flybaby
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What's next for mainstream jet engines?

Sun Sep 22, 2019 9:03 pm

In the Boeing 787 Deferred Production Cost thread (AKA the Boeing unique accounting system thread) someone made a comment to the effect of ‘well, you know, in 10-15 years they’ll have to roll out a 787neo variant’... that got me thinking, is that realistic?

We started out with turbojets, then 1.5:1 bypass ratio fans, then ~5:1 and now we’re up to ~10:1. How far can this be stretched? Seems to me at some point the laws of thermodynamics start kicking in and you can only get so much from a bigger front fan. Over the years there have been all sort of odd-looking turbine-based designs but nothing has really caught on. So I am wondering, what’s next, realistically? A giant GTF? Something else?
 
WIederling
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Re: What's next for mainstream jet engines?

Sun Sep 22, 2019 9:16 pm

"What's next for mainstream jet engines"

Less mainstream :-))
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Re: What's next for mainstream jet engines?

Sun Sep 22, 2019 9:28 pm

flybaby wrote:
We started out with turbojets, then 1.5:1 bypass ratio fans, then ~5:1 and now we’re up to ~10:1. How far can this be stretched?

https://aeroreport.de/en/innovation/hig ... the-future was written over a year ago and describes:

In the ENgine mOdule VALidators (ENOVAL) project, 35 partners from ten different countries-including aviation companies, research institutes and universities-are developing engine technology for bypass ratios higher than 12:1. Experts refer to an ultra-high bypass ratio (UHBR). "In ENOVAL, we're working with a range between 14:1 and 16:1," says Merkl. By virtue of the higher BPR, there will not only be an increase in thrust efficiency, with corresponding reductions in fuel consumption and emissions, explains the ENOVAL Coordinator, "but the new engines that result will be even quieter than the Geared Turbofan™ is already."

And:

"For the classic aircraft configuration, it will be possible to increase the BPR further up to 20:1-but then we have reached the maximum," says Merkl. Achieving this, however, will require new materials and improved sealing systems, which allow the pressure ratio in the core engine to be increased further. No progress can be expected on this front before 2035. The ENOVAL generation of UHBR engines will be ready long before then: "We expect entry into service to begin from 2025," says the ENOVAL Coordinator.
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lightsaber
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Re: What's next for mainstream jet engines?

Sun Sep 22, 2019 10:03 pm

Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber
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kalvado
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Re: What's next for mainstream jet engines?

Sun Sep 22, 2019 10:10 pm

lightsaber wrote:
New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber

Any published links for those? Google doesn't give anything..
 
Waterbomber2
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Re: What's next for mainstream jet engines?

Sun Sep 22, 2019 10:53 pm

I think that the next stage of evolution will be a lot more than the incremental small changes in current designs, a list of which has already been provided by other posters above.

My 2 cents are that from here on out, aircraft engines will become a lot more complex and integrated machines compared to the current relatively simple architecture.
 
flybaby
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Re: What's next for mainstream jet engines?

Sun Sep 22, 2019 11:15 pm

Thanks for the answers.

I didn’t realize that, at least theoretically, it is possible to squeeze more efficiency by going up to 20:1 ratio. In that case, I just hope Boeing gets their clean slate replacement for the 737 ready by then :D .

It sounds like there are some incremental improvements possible also although I would expect those to “fit” within existing engine interfaces.
 
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Re: What's next for mainstream jet engines?

Sun Sep 22, 2019 11:31 pm

At those ratios, B can always max enlarged hamster-pouched engines & put them over the wings, Russian style : safer with max ground clearance & way cheaper than a new frame. With the late 7M10, I don't see a replacement soon, say not before 2030.
 
patrickjp93
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 12:44 am

Combining GE's CMC technology from the GE9X with PW's GTF IP would be the next logical step rather than GE moving to a 3-spool architecture, though Lord knows they could probably milk a lot out of a 3-spool design too before leaping to a geared fan, but by then it might be TOO hard to just "pick it up and integrate" 25 years from now.

For smaller planes with smaller engine requirements, we need to efficiently shrink the core down rather than grow the fan much more. Even the A320 and A220 don't have much more room under them for bigger engines, and on planes that size, engine weight can be a dominating factor in airframe performance.
 
patrickjp93
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 12:50 am

flybaby wrote:
Thanks for the answers.

I didn’t realize that, at least theoretically, it is possible to squeeze more efficiency by going up to 20:1 ratio. In that case, I just hope Boeing gets their clean slate replacement for the 737 ready by then :D .

It sounds like there are some incremental improvements possible also although I would expect those to “fit” within existing engine interfaces.


Who needs a clean-sheet design when we can just move the wings a tad and attach bigger engines slightly further out?
 
LDRA
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 1:00 am

What about engine for CRJ or 717 mission profile?

Seems like new tech -> higher BPR -> larger fan -> heavier
 
patrickjp93
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 1:22 am

LDRA wrote:
What about engine for CRJ or 717 mission profile?

Seems like new tech -> higher BPR -> larger fan -> heavier


See above. We need to find ways of shrinking the cores, or there'll just be a limit on small engine efficiency.
 
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lightsaber
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 2:12 am

patrickjp93 wrote:
LDRA wrote:
What about engine for CRJ or 717 mission profile?

Seems like new tech -> higher BPR -> larger fan -> heavier


See above. We need to find ways of shrinking the cores, or there'll just be a limit on small engine efficiency.

RJs are optimized differently. First, get the pw1200G in service. ;)

The shorter the mission, the smaller the optimum bypass ratio. The smaller the engine, the lower the optimum pressure ratio.

Variable cycle technologym benifits on mission length. The variable turbine cooling scales well. The variable fan nozzle hurt the business case selling to LH's shorter missions, so was dropped. But it has merit.

To others:

For those looking for big changes,. We're still implimenting ideas Whittle came up with in the 1950s.

The next big thing will be fuel cells in the cargo hold powering ducted fans on the wings. That is what it takes for the leap in technology some want here.

Otherwise, the CMC turbine blades are late due to cuts in R&D funding by the government. That was first tested in the 1990s. It needed deep pockets to find and finally is happening. Gas turbines have always been waiting on the next great material. The T1000 issues highlight how much testing is required to verify.

