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Jet Engine's And Breakthrough Development  
User currently offlinejorisdebont From Netherlands, joined Sep 2012, 10 posts, RR: 0
Posted (1 year 10 months 2 weeks 4 days 16 hours ago) and read 6977 times:

Hi guys,
I am doing a project about aviation. And right now I am working on the engine part of my project.
I was wondering which breakthroughs in engine technology where vital in the development of the jet engine?
For prop- and jet engines, and possibly ramjets but since they are still in the prototype phase I won't be focusing on them.

Could you guys help me?
Thanks


Aviation is proof that given, the will, we have the capacity to achieve the impossible.
28 replies: All unread, showing first 25:
 
User currently offlineAKiss20 From United States of America, joined Sep 2007, 609 posts, RR: 5
Reply 1, posted (1 year 10 months 2 weeks 4 days 13 hours ago) and read 6986 times:

Like a lot of things there weren't many monumental breakthroughs but a steady progression, but some of the highlights/most important things were

-Development of viable aero-compressors. Compression is about the most difficult aspect of the jet engine, in terms of stability and efficiency. The earliest engines had ridiculously inefficient compressors, but they were good enough such that a sustainable Brayton cycle could be achieved. Compressor efficiency has been a focus of much research ever since

-Turbine cooling: Engine efficiency or specific power directly scales with turbine inlet total temperature (Tt4). Even the hottest engines today run around 2000K, which is less than 50% of the ideal Brayton cycle limit. Pushing Tt4 is by far the best means of gaining efficiency or specific power. Tt4 is limited by the the turbine blades as they simply will melt from the temperatures. The earliest engines had just normal blades and were thus quite Tt4 limited. The development of film cooling permitted pushing Tt4 past metal melt temperature

-Turbine material/coatings: As with cooling, a lot of focus has been put on developing better materials for turbine blades. The ultimate goal is to keep strength while increasing melt point so that Tt4 can be increased. Thermal coatings also are used to reduce the heat transfer coefficient.

-Multi-spool designs: The original engines had single spools which meant that all parts of the compressor are operating at the same physical speed. It is very difficult and inefficient to use the same speeds for the initial compression from ambient and later down in the compressor. Multi-spool designs allow the low-pressure compressor and high-pressure compressor (and similarly the turbines) to operate at different speeds which are much better for the given flow regime. Rolls has for quite a long time had a 3 spool design which separates the fan from the rest of the compression system. This is advantageous as the fan wants to spin much slower than even the LPC, especially as bypass ratio/fan-diameter increases. The 3 spool design adds weight and other mechanical complications though. PW recently has developed the geared-turbofan to achieve the same thing with a 2 spool design. The jury is still out on that design to some extent

-Move from Turbojet to Turbofan: Original engines were pure turbojets which means all thrust comes from air that has gone through the core. Turbofans divert a portion of the air (dictated by the bypass ratio) from the core, thus it only receives modest speed increases from the fan and fan OGVs. The reason for this is that it is more efficient (propulsive efficiency not thermal) to accelerate a lot of air a bit than a little amount of air a lot to get the same thrust. Propulsive efficiency scales with BPR, but the larger the BPR, the larger the engine typically, and also the larger the fan (this can introduce issues with tip mach numbers and wave drag/noise). Almost no modern engines are pure turbojets, even military engines are low-BPR turbofans.

Those are some of the highlights. If you want more info, feel free to PM me!



Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are
User currently offlineMarkC From United States of America, joined Apr 2006, 259 posts, RR: 0
Reply 2, posted (1 year 10 months 2 weeks 3 days 19 hours ago) and read 6985 times:

Well, looking at history, I would say:

1. The bypass duct. This made engines move air outside the combustion air for much better efficiency.

2. Varible vanes. This is used in the first stage of the HPC stators, and is similar to the wastegate of a turbo to limit the air into the engine at throttle increases and decreases.

3. Annular combustor. Better than burner cans.

4. Huge bypass ratios. Now, 10:1 is not a problem. Better efficiency. Slow fan. High temp core. All good.

Thats my take.

Mark


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 3, posted (1 year 10 months 2 weeks 3 days 14 hours ago) and read 6985 times:

In addition to all of the above...FADEC.

