-9/11 photos and I noticed this picture in particular: The closest item on the truck looks a bit like an airplane engine, but I can't tell for sure. Is it one ...
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99 views

Difference between engine rev up and run-up

Explain please the difference between these jet engine terms: rev up run up Obviously they are completely different procedures. The reason I ask this question is because I'm not a native speaker ...
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33 views

What is a jet engine tolerance for a bird strike? [duplicate]

Similar questions have been asked ; a partial answer is in 14 CFR part 33-76, stating 16 small birds ( 85 g) must be tolerated . But what other qualification tests are there ; for medium and large ...
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260 views

Does the auto thrust at takeoff compensate for asymmetric engine characteristics?

When a percentage thrust has been determined for take off the auto thrust system (Airbus) or the auto throttle (Boeing) will send the data to the engines FADECs to provide the required thrust. When ...
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Would a long pole help stablize a jet pack?

Jet packs are classically worn like a book-bag on the back. Would it be more stable if the exhaust ports were separated? Would the jet pack be easier to control if the turbines were at the ends of a ...
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1answer
223 views

Is it normal for a Boeing 757 engine to bounce under its fairing?

Earlier this week I was on a 757 flight from SFO to JFK and the right engine was bouncing under the fairing under mild turbulence, and really moving 2+ cm under moderate turbulence. Is that in any way ...
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How (often) are jet engines cleaned?

In the on-board magazine of my today's flight, there was a report on how fuel efficient the airline flies. They accomplish this by new scitimar winglets, daily optimized route planning, and regular ...
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138 views

What is the difference between an engine “shut down”, “cut-off” and “cut down”?

Explain please for non-native speakers the difference between these engine (jet or piston) terms: shut down cut-off cut down I'm studying at a civil aviation university to become a pilot and a ...
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Is it possible to overheat or damage the engine on an F-16?

The MiG-25 can supposedly damage its engines by commanding too much thrust and gaining too much speed. Somewhere around mach 3 damage to the engines is likely, I believe. What about the F-16? What ...
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Why do airplanes use an axial flow jet engine instead of a more compact centrifugal jet engine?

Axial flow jet engines take up a lot of space. Centrifugal jet engines create high pressure. Can you create a centrifugal air pump that pushes as much air as a axial jet engine. Centrifugal air ...
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Would jet fuel for an F-16 or F-35 be producible during WW2?

I understand that different types of engines use different types of fuel, and as the description of the [jet] tag says, turboprops and jet engines use different types of fuel. So if – like in the ...
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Why do the inlet cones on an SR-71 retract at higher speeds while the one on a MiG-21 extends at higher speeds?

As shown by this illustration in the SR-71 flight manual, its inlet cones (spikes) retract as its speed increases: (source) Meanwhile, the Wikipedia page for the MiG-21 describes the opposite ...
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269 views

Are turbine and compressor blades and vanes cast or forged?

I was wondering how blades and vanes are typically made in commercial jet engines. Would you typically use investment casting to make compressor blades or just in the turbine section to accommodate ...
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133 views

Why use turbofan engines for high altitude flight?

I noticed that a lot of high altitude aircraft have turbofans for engines. So I researched and figured out that turboprop engines are more efficient. But most high altitude aircraft like the Global ...
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45 views

How does Mach number of Jet engine vary with respect to Compression Ratio?

How does the performance of jet engine vary with Compression ratio. What are the variables that affect the Mach number of Jet engine.
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Can a protective mesh protect engines from bird strikes? [duplicate]

Can a protective mesh be installed on the front of the engines to stop birds from entering the engine and causing damage?
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8k views

Has a commercial or military jet bi-plane ever been manufactured?

Are there any, or have there ever been any commercial/military jet bi-planes? What would be some of the major advantages vs disadvantages if one was built? Electric radio controlled ducted fan model. ...
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1answer
183 views

How did this Vampire's takeoff damage the runway so much?

This appears to be real, but, what's the cause? Aircraft is a DeHavilland Vampire on takeoff from a small airfield, but the runway's surface disintegrates from jet blast Full file at https://i.imgur....
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1answer
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How heavy are turbofan and turboprop propeller blades?

How heavy are the blades from Turbofan (CFM56-5B, RRTrent800, PW4062A) and Turboprop (PW127M) engines? Is there a general appromixation like $$ m_\mathrm{Fan} = 0.1 \times m_\mathrm{Turbine} $$ ...
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216 views

Why does the DC-8-70 have the same MTOW as the DC-8-60, despite its more powerful engines?

The DC-8-70 is a more-or-less straight reengine of the DC-8-601, replacing the obsolete JT3D-3B low-bypass turbofans of the DC-8-60 with the CFM56-2C1 high-bypass turbofan. According to Wikipedia, ...
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How to measure thrust produced from combustion chamber of Gas Turbine Engine?

I'm conduction a scale model experiment of thrust production in combustion chamber by using different types of fuel source. Comparing the thrust produced by using hydrogen gas, kerosene and petrol. ...
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1answer
134 views

Is there any recorded instance of a passenger's hat or scarf being blown into an aircraft's engine?

Passengers climbing the stairs into an airliner are often subject to gusts of wind; I've had to hold onto my own scarf in the past. It doesn't seem beyond the bounds of probability that a passenger'...
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Oultlet vane guides

I have looked around the web and I could not fine this information. How many vanes are there for the CF6-80 and the CFM-56? Is the count dependant on anything particular, such as fan diameter?
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Does the person directing the plane to parking not risk getting ingested by a jet engine?

According to answers in this post, a jet engine can suck a human into its engines, even on idle power. Aircraft use their engines post landing taxi and into their parking space, and I notice people ...
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1answer
123 views

Which is better a push fan, a pull fan or both

intricate examination of modern by pass jet engines is despite where it is mounted, they use a pull fan configuration to generate thrust, which set up the most efficient, a pull fan or a combination ...
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What are the advantages/disadvantages of in-fuselage engines (eg most fighter jets) vs wing/fuselage mounted engines?

Most modern jet fighter designs incorporate their engine(s) within the fuselage, while most other medium/large aircraft mount them either under the wings or on the rear fuselage. What are the ...
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150 views

Jet engine throttle-down time

Apparently airline jet engines lose ~80% of their thrust within 1 second after fuel is cut. However this seems to conflict with long throttle-down times noted in another question. This lead to a ...
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115 views

How to apply the TO/GA time and EGT limits?

If there is a published 1) EGT limit and a 2) TO/GA time limit, which one should be applied when the EGT is well below the EGT limit and possibly even below the 'max continuous' EGT. Particularly with ...
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How does the power distribution change for a turbofan engine from being stationary to going at full speed?

I have found out that a turbofan engine of say an F-16 is producing zero power when stationary since $Power = Thrust × Velocity$. But assuming that the engine is producing the same thrust, it appears ...
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4answers
2k views

Are taller landing gear bad for aircraft, particulary large airliners?

Buiding larger engines for larger aircraft as opposed to smaller but many engines has proved to result in more fuel efficiency. Having established one of the main drawbacks or impediments to building ...
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Does the P&W F100 turbofan engine of the F-16 really produce this much power?

I've been trying to calculate the power a P&W F100 engine on a F-16 is producing using some of the available data on thrust and velocity and I ended up with a number that I want to confirm. Here's ...