It costs 7 to 9 billion to develop a jet engine family. Often more than the cost of developing the aircraft. Pratt has the PW812, PW815, PW1200, PW1500/1900, and some in work military derivatives off the small core PurePower. I know of two more planned derivatives I haven't seen yet.

The large core PurePower has the PW1500/1400 and at least one military derivative.

If it was cheap to develop engines, we wouldn't have had the CFM-56 for so long. A military engine with a SNECMA (now SAFRAN) low spool. Then another low spool for the 737. Then another low spool for the A320 and then an upgrade, but many parts kept, for the 737NG. The CFM-56 first run was in 1974. It will exit production with the A321CEO for DL to 2021:

https://news.delta.com/delta-expand-air ... deliveries

Aircraft and engines have accelerated fuel burn improvement to a 1.25% reduction per year. Company have looked for the big changes forever.

The issue is the remaining ideas are hard and have downsides.

E.g., variable pitch fans are another variable cycle technology. But RR had to drop the concept as it won't be ready for an EIS engine before 2030.

Open rotors are neat, but slow.
Turboprops are efficient, but limit cruise to Mach 0.6 or so
Open rotors Mach 0.7 to maybe 0.72

Shrouded fans (today's engines) are good up to Mach 0.92.

Until we switch technology, it will be incremental improvements of a mature technology. I believe fuel cells are next. Something friends of mine worked on in the early 1990s.

Technology costs. It took over $100/bbl oil to interest airlines in the A320NEO. Another much more problematic upgrade? Good luck selling that post GTF issues, LEAP issues, T1000 issues, GE9x delays...

Seriously, the GE9x is the most advanced engine I've seen. I believe it to be a full generation ahead thanks to variable cycle tech, CMCs, high Mach # compressor, advanced low turbine, the most advanced clearance control on the turbine, advanced blade shapes, and such complex cooling to optimize performance.

Off you want to see normal progress, look at RB211 to Trent 800 to Trent 700 to Trent 1000 to TxWB. There is 40 years of progress there.

Or CF6-6 to CF6-80E to GE-90 to GEnX to GE9x

Or JT8D-15 to JT8D-217 to V2500A1 to A5 to PW1100G/PW1500G

Now in that time engine reliability, durability, IFSD rates, and safety improved dramatically.

That is the rate of progress with large R&D teams.

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Exeiowa
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 2:22 am

Maybe the next advancements should be in the range of reliability, production cost and maintenance efficiency. While they get the next generation of tech ready. Seeing as the manufacturers themselves are having problems in these areas.
 
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lightsaber
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 3:29 am

Exeiowa wrote:
Maybe the next advancements should be in the range of reliability, production cost and maintenance efficiency. While they get the next generation of tech ready. Seeing as the manufacturers themselves are having problems in these areas.

Production cost is based on technology.
A CFM-56-5 or -7 costs about $1.6 million to make
V2500 about $2.1 million
LEAP about $4.5 million, similar for PW1100G

CFM would burn about $11.5 million of fuel per year
V2500 about $11 million
LEAP about $9.35 million
PW1200G about $9.16 million

Both the PW1100G and LEAP-1A save 30% or so in day to day maintenance thanks to predictive maintenance.

The following link goes into a little on how the NEO engines cut overhaul expenses:
https://speednews.com/article/6963

Basically, engine overhaul costs are currently about 5.2% of the total cost of flying. Engine day to day maintenance (I'm going from memory) is about 6% of the cost of flying. Fuel is for the CEO/NG (see link) about 31%.

The new engines will cut overhaul costs. Pratt by about 10%, LEAP by 20% per flight due to much longer overhaul intervals.

So yes, they are working costs. Reliability hasn't been as planned, but both engine vendors are working that.

But of engine expenses
31% of total for fuel
5.2% MRO maintenance.
6% line maintenance

The 15%+ fuel burn reduction did the most, saving 4.5%.
MRO maintenance will save 0.5% to 1% over prior engines.
The biggest deal is predictive maintenance. That will save 1.5% to 2% of total cost plus less compensation.

So 6.5% to 7.5% savings minus about 2.5% in higher purchase price.

Which brings us back to the promised about 5% drop in cost versus a prior generation aircraft.

Plus... Better airframe predictive maintenance (retrifitable to the A320CEO buy not 737NG, for another 1% to 2% cost savings.

So maintenance was addressed. Fuel burn is simply still the highest expense.

Putting it into perspective, aircraft ownership is 10% per link, but more for NEO/MAX. The new airframes, once debugged, will save half their ownership costs, mostly on the engine side.

Now, for a great new engine, there is a desire for better subsystems. E g., the electrical subsystems if the A220 add weight, but overall save about 3% in fuel burn vs. A320. CFRP wings save tons of weight which helps fuel burn.

I started the industry when 8,000 cycles until 1st engine MRO visit was outstanding. Now for narrowbody engines 20,000 is expected. The LEAP is promising 30,000. A LEAP-1A is in fact only expected to see two MRO shop visits on the A320NEO prior to aircraft scrapping. The PW1100G would have more (GE likes to point out 3 visits, but it is 24,,000 cycles, so some engines will have life at aircraft scrapping and be rotated to other aircraft that will skip the engine $3.5 million+ visit.

So maintenance and durability were addressed.

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WIederling
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 6:51 am

flybaby wrote:
Thanks for the answers.

I didn’t realize that, at least theoretically, it is possible to squeeze more efficiency by going up to 20:1 ratio. In that case, I just hope Boeing gets their clean slate replacement for the 737 ready by then :D .

It sounds like there are some incremental improvements possible also although I would expect those to “fit” within existing engine interfaces.

Increased power density in the core pushes for larger by pass ratios.
Murphy is an optimist
 
Exeiowa
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 11:38 am

My thoughts on the advancements needed were more for the health of the engine manufacturers, than the plane owners need. If they could make slightly more on each engine sold they would not look as vulnerable as they currently do, reliability is killing their reputation and I will concede the maintenance point.
 
