imiakhtar
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Fan Blades: Titanium Vs Composite

Fri Jun 22, 2012 7:50 pm

This side-by-side image of the trent 1000 and GEnx got me thinking:

http://farm8.staticflickr.com/7105/7173056585_65ca6e265a_c.jpg
Rolls-Royce Trent 1000 v. General Electric GEnx-1B by Jon Ostrower, on Flickr

RR on the left and the GE is on the right.

RR, for the past 40 years has been using titanium fan blades (it's first attempt on the Rb211-22B resulted in bankruptcy). GE also used Ti blades until 1995 when it introduced the GE90 with composite blades with Ti leading edges. Pratt, on it's last major engine the GP7200, decided to stick with a Ti fan.

Recently however, RR has anounced that it will make a switch to composite blades for high thrust engines when the Trent XWB comes into service.

My question is, why has it taken RR and Pratt so long to make the switch when the technology has been mature for a long while, and what advantages do Ti fans have over carbon composite blades?
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tdscanuck
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RE: Fan Blades: Titanium Vs Composite

Fri Jun 22, 2012 8:14 pm

Quoting imiakhtar (Thread starter):
RR, for the past 40 years has been using titanium fan blades (it's first attempt on the Rb211-22B resulted in bankruptcy).

The RB211 was originally supposed to have a Hyfil (carbon fiber) fan...the Ti blades did not go well on the RB211 but they weren't the cause of the bankruptcy.

Quoting imiakhtar (Thread starter):
My question is, why has it taken RR and Pratt so long to make the switch when the technology has been mature for a long while

The technology has been mature *inside GE*. The ability to make large CFRP fan blades is a huge piece of valuable intellectual property for GE and they're not sharing. PW and RR had to re-engineer how to do it all while maintaining their Ti blade production. It's also an extremely different process than building Ti blades; most OEM's don't have the resources to be developing both at the same time.

Quoting imiakhtar (Thread starter):
what advantages do Ti fans have over carbon composite blades?

Easier to build. Not that a Ti blade is easy, just easier. They also take temperature much better, which is more of a factor for very fast engines (i.e. military) than civilian.

Tom.
 
imiakhtar
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RE: Fan Blades: Titanium Vs Composite

Fri Jun 22, 2012 8:28 pm

Thanks Tom. I was hoping you'd participate.

Quoting tdscanuck (Reply 1):
The RB211 was originally supposed to have a Hyfil (carbon fiber) fan...the Ti blades did not go well on the RB211 but they weren't the cause of the bankruptcy.

Right you are. I wasn't clear enough. I seem to recall reading the the Hyfil blades weren't very strong and were susceptible to FOD.

Is there any appreciable difference in fan blade weight between the two?

Also, as you can see on the GE90 and GEnx, the fan blade leading edge is Ti. Is this to ensure the fan blades can withstand FOD/bird strikes?

Lastly, how do the two compare in terms of ease of maintenance and longevity? Are the creep properties of the materials comparable?

Thanks in advance.
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tdscanuck
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RE: Fan Blades: Titanium Vs Composite

Fri Jun 22, 2012 10:10 pm

Quoting imiakhtar (Reply 2):
I seem to recall reading the the Hyfil blades weren't very strong and were susceptible to FOD.

They were plenty strong in normal loading; it was impact (FOD) that did them in.

Quoting imiakhtar (Reply 2):
Is there any appreciable difference in fan blade weight between the two?

I don't know numbers but they've got to be close, otherwise there'd be a really significant difference in the fan case containment.

Quoting imiakhtar (Reply 2):
Also, as you can see on the GE90 and GEnx, the fan blade leading edge is Ti. Is this to ensure the fan blades can withstand FOD/bird strikes?

I believe it's more for errosion protection; the CFRP area is a lot larger than the Ti area so you wouldn't be able to count on the FOD hitting the Ti leading edge.

