Comments
Aviator506 t1_irozpeh wrote
Yup, but the concept is still very simple at its core. Follows the same 4 stages of a traditional internal combustion engine like what's in most cars. Suck, squeeze, bang, blow.
The fan and the outer stages of the compressor is driven by the turbine and sucks the air in
The inner stages of the compressor squeezes the air.
Fuel is mixed in and goes bang in the combustion chamber
The burnt exhaust gas blows out the back and spins the turbine
Turbine spins the fan and compressor and the cycle continues.
brainblasttt t1_irpho3i wrote
It’s funny cause even in the military when they teach you about jet engines they still teach you “suck, squeeze, bang, blow” instead of the proper “intake, compression, combustion, exhaust”
WavingWookiee t1_irqnolx wrote
I was very disappointed when I was doing an engineering seminar with some school kids and I put a big picture up of "Suck, Squeeze, Bang, Blow" related to an engine and I didn't even get even a stiffled snigger, I worry about the next generation! When I was in school, had someone come into class and put that up, I'd have been howling and quite possibly asked to leave the classroom!
julie78787 t1_irqud4l wrote
That's been going on for a very long time.
zutonofgoth t1_irpbsnh wrote
It's important to note there is more accelerate than squeeze. It's almost an order of magnitude less than a car engine. The back end of the jet is open with only some blades blocking the exit of the heated gas.
Some people get the idea the pressure is massive but it's more like bike tyre pressure, so jet engine shrouds don't need to be very strong.
straighttoplaid t1_irpgao3 wrote
Modern engines can run pretty high compression ratios. The GE9X is advertised as having a 61:1 overall pressure ratio. I don't think you're going to see ~900 psi in a bike tire.
zutonofgoth t1_irpquv6 wrote
The compression ratio is the difference between the static air pressure at the front of the engine and the dynamic pressure at the rear of the engine. The dynamic pressure includes velocity in the calculation. It's not really comparing apples with apples. So you can not just multiply the values out.
900psi is more like rocket engines?
julie78787 t1_irqujss wrote
A lot of rocket engines have maximum pressures in the combustion chamber of 200-300 bar, so 3,000 to 4,500 PSI.
Aviator506 t1_irpfbmr wrote
Yeah, most of the squeeze is done by the forward momentum of the engine through the air. And at a certain speed (~mach 3) you don't even need compressors, it will act as a ram jet, which is what the SR-71 would do as well as the fictional DarkStar in TopGun Maverick. It's certainly MUCH more complicated than how I explained, I just did the basic principles of it.
straighttoplaid t1_irpggj7 wrote
> Yeah, most of the squeeze is done by the forward momentum of the engine through the air.
That is not true for commercial engines.
Aviator506 t1_irpx2ly wrote
High bypass turbo fans like airliners do get a significant bit of the compression from the forward momentum. They will never be able to function like ram jets, but the momentum makes a big difference especially at high altitude where the air is less dense and there isn't as much to suck in from the fans/compressors alone. The high bypass engines of the airliners will function much more efficiently at high altitude because of this than that of a low bypass military fighter, however it won't be able to achieve as high of a top speed as that same fighter under the same conditions. Basically the low bypass gets the advantage of speed while the high bypass gets the advantage of fuel efficiency, but both greatly benefit from momentum based compression.
KGandtheVividGirls t1_iruxjqu wrote
Think what you’re saying here is engine pressure ratio, or EPR. Ratio across the entire engine, not at a particular location, or station. The speed of the air doesn’t change that much after hitting the inlet and first stage of the compressor. A series of blades do accelerate the air then the air passes through a set of stators which are divergent ducts which slow the air converting that energy into pressure. This happens across multiple stages. At the end of the compressor is a diffuser which acts like an extra special stator. Air is at the highest pressure here. On a large modern engine it could be 800psig and over 1000F. This is simplified, there are things that need done with a compressor to get it working across the operating range.
rafaeldiasms t1_irpr3cz wrote
Suck, squeeze, bang, blow. So, just a regular Saturday then
Wasabi_Guacamole t1_irqekiy wrote
You get it regularly? Lucky lad.
julie78787 t1_irquege wrote
I drive an electric car. Explains why I'm not having any fun :(
Awellplanned t1_irqwo3c wrote
You are just soaking. That’s the Mormon version.
mcampo84 t1_irrd46f wrote
Guy’s gotta work, amirite?
