RJMAZ
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How will ultrafan seal the variable pitch fan?

Sat Jul 27, 2019 5:30 am

We have heard the Rolls Royce ultrafan will combine a gearbox and a variable pitch fan. The edge of a typical fixed fan blade will have the same curvature of the inside of the cowl. This allows a very tight air seal. However when the blade pitch is changes on the Rolls Royce Ultrafan it will create gaps.

The blade tip clearance is one of the most important steps in getting high efficiency.

What are your thoughts?
 
flipdewaf
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Re: How will ultrafan seal the variable pitch fan?

Sat Jul 27, 2019 7:00 am

I think RR have stepped back from the variable pitch part of the system and are just going for the gearbox.

I’m struggling to understand in my head in which orientation the greater effective curvature with respect to the axial flow would be and then which would be the pitch that would there for most efficiency during cruise. If it’s ok for cruise and then drops efficiency for takeoff/landing and reverse then probably just live with it but if it’s the other way then I’m not sure.

Currently there is abradable liners used for the fans to take count of rubbing so I’m not sure of the issue is all that great because there must be gaps already. There is a large issue for the core of the engine as a lot of the components creep over time and so need to manage the gaps in various ways there but I wasn’t aware of it being such an issue for the main fan.

Fred


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strfyr51
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Re: How will ultrafan seal the variable pitch fan?

Mon Jul 29, 2019 11:48 pm

Rolls now owns the technology on Gearboxes they got from Allison and the D501/T56 technology. They can duplicate the Gearbox and reasonably het the Fan right as they also have the Turbo-products Prop Technology that GM owned with the D501/ T56. Also? Dowty- Rotol is a British company isn't it? I'm not sure the Scimitar blades would even require an outer shroud though it might reduce the noise from the blade tips and Harmonic Vibrations on the Airframe Which is why we had Syncrophasers on the P3 to keep blades from passing the leading edge of the wink at the exact same time.
 
CowAnon
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Re: How will ultrafan seal the variable pitch fan?

Tue Jul 30, 2019 7:08 pm

Dowty-Rotol is British, and "Rolls-Royce" is actually represented in the name "Rotol", but the company is owned by its competitor General Electric now.

http://avstop.com/news_december_2010/ge ... _c130j.htm
 
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rjsampson
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Re: How will ultrafan seal the variable pitch fan?

Tue Jul 30, 2019 8:09 pm

flipdewaf wrote:
I think RR have stepped back from the variable pitch part of the system and are just going for the gearbox.


Hadn't heard that... So is the variable-pitch fan concept initially presented in the Ultrafan promotions.... essentially dead now? If so, why?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
flipdewaf
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How will ultrafan seal the variable pitch fan?

Wed Jul 31, 2019 4:22 am

rjsampson wrote:
flipdewaf wrote:
I think RR have stepped back from the variable pitch part of the system and are just going for the gearbox.


Hadn't heard that... So is the variable-pitch fan concept initially presented in the Ultrafan promotions.... essentially dead now? If so, why?

I’m not sure to be honest, I think it was that they were concerned about the implementation of two major architecture changes in a single engine and an eis on the A350neo. My guess would be that the variable pitch version has more benefits on shorter stages due to lighter weight and ability to Tailor pitch to the climb if requires. On a long flight the effect would be diminished through being able to be optimised for the cruise stage.

Fred


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CowAnon
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Re: How will ultrafan seal the variable pitch fan?

Sun Aug 25, 2019 7:22 pm

If you do a news search of
ultrafan "variable pitch"
in DuckDuckGo, the most recent hit from a standard aviation media website is from 5 years ago, so I think it's safe to assume that variable pitch won't be a feature. Since Rolls Royce is targeting long-range engines with its first UltraFan application, not having variable pitch won't be a huge loss. For short-range aircraft where cruise isn't the dominant flight stage (which you'd think RR would eventually target the UltraFan toward), the feature would have a huge benefit.

The following table compares the projected TSFC at sea level and at top of climb for geared turbofans, direct-drive (ungeared) turbofans, and open rotor engines in the ~25,000-pound thrust range. Notice that at top of climb, OR beats a GTF by about 12%, but at sea level, it outperforms the GTF by 39% because of the pitch control capability. It's not a 100% solid analogy, but you might assume that a variable-pitch GTF would come a lot closer to the performance of an open rotor engine than a fixed-pitch GTF.

Image

I'm puzzled by many aspects about the Ultrafan program. For example, RR first mentioned the Ultrafan as a concept in 2012 and officially got the ball rolling in 2014, but it's not supposed to do a full ground test until 2021 and be certified in 2025? GE's unducted fan wasn't even announced to the public until end of 1983 or early 1984, but it started ground tests in August 1985, began flight tests in August 1986, and finished initial flight testing on two different OEM testbeds by September 1988. The UDF was also scheduled for certification by the end of 1990, so the time from public announcement to certification would've been about six full years - less time than RR needs just to reach the ground testing stage.