Quoting imiakhtar (Reply 2):
Lastly, how do the two compare in terms of ease of maintenance and longevity? Are the creep properties of the materials comparable?

As far as I know, they both last practically forever. I've heard GE claim that a GE90 blade has never been removed in service for anything to do with the blade (just for FOD damage). The Ti blades also basically don't corrode, although I think they have a higher chance of developing fatigue cracks over their life. They're both amazing technologies and components. I've been trying to get a GE90 fan blade just for my own display for ages.

Tom.
 
Northwest727
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RE: Fan Blades: Titanium Vs Composite

Fri Jun 22, 2012 11:38 pm

Carbon fiber I've noticed is also making its way to propellers as well. Its amazing how lightweight yet strong the blades are. Based on the cost difference of carbon fiber propellers vs. standard metal propellers, I'm curious if cost has anything to do with it. Not that titanium is cheap either.

Quoting tdscanuck (Reply 3):
I've been trying to get a GE90 fan blade just for my own display for ages.

Dare I ask how much one of those blades costs...probably more than a brand new luxury sedan!
 
tdscanuck
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RE: Fan Blades: Titanium Vs Composite

Sat Jun 23, 2012 3:05 am

Quoting Northwest727 (Reply 4):
Dare I ask how much one of those blades costs...probably more than a brand new luxury sedan!

I assume one can buy replacement blades from GE but I don't know what they charge...I wouldn't be very surprised if it was north of $100,000 as a spare.

I know a guy who's got one...apparently GE used to put a GE90 fan blade in an internal charity auction some years. Needless to say, the guys who have them know what they've got and aren't letting go.

Tom.
 
jetlife2
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RE: Fan Blades: Titanium Vs Composite

Mon Jun 25, 2012 11:14 pm

Tom your answers are right on. By now after 30 million hrs, there have been GE90 blades removed for damage, but very few. The Ti leading edge is for protection from stones etc. The blades are really, really strong. We have taken very very big birds, far in excess of requirements (2x Canada Geese) and kept on running.

We like our composite solution better for total system weight (rotor, blades, case): on the GEnx we now have both composite blades and composite case; but we could start a long debate here about that...

Other point: Yes it is true we have auctioned a blade for charity internally a few times. The final donation has been into 5 digits on occasion....which is a great way for the charity to benefit.

Cheers

GHR
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DocLightning
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RE: Fan Blades: Titanium Vs Composite

Mon Jun 25, 2012 11:47 pm

Quoting jetlife2 (Reply 6):
We like our composite solution better for total system weight (rotor, blades, case): on the GEnx we now have both composite blades and composite case; but we could start a long debate here about that...

I'm confused by this sentence. Does this mean that you see weight as being the main advantage of composite blades,or do you mean that among the advantages are total system weight?

What is the weight difference between a Trent 1000 blade and a GEnX blade?

Also, I was under the impression that RR tended to spin their fans counter-clockwise. Apparently this is not true for the Trent 1000?
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jetlife2
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 1:05 am

Quoting DocLightning (Reply 7):
I'm confused by this sentence. Does this mean that you see weight as being the main advantage of composite blades,or do you mean that among the advantages are total system weight?

What is the weight difference between a Trent 1000 blade and a GEnX blade?

Also, I was under the impression that RR tended to spin their fans counter-clockwise. Apparently this is not true for the Trent 1000?

Sorry if I was not clear. I meant "we like our composite blade solution better than a design using titanium blades, because of the benefit to total system weight". Yes the system weight is the main benefit.

I don't personally know the difference in the blade weights, and I'm not sure the data has been published.

Rotation direction is quoted ALF so the Trent is indeed counter-clockwise. What is unusual, as the picture shows, is that the GEnx is also. This is the opposite of most GE designs including the GE90, which rotates the other way. I'm pretty sure the reason for this would have been documented in another thread here somewhere so I wont reiterate.