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 11:55 am

WIederling wrote:
"What's next for mainstream jet engines"

Less mainstream :-))


Genuine LOL.
"As with most things related to aircraft design, it's all about the trade-offs and much more nuanced than A.net likes to make out."
 
patrickjp93
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 12:47 pm

lightsaber wrote:
For those looking for big changes,. We're still implimenting ideas Whittle came up with in the 1950s.

The next big thing will be fuel cells in the cargo hold powering ducted fans on the wings. That is what it takes for the leap in technology some want here.


That is most certainly NOT the next big thing unless we have completely different concepts of the term. Instant turnoff for a lot of flag carrier airlines relying on cargo to subsidize tickets. We're a good 30 years away from having graphene super capacitors producible at scale along with superconducting nanowire able to deliver the goods on that even in a hybrid engine capability framework. We're a good 50 years away from having the power infrastructure at airports (except perhaps, with disgusting irony, at CDG which is surrounded by nuclear power plants) to support having a sizable fleet of even E 190s coming in and out regularly.

The next big thing in engines is the convergence of the technologies we see flying from GE and PW today: geared fans and ceramic core sections along with carbon fan cases and blades.

Otherwise, the CMC turbine blades are late due to cuts in R&D funding by the government. That was first tested in the 1990s. It needed deep pockets to find and finally is happening. Gas turbines have always been waiting on the next great material. The T1000 issues highlight how much testing is required to verify.

Ceramics was more of a lacking of economical production techniques. We had nothing beyond a concept of additive manufacturing in the 90s.

The T1000 I swear is either cursed or deliberate sabotage. The 7000 and XWB are in perfect working order and are derivatives of the same architecture for crying out loud, and the T1000 has been getting PIPs fairly regularly from those programs.

Open rotors are neat, but slow.
Turboprops are efficient, but limit cruise to Mach 0.6 or so
Open rotors Mach 0.7 to maybe 0.72

Shrouded fans (today's engines) are good up to Mach 0.92.

Come to think of it, despite GE putting a brand new prop into service a few years ago, I don't think I've yet heard of a re-engining program for the Dash planes yet, and after so many years, shouldn't there be one?
 
Exeiowa
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 4:26 pm

Fuel cells are not batteries, they convert chemical energy to electricity directly without setting them onfire. A few years ago these were heralded as the next big thing, they are already used in certain applications, but held great potential as a more mass market application, because of the potential efficiencies, if the cost could be brought down and technological considerations met. However their thunder seems to have been stolen in recent years by batteries, but as we seem to have hit some limits on these maybe fuel cells will get the spotlight again.
 
CowAnon
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 5:07 pm

lightsaber wrote:
Open rotors are neat, but slow.
Turboprops are efficient, but limit cruise to Mach 0.6 or so
Open rotors Mach 0.7 to maybe 0.72

When McDonnell Douglas ran the GE36 unducted fan on its MD-81 testbed aircraft in 1987-1988, it devoted 49 of the 137 test flights to cabin noise testing. 31 of those 49 flights were done at the MD-80's normal cruise regime of Mach 0.76 and 35,000 feet altitude. If open rotors couldn't routinely perform past M0.72, I doubt McDD would have bothered testing the engine at those levels. One of the tests even flew the engine successfully to M0.86 at 35,000'.

From NASA report UHB demonstrator interior noise control flight tests and analysis, page 9:

Image
 
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kitplane01
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 5:34 pm

lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


First, love this post.

Second, how about variable pitch fans? Would eliminate the need for reversing buckets. I assume right now fans are pitched for optimum cruise, and therefore variable pitch fans would help most during takeoff and climb and descent. Might they even reduce noise levels during takeoff, if just by allowing a shorter roll and steeper climb???

I'd love to hear more about variable pitch fans.
 
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lightsaber
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 7:10 pm

kitplane01 wrote:
lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


First, love this post.

Second, how about variable pitch fans? Would eliminate the need for reversing buckets. I assume right now fans are pitched for optimum cruise, and therefore variable pitch fans would help most during takeoff and climb and descent. Might they even reduce noise levels during takeoff, if just by allowing a shorter roll and steeper climb???

I'd love to hear more about variable pitch fans.

I forgot variable pitch fans. Improved thrust at takeoff, improved climb and cruise fuel burn, about 2% in climb, maybe 0.6% in cruise (I am less familiar with test data, so please understand that is a SWAG).

The big benefit of variable pitch is reduced wear during climb. It allows efficiency gains and adds about 20% to the cycle life of the engine. Maybe 25%.

The simplified nacelle pays for the variable pitch. Small noise reduction, but since at where the ground absorbs, it doesn't effect the outside the airport noise profiles.

It is good tech.

I'm sure I forgot other stuff.
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lightsaber
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 7:19 pm

CowAnon wrote:
lightsaber wrote:
Open rotors are neat, but slow.
Turboprops are efficient, but limit cruise to Mach 0.6 or so
Open rotors Mach 0.7 to maybe 0.72

When McDonnell Douglas ran the GE36 unducted fan on its MD-81 testbed aircraft in 1987-1988, it devoted 49 of the 137 test flights to cabin noise testing. 31 of those 49 flights were done at the MD-80's normal cruise regime of Mach 0.76 and 35,000 feet altitude. If open rotors couldn't routinely perform past M0.72, I doubt McDD would have bothered testing the engine at those levels. One of the tests even flew the engine successfully to M0.86 at 35,000'.

From NASA report UHB demonstrator interior noise control flight tests and analysis, page 9:

Image

Open rotors have an efficiency curve. My Mach #s were for efficient cruise, derived partially from the data you reference.

I've tested engines with Mach 0.84 redlines supersonic. That doesn't mean they are ready. I do the dangerous, disable the safeties testing. Y prior numbers are for in service, all the safeties on, limiting cruise speed on engine wear.

I've taken engines that don't wear in allowed cruise and worn them in beyond spec high speed cruise. Get me an engine good for 20,000 FC and minimum 40,000 FH between overhauls when talking narrowbody engines. Widebody engines sacrifice cycles, rarely good for more than 8,000 FC. But they are pulled at flight hours (FH) or more precisely efficiency to minimize cost. Oh, hours too. When the backpressure sump regulator starts to stick, efficiency and wear suddenly turn for the worst.