ViolaPurpurea t1_irqjetz wrote
> the concept is still very simple at its core.
I see what you did there!
ChuckFerrera t1_irr84da wrote
Mostly correct. The compressor is directly attached to the high pressure turbine (HPT) via the high pressure shaft. The low pressure turbine (the 4 stages aft of the HPT), are directly connected forward to the high bypass fan through the center of the engine via the low pressure shaft. That is, the compressor and the HPT spins independent of the LPT and fan.
Clay_Statue t1_irp3ab5 wrote
I'm impressed that they could figure this out 80 years ago with slide rules and data tables.
RJFerret t1_irp3q8h wrote
Easier as slide rules don't auto-update in the midst of needing them.
kled7 t1_irp75wu wrote
It’s not so much the math. It’s testing. The math is pretty straightforward, but it was the prototyping and testing that got the engines we have today.
HEBushido t1_irp93tc wrote
You need the components to actually fit the math
Stealth_NotABomber t1_irpbq2s wrote
And the material sciences/metallurgy to make parts that can withstand the heat and pressure.
gnusmas5441 t1_irpczq6 wrote
If I understand correctly, another challenge is finding and shaping materials that can withstand the forces generated by the fan blades spinning very fast and having to withstand, among other things, the forces generated by their tips moving much faster than their base at the center if the engine.
evanc3 t1_irpejoo wrote
Plenty of materials that can do this, the trick is to get one that doesn't creep over time because the blade tips are remarkably close to the engine wall (tip clearance)
slater_just_slater t1_irq2fgg wrote
Creep is why most 1st stage turbine blades are single crystal. Fun fact, single crystal blades are "grown" not cast.
They are also the most boring thing ever to look at under a metallograph.
evanc3 t1_irq2u47 wrote
Still blows my mind!
But yeah I can imagine lol
slater_just_slater t1_irq4gst wrote
What is interesting is that it's the same principle to how single crystal silicone is grown for microchip substrates. However the blades are hollow.
Since they have no grain structure, nothing responds to an acid etc, on a metallograph it's just a white blob.
They do have a thermal barrier coating (TBC)
One of my jobs as a process engineer at Rolls Royce was the TBC coating. If you are bored here is a link about it.
Sands43 t1_irpaqbm wrote
Also metallurgy and lubricant technology
NativeMasshole t1_irp6gcs wrote
Math took a hell of a lot more manpower than it does now. It's crazy to think how much labor supercomputers save us compared to calculating by pen and paper.
[deleted] t1_irpcdn1 wrote
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Archmagnance1 t1_irpkcq4 wrote
That's saving labor. You need less man hours to do the same amount of calculations with the same amount of accuracy. If you do more with the same amount of labor, you're still saving labor compared to if you didn't have supercomputers.
Imagine how many man hours it would take to do a complex weather simulation to track the probability path of a hurricane? How many teams would you need working on the problem to give updates every 2 or 3 hours? Using information that is old and probably no longer valuable when they started?
[deleted] t1_irpp8uo wrote
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Archmagnance1 t1_irpu9s2 wrote
That's still saving labor though. It wouldn't be done because it takes too much labor to do then verify.
[deleted] t1_irpuew6 wrote
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Kumqwatwhat t1_irpnu64 wrote
> Thermodynamics are weird.
You just summed up like my whole third year of university.
SatanLifeProTips t1_irpjcrb wrote
Turboprops work the same way. It is more efficient to take a shaft drive output out a jet engine than it is to shoot all the air through the jet engine. Running a prop or a ducted fan is the most efficient way to do it
The prop IS slightly more efficient than the ducted fan at lower speeds/altitude, that’s why you see them on lower speed aircraft that do regional flights like the (miserable to be inside) Dash 8.
But get up to cruising altitude and the ducted fan is king.
Apotropaic_Sphinx t1_irppu1t wrote
Also you can reverse thrust on a turboprop. The C-130 can literary do a 3-point turn while taxiing.
High-bypass jets do have thrust reversers, but they're more for slowing down while landing.
slater_just_slater t1_irq2mxh wrote
Another big issue is blade tips going supersonic. It makes it really really loud. The Tu-95 is ungodly loud because of this.