Tom.


User currently offlineAKiss20 From United States of America, joined Sep 2007, 609 posts, RR: 5
Reply 4, posted (1 year 10 months 2 weeks 3 days 12 hours ago) and read 6979 times:

Quoting tdscanuck (Reply 3):
In addition to all of the above...FADEC.

We don't need your stinkin' FADEC, my hydro-controllers work just fine!

Said no engine manufacturer ever 



Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are
User currently offlineweb500sjc From United States of America, joined Sep 2009, 739 posts, RR: 0
Reply 5, posted (1 year 10 months 2 weeks 3 days 12 hours ago) and read 6979 times:
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Quoting AKiss20 (Reply 1):
-Turbine material/coatings: As with cooling, a lot of focus has been put on developing better materials for turbine blades. The ultimate goal is to keep strength while increasing melt point so that Tt4 can be increased. Thermal coatings also are used to reduce the heat transfer coefficient.

why not use something similar to the space shuttle tiles (or something like a carbon carbon coating) for the turbine?
-I Know thew are brittle, but at that point in the engine, you would be hard pressed to find a piece of debris.



Boiler Up!
User currently offlinejorisdebont From Netherlands, joined Sep 2012, 10 posts, RR: 0
Reply 6, posted (1 year 10 months 2 weeks 3 days 9 hours ago) and read 6977 times:

Thanks guys, this should help me along.
Does Fadec work something like the ECU in your car?



Aviation is proof that given, the will, we have the capacity to achieve the impossible.
User currently offlineflyingturtle From Switzerland, joined Oct 2011, 2409 posts, RR: 13
Reply 7, posted (1 year 10 months 2 weeks 3 days 8 hours ago) and read 6977 times:

Quoting jorisdebont (Reply 6):



This should explain it: FADEC = Full authority digital engine control.

As I understand it, an ECU just optimizes how the car engine runs, by fine-tuning ignition and valve openings. But there is still a mechanical link between the driver and the engine (the gas pedal, for example).

With FADEC, the engine is purely controlled by electronic signals. Imagine a car where the gas & the clutch pedal as well as the gear lever have no mechanical links to the engine whatsoever - only electronic ones.



David



Keeping calm is terrorism against those who want to live in fear.
User currently offlineAKiss20 From United States of America, joined Sep 2007, 609 posts, RR: 5
Reply 8, posted (1 year 10 months 2 weeks 3 days 6 hours ago) and read 6977 times:

Quoting web500sjc (Reply 5):
Quoting AKiss20 (Reply 1):
-Turbine material/coatings: As with cooling, a lot of focus has been put on developing better materials for turbine blades. The ultimate goal is to keep strength while increasing melt point so that Tt4 can be increased. Thermal coatings also are used to reduce the heat transfer coefficient.

why not use something similar to the space shuttle tiles (or something like a carbon carbon coating) for the turbine?
-I Know thew are brittle, but at that point in the engine, you would be hard pressed to find a piece of debris.

The main reason is re-entry is not actually as hot as you think, peaking around 2300F (approx 1530K) which is substantially lower than what engines are running at these days (source http://www.airspacemag.com/how-things-work/shuttle_tiles.html) so using that material wouldn't be advantageous and actually probably a step back. The exact properties of turbine blade materials are among the most closely guarded secrets of engine companies, not to mention subject to classification and export control by the US Government, so I don't actually know what melt temperatures we are hitting now. I wouldn't be surprised if it is a bit higher than that though.

Also, Shuttle tiles are not really load bearing, so they don't have to be very strong. Turbine blades are spinning at 20-25,000 RPM. The centrifugal forces on those things are huge, so strength is a very big issue. Furthermore, the tiles on the space shuttle are not designed for extended heat exposure and longevity as re-entry is a 5 minute ordeal and the tiles get inspected/replaced after every flight. Can't do that with turbine blades!

Boiler plate: I am not a metallurgist so this is all speculation. Take with a grain (or 5) of salt



Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 9, posted (1 year 10 months 2 weeks 3 days 4 hours ago) and read 6976 times:

Quoting web500sjc (Reply 5):
why not use something similar to the space shuttle tiles (or something like a carbon carbon coating) for the turbine?