I like open rotor, but if they were all that, we would be flying in aircraft powered by them.

Instead, we have GTF. There is a market, but not TCON.

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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 9:37 pm

kitplane01 wrote:
lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


First, love this post.

Second, how about variable pitch fans? Would eliminate the need for reversing buckets. I assume right now fans are pitched for optimum cruise, and therefore variable pitch fans would help most during takeoff and climb and descent. Might they even reduce noise levels during takeoff, if just by allowing a shorter roll and steeper climb???

I'd love to hear more about variable pitch fans.

I’m trying to envision what you are suggesting here. Reversing of pitch on fan for reverse thrust? What would this do to core airflow, as I am imagining very bad things, unless the fan pitch only changes outboard of core flow.
The last of the famous international playboys
 
Waterbomber2
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Re: What's next for mainstream jet engines?

Mon Sep 23, 2019 11:23 pm

Variable pitch fans also bring a lot of additional issues that require complex solutions.
On a six-bladed turboprop or helicopter that have a huge "bypass ratio" it's one thing, but on a 22-bladed turbofan spinning at higher speeds, it's not easy to implement something reliable, fail-safe and compact.
Failure of variable pitch systems has also caused a lot of accidents and deaths on turboprops and helicopters, do we really want to go through the whole cycle of trial and error with turbofans considering all the agony that this will cause?
I could see this being implemented sooner or later, yes, but I'm not a big fan of it because I think that the added risk outweighs the reward.

Shrinking the core while maintaining the fan size does not increase bypass ratio by much nor does it increase efficiency by much.
The outboard 50% of the fan disc would have 75% of the fan disc's area. In addition, lift is proportional to the square of speed of the airfoil so given higher angular velocity the farther from the center of rotation, you have another square factor there.
To get an approximation, one could say that the outboard 1/3rd of a fan generates 2/3rd of the fan's thrust.
So you either need a combination of a bigger fan with a smaller core, or a bigger fan with the same core.

Unducted fans have major limitations in terms of noise pollution both outside and inside the cabin.
In terms of certification, fan blade separation forms a major challenge, given higher rotational speeds and higher number of blades compared to turboprops.
Another risk is FOD hiting the blades and being thrown out with high energy and damaging aircraft/property/people.This not an issue with turboprops as they often have high wing configurations.
So your engine configuration will have limited options and may impact efficiency negatively.
 
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lightsaber
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 12:28 am

Spacepope wrote:
kitplane01 wrote:
lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


First, love this post.

Second, how about variable pitch fans? Would eliminate the need for reversing buckets. I assume right now fans are pitched for optimum cruise, and therefore variable pitch fans would help most during takeoff and climb and descent. Might they even reduce noise levels during takeoff, if just by allowing a shorter roll and steeper climb???

I'd love to hear more about variable pitch fans.

I’m trying to envision what you are suggesting here. Reversing of pitch on fan for reverse thrust? What would this do to core airflow, as I am imagining very bad things, unless the fan pitch only changes outboard of core flow.

We had a thread on the variable pitch concept a month ago with good links:

viewtopic.php?f=5&t=1427925

Basically, at takeoff the thrust is so increased a nice fuel savings happens by varying blade pitch. I've heard numbers around 20 to 25%.

At climb you might save 10%, numbers for discussion sake.

A cruise, just a little with variable pitch.

I one is going to design a variable pitch fan why not vary the pitch that little bit more to get rid of a thrust reverser?

RR has backed off a near term introduction of a variable pitch fan, but are still studying the concept.

You can shape the center of the fan to not be impacted as much. But you are right, if done poorly, a compressor stall would occur.

Nothing is without risk in aviation.

Lightsaber
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kitplane01
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 1:52 am

Spacepope wrote:
kitplane01 wrote:
lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


First, love this post.

Second, how about variable pitch fans? Would eliminate the need for reversing buckets. I assume right now fans are pitched for optimum cruise, and therefore variable pitch fans would help most during takeoff and climb and descent. Might they even reduce noise levels during takeoff, if just by allowing a shorter roll and steeper climb???

I'd love to hear more about variable pitch fans.

I’m trying to envision what you are suggesting here. Reversing of pitch on fan for reverse thrust? What would this do to core airflow, as I am imagining very bad things, unless the fan pitch only changes outboard of core flow.



I understand that it's been tried in practice, and one can run the fan in reverse mode and the core still functions. I'm sorry I don't have a cite.
 
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kitplane01
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 1:57 am

lightsaber wrote:
kitplane01 wrote:
lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


First, love this post.

Second, how about variable pitch fans? Would eliminate the need for reversing buckets. I assume right now fans are pitched for optimum cruise, and therefore variable pitch fans would help most during takeoff and climb and descent. Might they even reduce noise levels during takeoff, if just by allowing a shorter roll and steeper climb???

I'd love to hear more about variable pitch fans.

I forgot variable pitch fans. Improved thrust at takeoff, improved climb and cruise fuel burn, about 2% in climb, maybe 0.6% in cruise (I am less familiar with test data, so please understand that is a SWAG).

The big benefit of variable pitch is reduced wear during climb. It allows efficiency gains and adds about 20% to the cycle life of the engine. Maybe 25%.

The simplified nacelle pays for the variable pitch. Small noise reduction, but since at where the ground absorbs, it doesn't effect the outside the airport noise profiles.

It is good tech.

I'm sure I forgot other stuff.
Lightsaber



Much of what you wrote surprises me. If fans are optimized for cruise conditions, why would a variable fan improve cruise? Are normal fixed fans set to a compromise between climb and cruise?

Any why would a variable fan reduce wear during climb? I imagine you'd run the core at some reasonable maximum thrust with either a fixed or variable fan pitch, and take the better climb performance with the variable pitch. The core would see a similar work load in both cases, but less time of climb in the variable case. (I'm not stating a fact, I'm asking if this is true).
 
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kitplane01
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 2:00 am

lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


I note that adding all the CMC numbers together is about a 6% efficiency improvement. That's where my investment would be.
 