InitechSecurity t1_irpfhr5 wrote
How Jet Engines Work https://youtu.be/L24Wf0VlTE0
Bananenweizen t1_irqhsll wrote
In principle, it is not different than your car engine. Burn fuel to get energy available, then use this energy to spin parts of your vehicle designed to push the vehicle forward when spinning. Only instead of ICE and wheels pushing against the road (with a lot of gears in-between) you have a turbine and a propeller pushing against the air (while mounted in the same axle).
pzerr t1_irrv9jy wrote
The fan at the front is really just a form of a turbojet with normal propellers. It is just propellers with a shroud around it.
Fun fact. The shroud makes these engines slightly less efficient but people dislike open propellers.
ash_274 t1_irny6qk wrote
Yep. The newest 777 model has insanely massive fans. The engines are wider than the body of a 737.
twoinvenice t1_irs3iu5 wrote
They look not so big when you are sitting in an airport waiting to board, or in a seat on the plane, but I distinctly remember the first time I deplaned onto the tarmac next to a 777 and walked past one of the engines. All I could think was “fucking hell, that is a goddamn big engine.”
dyskinet1c t1_iroh3t5 wrote
Also, a Turboprop has a jet core but uses all the power to turn the propeller.
InevitableRip8968 t1_irp3kxd wrote
Turboprops are considered the most efficient of all the different turbines, burns less fuel than the rest. But you trade speed for the efficiency.
allergic2Luxembourg t1_irq5k04 wrote
That's an oversimplification. Turboprops are more efficient at certain altitudes and Mach numbers, and jet engines at others. Thus why turboprops are used in shorter-range applications and jet engines in longer-range. The industry is most certainly choosing the right engine for efficiency as one of the major driving factors (though weight is also considered).
LazerWolfe53 t1_irqnzjc wrote
I feel like altitude is missing from most of these conversations. IIRC the high bypass jet engines get most of their thrust from the jet at high altitude.
IvorTheEngine t1_irqpkyt wrote
And flying higher means the air is thinner, so there's less drag. So even if the engine is less efficient, the overall flight can be more efficient.
dyskinet1c t1_irqttx5 wrote
Turboprops are also limited to rotation speeds where the tips of the blades are below the speed of sound.
If the blades rotate above the speed of sound, the tips generate shock waves that reduces the efficiency significantly.
barath_s t1_iryxaky wrote
> Turboprops are also limited to rotation speeds where the tips of the blades are below the speed of sound.
Laughs in Tu-95 and XF-84 Thunderscreech
> the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run. Coupled with the already considerable noise from the subsonic aspect of the propeller and the T40's dual turbine sections, the aircraft was notorious for inducing severe nausea and headaches among ground crews. In one report, a Republic engineer suffered a seizure after close range exposure to the shock waves emanating from a powered-up XF-84H
> The tips of the fan blades of a modern turbofan also move at supersonic speed, so the supersonic propellers on the Tu-95 do not create a direct disadvantage.
also
> The Tu-95 is one of the loudest military aircraft, particularly because the tips of the propeller blades move faster than the speed of sound.
Doggydog123579 t1_irzbsw1 wrote
WHAT DID YOU SAY? I COULDN'T HEAR YOU OVER THE SOUND OF MY EARS MELTING.
barath_s t1_is0chgy wrote
SERVES YOU RIGHT FOR LOOKING AT THE ARK OF THE COVENANT BEING IN THE VICINITY OF THE THUNDERSCREECH
OlDirtyTriple t1_irp9mj9 wrote
They're also incredibly noisy. Passengers would need hearing protection.
8bitslime t1_irpcb1t wrote
The Q400 exists and passengers certainly don't wear any hearing protection. It does have a lot of features in the realm of noise reduction inside the cabin though, much more than a turbofan airliner.
camwhat t1_irqklnp wrote
I tend to fall asleep quickly in Q400s. Ironically most of my family does so
Zebidee t1_irpmmkf wrote
>They're also incredibly noisy. Passengers would need hearing protection.
What are you even talking about??
There's thousands of turboprop passenger planes operating every day without passengers wearing hearing protection.
barath_s t1_iryxkfd wrote
Probably talking about turboprops where the prop tips are supersonic. These tend to be noisy.