What AKiss20 said...shuttle tiles are basically non-structural and taking "moderate" (in engine terms) heat for a few minutes. Turbine blades are stressed extremely close to their yield strength for years. It's a whole different design space. That type of strength at heat means very very dense materials...ceramics and superalloys, not carbon composites. If we could figure out a way to encapsulate carbon nanotubes in something to keep the oxygen out that would be awesome, but that's probably a loooooong way away.

Quoting AKiss20 (Reply 4):
We don't need your stinkin' FADEC, my hydro-controllers work just fine!

Said no engine manufacturer ever

Once I realized they were running 3D cams inside those things, I totally gave up. At least I can understand code.

Quoting AKiss20 (Reply 8):
Boiler plate: I am not a metallurgist so this is all speculation. Take with a grain (or 5) of salt

You're dead on.

Tom.


User currently offlineMrChips From Canada, joined Mar 2005, 932 posts, RR: 0
Reply 10, posted (1 year 10 months 2 weeks 3 days ago) and read 6976 times:

Quoting flyingturtle (Reply 7):
As I understand it, an ECU just optimizes how the car engine runs, by fine-tuning ignition and valve openings. But there is still a mechanical link between the driver and the engine (the gas pedal, for example).

With FADEC, the engine is purely controlled by electronic signals. Imagine a car where the gas & the clutch pedal as well as the gear lever have no mechanical links to the engine whatsoever - only electronic ones.

Off topic a bit, but most modern cars (and basically every one on sale today) run a computer system that is essentially equivalent to an aircraft FADEC. With such technology as direct fuel injection, variable geometry turbochargers, throttle by wire and some of the more advanced means of variable valve control and spark control, a modern auto engine simply will not run without a computer controlling these systems; at very least, it won't be anywhere near as smooth, powerful or efficient.

Back on topic, one of the biggest things driving jet engine development these days is both a better understanding of airflow within the engine coupled with better computer simulations of that airflow as well as the materials and manufacturing capabilities to make these simulations reality.

It seems to me that we've really only just started to make inroads into realising the full potential of all three of these things working together. Granted, there have been a lot of engines that have had this applied in their design, but I can't help but think that compared to what will be going into engines such as the GE90X, everything before that is merely just baby steps.



Time...to un-pimp...ze auto!
User currently offlineAKiss20 From United States of America, joined Sep 2007, 609 posts, RR: 5
Reply 11, posted (1 year 10 months 2 weeks 2 days 22 hours ago) and read 6976 times:

Quoting MrChips (Reply 10):
better computer simulations of that airflow as well as the materials and manufacturing capabilities to make these simulations reality.

While I could write pages about how CFD and other computational models are becoming more and more relevant, I think a really cool, important, and cutting-edge aspect is that we are finally starting to be able to use LES on scales of engineering relevance (LES = Large Eddy Simulation, a category of turbulence models that are a level inbetween Reynolds Averaged Navier-Stokes (RANS) and Direct Numerical Simulation (DNS) that offer higher fidelity than what we've been using thusfar). There is a lot of work on using LES in combustor design, which has historically been more of a combination of black arts and guessing than actual science. The need for proper mixing balanced with the dangers of having high turbulence intensities entering the turbine, coupled with the fact that it is a reacting flow, make all of this very difficult to model and predict.



Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are
User currently offlineflyingturtle From Switzerland, joined Oct 2011, 2409 posts, RR: 13
Reply 12, posted (1 year 10 months 2 weeks 2 days 18 hours ago) and read 6976 times:

Quoting MrChips (Reply 10):

OT, but what you describe is still not FADEC. True, it needs computers so that the engine can run. But FADEC means that the engine is fully controlled only by electric or electronic signals. A true example of FADEC are custom-built cars for handicapped people. But for safety reasons, a mechanical link between driver and the engine is still required in series-built cars.


David



Keeping calm is terrorism against those who want to live in fear.
User currently offlineDocLightning From United States of America, joined Nov 2005, 19712 posts, RR: 58
Reply 13, posted (1 year 10 months 2 weeks 2 days 10 hours ago) and read 6977 times:

Quoting flyingturtle (Reply 12):
But for safety reasons, a mechanical link between driver and the engine is still required in series-built cars.

