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GTF Or UDF Which Is The Engine Of Future?  
User currently offlineTangowhisky From United States of America, joined Jun 2006, 910 posts, RR: 7
Posted (6 years 2 months 1 week 6 days 22 hours ago) and read 16231 times:

Even though the unducted fan has the potential for significant fuel savings over today's ducted turbofans, I have serious doubts that the unducted fan will become a success due to practical reasons. Here is why:

1) It has been documented that a UDF will have speed and altitude limitations. It will not fly even close to today's narrowbody cruise speeds, and will not be capable of climbing to high altitudes. These are due to the fact that there is very little jet thrust, and almost all the thrust is generated by the fan blades (like a turboprop).
2) Flying slower will make trips less than 600 miles less appealing. It will also increase block times, reduce utilization for adding more flights. It will encourage more rail systems in the US, and greater usage of the success of rail in Europe and now it seems Asia where they are investing in rail.
3) UDF poses significant challenges when it comes to configuration of the engine on the airframe. The large and unprotected blades will require that the engines be mounted high and aft. I have seen configurations where the engines are supported in the rear of the aircraft with additional structure (this means more weight, additional maintenance inspections, additional manufacturing costs, more difficult maintenance access, etc.)
4) If the UDF engines are not on the wings, then it brings back a whole host of systems engineering issues when it is located at the back of the plane. For example, the high temperature engine bleed lines for wing deicing have to be longer, require more sensors for leak detection, and will increase weight and maintenance costs. This is just one of many such systems design issues.
5) Last I don't see the UDF engine making it on long range widebodies as the speed and altitude restrictions alone will not be practical for the purpose of widebodies.

I would like to read others' comments and views as GE and RR are downplaying the GTF and talking up the UDF.


Only the paranoid survive
133 replies: All unread, showing first 25:
 
User currently offlineBurkhard From Germany, joined Nov 2006, 4395 posts, RR: 2
Reply 1, posted (6 years 2 months 1 week 6 days 21 hours ago) and read 16231 times:

The biggest advantage I see on the GTF is that is can be available much earlier in real application, 2012 or 2013. It is the smaller change in a very conservative industry.

The UDF I see more as an extension of what Turboprops do today. I would not wonder to have a UDF on a hundred seater optimized for below 800 miles, where top speeds just means a few minutes, in 2018.


User currently offlineCpd From Australia, joined Jun 2008, 4879 posts, RR: 38
Reply 2, posted (6 years 2 months 1 week 6 days 21 hours ago) and read 16221 times:

GTF appears to be much more of a almost here and almost now thing. The UDF I doubt will be accepted by the travelling public, we don't like slower speeds than what we already have. But that's just from a end user point of view. We want to get home quickly to our families rather than being cramped up on a tiny and noisy flying toothpaste tube.

Wasn't the other advantage of the GTF the fact that it would be quieter?


User currently offlineDocLightning From United States of America, joined Nov 2005, 19513 posts, RR: 58
Reply 3, posted (6 years 2 months 1 week 6 days 21 hours ago) and read 16193 times:



Quoting Tangowhisky (Thread starter):
Flying slower will make trips less than 600 miles less appealing. It will also increase block times, reduce utilization for adding more flights. It will encourage more rail systems in the US

Stop right there. I have come to the conclusion that you could hit Americans with "Build High-Speed Rail or the aliens will invade" and provide good evidence...and no HSR would be built.


User currently offlineBoeing4ever From , joined Dec 1969, posts, RR:
Reply 4, posted (6 years 2 months 1 week 6 days 21 hours ago) and read 16187 times:

Interesting thread.

Quoting Tangowhisky (Thread starter):
1) It has been documented that a UDF will have speed and altitude limitations. It will not fly even close to today's narrowbody cruise speeds, and will not be capable of climbing to high altitudes. These are due to the fact that there is very little jet thrust, and almost all the thrust is generated by the fan blades (like a turboprop).

Don't forget noise restrictions. From what I've read UDFs were noisy during flight tests in the late '80's. But it may come down to noise pollution vs. air pollution.

Quoting Tangowhisky (Thread starter):
2) Flying slower will make trips less than 600 miles less appealing. It will also increase block times, reduce utilization for adding more flights. It will encourage more rail systems in the US, and greater usage of the success of rail in Europe and now it seems Asia where they are investing in rail.

I would imagine they'd be ideal for short range trips...it's long range trips where the lack of speed hurts IMO. To get rail systems in the US as well developed as in Europe will take significant capital investment. Road systems on the other hand...I dunno, 600 miles, if it's cheap I'd probably fly, inspite of the lower cruise speed.