Such as the Tu-95 and XF-84 Thunderscreech
> the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run. Coupled with the already considerable noise from the subsonic aspect of the propeller and the T40's dual turbine sections, the aircraft was notorious for inducing severe nausea and headaches among ground crews. In one report, a Republic engineer suffered a seizure after close range exposure to the shock waves emanating from a powered-up XF-84H
also wiki for Tu-95
> The Tu-95 is one of the loudest military aircraft, particularly because the tips of the propeller blades move faster than the speed of sound.
Note that turbofan tips for modern engines may also be supersonic
Reascr t1_irpbxeq wrote
Turbofans are plenty loud too, you still need hearing protection for them. But commercial aircraft go heavy on sound deadening for passenger comfort, so even turboprop civilian aircraft aren't too bad.
Military ones though? Yeah you'll get hearing damage if you don't use something.
elmwoodblues t1_irpm20v wrote
WHAT?
FriendlyDespot t1_irplecs wrote
There are plenty of turboprop commercial passenger aircraft flying around, and while you can notice the difference, it's not really much louder inside the cabin.
Prophet_of_Entropy t1_irs2cs2 wrote
only when the props exceed the speed of sound. not every turbo prop is a thunderscreech https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech
FLEXXMAN33 t1_irrnkmm wrote
Next you'll tell me there's a tuboshaft version used by helicopters.
dyskinet1c t1_irrp6oe wrote
Next you're going to tell me there are non-aviation uses for turbines.
Boomshrooom t1_irp8jlr wrote
No, the fans are there to cool the plane down, you can tell because when they stop in the air the pilot starts to sweat.
shadowphlare t1_irrc1rz wrote
Amazing dad joke 10/10
Regular-Cranberry-91 t1_irobs6s wrote
Serious question, who don't they put like chicken wire or some kind of barrier over the intake side of the engine to stop bird strikes?
balrob t1_iroltjf wrote
Because at 600mph no wire will stop a bird. The barrier would be destroyed and parts of it will enter the engine along with the bird.
feor1300 t1_irov9ep wrote
On top of what others have said such a mesh would also disturb airflow going into the engines, think about the difference between water coming out of the end of a hose and water coming out of your kitchen tap that has that little mesh bit on the end of it. Turbulent air entering the engines increases the risk of the engines surging, and can potentially cause them to damage themselves or even fail entirely. That's a good chunk of why wake turbulence is such a big deal.
Wov t1_irodlt8 wrote
because then you just have 100 bird bits flying into the engine instead of 1 whole bird
ctothel t1_irohxmc wrote
Plus the wire mesh.
JJohnston015 t1_irp8sz1 wrote
Well, you know, if you watch those super slo-mo videos of bird strike tests, you'll see that the first fan makes a pretty good food processor.
[deleted] t1_irojfi9 wrote
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clegane t1_iroxu3y wrote
This video explains it pretty well: https://www.youtube.com/watch?v=Wm4Z7dAfrP0
Regular-Cranberry-91 t1_irr3eov wrote
Yep that explains it thanks.
danimal207 t1_irr6j5k wrote
Pratt & Whitney has a facility in Canada where frozen turkeys are launched into running jet engines.
BobbyP27 t1_irsar0c wrote
Formerly frozen turkeys. They thaw them out before they fire the into the engines, as a large block of ice is rather more damaging to an engine than a bird. The bird ingestion test is part of the type approval for all aero-engines, not just P&W.
TheNiftyReptile t1_irnxpkm wrote
This is half true. At low altitudes with higher air density most of the thrust does come from the turbofan bypass, but as altitude increases and air density decreases, it is actually the jet engine core that contributes to most of the thrust.
InevitableRip8968 t1_irothk8 wrote
This is very wrong. Even at altitude the fan is what’s creating most of the thrust. The ratio of thrust between the core and high bypass stays the same at all altitudes. The overall performance decreases at altitude due to the air thinning out.
mrkmg t1_iroxar6 wrote
Well... The ratio does shift slightly, but not enough for the jet thrust overtake the fan.
But really I wanted to add:
Performance =/= efficiency. If you take the entire system (the thrust, fuel consumption, drag, etc) there is an ideal altitude that's really high up where the whole aircraft is most fuel efficient.
