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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19
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3answers
17k views

Do F-22's use cartridge start to start engines?

What method does the F-22 use to start its engines? In the video below, you can see a flap open and flame and steam shoot out as the engine starts to spin up. Is this an example of cartridge start? ...
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6answers
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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]
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1answer
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What were/are the military designations of the JT8D and PW4000?

Turbine engines on U.S. military aircraft, in addition to their manufacturer-given names, receive separate designations (consisting of J [for turbojets], F [for turbofans; formerly TF], or T [for ...
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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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Why would changes in jet-engine power settings not result in changes in engine loudness?

My casual AAR reading has dredged up another counterintuitive detail of aircraft behaviour, this time regarding the relationship between engine power and engine loudness: 1.16.7.3 Sound Similar to ...
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1answer
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Are centrifugal compressors/turbines less efficient internally, and if so, why?

From my related question which found a good example of a centrifugal turbine jet engine, the Henkel Hes 3. Picture Source Website (it's in Czech). Thanks to Jan Hudec for finding it. My understanding ...
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1answer
133 views

What turbine temp. would result from burning pure stoichiometrically?

I've heard that jet engine efficiency is limited by turbine temperatures---that is, the max temp. that the turbine blade alloy can withstand before weakening too much. So jet engines are run fuel-lean....
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2answers
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Does airspeed impact fuel flow?

Let's say an F-104 Starfighter is flying at sea level at 600 KIAS with throttle at 100% RPM. Then, let's say the F-104 is still flying at sea level, but the pilot reduces throttle and airspeed falls ...
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Why is the F-104 Starfighter’s afterburner thrust not greatly impacted by altitude?

Here is a page from the F-104 flight manual. It shows the flight envelope for the F-104 Starfighter with the powerful J79-GE-19 turbojet engine: I have a question regarding the shape of the ...
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1answer
322 views

If Sweden wants to export JAS39 to a 3rd country, will they have to get permission from the US govt.?

Does Sweden manufacture its own jet engine for JAS Gripen, or does it purchase engines from the USA? JAS39 C/D uses Volvo RM12 JAS39 E/F uses Volvo RM16 I read on the internet that Gripen's engine ...
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2answers
702 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 ...
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1answer
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What's the name of this part of combustion chamber and what is it for?

There are two "excrescences" Near the end of diffuser of some combustion chambers. e.g. CFM56 and F101 What's the name of this part of combustion chamber and what is it for?
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2answers
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Is this plasma-thruster experiment actually measuring thrust? [closed]

This experiment, which is being presented as an initial exploration of the feasibility of using microwave-generated plasmas in a sort of electic jet engine, has been attracting some attention in the ...
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4answers
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Is there any theoretical problem powering the fan with an electric motor [duplicate]

A question that I have been wondering about lately is whether it would be possible to power the fan in a modern hi-bypass turbofan with an electric motor and achieve performance comparable to the ...
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In general, what are the RPM ranges/differences between the various compression stages on a 2 or 3 spool (LP,IP,HP) turbojet/fan engine?

I have a general interest in jet engines and am pretty new to the topic so I wanted to toss this question into the wind as I don't have any previous experience or knowledge to pull from and haven't ...
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is boundary-layer jet-turbine a scam?

While exploring open jet turbine designs, I've stumbled upon one CAD drawing which has made me wonder. It is based on a famous Tesla turbine and its highly-efficient way of compressing the fluid. At ...
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What's this outlet of IAE V2500 for? [duplicate]

Anybody knows what is this outlet for and why it is designed in such way? Edit: On MD-90 didn't see such thingy
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2answers
249 views

What kind of test is going on in this image?

Some times we see images of jet engines on the net that have strange colors. For example take a look at the bellow image. What the operator is doing? Why the color of blades are white with red on its ...
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0answers
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What are these painted lines on the fan blades of Rolls Royce Pearl 15?

I'm not sure that they are painted lines but it looks they are. What are they for? More images:
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2answers
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What is so special about new Russian jet engine called PD-14?

I think PD-14 engine is being promoted by Russians as something extraordinary. What is so special about PD-14 that the West doesn't have? Can you explain this in layman's terms?
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Are we at peak speed efficiency for jet airliners at Mach 0.85?

The cruising speed of large jet airliners has not increased in the past four decades. The 747 cruised at Mach 0.85 and the new Dreamliner 787 also cruises at Mach 0.85 even though it was designed 40 ...
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Are variable area exhaust nozzles or variable area throats more impactful?

I was reading this NACA research paper where, while discussing an adjustable plug-type nozzle, they state: Although this nozzle did not have independently variable area throat and exit areas, as ...
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Is everything OK with engine placement depicted in Flight Simulator poster?

Does the Airbus A320neo depicted in Microsoft Flight Simulator 2020 box cover photo has the right engine in all the wrong place? Here is the snapshot: Is it only me, who clearly sees that it is way ...
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Why does the LEAP 1A HPT run at such a high RPM?

I've watched the N2 on the LEAP sit at 100% at cruise and fluctuate as high as 101%. Why does the HPT run at such a high RPM?
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1answer
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What does unmixed mean?

For a unmixed turbofan engine what does ‘unmixed’ mean in regards to the flow of air? How does this differ from ‘mixed’ also in terms of air flow ?
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1answer
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Does the flow in an afterburner have to be subsonic?