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kitplane01
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 2:11 am

Waterbomber2 wrote:
Variable pitch fans also bring a lot of additional issues that require complex solutions.
On a six-bladed turboprop or helicopter that have a huge "bypass ratio" it's one thing, but on a 22-bladed turbofan spinning at higher speeds, it's not easy to implement something reliable, fail-safe and compact.
Failure of variable pitch systems has also caused a lot of accidents and deaths on turboprops and helicopters, do we really want to go through the whole cycle of trial and error with turbofans considering all the agony that this will cause?
I could see this being implemented sooner or later, yes, but I'm not a big fan of it because I think that the added risk outweighs the reward.

Shrinking the core while maintaining the fan size does not increase bypass ratio by much nor does it increase efficiency by much.
The outboard 50% of the fan disc would have 75% of the fan disc's area. In addition, lift is proportional to the square of speed of the airfoil so given higher angular velocity the farther from the center of rotation, you have another square factor there.
To get an approximation, one could say that the outboard 1/3rd of a fan generates 2/3rd of the fan's thrust.
So you either need a combination of a bigger fan with a smaller core, or a bigger fan with the same core.

Unducted fans have major limitations in terms of noise pollution both outside and inside the cabin.
In terms of certification, fan blade separation forms a major challenge, given higher rotational speeds and higher number of blades compared to turboprops.
Another risk is FOD hiting the blades and being thrown out with high energy and damaging aircraft/property/people.This not an issue with turboprops as they often have high wing configurations.
So your engine configuration will have limited options and may impact efficiency negatively.


I assume an unduct fan will be certified under propeller regulations. It will have to meet propeller rules. I don't see how it could be certified under the same rules as a duct fan. In particular, there would be no way to implement loss of blade containment without the duct. And to be clear, modern propellers are safe.

Noise might be a real issue, but people who have studied it claim it's a controllable/solvable issue.
 
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lightsaber
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 2:17 am

kitplane01 wrote:
lightsaber wrote:
kitplane01 wrote:

First, love this post.

Second, how about variable pitch fans? Would eliminate the need for reversing buckets. I assume right now fans are pitched for optimum cruise, and therefore variable pitch fans would help most during takeoff and climb and descent. Might they even reduce noise levels during takeoff, if just by allowing a shorter roll and steeper climb???

I'd love to hear more about variable pitch fans.

I forgot variable pitch fans. Improved thrust at takeoff, improved climb and cruise fuel burn, about 2% in climb, maybe 0.6% in cruise (I am less familiar with test data, so please understand that is a SWAG).

The big benefit of variable pitch is reduced wear during climb. It allows efficiency gains and adds about 20% to the cycle life of the engine. Maybe 25%.

The simplified nacelle pays for the variable pitch. Small noise reduction, but since at where the ground absorbs, it doesn't effect the outside the airport noise profiles.

It is good tech.

I'm sure I forgot other stuff.
Lightsaber



Much of what you wrote surprises me. If fans are optimized for cruise conditions, why would a variable fan improve cruise? Are normal fixed fans set to a compromise between climb and cruise?

Any why would a variable fan reduce wear during climb? I imagine you'd run the core at some reasonable maximum thrust with either a fixed or variable fan pitch, and take the better climb performance with the variable pitch. The core would see a similar work load in both cases, but less time of climb in the variable case. (I'm not stating a fact, I'm asking if this is true).

Fans are optimized for cruise, but then compromises on stall margins.

During climb the fence Lowe's the Lowe's spool down too much. This means there is not sufficient pressure ratio for cooling. a low pressure ratio means the engine is also struggling to provide the thrust so there is a lot more turbine wear. turn climb the court is starved of turbine cooling cuz you have lots of heat but is not as much pressure to remove the heat. by having a variable pitch fan you can increase the RPM in there for the loading of the loads will which increases the pressure ratio which gives the high school more air to burn so you're not burning his Rich so you're not burning as hot.

Lightsaber
IM messages to mods on warnings and bans will be ignored and nasty ones will result in a ban.
 
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lightsaber
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 2:18 am

kitplane01 wrote:
lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


I note that adding all the CMC numbers together is about a 6% efficiency improvement. That's where my investment would be.

For 35 years the industry would agree with you invest in cmcs. It wasn't easy to get it right. the really hard part will be to mass produce CMCs in volume for good cost.
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cpd
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 2:28 am

A modern technology SST suitable engine must surely be in the minds of some engine designers.

Given the vast improvements we’ve seen for other engines, surely similar is possible for SST engines.

The Olympus 593 was pretty good in its day, but surely we can advance on that with all the modern technology available these days.

I guess the success or failure of the new scaled down SSTs like Boom will determine this.

It’s not clear if they will even reach a flying prototype.
 
Waterbomber2
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 6:12 am

cpd wrote:
A modern technology SST suitable engine must surely be in the minds of some engine designers.

Given the vast improvements we’ve seen for other engines, surely similar is possible for SST engines.

The Olympus 593 was pretty good in its day, but surely we can advance on that with all the modern technology available these days.

I guess the success or failure of the new scaled down SSTs like Boom will determine this.

It’s not clear if they will even reach a flying prototype.


For SST, the problem is not the engine but all the rest.
Technology is not here yet to mitigate compressibility effects efficiently. They will come eventually, but until then, the engines are the least of the problems.
Also, few technologies applied to high BPR turbofans are really useful for supersonic engines.
On the military side, engines are becoming more versatile and more capable but not less thirsty.
 
Waterbomber2
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 6:38 am

lightsaber wrote:
kitplane01 wrote:
lightsaber wrote:
Let us talk technology.

Ready today:
3.5:1 GTF gearbox vs. current 3:1 ratio gearbox, a small but easy 1.5% drop in fuel burn.

Variable turbine cooling (in LEAP), about 1.8% reduction in LEAP, about 2.75% in GE9x, the benefit scales with engine thrust

Variable fan nozzle. About 1.2% for the PW1100, about 1.5% for a 65k thrust engine. Maybe 1.6% for a 100k lbf engine. Yes, technology has a dimensional factor.

1st generation CMC turbine blades for 2nd stage turbine. 1st application is GE9x with about 2.75% fuel burn reduction. I expect about 1.8% reduction when retrofitted to the LEAP and somewhere in between for GEnX. Only GE is ready. Pratt is close.