Not in a hybrid it isn't, I don't think.


User currently offlineAKiss20 From United States of America, joined Sep 2007, 609 posts, RR: 5
Reply 14, posted (1 year 10 months 2 weeks 2 days 9 hours ago) and read 6978 times:

Quoting DocLightning (Reply 13):
Quoting flyingturtle (Reply 12):
But for safety reasons, a mechanical link between driver and the engine is still required in series-built cars.

Not in a hybrid it isn't, I don't think.

Full electronic throttle is quite common and sees pretty widespread use. Electronic braking and steering has yet to be used in a commercial car afaik, although apparently Nissan is trying:

http://news.cnet.com/8301-17938_105-...roduce-steer-by-wire-cars-in-2013/

I would assume the logic is that you can always shut off the engine manually (take the key out or put it in neutral if you have a fancy key fob   ) so a bad failure mode with throttle is controllable. Bad failure modes in braking and steering are much worse, and consequently, need a lot more redundancy in the system.



Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are
User currently offlineEaglePower83 From United States of America, joined Oct 2011, 236 posts, RR: 0
Reply 15, posted (1 year 10 months 2 weeks 1 day 9 hours ago) and read 6976 times:

Modern cars today are essentially FADEC.
Even my 2012 Charger has full compueter controlled operation sans the brakes and transmission lever.
There's no mechanical key, no mechanical throttle.
AND, the ZF transmissions used in many Chryslers, VWs and Audis now, don't even have a mechanical link.
Like the Prius' "joystick" transmission, it's a full electronic actuation.

Personally, I hope the brakes stay mechanical. But maybe I'm just paranoid.

Oh, and tell me how those words taste when the Geared Turbofan kicks major butt   


User currently offlineAKiss20 From United States of America, joined Sep 2007, 609 posts, RR: 5
Reply 16, posted (1 year 10 months 2 weeks 1 day 7 hours ago) and read 6976 times:

Quoting EaglePower83 (Reply 15):
Oh, and tell me how those words taste when the Geared Turbofan kicks major butt

What words? That the jury is still out on that design? It is, the design has yet to be proven, hence the jury is still out. It isn't making a statement about the quality of the design.

I do forsee a bit of an issue with the GTF for PW though. From my perspective, the benefit of the GTF quickly tops out. Once you get the fan spinning at the speed it ideally should be, there is nowhere further to go. GE has gone the route of focusing on CMCs and thermal coatings to push Tt4 rather than focus on fan matching so heavily. That sets up a base of knowledge and an entire infrastructure for materials development for the next 30 years, and there is a LOT of room to push Tt4.

But who knows what will happen. Just my 2 cents.



Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 17, posted (1 year 10 months 2 weeks 1 day 1 hour ago) and read 6976 times:

Quoting AKiss20 (Reply 16):
It is, the design has yet to be proven, hence the jury is still out.

Pratt's specific GTF design hasn't been proven in service (yet), but they've got a hell of a lot of testing behind it and the general principle of GTF's is well proven, albeit at smaller scale than we're seeing now.

Quoting AKiss20 (Reply 16):
From my perspective, the benefit of the GTF quickly tops out. Once you get the fan spinning at the speed it ideally should be, there is nowhere further to go.

But the beauty is that you can strap that gearbox onto the front of *any* core and immediately reap the benefits of having the fan and LPT Mach numbers much better matched. Any advance in Tt4 or pressure ratio immediately "falls through" the GTF to give you better results than the Tt4 or pressure ratio will alone. I have to assume that Pratt didn't neglect core performance technology while they were working on their gearbox.

Tom.


User currently offline737tdi From United States of America, joined Sep 2007, 843 posts, RR: 1
Reply 18, posted (1 year 10 months 2 weeks 23 hours ago) and read 6976 times:
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Quoting flyingturtle (Reply 12):
Quoting MrChips (Reply 10):


OT, but what you describe is still not FADEC. True, it needs computers so that the engine can run. But FADEC means that the engine is fully controlled only by electric or electronic signals. A true example of FADEC are custom-built cars for handicapped people. But for safety reasons, a mechanical link between driver and the engine is still required in series-built cars.