Quoting Tangowhisky (Thread starter):
3) UDF poses significant challenges when it comes to configuration of the engine on the airframe. The large and unprotected blades will require that the engines be mounted high and aft. I have seen configurations where the engines are supported in the rear of the aircraft with additional structure (this means more weight, additional maintenance inspections, additional manufacturing costs, more difficult maintenance access, etc.)



Quoting Tangowhisky (Thread starter):
4) If the UDF engines are not on the wings, then it brings back a whole host of systems engineering issues when it is located at the back of the plane. For example, the high temperature engine bleed lines for wing deicing have to be longer, require more sensors for leak detection, and will increase weight and maintenance costs. This is just one of many such systems design issues.

Why not mount them above the wing a la Hondajet HA-420?







This might alleviate some of the structural issues with tail mounted engines. You also wouldn't have to create unconventional and possibly heavy tail configurations for UDFs such as some H-tails and some other ideas that I've seen. A T-tail will be a must though to prevent wash from going over the horizontal stabilizer. It would also make systems integration much easier keeping the engines by the fuel tanks and shortening the bleed lines. Don't know if that's really an issue though. Tail mounted configs seem to work for most biz jets, and don't you have to protect the tail from icing just the same? I'd imagine bleed lines would be run to the tail as well.

Well, the HondaJet config for a UDF would look cool.  Smile

Quoting Tangowhisky (Thread starter):
5) Last I don't see the UDF engine making it on long range widebodies as the speed and altitude restrictions alone will not be practical for the purpose of widebodies.

Agreed.

Quoting Tangowhisky (Thread starter):
I would like to read others' comments and views as GE and RR are downplaying the GTF and talking up the UDF.

You go with what you've researched. P & W has put the most work into GTF so far. GE and RR sunk much more money in UDF.

In the long run, I wouldn't be surprised to see GTFs dominate widebodies and longer range, high density NBs, while UDFs take over everything below those but just above 70 seat turboprops. Again, that's my hunch.

 airplane B4e-Forever New Frontiers airplane 


User currently offlineTangowhisky From United States of America, joined Jun 2006, 910 posts, RR: 7
Reply 5, posted (6 years 2 months 1 week 6 days 21 hours ago) and read 16144 times:



Quoting Cpd (Reply 2):
Wasn't the other advantage of the GTF the fact that it would be quieter?

Yes as further commented by Boeing4ever

Quoting DocLightning (Reply 3):
have come to the conclusion that you could hit Americans with "Build High-Speed Rail or the aliens will invade" and provide good evidence...and no HSR would be built.

I saw an interesting segment on Charlie Rose last night. they were saying that the US not only does not have an energy policy but we are sending our wealth abroad by purchasing oil, rather than investing in our wealth in sustainable mass transit, commuter rail, and intercity rail systems.

I also read in the WSJ yesterday that suburban homes in the US that have commuter rail access better retain their values, than suburbs where people have no choice but must rely on their cars and SUVs.

Quoting Boeing4ever (Reply 4):
ut it may come down to noise pollution vs. air pollution.

Not for the NIMBYs

Quoting Boeing4ever (Reply 4):
In the long run, I wouldn't be surprised to see GTFs dominate widebodies and longer range, high density NBs, while UDFs take over everything below those but just above 70 seat turboprops.

Sounds probable.



Only the paranoid survive
User currently offlineBoeing4ever From , joined Dec 1969, posts, RR:
Reply 6, posted (6 years 2 months 1 week 6 days 20 hours ago) and read 16077 times:



Quoting Tangowhisky (Reply 5):
Not for the NIMBYs

They'll just have to move closer to where they work.  Wink

But yeah, the NIMBY factor sounds like an insurmountable obstacle for UDFs. That is assuming of course they can't be quieted down a little bit.

Quoting Tangowhisky (Reply 5):
I saw an interesting segment on Charlie Rose last night. they were saying that the US not only does not have an energy policy but we are sending our wealth abroad by purchasing oil, rather than investing in our wealth in sustainable mass transit, commuter rail, and intercity rail systems.

While more investment in this sort of infrastructure is needed, the fact that US metorpolitan areas are so much more spread out makes this difficult to successfully implement outside of city centers and immediate suburbs. At least makes it difficult to cheaply implment it. Fortunately, higher energy costs are also dictating changes in automotive propulsion technology with more efficient engines in the short term, and hopefully, something non-fossil fuel reliant in the long run.