Additional turbine clearance control valves.
For 2nd stage of high turbine a 0.75% fuel reduction. For low turbine maybe 0.3% fuel burn reduction, only viable on long haul (missions optimized for 4+ hours).

Full scimitar blade compressors. About 1.25% fuel burn reduction.

Better modeling of engine stages to feed each other; 1% fuel burn reduction. Costs development time.

CMC turbine inlet guide vanes, about 1.5% fuel burn reduction. This requires higher temperature CMCs than currently qualified.

1st stage turbine CMCs. This requires higher density CMCs. All companies are working, 10+ years away. A 3 to 3.5% reduction in fuel burn (larger engines will benefit more, if you haven't noticed, component efficiency scales with thrust).

Higher mach# compressors. This is to increase pressure ratio as well as compressor efficiency. About 2.5% reduction in fuel burn.

Variable component cooling. About 0.75% available here. GE9x is starting, but do so in a way that adds so much weight, only a 0.3% fuel burn reduction .

New foam cast low turbine blades, why lighter, the main benefit is better blade shapes. 1% with a non GTF, 3% with (faster spinning turbines are needed to extract the benefit).

Lightsaber


I note that adding all the CMC numbers together is about a 6% efficiency improvement. That's where my investment would be.

For 35 years the industry would agree with you invest in cmcs. It wasn't easy to get it right. the really hard part will be to mass produce CMCs in volume for good cost.


I think that CMC will play a role but that it will be surpassed. CMC alone can't solve the TIT issue and I don't think that stoichiometric combustion can be achieved with the current engine architecture. We are still 400-500 Kelvins away from reaching stoichiometric combustion and we will get there within 5 years with SFC reductions of up to 40% (hence my suggestion in other threads of an A380 with the fuel burn of a B77W being within reach), but be prepared to see architectural changes.

When that new architecture hits the market, it will be interesting to watch if GE/RR/PW will take a lead or new entrants and even aircraft manufacturers start doing their own engine work.
 
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SomebodyInTLS
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 6:58 am

Exeiowa wrote:
Fuel cells are not batteries, they convert chemical energy to electricity directly.


Fuel cells have the advantage of higher energy density and constant high energy output. The disadvantage is that their output can't be switched on and off at the flick of a switch, nor can it be ramped up and down at will.

Which actually makes them ideal for use in aircraft where they can be used to provide a steady supply in cruise, supplemented by a battery for peak requirements during take off etc. They have the additional advantage that they use fuel during flight, so aircraft can still be designed to lower landing weights than take off weights.
"As with most things related to aircraft design, it's all about the trade-offs and much more nuanced than A.net likes to make out."
 
WIederling
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 7:42 am

Spacepope wrote:
kitplane01 wrote:
I'd love to hear more about variable pitch fans.

I’m trying to envision what you are suggesting here. Reversing of pitch on fan for reverse thrust? What would this do to core airflow, as I am imagining very bad things, unless the fan pitch only changes outboard of core flow.


There was a cross sectional drawing around that shew the solution.
( imu in reverse the fan section was not part of the core intake pressure line.
you lose the pressure step from the fan section in reverse )
Murphy is an optimist
 
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lightsaber
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 11:15 am

Waterbomber2 wrote:
lightsaber wrote:
kitplane01 wrote:

I note that adding all the CMC numbers together is about a 6% efficiency improvement. That's where my investment would be.

For 35 years the industry would agree with you invest in cmcs. It wasn't easy to get it right. the really hard part will be to mass produce CMCs in volume for good cost.


I think that CMC will play a role but that it will be surpassed. CMC alone can't solve the TIT issue and I don't think that stoichiometric combustion can be achieved with the current engine architecture. We are still 400-500 Kelvins away from reaching stoichiometric combustion and we will get there within 5 years with SFC reductions of up to 40% (hence my suggestion in other threads of an A380 with the fuel burn of a B77W being within reach), but be prepared to see architectural changes.

When that new architecture hits the market, it will be interesting to watch if GE/RR/PW will take a lead or new entrants and even aircraft manufacturers start doing their own engine work.

Due to NOx emission requirements, gas turbines will run overall lean.
Get there in 4-5 years?!? No. It takes 10 years to develop today's advanced engines. The GTF was in work for decades.

What architecture are you suggesting? Aircraft manufacturers doing engines? Do you have any concept of how specialized advanced jet engine design is? Business jet engines have technology typically 20+ years out of date, so are the easiest to compete.

For example, the Hondajet still has a centrifugal compressor! But that saves over $100,000 in manufacturing costs per engine.

The BR710/715/725 were only so advanced as they are shrunk V2500s with simplified subsystems to cut manufacturing costs. The Pearl is a highly evolved BR710, but is no where near a radical new design.

The Passport cannot pay it's development costs, GE is betting on an RJ engine a la BR715. The PW812 and PW815 both are hand me down tech.

This is like United Technologies developing an airframe. They could do it, but it would be tough to compete.

Please realize the longest lead time item for a new clean sheet aircraft is the advanced engine. Now, if you want yesterday's tech a la T500/T900 it is quicker, but on the order of the airframe development timeline. I worked on the OW8133 in the late 90s that evolved into the PW1100G.

HondaJet found out secondary system design was beyond their capability and partnered with GE. For example, turbine clearance control is tough. Even partnering with experienced vendors requires the integrator to know their system well. I had the pleasure of designing turbine clearance control systems for 4 different engine vendors and it isn't easy. No new entrant could match the GE9x or Pearl technology. (RR paid development costs to have new technology available for their other engines.).

At this time the Chinese, Russians, Germans, and French spend big to attempt to have new competitive engines. At this time there are the big 3 plus Honeywell and that is all. Look at the Silver rest, a moderate risk engine (whose concept I adored), failed on casing design. If one thing is wrong on a jet engine, it is a botched engine. See Early RB211 fans, Pratt seals, early GE-90 fuel injectors...

New entrants are not a contender until the 4th or 5th generation engine. At 7 to 10 billion USD per generation, that is deep pockets.

