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william
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RR Ultrafan vs P&W GTF

Tue Jan 16, 2018 7:21 pm

https://www.rolls-royce.com/innovation/ ... x#solution

https://www.youtube.com/watch?v=7CU0B7VeLFU

For the laymen lurkers here (including myself) what are the differences in technology between the two powerplants?
One is claiming 12:1 and another 15:1. Both appear to be geared reduction (GE where are you on this front?).
 
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Channex757
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Re: RR Ultrafan vs P&W GTF

Tue Jan 16, 2018 7:35 pm

The main difference is that the Rolls Royce engine can change the pitch of its blades in operation. It can potentially also reverse the fan thrust like a turboprop, meaning that heavy thrust reverser mechanisms are not required.

GTF is a turbofan where the gearbox allows the fan to rotate at optimal speed. Ultrafan is almost like the combination of turbofan and ducted fan technologies. Two very different but also linked approaches.

GE is busy with their materials science, and running cores faster and hotter with CMC and other pushes past existing materials boundaries.
 
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frigatebird
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 9:23 am

Would there be any practical limits to the thrust levels applied to the GTF and Ultrafan? What I mean is if it's possible to have a large widebody twin like the (still theoretical) 777-10 or A350-2000 being powered by a GTF or Ultrafan engine.
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lightsaber
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 2:32 pm

frigatebird wrote:
Would there be any practical limits to the thrust levels applied to the GTF and Ultrafan? What I mean is if it's possible to have a large widebody twin like the (still theoretical) 777-10 or A350-2000 being powered by a GTF or Ultrafan engine.

At this time I would estimate they would be limited to 125k of thrust while a conventional engine could be designed up to 150k. With enough investment, they could go higher. With gearboxes, it requires adding a different active cooling system that must be developed, debugged, and understand the new failure modes for this ETOPS application for certification.

Lightsaber
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william
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 2:48 pm

Channex757 wrote:
The main difference is that the Rolls Royce engine can change the pitch of its blades in operation. It can potentially also reverse the fan thrust like a turboprop, meaning that heavy thrust reverser mechanisms are not required.

GTF is a turbofan where the gearbox allows the fan to rotate at optimal speed. Ultrafan is almost like the combination of turbofan and ducted fan technologies. Two very different but also linked approaches.

GE is busy with their materials science, and running cores faster and hotter with CMC and other pushes past existing materials boundaries.


The ability to change pitch like a turboprop? Wow, it is the 80s unducted prop fan come true. Surprised its only 15;1 ratio though.

What benefit is it for GE to run hotter cores? How is that more efficient than RRs Ultrafan?
 
mxaxai
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 5:32 pm

william wrote:
The ability to change pitch like a turboprop? Wow, it is the 80s unducted prop fan come true. Surprised its only 15;1 ratio though.

What benefit is it for GE to run hotter cores? How is that more efficient than RRs Ultrafan?

I don't know how much you know about turbofans and engines but in general, the hotter the combustion process is, the more efficient it is. Increasing temperature comes with some drawbacks though, such as
a) Increased NOx emissions
b) Increased need for cooling
c) New materials
d) (Usually) increased maintenance cost, and others.

The variable pitch is nice but remember that the mechanism is probably quite heavy. There's a reason it hasn't been implemented so far. It will be really interesting to see it in operation.
 
mxaxai
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 5:34 pm

lightsaber wrote:
frigatebird wrote:
Would there be any practical limits to the thrust levels applied to the GTF and Ultrafan? What I mean is if it's possible to have a large widebody twin like the (still theoretical) 777-10 or A350-2000 being powered by a GTF or Ultrafan engine.

At this time I would estimate they would be limited to 125k of thrust while a conventional engine could be designed up to 150k. With enough investment, they could go higher. With gearboxes, it requires adding a different active cooling system that must be developed, debugged, and understand the new failure modes for this ETOPS application for certification.

Lightsaber

Would that be 125 kN or 125 klbf? If the latter, it seems excessive for all aircraft in development today, and therefore no problem.
 
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Channex757
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 5:54 pm

Rolls Royce have been suggesting recently that Ultrafan is going to initially be aimed at the middle of the market, where potential applications will be at first. Forthcoming A320 and 737 replacements, then up to the A330 replacement and 787 re-engines which are under 80klbf

There isn't really a market for a high thrust version for the next 25 years or so as the Trent XWB-97 growth and PIP options will be out there, and the GE9X will be in its life cycle.