David




Haven't worked on a car in while have you???   I have owned many modern diesel vehicles and they are fully electronic (as far as the engine). No mechanical link between the engine and operator. FADEC simply means that there is no longer a mechanical connection between the pilot and engine. Which is true for alot of cars today. Granted there is to the transmission but since aircraft don't have transmissions to drive the wheels it is quite equivalent. When I push the throttle of my 08 F350 I am merely operating a Variable Differential Transformer (some cars have LVDTs and some RVDTs). Same as my 03 VW TDI..

As far as engines on aircraft of the past, the turbo/supercharger were the first step into truly high performance. Compound turbochargers, WOW. Study those. They boggle the mind. The supercharger allowed fighter aircraft to achieve speeds and altitudes that were phenomenal. The compound turbocharger allowed passenger travel at speeds and altitudes never heard of before.

Not jet engine tech. but it did contribute.

The next big thing in commercial jet engines is definitely composites.


User currently offlineAKiss20 From United States of America, joined Sep 2007, 609 posts, RR: 5
Reply 19, posted (1 year 10 months 2 weeks 21 hours ago) and read 6976 times:

Quoting tdscanuck (Reply 17):
Quoting AKiss20 (Reply 16):
It is, the design has yet to be proven, hence the jury is still out.

Pratt's specific GTF design hasn't been proven in service (yet), but they've got a hell of a lot of testing behind it and the general principle of GTF's is well proven, albeit at smaller scale than we're seeing now.

I'm not doubting that it can provide the performance it aims, because fundamentally that is a pretty straightforward gain. I think where the GTF might see problems is reliability and maintenance. From what I've seen, that is the main concern of the GTF. Putting that much power through a gearbox is pretty hard on the components and can lead to failure. That kind of thing comes out after the first few years of service. Like I said, I am perfectly willing to accept that it is a great design, it just hasn't been proven in the field yet.

Quoting tdscanuck (Reply 17):
Quoting AKiss20 (Reply 16):
From my perspective, the benefit of the GTF quickly tops out. Once you get the fan spinning at the speed it ideally should be, there is nowhere further to go.

But the beauty is that you can strap that gearbox onto the front of *any* core and immediately reap the benefits of having the fan and LPT Mach numbers much better matched. Any advance in Tt4 or pressure ratio immediately "falls through" the GTF to give you better results than the Tt4 or pressure ratio will alone. I have to assume that Pratt didn't neglect core performance technology while they were working on their gearbox.

What you say is entirely true. But I have to believe that if Pratt devotes resources to both GTF and core development, while the competition devotes resources to just core development, that the competition will be ahead in core development. This just comes from the idea that they are relatively equal in terms of experience, resources etc. I do believe that experience in core development is non-linear, so while the GTF will provide a set benefit to any core, the knowledge and infrastructure developed by the competition will eventually grow to be a benefit greater than the GTF plus Pratt's hindered core development. But I don't have any horses in this race, so I am perfectly willing to be proved wrong, only time will tell.



Change will not come if we wait for some other person or some other time. We are the ones we've been waiting for. We are
User currently online747classic From Netherlands, joined Aug 2009, 2141 posts, RR: 14
Reply 20, posted (1 year 10 months 2 weeks 20 hours ago) and read 6976 times:

If you want accurate background info and a historical overview of the development of Jet and Turbine Aero Engines,
pls. search for this book of Bill Gunston about this subject.
See : http://www.amazon.com/Development-Je...Turbine-Aero-Engines/dp/1852606185

AFAIK edition #4 is the last one.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 21, posted (1 year 10 months 2 weeks 16 hours ago) and read 6976 times:

Quoting 737tdi (Reply 18):
FADEC simply means that there is no longer a mechanical connection between the pilot and engine.

That is not what FADEC means. Having no mechanical connection can be done easily with analog throttle-by-wire where, for example, you have the throttle hooked to an RVDT that's hooked to a servo on the throttle body or fuel injectors. That wouldn't be a FADEC (it wouldn't even be a DEC).