How does the UltraFan with a more recent program like the Pratt & Whitney GTF? The PW GTF began ground testing in November 2007, started its first flight tests in July 2008, and got its first engine certification from Canada in February 2013. So that's 63 months between ground testing and certification. Under RR's schedule, the Ultrafan would need between 49 and 60 months after ground tests to achieve certification - an aggressive target IMO, considering how long RR is taking just to get to a ground test.
 
WIederling
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Re: How will ultrafan seal the variable pitch fan?

Mon Aug 26, 2019 7:18 am

"Performance prediction methodology and analysis of
a variable pitch fan turbofan engine" (2018)

https://hal.archives-ouvertes.fr/hal-02074473/document

looks interesting. ( not gone over yet.)
Murphy is an optimist
 
WIederling
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Re: How will ultrafan seal the variable pitch fan?

Mon Aug 26, 2019 7:38 am

CowAnon wrote:
https://ia801201.us.archive.org/BookReader/BookReaderImages.php?zip=/31/items/NASA_NTRS_Archive_20120014381/NASA_NTRS_Archive_20120014381_jp2.zip&file=NASA_NTRS_Archive_20120014381_jp2/NASA_NTRS_Archive_20120014381_0015.jp2&scale=4&rotate=0


Sample designs are 5000lbf thrust.

That is a very small engine.

Any idea on how that scales to a WB Twin sized engine?
Murphy is an optimist
 
OldAeroGuy
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Re: How will ultrafan seal the variable pitch fan?

Mon Aug 26, 2019 11:02 am

The 5000 lb is at Top of Climb.

For a modern Twin, L/D = 20, so ToC Weight = 200,000 lb.

At SL, Thrust = 23,000 to 27,000 lb

So it appears the engine would be in the size ballpark for a NB Twin.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Amiga500
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Re: How will ultrafan seal the variable pitch fan?

Mon Aug 26, 2019 11:26 am

RJMAZ wrote:
We have heard the Rolls Royce ultrafan will combine a gearbox and a variable pitch fan. The edge of a typical fixed fan blade will have the same curvature of the inside of the cowl. This allows a very tight air seal. However when the blade pitch is changes on the Rolls Royce Ultrafan it will create gaps.

The blade tip clearance is one of the most important steps in getting high efficiency.

What are your thoughts?


It'd need a very different approach I'd guess.

If you had a ring around the outside of the stage - kinda like [1], and the blades were slotted through that in something akin to a dome headed rivet that was mounted on bearings and free to rotate within the ring, then your clearance problem is at the fore and aft parts of the ring and not around the blade.

Problem of course is that while this won't see much tip vortex loads from individual blades - it will experience large longitudinal loads from the entire stage - which would affect tolerances for sealing. But I'm not sure if that would really matter anyway given the tip vortex should be limited by the presence of the ring anyway - which could theoretically be extended fore and aft of the blades to improve efficiency.

Would be heavy though I'd think.

[1] - this was probably intended for something very different than what I'm on about
Image
 
WIederling
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Re: How will ultrafan seal the variable pitch fan?

Mon Aug 26, 2019 3:30 pm

OldAeroGuy wrote:
The 5000 lb is at Top of Climb.

For a modern Twin, L/D = 20, so ToC Weight = 200,000 lb.

At SL, Thrust = 23,000 to 27,000 lb

So it appears the engine would be in the size ballpark for a NB Twin.


Look at the fan diameters in the paper. :-)
Murphy is an optimist
 
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rjsampson
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Re: How will ultrafan seal the variable pitch fan?

Mon Aug 26, 2019 7:57 pm

CowAnon wrote:
I'm puzzled by many aspects about the Ultrafan program.


So am I. My understanding (years ago) was that the "Advance" would be the technological breakthrough, which would evolve into the "Ultrafan."

And I sure don't see references to a variable-pitch fan any longer on the RR site. I had always assumed that RR's VPF was supposed to be a breakthrough akin to variable pitch stators from decades ago.

Seems like so many on this site when, thinking about future re-engines and future aircraft always mention they "will have the Ultrafan". I'm getting a bit lost in all this: We already have a GTF. As things stand now: For a fully-assembled engine that has yet to see the light of day: What is it about (promised) Ultrafan technology, that continues to inspire excited speculation?

At this point: I to am very puzzled, to say the least. (compression ratios? new materials? blisks? is that all?) ...I thank you in advance: Can some of you please, objectively, break down the promise of this "revolutionary" engine?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
OldAeroGuy
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Re: How will ultrafan seal the variable pitch fan?