As we are on the subject, it's no surprise that the two engine suppliers with wide experience of turboprops are the ones leading the gearing charge. It would be nice of there was less friction over patents. Rolls Royce Deutschland is the division doing the work on Ultrafan at the moment.
 
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kitplane01
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 5:55 pm

Channex757 wrote:
The main difference is that the Rolls Royce engine can change the pitch of its blades in operation. It can potentially also reverse the fan thrust like a turboprop, meaning that heavy thrust reverser mechanisms are not required.

GTF is a turbofan where the gearbox allows the fan to rotate at optimal speed. Ultrafan is almost like the combination of turbofan and ducted fan technologies. Two very different but also linked approaches.

GE is busy with their materials science, and running cores faster and hotter with CMC and other pushes past existing materials boundaries.


I always understood "ducted fan" and "turbo fan" to regions on a continuum. Both are fan blades running in a cowling .. the only difference being bypass ratio. There is no cutoff and it's totally possible to be in the middle, just like there is no cutoff between "hot" and "cold".
 
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kitplane01
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 5:56 pm

lightsaber wrote:
frigatebird wrote:
Would there be any practical limits to the thrust levels applied to the GTF and Ultrafan? What I mean is if it's possible to have a large widebody twin like the (still theoretical) 777-10 or A350-2000 being powered by a GTF or Ultrafan engine.

At this time I would estimate they would be limited to 125k of thrust while a conventional engine could be designed up to 150k. With enough investment, they could go higher. With gearboxes, it requires adding a different active cooling system that must be developed, debugged, and understand the new failure modes for this ETOPS application for certification.

Lightsaber


Do current gearboxes have a cooling system, beyond the oil?

If a gearbox absorbs even one percent of 30,000 horsepower, that's a lot of heat into a very small thing.
 
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kitplane01
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 5:58 pm

mxaxai wrote:

The variable pitch is nice but remember that the mechanism is probably quite heavy. There's a reason it hasn't been implemented so far. It will be really interesting to see it in operation.



That's not obviosuly true. The variable pitch mechanism for normal props is quite small and light, and there are props aborbing 11,000 hp with eight blades.
 
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kitplane01
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 6:01 pm

GE seems to be all about material science and a hotter core. RR and PW both seem to be into better fans, with gears and maybe variable pitch. Anyone wanna guess what the result of a combination might produce, in terms of fuel consumption compared to current technology.
 
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Channex757
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 6:10 pm

An engine using a GE core, powering a Pratt gearbox and a new RR carbon-titanium fan assembly would be a huge step forward. Hardly likely to happen though. The most recent collaboration, the Engine Alliance GP7200, was after all a blend of two mature engines. These technologies are cutting edge.

I would expect as a guess a 25% or better saving over today's best engines thanks also due to weight savings and that core efficiency. If you then recast the project to a GE core and RR Ultrafan with variable pitch C-Ti blades then that figure goes even higher as more weight gets saved in the deletion of reversers.
 
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 6:14 pm

IMO, the fan innovations like gearing and variable pitch blades are "low hanging fruit" compared to the materials advancement in the core. (Relatively speaking - GTF and Ultrafan are very impressive pieces of technology)

Once the materials improvements are mature, a geared or variable pitch fan could be added to a future design with much less relative effort/investment.
 
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william
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 7:24 pm

mxaxai wrote:
william wrote:
The ability to change pitch like a turboprop? Wow, it is the 80s unducted prop fan come true. Surprised its only 15;1 ratio though.

What benefit is it for GE to run hotter cores? How is that more efficient than RRs Ultrafan?

I don't know how much you know about turbofans and engines but in general, the hotter the combustion process is, the more efficient it is. Increasing temperature comes with some drawbacks though, such as
a) Increased NOx emissions
b) Increased need for cooling
c) New materials
d) (Usually) increased maintenance cost, and others.

The variable pitch is nice but remember that the mechanism is probably quite heavy. There's a reason it hasn't been implemented so far. It will be really interesting to see it in operation.