Cheers
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tdscanuck
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 1:12 am

Quoting DocLightning (Reply 7):
Also, I was under the impression that RR tended to spin their fans counter-clockwise. Apparently this is not true for the Trent 1000?

The Trent1000 went to counter-rotating spools. Something had to change direction.

Tom.
 
ecbomberman
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 12:36 pm

Quoting tdscanuck (Reply 3):


I'm a poor Biomedical Materials Scientist who have forgotten almost everything I've studied. I would appreciate if you can tell me whether creep would be a factor considering the huge amount of centrifugal force and heat present when the engines are running. Wouldn't this affect the usable period of the blades/engine?

Just some interesting facts. My Uni did lots of research for RR and in one of the lectures the lecturer brought an RR RBxxx fan blade up. For those who think that Ti fan blades is just pure solid Ti, they're wrong. Ti itself will melt inside the engine core when it is up and running. All that my lecturer is willing to say is that they have vanes that guide cool air to the fan blades to cool them down
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ecbomberman
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 12:42 pm

Quoting imiakhtar (Thread starter):
Quoting imiakhtar (Thread starter):
GE also used Ti blades until 1995 when it introduced the GE90 with composite blades with Ti leading edges.

Just out of curiosity, aren't 77E with GE90 heavier than those with Trent's? Hence the question, does the way that each manufacture make their engine (a well hidden secret) matters as much as the materials used?
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imiakhtar
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 1:10 pm

Quoting ecbomberman (Reply 10):
Just some interesting facts. My Uni did lots of research for RR and in one of the lectures the lecturer brought an RR RBxxx fan blade up. For those who think that Ti fan blades is just pure solid Ti, they're wrong. Ti itself will melt inside the engine core when it is up and running. All that my lecturer is willing to say is that they have vanes that guide cool air to the fan blades to cool them down

It seems you are confusing fan blades (see pic of fan in opening post) with turbine blades in the core of the engine. As you correctly noted, turbine blades are made of a blend of exotic metals, usually nickel-chromium superalloys, to withstand the high temperatures in the engine core.

Quoting ecbomberman (Reply 11):
Just out of curiosity, aren't 77E with GE90 heavier than those with Trent's? Hence the question, does the way that each manufacture make their engine (a well hidden secret) matters as much as the materials used?

A GE90 powered 77E is in the region of 6000lbs heavier than a Trent 800 powered 77E. Though I believe that's more to do with the triple spool architecture of the Trent than the materials used.

Some relevant reading can be found here:

http://www.google.co.uk/search?q=lig...dir_esc=&ei=qLHpT7j5KsqQ0AWb5_WpAQ
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tdscanuck
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 5:05 pm

Quoting ecbomberman (Reply 10):
I would appreciate if you can tell me whether creep would be a factor considering the huge amount of centrifugal force and heat present when the engines are running. Wouldn't this affect the usable period of the blades/engine?

Creep requires stress to be extremely high (very close to the yield stress) or the temperature to be high. Neither condition typically occurs in fan blades so creep typically isn't such a big deal for them. Fretting at the blade/hub joint and fatigue are bigger factors in the fan.

Creep is a huge issue for turbine blades because they're operating in a gas stream well above their melting temperature.

Quoting ecbomberman (Reply 10):
For those who think that Ti fan blades is just pure solid Ti, they're wrong.

This is true for modern large wide-chord blades. Small Ti fans, like the CF34, are still solid.

Quoting ecbomberman (Reply 10):
Ti itself will melt inside the engine core when it is up and running.

That's why they typically don't use Ti for HP turbine blades.

Quoting ecbomberman (Reply 10):
All that my lecturer is willing to say is that they have vanes that guide cool air to the fan blades to cool them down

I've never seen a fan with actively cooled blades; what you're describing is much more likely in the turbine. That said, it all depends where you are in the engine. For example, the PT-6 power turbine has Ti blades with no active cooling.

Tom.
 