This stuff is so complicated that they use entire farms of servers to calculate expected performance and efficiency of aircraft designs.
InevitableRip8968 t1_irp38q4 wrote
Can you show me proof? Bypass ratio always stays the same. This is taking in to factor if you ignore bypass ducts that newer engines use.
AudibleNod t1_irntmnx wrote
Fukkin science, man.
I never knew.
[deleted] t1_irora9i wrote
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fuzzy9691 t1_irphb7e wrote
Yes… turbine jet engines and jet engines aren’t the same. Hence turbine… it’s really a disservice that the general population call passenger aircraft ‘jet engines’ because those in the industry don’t.
I’m sure every profession has this annoying situation where public knowledge doesn’t align with actual industry terminology.
allergic2Luxembourg t1_irq5sa4 wrote
I work at an aircraft engine company and we really do call them jet engines. Properly speaking we build turbofans but those are a subset of jet engines.
ytilonhdbfgvds t1_irppc6o wrote
Yes , they do. I have a PSA for anyone with a relative who is a software engineer, we do not fix printers. Also printers are much cheaper than sw engineering hours, go buy a new one.
Gl0balCD t1_irppcua wrote
To be fair, it's one of the few industries with standardized language over the entire world.
BobbyP27 t1_irsb4zr wrote
I've worked for two different aero-engine companies, one based in Europe and one based in the US. There are significant differences in terminology between them. There is also the issue that the engines spin the other way.
elmwoodblues t1_irpmrou wrote
As a kid who lived a long time ago along a major airport final, I'm always a little surprised when civilians hear a military jet engine and comment on how loud it is.
Boomshrooom t1_irp9irk wrote
Jet engines and their principles were one of the main reasons I knew I wanted to be an Aerospace engineer.
xboxwirelessmic t1_irqptk3 wrote
I love jet engines. Such an incredibly simple concept on the surface yet so complex and capable of so much power.
GmeGoBrrr123 t1_irox752 wrote
I was flabbergasted by this too a few months ago. Just how does a “fan” create this much thrust?
Aviator506 t1_iroyjdr wrote
The fan essentially functions like a propeller that's enclosed by an engine nacelle. Just instead of the fan being turned by engine cylinders like on a traditional propeller driven piston airplane, the fan is turned by the turbines in the jet engine.
JJohnston015 t1_irp91sh wrote
It's also huge, so it has an enormous area. That means it's moving a lot of air, and thrust is a function of how much air you move, and how hard you move it.
Thecna2 t1_irphtnw wrote
This change from Low Bypass Turbofan to High Bypass occurred in the 80s. Engines prior to this point provided all/most of their thrust from the central exhaust core.
The change occurred mainly because of fuel efficiency but it did require changes. The newer type have much larger fans than the old type and thus the engines on the wings will get closer to the ground meaning some design changes (higher wings/mounts).
The fan creates the thrust because it is very big and running very fast, like a prop. No real other reason.
I worked on the old style engines as they changed over to the new style.
p33k4y t1_irqpdit wrote
>This change from Low Bypass Turbofan to High Bypass occurred in the 80s.
1970s:
- Pratt & Whitney JT9D on the Boeing 747-100 (in service 1970)
- GE TF39 on the Lockheed C-5 Galaxy (1970)
- GE CF6 on the McDonnell Douglas DC-10 (1971)
The CFM56 also started production in 1974 but did not enter commercial service until 1982.
[deleted] t1_irr5od3 wrote
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Diligent_Fact2236 t1_irrhccw wrote
Sorry, but this answer is actually the wrong one.
- The fan does move the air. The blades are an aerofoil shape, pulling the air in front of it in. Much like a normal propellor on a GA plane, where the propellors create a pressure difference behind itself and push the aircraft along. turbofans do exactly the same, but just with an enclosure around it
- Much of the air (upto 80% on some designs) goes around the compressor stages.The fan compresses all of the air (due to it's aerofoil shape pulling air in) evenly. It's only the air that goes through the core that is compressed in relation to the air around it.
- The air is not heated at all at this stage, and the bypass air temp is slightly raised by the slight compression at the fan stage, and again when it passes over the combustion chamber. The heat of the air comes from it's compression in the core.