Lightsaber
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patrickjp93
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 3:00 pm

Exeiowa wrote:
Fuel cells are not batteries, they convert chemical energy to electricity directly without setting them onfire. A few years ago these were heralded as the next big thing, they are already used in certain applications, but held great potential as a more mass market application, because of the potential efficiencies, if the cost could be brought down and technological considerations met. However their thunder seems to have been stolen in recent years by batteries, but as we seem to have hit some limits on these maybe fuel cells will get the spotlight again.


We're not really hitting limits with batteries yes. MIT's been making huge strides with carbon cathode & anode tech that puts even LiCo to shame, and it's far less dangerous.
 
patrickjp93
Posts: 384
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 3:18 pm

cpd wrote:
A modern technology SST suitable engine must surely be in the minds of some engine designers.

Given the vast improvements we’ve seen for other engines, surely similar is possible for SST engines.

The Olympus 593 was pretty good in its day, but surely we can advance on that with all the modern technology available these days.

I guess the success or failure of the new scaled down SSTs like Boom will determine this.

It’s not clear if they will even reach a flying prototype.


GE Affinity
https://www.youtube.com/watch?v=pESZu-m ... gs=pl%2Cwn
https://www.youtube.com/watch?v=T3eudKV ... gs=pl%2Cwn

It's using a lot of CMC experience from the GE9X and their Adaptive Cycle fighter engine. It's good up to M 1.6. Past that you'd want a Ramjet.
 
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kitplane01
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Re: What's next for mainstream jet engines?

Tue Sep 24, 2019 3:44 pm

Waterbomber2 wrote:
lightsaber wrote:
kitplane01 wrote:

I note that adding all the CMC numbers together is about a 6% efficiency improvement. That's where my investment would be.

For 35 years the industry would agree with you invest in cmcs. It wasn't easy to get it right. the really hard part will be to mass produce CMCs in volume for good cost.


I think that CMC will play a role but that it will be surpassed. CMC alone can't solve the TIT issue and I don't think that stoichiometric combustion can be achieved with the current engine architecture. We are still 400-500 Kelvins away from reaching stoichiometric combustion and we will get there within 5 years with SFC reductions of up to 40% (hence my suggestion in other threads of an A380 with the fuel burn of a B77W being within reach), but be prepared to see architectural changes.

When that new architecture hits the market, it will be interesting to watch if GE/RR/PW will take a lead or new entrants and even aircraft manufacturers start doing their own engine work.


How do you imagine another 400K? I don't think even CMC can do that, and I was under the correctable impression that we were doing about all that can be done in the way of turbine cooling with compressed air.
 
Exeiowa
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Re: What's next for mainstream jet engines?

Wed Sep 25, 2019 1:23 am

The energy density of a fuel cell system can be superior to a battery even newer potential systems will weigh more. The problem is the cost, and the nature of the fuel, hydrogen gas is difficult to store, absorbed on a palladium surface you can hold a lot or you can reform hydrocarbons in situ, but get unfortunate byproducts that eventually poison the platinum catalysts rendering them less efficient with time. This would be a.much more viable tech for long haul than a battery.
 
LH707330
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Re: What's next for mainstream jet engines?

Wed Sep 25, 2019 4:09 am

Thanks to all of you for an engaging discussion, always good to learn more. One technology that I've been curious about seeing again is water injection. I found these two papers that were a fun read:
https://mdao.grc.nasa.gov/publications/ ... _20_04.pdf
https://ntrs.nasa.gov/archive/nasa/casi ... 015629.pdf

The LPC misting system had a few major advantages:

1. Lowering NOx levels
2. Reducing TIT and hence engine maintenance costs
3. Minor improvements in takeoff fuel burn from the improved mass flow
4. Better SFC from the intercooling effect (less work for the HPC to do)

Those studies assumed that this would be implemented in an existing engine, most likely a T800. If a new engine/aircraft were designed to take this into account from the beginning, I could see it having the following advantages:

a. For a given amount of thrust, a smaller, higher-work core due to the increased mass flow of the water and the ability to have a higher air:fuel ratio due to the lower temperatures (use up the margin to get a higher overall temperature)
b. Lower engine weight due to the smaller core (not sure if this would offset the water plumbing weight)
c. Improved cruise SFC due to operating at a higher N1/N2 (most engines are sized for takeoff thrust, and in cruise are at a lower N1/N2, so having a smaller engine working at a higher % will give a better OPR and thus better SFC in cruise)

Thinking about this at a systems level, this could possibly also be used to increase ZFW near MTOW: you build an outboard water tank in the leading edge dry bays and use the water for bending moment relief on takeoff. As you climb out, you burn fuel from the center wing tank while taking water from the ends, thus keeping bending loads within margin until the CWT fuel has been sufficiently drawn down. Not sure if this is a dead end from a weight standpoint (longer water lines) or a reliability standpoint (water pump failure->imbalance, tank freezing at higher levels, etc.).

I heard mumbling of GE considering this for the GE9x a few years back, they must have nuked it for some reason.
 
CowAnon
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Re: What's next for mainstream jet engines?

Wed Sep 25, 2019 4:17 am

lightsaber wrote:
Open rotors have an efficiency curve. My Mach #s were for efficient cruise, derived partially from the data you reference.

The latest efficiency curve comes from a GE paper (I think) earlier this decade (see Figure 17 below). Open rotor peaks at 87% for Mach 0.73, but only declines to a little less than 86% at M0.80 before dropping to 80.x% at M0.85. So O.R. does fine at least to current narrowbody cruise speeds, and it might even be feasible for long-distance widebodies (not sure what the turbofan efficiency value is at M0.85).

Image

I've tested engines with Mach 0.84 redlines supersonic. That doesn't mean they are ready. I do the dangerous, disable the safeties testing. Y prior numbers are for in service, all the safeties on, limiting cruise speed on engine wear.

McDonnell Douglas flew airline executives and aviation reporters on the UDF demonstrator at Mach 0.76, so they didn't consider that speed particularly dangerous. From the data, they didn't really "let 'er rip" until the second-to-last day of testing (going to M0.81, M0.84, and then M0.86). Apparently the engine remained in good enough shape for McDD to fly it again the next day at Mach 0.77...