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bikerthai
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 7:29 pm

Quoting imiakhtar (Thread starter):

My question is, why has it taken RR and Pratt so long to make the switch when the technology has been mature for a long while,
Quoting tdscanuck (Reply 1):
The technology has been mature *inside GE*. The ability to make large CFRP fan blades is a huge piece of valuable intellectual property for GE and they're not sharing.

The original GE fan blade used fiber placed technology which was in it's infancy when the 777 came about. GE, and Boeing did much development work then and had many patents which may have restricted uses by other companies until now.

Fiber placed technology is stronger than filament winding and cheaper than hand lay-up. The ability to control the fiber direction makes it more efficient for fan blades where stress direction can vary along the length and cord. With hand lay-up, it is more difficult with unidirectional fiber and less efficient if you use a weave. Thing like resin transfer molding and knitted system do not provide sufficient fiber to resin ratio (efficiency)

Quoting tdscanuck (Reply 3):
otherwise there'd be a really significant difference in the fan case containment.
Quoting jetlife2 (Reply 8):
I don't personally know the difference in the blade weights, and I'm not sure the data has been published.

This is why jetlife2 mentioned "system" as the fan case should be considered into the equation because the failure mode for a composite blade and titanium blade are different. I do not know if GE have had any luck convincing the FAA though.

Glad hear from a "engine" guy. Not an expert on engines, but did rub elbows with those guys back in the days and got some knowledge through osmosis.

As for the titanium blades. They used to be machined hollow core blades that are diffusion bonded together. But I think the more efficient Ti blades are now super plastic formed/diffusion bonded titanium.

If you take the fan case out of the equation, then what I recall (from osmosis) is that for the smaller blades, it may be for effective to use SPF/DB titanium. As the blade size gets bigger, then the fiber placed blades are better. Of course fabrication economics can often comes in to the equation, and those economics have changed since those days . . .

bt
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MD11Engineer
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 9:47 pm

Overheated turbine vanes look first like this:
http://www.airliners.net/uf/6241/phpgdApeR.jpeg
(Burn with cracks forming, but still in limits, since it is a vane and not a blade)

and later like this:
http://www.airliners.net/uf/6241/phpMSNW0U.jpeg

Defintely out of limits! The engine was sent for overhaul.

The cracks have propogated and joined, so that parts of the trailing edge have broken off. This in turn reduced the internal cooling of the vane because the cooling air could escape through the resulting hole, leading to more burnthroughs and damage.

The engine is a PW4000 and the vanes are of the second stage HPT. This is a known problem, as the engine gets older the performance of the airfoils of the compressor and turbine decreases through wear and the EEC tries to compensate for the loss of performance by adding more fuel to reach the commanded EPR, running on a higher EGT. Eventually the internal cooling of the turbine blades and vanes will not be sufficient anymore and the metal will be affected. Additionally the ceramic coating of the blades and vanes will wear down through erosion so that the bare base metal will be exposed to the hot gases.
PW has issued a service bulletin adressing this issue with regular inspections.

Last week I condemned another engine for this reason. My boss (and airline CEO) was not happy (the overhaul will cost about $ 3 million, plus the loss of several flights while the aircraft was grounded and the expenses of getting a lease engine from the US to Europe).

Jan
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jetlife2
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RE: Fan Blades: Titanium Vs Composite

Tue Jun 26, 2012 11:04 pm

If you are interested in some of the nitty gritty (this is the Tech Ops forum after all!):

There is an excellent public domain presentation by a couple of very knowledgeable GE guys, about the GE90 fan blade (Base Engine, i.e. GE90-94B series) service experience here:

http://www.google.com/url?sa=t&rct=j...aGdVBWuPaoE4atco9WUnRGWOjg&cad=rja

Cheers

GHR
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DocLightning
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RE: Fan Blades: Titanium Vs Composite

Wed Jun 27, 2012 1:17 am

Quoting jetlife2 (Reply 8):
Rotation direction is quoted ALF so the Trent is indeed counter-clockwise. What is unusual, as the picture shows, is that the GEnx is also

Unless they changed the design of clocks, I'm pretty sure that both seem to look like clockwise rotators to me.