The important part of FADEC is really the "FA" : Full Authority. It's all about command paths. In a FADEC, there is *no* way to give the engine a direct command that it has to obey. The engine computer retains full authority to operate the engine as it sees fit. It will do its best to give you what you ask but it retains full authority on what the engine actually does and you can't override it. Think of it like engine hard envelope protection.

Quoting AKiss20 (Reply 19):
I think where the GTF might see problems is reliability and maintenance. From what I've seen, that is the main concern of the GTF. Putting that much power through a gearbox is pretty hard on the components and can lead to failure. That kind of thing comes out after the first few years of service. Like I said, I am perfectly willing to accept that it is a great design, it just hasn't been proven in the field yet.

That's a concern about the specific Pratt design, but not about GTF in general. The ALF 502 has been certified for 30+ years, the TFE731 is even older.

Tom.


User currently offlineflyingturtle From Switzerland, joined Oct 2011, 2409 posts, RR: 13
Reply 22, posted (1 year 10 months 2 weeks 15 hours ago) and read 6976 times:

Quoting DocLightning (Reply 13):
Not in a hybrid it isn't, I don't think.
Quoting AKiss20 (Reply 14):
Full electronic throttle is quite common and sees pretty widespread use.
Quoting EaglePower83 (Reply 15):
Quoting 737tdi (Reply 18):

Oh... I stand corrected.   

I have very little to do with cars, and I only have followed the development of very modern hybrid cars. Well, I still have more driving experience with a Re 4/4 engine (with 1000 tonnes of railcars and freight)


than with any motorized road vehicle. 

Quoting tdscanuck (Reply 21):
The important part of FADEC is really the "FA" : Full Authority. It's all about command paths. In a FADEC, there is *no* way to give the engine a direct command that it has to obey. The engine computer retains full authority to operate the engine as it sees fit. It will do its best to give you what you ask but it retains full authority on what the engine actually does and you can't override it. Think of it like engine hard envelope protection.


Thank you, this really clears it up... back in the old days, the FE had to set the throttles because he knew what could damage the engine. So nowadays the FADEC computer is dealing how fast the pilots advance or retard the throttles?


David



Keeping calm is terrorism against those who want to live in fear.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 23, posted (1 year 10 months 2 weeks 13 hours ago) and read 6976 times:

Quoting flyingturtle (Reply 22):
So nowadays the FADEC computer is dealing how fast the pilots advance or retard the throttles?

Yes. In a FADEC engine (assuming the FADEC doesn't have a fault in it) you can slam the throttle back and forth to your heart's content at any speed and the engine will just do whatever it can. In FADEC engines, all the commands from the flight deck (or the autothrottle or whatever) are just reference commands. The FADEC is the control system that will attempt to follow the reference commands but it will prioritize the safety of the aircraft over command tracking. So, for example, if you slam the throttle to idle the FADEC will limit the engine deceleration rate to prevent a compressor surge.

Modern FBW also works this way, for the most part.

Tom.


User currently offlineEaglePower83 From United States of America, joined Oct 2011, 236 posts, RR: 0
Reply 24, posted (1 year 10 months 2 weeks 12 hours ago) and read 6976 times:

Pratt's been working on this gearbox for near 20 years.
It's been run through torturous tests on both rigs and engines in the air.
Reports that I've seen the company make public in Aviation Week have stated that reliability and maintenance issues seem to be on par with other engine wear items.
The thing is pretty freakin' robust with an oil system out of this world and with characteristics that make it 99% or more efficient.
In all honesty, the challenge will be in scalability if they try to take it to multi-aisle thrust classes.
Things may be a different story. We shall see.


25 Fabo : Might also be worth noting that FADEC often also limits maximum fuel intake, so that you can not "overthrust" the engine when firewalling the throttl
26 tdscanuck : Absolutely. The newest FADECs are constantly protecting a huge number of engine parameters, including compressor margin in all spools, speed in all s
27 redflyer : Great and informative thread. One aspect of jet engine breakthrough and development I haven't seen discussed is reliability/safety and service life. W
28 flyingturtle : Additional aspect... have there been any airliner engines that were notoriously difficult to maintain? Which engines were a breakthrough in serviceabi
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