Also, McDD published a paper in summer 1989, which compared the performance specs of a GE36 UDF-equipped MD-91/92 against an IAE V2500-equipped MD-91V/92V and the existing MD-87/82. The UDF airliners were listed at Mach 0.76 cruise, just like the V2500 airliners and the MD-87/82.

I've taken engines that don't wear in allowed cruise and worn them in beyond spec high speed cruise. Get me an engine good for 20,000 FC and minimum 40,000 FH between overhauls when talking narrowbody engines. Widebody engines sacrifice cycles, rarely good for more than 8,000 FC. But they are pulled at flight hours (FH) or more precisely efficiency to minimize cost. Oh, hours too. When the backpressure sump regulator starts to stick, efficiency and wear suddenly turn for the worst.

That kind of reasoning I can accept. Alan Mulally did say that reliability and maintenance were the biggest issues for the UDF. I have no idea what the reliability specs for UDFs/propfans are, other than PW-Allison promising a 30,000-hour mean time between unexpected removals of the gearbox on its 578-DX propfan.

I like open rotor, but if they were all that, we would be flying in aircraft powered by them.

I find this "scoreboard" / "rational market" type of explanation unsatisfying for a couple of reasons. First, anybody could've said the same thing about features like geared turbofans on high-capacity airliners and been considered credible for most of the last half-century, but ultimately they would be wrong. Second, when Airbus announced that their proposed A340 widebody, which had been offered for months without gaining any orders, would have a high-bypass ducted fan (IAE SuperFan) as a powerplant option in 1986/1987, airlines (including "blue chip customer" Lufthansa) began buying the A340 left and right until IAE admitted after four months that they couldn't build the engine. If the more-efficient UDF, which proved itself in test flights on the Boeing 727 and the MD-81 over two years, can't attract any public orders, but the SuperFan can get ordered by 10 airlines for over 100 aircraft without having any test hardware or even an official diagram (the term "paper engine" might be giving the SuperFan too much credit!), doesn't that call into question the wisdom of the entire airline industry?
 
Waterbomber2
Posts: 448
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Re: What's next for mainstream jet engines?

Sat Sep 28, 2019 12:46 am

kitplane01 wrote:
Waterbomber2 wrote:
lightsaber wrote:
For 35 years the industry would agree with you invest in cmcs. It wasn't easy to get it right. the really hard part will be to mass produce CMCs in volume for good cost.


I think that CMC will play a role but that it will be surpassed. CMC alone can't solve the TIT issue and I don't think that stoichiometric combustion can be achieved with the current engine architecture. We are still 400-500 Kelvins away from reaching stoichiometric combustion and we will get there within 5 years with SFC reductions of up to 40% (hence my suggestion in other threads of an A380 with the fuel burn of a B77W being within reach), but be prepared to see architectural changes.

When that new architecture hits the market, it will be interesting to watch if GE/RR/PW will take a lead or new entrants and even aircraft manufacturers start doing their own engine work.


How do you imagine another 400K? I don't think even CMC can do that, and I was under the correctable impression that we were doing about all that can be done in the way of turbine cooling with compressed air.


There could be more than one solution.
But as said, a (major) architectural change may need to be considered.
 
WIederling
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Re: What's next for mainstream jet engines?

Sat Sep 28, 2019 9:15 pm

lightsaber wrote:
Due to NOx emission requirements, gas turbines will run overall lean.


I've seen approaches to that issue with reducing nitrogen in the equation ( for stationary applications. )

mobile: something like recirculating exhaust is a possibility.?
Murphy is an optimist
 
LH707330
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Re: What's next for mainstream jet engines?

Sun Sep 29, 2019 2:24 am

WIederling wrote:
lightsaber wrote:
Due to NOx emission requirements, gas turbines will run overall lean.


I've seen approaches to that issue with reducing nitrogen in the equation ( for stationary applications. )

mobile: something like recirculating exhaust is a possibility.?

Recirc like on a piston engine likely won't work at this scale, and would rob the engine of efficiency. The NOx issue is a problem for local air quality and is a bigger problem on takeoff, so I'm tempted to think that water injection might be a better bet there, as in the articles I linked earlier.
 
CowAnon
Posts: 76
Joined: Fri Nov 03, 2017 12:03 am

Re: What's next for mainstream jet engines?

Tue Oct 01, 2019 11:00 pm

flybaby wrote:
In the Boeing 787 Deferred Production Cost thread (AKA the Boeing unique accounting system thread) someone made a comment to the effect of ‘well, you know, in 10-15 years they’ll have to roll out a 787neo variant’... that got me thinking, is that realistic?

We started out with turbojets, then 1.5:1 bypass ratio fans, then ~5:1 and now we’re up to ~10:1. How far can this be stretched? Seems to me at some point the laws of thermodynamics start kicking in and you can only get so much from a bigger front fan. Over the years there have been all sort of odd-looking turbine-based designs but nothing has really caught on. So I am wondering, what’s next, realistically? A giant GTF? Something else?

I don't know if you consider this "mainstream", but the Kuznetsov NK-93 is a geared, ducted fan with a 16.6 bypass ratio and a variable pitch, reverse thrust fan.

https://www.flightglobal.com/news/artic ... gle-25218/
http://web.archive.org/web/201203140225 ... ation.html

Kuznetsov was confident enough in the NK-93's future success that it built a number of those engines in the early 1990s. The pace of development slowed to a crawl after the Soviet Union broke up, but Airbus and Snecma remained interested in adopting the engine in the mid-2000s, and the NK-93 made it to flight testing for a handful of flights in the late 2000s. Kuznetsov (or whatever their name is now) is actually working on NK-93 engine development to this day.

The NK-93's fan is 114 inches in diameter and produces 40,000 pounds of thrust, so it's kind of big (physically and thrust-wise) for a narrowbody, but too small for a twin-engine widebody. Still, something like the (~30-year-old!) NK-93 really should be the baseline engine technology for ducted fans at this point.
 
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Faro
Posts: 1929
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Re: What's next for mainstream jet engines?

Fri Oct 04, 2019 6:39 pm

Given the present issues dogging certain engine manufacturers...any significant engine innovation will have to have some very very serious durability/reliability testing done...

That in itself may become an industry innovation...


Faro
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