This question is prompted by the problem on page 350 of the fluid mechanics book by Landau and Lifshitz. The problem states, "A small amount of heat is supplied over a short segment of a tube in ...
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2answers
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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 ...
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2answers
227 views

Do pilots turn off the engines during de-icing?

During winter operations and de-icing are the engines (jet engines) usually in operation? If not, what is the reason for that? Also I was wondering if the engine nacelles require de-icing since I have ...
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1answer
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Why are Stratolaunch's engines so far forward?

Stratolaunch's engines hang from pylons, not under the wing, but entirely forward of the wing's leading edge. (Even farther forward than, say, the 747's.) What benefit does this have, to compensate ...
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2answers
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Why do new engines have a case with a triangular tiling pattern?

Take a look at the case of new engines such as the F-135: or the F-119: Why do they have a case with a triangular tiling pattern? Is this a new technology? A new material?
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1answer
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How does afterburner efficiency vary with thrust?

Afterburners are much less efficient than turbine engines at converting fuel into thrust, so AFAIK no jet will engage afterburner unless it is already at full throttle on the turbine. But what if an ...
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3answers
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Do afterburners use excessive amounts of fuel?

The purpose of an afterburner is to provide additional thrust, and it is obvious that more fuel is needed for that. But that is to be expected independent of an afterburner. That more thrust needs ...
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6answers
48k views

What is an afterburner and how long can a jet fly on afterburner?

I heard this word so many time in military documentary about jets, especially fighter jets, but I don't fully understand what it is or how it works. In a documentary from the Discovery Channel, all ...
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How do jet engines work?

I was doing research about jet engines, and they seem really difficult to fully understand. So, can anyone explain it in a simple way? An afterburner glows on an F-15 Eagle engine, source: Wikimedia. ...
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6answers
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On which point(s) in a jet engine does the reaction force act?

Turbojet and turbofan engines are part of a family of engines referred to as reaction engines to emphasize the fact the aircraft is pushed forward mostly by Newton's 3rd law of motion when gases are ...
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2answers
229 views

How does fuel economy quantitatively depend on altitude for a jet?

We already have a few questions and answers about the qualitative effects of altitude on fuel economy: How do I determine the best altitude to fly for fuel economy? Why does fuel consumption decrease ...
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1answer
232 views

What causes the horn-like noise during the start-up of some jet engines?

Here's the specific sound I'm talking about (it starts specifically 56 seconds into the video, as well as at 2:02 for the second engine): I've only really heard that ...
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0answers
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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 ...
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5answers
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How are off-wing jet engines transported?

One of the optional services in Rolls-Royce TotalCare is "Engine Transportation" This service includes routine transportation of engines between the customer’s main base (or designated station) and ...
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2answers
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If the intake of a running jet engine is blocked for some short duration what would be the sequence of events following it?

If the intake of a running jet engine is blocked for some short duration what would be the sequence of events following it? Will it cause any damage to the engine parts?
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1answer
197 views

How do power and thrust curves compare?

I would like to really understand why when talking about jets we care about thrust but when talking about propeller aircraft we care about power. (THRUST)="Just a force" (POWER)= work/time = ...
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2answers
3k views

What is this turbine engine panel that opens on landing?

Tonight I flew from Munich to Dortmund on an A319 and I happened to sit just above the wings and turbine on the right side. Upon landing, the turbine opened a window or panel which exposed some grid ...
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4answers
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If pilots in a A320 or 737 had a dual engine failure, would they add flaps for the landing?

Would this not be smart to do because you may come in a little fast, therefore the flaps would send you back up? Or would you absolutely want flaps in this situation
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1answer
150 views

Is Flight Idle a constant?

Is "Flight Idle" for a jet engine a constant N1% value or does it vary with Altitude, and OAT?
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1answer
112 views

Can ramjets reach higher thermal efficiencies than gas turbines?

Since a ramjet isn't constrained by turbine inlet temperature like a gas turbine is, it seems to me that it should be able to achieve a higher thermal efficiency, given that it's operating at a speed ...
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2answers
100 views

Is this the relationship between rpm and thrust of a Turbofan? [duplicate]

In this graph from the FAA Airplane Handbook Chapter 15, page 5: It looks like it is talking about "jet engines" but is it engine type specific or it is for both turbojet/fan/prop/shaft? It ...
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2answers
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Are large jet turbofans so easy to spin?

In this question, in the accepted answer, there is a comment by alephzero that says one can actually rotate a large turbofan's blades with one finger! Is that true, ...
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2answers
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Why would sea level static thrust have a takeoff and a maximum continuous value?

In the type certificate data sheet for a jet engine, there is this table static thrust is the thrust generated by the engine when the plane is at rest with respect to the Earth and the surrounding ...
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1answer
135 views

Why is thrust said to be constant over speed for a jet engine?

I'm just interested in some basic facts regarding flight. On reading the rather "low level" book "Understanding Flight, David F. Anderson, Scott Eberhardt), I recently came up to the ...
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2answers
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Is the well known textbook-formula for net-thrust oversimplified or do I have a misinterpretation?

In order to understand how Jet-Engines works I came across the "famous" formula for net-thrust: https://en.wikipedia.org/wiki/Turbojet#Net_thrust $F_{thrust} = Q_{out} \cdot v_{out} - Q_{in}\...

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