Tue Aug 27, 2019 2:05 pm

WIederling wrote:
OldAeroGuy wrote:
The 5000 lb is at Top of Climb.

For a modern Twin, L/D = 20, so ToC Weight = 200,000 lb.

At SL, Thrust = 23,000 to 27,000 lb

So it appears the engine would be in the size ballpark for a NB Twin.


Look at the fan diameters in the paper. :-)


OK, let's compare the Direct Drive Turbofan with the CFM56-5.

Direct Drive Turbofan
Fan Diameter: 66 in
Takeoff Thrust: 22,700 lb

CFM56-5
Fan Diameter: 68.3 in
Takeoff Thrust: 22,000 - 26,500 lb

Seems to be fairly consistent.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
WIederling
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Re: How will ultrafan seal the variable pitch fan?

Tue Aug 27, 2019 5:18 pm

Amiga500 wrote:
[1] - this was probably intended for something very different than what I'm on about
Image


electric drive for boats, i'd guess:
https://en.wikipedia.org/wiki/Rim-driven_thruster
Murphy is an optimist
 
Karlsands
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Re: How will ultrafan seal the variable pitch fan?

Mon Sep 02, 2019 4:01 am

So this would be a “constant speed prop” in ways but with the jet fans ?
 
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DocLightning
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Re: How will ultrafan seal the variable pitch fan?

Mon Sep 02, 2019 10:39 pm

CowAnon wrote:
If you do a news search of
ultrafan "variable pitch"
in DuckDuckGo, the most recent hit from a standard aviation media website is from 5 years ago, so I think it's safe to assume that variable pitch won't be a feature. Since Rolls Royce is targeting long-range engines with its first UltraFan application, not having variable pitch won't be a huge loss. For short-range aircraft where cruise isn't the dominant flight stage (which you'd think RR would eventually target the UltraFan toward), the feature would have a huge benefit.


There is a secondary benefit. In a variable-pitch fan, if designed correctly, the pitch can actually be reversed so that the engine is now blowing air forward. Propellers already do this.

This means that you can get rid of about 500kg of thrust reverser mechanism on each engine. That's a lighter plane, or 1000kg more payload or fuel, depending on...many things.

The issues are 1) can the blades actually reverse without running into each other? If there's enough gap between blades to allow full rotation, will that hit efficiency? 2) Will having the engine in reverse risk starving the core of air?
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
CowAnon
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Re: How will ultrafan seal the variable pitch fan?

Wed Sep 11, 2019 6:57 pm

DocLightning wrote:
There is a secondary benefit. In a variable-pitch fan, if designed correctly, the pitch can actually be reversed so that the engine is now blowing air forward. Propellers already do this.

This means that you can get rid of about 500kg of thrust reverser mechanism on each engine. That's a lighter plane, or 1000kg more payload or fuel, depending on...many things.

The issues are 1) can the blades actually reverse without running into each other? If there's enough gap between blades to allow full rotation, will that hit efficiency? 2) Will having the engine in reverse risk starving the core of air?

Thanks for describing that. It's nice to see the benefits quantified in terms of weight.

rjsampson wrote:
Seems like so many on this site when, thinking about future re-engines and future aircraft always mention they "will have the Ultrafan". I'm getting a bit lost in all this: We already have a GTF. As things stand now: For a fully-assembled engine that has yet to see the light of day: What is it about (promised) Ultrafan technology, that continues to inspire excited speculation?

At this point: I to am very puzzled, to say the least. (compression ratios? new materials? blisks? is that all?) ...I thank you in advance: Can some of you please, objectively, break down the promise of this "revolutionary" engine?

Excellent questions, and I'm disappointed that nobody's chimed in on these yet. Maybe a geared turbofan at higher thrust levels by itself should be worthy of the hoopla, but why wouldn't people just refer to it as a widebody GTF then? The UltraFan branding and marketing has been working for RR, and I don't understand why. The name is similar in style to the IAE SuperFan, the engine that RR and its partners backed away from producing after it gained lots of orders in 1987. You'd think RR wouldn't want to call attention to that debacle.

I expect the UltraFan to be produced, but if variable pitch isn't included, it'll be the second time (along with the SuperFan) in about 3 decades that Rolls promised that feature and not delivered on it. Also, a few years after the SuperFan was killed, the Kuznetsov NK-93 ducted fan engine with variable pitch was introduced, which makes it curious why none of the major engine makers can offer that capability decades later.
 
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rjsampson
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Re: How will ultrafan seal the variable pitch fan?

Thu Sep 12, 2019 7:43 pm

So I guess it's save to assume the variable-pitch idea for the Ultrafan isn't going to happen. Really, the only REAL innovation I can see here are the cool-looking, blue CTi fan blades. I wonder why information on the Ultrafan is so hard to come by?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(

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