Quoting MD11Engineer (Reply 15):
The cracks have propogated and joined, so that parts of the trailing edge have broken off.

Wouldn't the debris damage downstream components?
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MD11Engineer
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RE: Fan Blades: Titanium Vs Composite

Wed Jun 27, 2012 8:46 am

Quoting DocLightning (Reply 17):
Quoting MD11Engineer (Reply 15):
The cracks have propogated and joined, so that parts of the trailing edge have broken off.

Wouldn't the debris damage downstream components?

Yup. The danger exists. PW tolerates debris up to a size of 3 x 3 mm, but anything bigger can cause damage in the LP turbine. This is also when our boss was trying to cajole us to release the aircraft we sent the pictures to our PW rep and the answer came quickly that it was out of limits.

Jan
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ecbomberman
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RE: Fan Blades: Titanium Vs Composite

Wed Jun 27, 2012 12:31 pm

Quoting tdscanuck (Reply 13):

Sorry, I sometimes do have the tendency to drift away from the topic.
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imiakhtar
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RE: Fan Blades: Titanium Vs Composite

Wed Jun 27, 2012 12:39 pm

Quoting bikerthai (Reply 14):
As for the titanium blades. They used to be machined hollow core blades that are diffusion bonded together. But I think the more efficient Ti blades are now super plastic formed/diffusion bonded titanium.

I climbed into my attic and managed to find my old RR jet engine copy. You're on the money:

'A hollow blade has a cavity within the aerofoil and is formed from three sheets of titanium: two outer sheets and one inner sheet - a very thin membrane. These blades are produced using diffusion bonding and super-plastic forming processes.'

Rolls Royce The Jet Engine 2005 edition (page 103).

Best £35 I ever spent.
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jetlife2
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RE: Fan Blades: Titanium Vs Composite

Wed Jun 27, 2012 1:35 pm

Quoting DocLightning (Reply 17):
Quoting jetlife2 (Reply 8):
Rotation direction is quoted ALF so the Trent is indeed counter-clockwise. What is unusual, as the picture shows, is that the GEnx is also

Unless they changed the design of clocks, I'm pretty sure that both seem to look like clockwise rotators to me.

They do look that way FLA (forward looking aft), as in the photos, but the point I was making is that rotation direction is always quoted ALF (aft looking forward), so they are actually counter-clockwise.
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bikerthai
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RE: Fan Blades: Titanium Vs Composite

Wed Jun 27, 2012 1:59 pm

Quoting jetlife2 (Reply 16):

Good read. Would have liked more details.

However, it seems that most of the damage on the composite blade can be repaired.

How would you do the same for a SPF/DB Titanium fan blade (given that the titanium blade would get less damage).

- Pound out the deformed edges?
- Trim and weld new pieces?
- Just re-cycle the whole blade?

bt
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jetlife2
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RE: Fan Blades: Titanium Vs Composite

Wed Jun 27, 2012 2:49 pm

Quoting bikerthai (Reply 22):
How would you do the same for a SPF/DB Titanium fan blade (given that the titanium blade would get less damage).

- Pound out the deformed edges?
- Trim and weld new pieces?
- Just re-cycle the whole blade?

bt

It's not a given that the titanium blade gets less damage. As the presentation shows, composite blades are very tough and very tolerant, and the scrap rate is nearly zero.

Having said that, I would also be curious in the answers to these questions!  
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DocLightning
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RE: Fan Blades: Titanium Vs Composite

Thu Jun 28, 2012 12:53 am

Quoting jetlife2 (Reply 21):
They do look that way FLA (forward looking aft), as in the photos, but the point I was making is that rotation direction is always quoted ALF (aft looking forward), so they are actually counter-clockwise.

Ah. I didn't know that.
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