I have a pretty good grasp how turbofans work, why would a hotter core be more efficient? Heat is a form of energy wasted in some respects. More efficient combustion burn? In the end one still needs GTF to slow the main blade to a more efficient RPM. I know I am simplifying things.
 
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william
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 7:30 pm

Who of us have experienced landing on a short runway in a turboprop at full reverse? Yeah, I still remember the first time. Trying to imagine that same feeling in a WB the size of an A330.
 
bhill
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 7:31 pm

For the bigger..>100k thrust engines, what is the market? I ask because of the A380 possible line closure....
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WIederling
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Re: RR Ultrafan vs P&W GTF

Wed Jan 17, 2018 10:59 pm

william wrote:
I have a pretty good grasp how turbofans work, why would a hotter core be more efficient? Heat is a form of energy wasted in some respects. More efficient combustion burn? In the end one still needs GTF to slow the main blade to a more efficient RPM. I know I am simplifying things.


The Carnot (cycle) equation defines the maximum achievable efficiency. N_carnot = 1 - (T_low / T_high) (T in °Kelvin absolute temp.)
T_low is your environment and thus fixed. T_high is the screw you can "turn".

Similar effect works for higher pressure ratio.

Limit at any time is where the technology shortcomings limit your access to the theoretical optima.
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Channex757
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Re: RR Ultrafan vs P&W GTF

Thu Jan 18, 2018 12:16 am

bhill wrote:
For the bigger..>100k thrust engines, what is the market? I ask because of the A380 possible line closure....

A350NEO is a possibility plus whatever the Chinese and Russians manage to cook up in their collaboration.

We are talking about twenty years in the future. The A380 would not require an engine of that size anyway. Only big twins need >100k motors and even then in 25 years who knows what will be flying. A hybrid widebody prototype with graphene batteries in the wings....?
 
mxaxai
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Re: RR Ultrafan vs P&W GTF

Thu Jan 18, 2018 4:52 pm

william wrote:
I have a pretty good grasp how turbofans work, why would a hotter core be more efficient? Heat is a form of energy wasted in some respects. More efficient combustion burn? In the end one still needs GTF to slow the main blade to a more efficient RPM. I know I am simplifying things.

This is an ideal carnot (combustion) cycle (1-2-3-4). I will use it for explanation, an actual jet engine's cycle is slightly different. This cycle achieves the maximum possible efficiency of all cycles with the same maximum and minimum temperatures.
Image
Any transfer of heat is connected with a transfer of entropy. Since overall entropy in the engine must not increase, the cycle needs to be closed. The added heat (in the combustion chamber) can be viewed as the area under the line 1->2 (blue). The heat lost (in the nozzle) is accordingly the area under the line 3->4 (red). The usable energy is the heat added minus the heat lost, i. e. the area enclosed within this cycle (green). This energy is all that matters to the aircraft manufacturer because it determines the engine's thrust (or power). Typically, the lower temperature is set by the surrounding conditions, e. g. the ambient air temperature. Therefore, increasing the upper temperature can reduce the red rectangle's size without changing the green rectangle's area. So you get the same thrust but waste less heat/energy, which is stored in the fuel.

This is an enthalpy-entropy diagram of a turbofan from my textbook on jet engines:
Image
QB is the heat added during the combustion process.
 
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william
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Re: RR Ultrafan vs P&W GTF

Sat Jan 27, 2018 6:04 am

Thank you for the responses and explanations but GE is just too quiet. P&W and RR have been getting good PR from their latest and emerging technologies. I have a feeling GE is working on their own "ultra fan" engine with their higher core temps as their ace in the hole.
 
WIederling
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Re: RR Ultrafan vs P&W GTF

Sat Jan 27, 2018 11:14 am

william wrote:
Thank you for the responses and explanations but GE is just too quiet.


GE has bought AVIO. AVIO manufactures the gearbox for the GTF range and TP400D6 :-)


Amusing article by Richard Aboulafia from 2015:
http://aviationweek.com/commercial-avia ... disruption
Murphy is an optimist
 
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KarelXWB
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Re: RR Ultrafan vs P&W GTF

Wed Feb 07, 2018 6:27 pm

I'm not sure if we can simply compare a 2025 Ultrafan against a 2015 GTF. Aside from further PIPs, P&W is working on a second generation GTF that should go into service around 2025.
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