- The exhaust velocity of the bypass air is directly controlled by how much thrust is presented to the compressor at the rear of the turbine. Say there are 3 shafts. One shaft connects the fan at the front to the low pressure turbine at the rear of the engine. The faster that the exhaust gasses from the combustion chamber spin this low pressure turbine, the faster the fan at the front spins. The other 2 shafts drive 1st/2nd stage turbines to compress some of the bypass air to direct it to the combustion chamber core
​
No doubt someone else will correct me where I am wrong, but by and large, that's the gist of how high bypass turbofan engines work
[deleted] t1_irtnebq wrote
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Boomshrooom t1_irp9etq wrote
Massive blades spinning at incredibly high speeds move a shit ton of air, beyond that its just a matter of Newtons third law. If you throw a lot of stuff out of the back at high speed, you're gonna move forward.
slater_just_slater t1_irq3c05 wrote
The fans don't actually spin very fast (compared to the compressor) fans only spin about 3000 rpm so the tips don't go supersonic. The compressor spins much faster (12,000 rpm is typical however small engines can spin much faster up to 50,000 rpm) they do this by using 2, sometimes 3 shafts in the engine (one shaft inside the other). The fan is powered by 1 or 2 turbine at the very back, the compressor is powered by separate turbines at the front of the turbine section, just ahead of the fan turbines
Boomshrooom t1_irqiqsl wrote
I'm aware of this, my point is that the fan is still spinning at a very high speed, and moves a ridiculous amount of air. 3000rpm still gives 50 rps which is very high especially given the size of the fan.
BobbyP27 t1_irsbfwc wrote
Typically the fan tips are supersonic at the design condition. Tip Mach numbers of about 1.3 are typical.
Wizatek t1_irqxbdr wrote
Compared to a small consumer pc-case fan and similar, a turbofan is running at much higher Reynolds Number, which allows you to have more aggressive aerofoil profiles for generating lift. At small scales, aerofoils do not work better than flat plates (hence insects evolved thin wings), while at medium scales you need aerofoils that can keep a laminar flow attached. At high reynolds numbers, you have a similar effect as the dimpled golf ball keeping the air from detaching and recirculating early when it passes over the aerofoil of the fan blade, so you can give it an aggressive, high thrust shape.
Of course you cannot put a very high lift aerofoil near the blade tip as you would otherwise run into problems with locally supersonic flow creating lots of drag.
BobbyP27 t1_irsbpb4 wrote
Because density plays a role in Reynolds number, for smaller engines at high altitude (low air density), you can't always count on the flow being turbulent. Laminar flow and transition to turbulence are significant design issues for things like business jet size engine compressors.
coop_dogg t1_iroy2o8 wrote
This image bout to make me act up
TacticalTilePlacemen t1_irq3nsi wrote
In 1/2mv^2 for a given amount of energy from the combustion of fuel it is easier to move more mass at a slower speed than it is to move less mass at a higher speed hence the drive towards high bypass engines. This starts to not work so much at higher speeds when drag (function of velocity squared) and shocks (which are exasperated by the fact that large fan blades go supersonic before the aircraft does for turboprops) become real obstacles that necessitate lower bypass ratios.
Nafeels t1_irpmvdx wrote
The development for the turbofans throughout history were turbulent for the most part (no pun intended).
For example, the Rolls-Royce RB211 program nearly killed the company trying to achieve the necessary efficiency goals required by the Lockheed TriStar program. They had to bring in a lot of veteran engineers from WWII to figure out the fan blade designs.
slater_just_slater t1_irq3jgr wrote
It paid off in the end. The RB211 became one of the best sellers for Rolls and the basis for later engines such as the Trent.
InappropriateTA t1_irov5uu wrote
Isn’t the thrust generated by the turbine in the exhaust path, though?
Or are you contrasting this with thrust from exhaust impulse(?) like a rocket engine.
kassienaravi t1_irovupd wrote
Thrust is not generated by the turbine. Turbine spins the compressor and fan. Thrust is generated by the fan and by the combustion of fuel in the combustion chamber.
InevitableRip8968 t1_irp5jyq wrote
20-30% of the thrust comes from the core, or turbine. The other 70-80% comes from the fan.
857477459 t1_irp92jw wrote
His point is all the energy is coming from the core. Its just being captured by the turbine and used to spin the fan.
InappropriateTA t1_irozjfu wrote
Fan via link to the turbine, I mean.
InevitableRip8968 t1_irp5fv0 wrote
Thrust is generated by the core and the high bypass. It’s around 70% thrust from the high bypass and 30% from the core. On newer engines it’s getting closer to 80% from the high bypass and 20% from the core.
Thecna2 t1_irph6z8 wrote
In this case the term 'jet exhaust' mean the exhaust after it leaves the engines.
phasedsingularity t1_irqmyb7 wrote
Thrust is generated by the internal forces in the engine - namely the exhaust and bypass gases pushing against the nozzle.
belovedeagle t1_irpj0qk wrote
Well, yeah, where did you think the thrust was being generated? They're not shooting flames out the back so, a priori, the reaction thrust has to be low to none. I think I'm more surprised that the reaction thrust is as high as 1/4 of the total thrust. I always imagined it was basically a turboprop but the primary fan helped the compressors out a bit but I guess that's not quite right.
PM_UR_NUMBER_IN_HEX t1_irqj9gl wrote
Flames would come from an afterburner (which would need to be activated) , a low bypass jet engine doesn't normally shoot flames either.
Inquisitivefish t1_irq1o81 wrote
Technically the fan is connected to the turbine... which is powered by the exhaust.
Suck squeeze bang blow. All gas powered engines use this concept.
MacDegger t1_irqjgdz wrote
Kinda the same for a helicopter: those blades 'pull' the helicopter up, they do not 'push' it up :)
simonannitsford t1_irqkou5 wrote
Do this mean the the aircraft are effectively being pulled along, rather than being pushed along?
blue-november t1_irqo9yu wrote
This isn’t anything special. Gas turbines produce more power than they exhaust so the excess is shoved into a fan at the front, which happens to come out the same hole.
DurinsBane1 t1_irqpd88 wrote
Look up how scram jets work, it’s even crazier.
retarded_player t1_irqpoe2 wrote
"In a high-bypass design, the ducted fan and nozzle produce most of the thrust."
Can anyone share a reference to an article that backs up OP's claim? I'm genuinely curious. I've always assumed the bypass thrust was generated from a venturi-like interaction between the nozzle exhaust and the bypass airflow. I'm open to being schooled though.
[deleted] t1_irr6wzu wrote
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[deleted] t1_irr3zcu wrote
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Own-Reflection-8182 t1_irr5v25 wrote
Turbofan engines produce 80% of thrust from the fan. The jet engine is there mostly to power the fan.
Smartguyonline t1_irr6xf3 wrote
That’s why it’s called a turbofan and not a jet engine.
AnthillOmbudsman t1_irrgkhf wrote
If there's no combustion in the forward fan, why not just take the cowling off and have the forward fan running like a propeller? Would this still work? I know there's propfans but I still want to know what happens if you take the forward fan cowling off a GE90 and run it that way with the fan exposed.
timberwolf0122 t1_irrhvh8 wrote
It would work, just not as well. The ducted fans are upto 90% more efficient than a free fan and quieter too. Additionally the duct protects the fan from debris and protects ground crew from accidental contact
PossiblyLinux127 t1_irrhu99 wrote
Its called a turbo fan. The bigger the fan the more efficient the engine is. That's why the engines keep getting bigger
[deleted] t1_irrovkf wrote
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DirtySingh t1_irstk5n wrote
I just always assumed the blades pull the plane forward not the back of the engine pushing it forward
Good-Cardiologist679 t1_irowqz9 wrote
And that the fans inside turn On at different speeds. Saves fuel.
SundogZeus t1_irp6ydl wrote
Yes. But only in geared turbofan engines. Like the Pratt and Whitney 1900 series engines. This enables the fan to rotate more slowly compared to the high pressure compressor. Much more efficient than previous engines
Good-Cardiologist679 t1_irp78er wrote
I was trying to find the article thank you.
InevitableRip8968 t1_irp5ln6 wrote
No
Good-Cardiologist679 t1_irp7a93 wrote
You don’t know anything clearly.
Ok-disaster2022 t1_irnxgcc wrote
Yeah but it needs the entire system to achieve that. Thermodynamics are weird.