You design planes for the world of course, so both highway networks and rail systems are competition that must be looked at when considering a plane for short range hops. When fuel was cheap, it didn't matter. Nowadays, demand for 50-seat RJs is zero.

 airplane B4e-Forever New Frontiers airplane 


User currently offlineAirbusA6 From United Kingdom, joined Apr 2005, 2012 posts, RR: 0
Reply 7, posted (6 years 2 months 1 week 6 days 20 hours ago) and read 16072 times:

The biggest advantage of the GTF is that it can be slotted onto currently available airliners such as the A320, whereas the GTF would require rear engined planes to be reintroduced, with all their disadvantages.

I remember a prototype UDF being tried out on an MD80, as it has the necessary layout. Perhaps Boeing should put the 717 back into production  Wink



it's the bus to stansted (now renamed national express a4 to ruin my username)
User currently offlinePlaneWasted From Sweden, joined Jan 2008, 516 posts, RR: 0
Reply 8, posted (6 years 2 months 1 week 6 days 20 hours ago) and read 16056 times:

What are the big differences between UDF and turboprop (the UDF spins faster?)?
And is there any big difference between a turboprop and a GTF other then the duct (from what I understand the duct allows higher pressure and therefore higher speeds)?

[Edited 2008-06-11 09:01:04]

User currently offlineBoeing4ever From , joined Dec 1969, posts, RR:
Reply 9, posted (6 years 2 months 1 week 6 days 19 hours ago) and read 16044 times:



Quoting PlaneWasted (Reply 8):
And is there any big difference between a turboprop and a GTF other then the duct?

A GTF is as its name implies...a turbofan jet engine with a gearbox essentially. This allows the turbine and fan to spin at their optimum RPM instead of being connected by one shaft. The big difference of course is while a turboprop has a gas turbine, it uses a propeller while a GTF is essentially still a turbofan jet engine.

That's the quick n' dirty gist of it. Someone else can give you much more detail.

 airplane B4e-Forever New Frontiers airplane 


User currently offlineBoeing4ever From , joined Dec 1969, posts, RR:
Reply 10, posted (6 years 2 months 1 week 6 days 19 hours ago) and read 16034 times:



Quoting AirbusA6 (Reply 7):
The biggest advantage of the GTF is that it can be slotted onto currently available airliners such as the A320, whereas the GTF would require rear engined planes to be reintroduced, with all their disadvantages.

I think you meant to say that the UDF would have to be tail mounted. Not true though, see above for a wing mounted configuration idea.  Smile

Quoting AirbusA6 (Reply 7):
I remember a prototype UDF being tried out on an MD80, as it has the necessary layout. Perhaps Boeing should put the 717 back into production

Or just slap some UDFs over the 737NG's wings.  spin 

 airplane B4e-Forever New Frontiers airplane 


User currently offlineTangowhisky From United States of America, joined Jun 2006, 910 posts, RR: 7
Reply 11, posted (6 years 2 months 1 week 6 days 19 hours ago) and read 15994 times:



Quoting PlaneWasted (Reply 8):
What are the big differences between UDF and turboprop (the UDF spins faster?)?

They are closer in principle. The UDF has bigger blades and are generally counter rotating, whereas the turboprop has smaller cord blades. The UDF as I understand it has variable pitch allowing for constant speed operations of the blades like a turboprop.

Quoting PlaneWasted (Reply 8):
is there any big difference between a turboprop and a GTF

GTF is basically a turbofan, but the fan speed and the low pressure turbine speed are no longer the same with the use of a gearing down ratio. This allows the two to rotate at their more optimum speeds with less compromise. Also the turboprop blades have variable pitch, whereas the GTF fan blades are not varied.

Quoting Boeing4ever (Reply 6):
While more investment in this sort of infrastructure is needed, the fact that US metorpolitan areas are so much more spread out makes this difficult to successfully implement outside of city centers and immediate suburbs.

This is very true, but there is a simple reason. When there is no rail service, or when driving was cheap, urban sprawl has no stop. However, if rail service becomes available, suburbs can be better developed. Think of subway lines. Each time a new subway line is opened or a new station stop is added, there is a tremendous residential and commercial developmental result. Rail lines and mass transit systems help better shape development.



Only the paranoid survive
User currently offlineBoeing4ever From , joined Dec 1969, posts, RR:
Reply 12, posted (6 years 2 months 1 week 6 days 18 hours ago) and read 15956 times:



Quoting Tangowhisky (Reply 11):
This is very true, but there is a simple reason. When there is no rail service, or when driving was cheap, urban sprawl has no stop. However, if rail service becomes available, suburbs can be better developed. Think of subway lines. Each time a new subway line is opened or a new station stop is added, there is a tremendous residential and commercial developmental result. Rail lines and mass transit systems help better shape development.

In the short to medium term we'll be seeing a mixed bag. Increased investment and consideratin of transit links will got into new development. For existing sprawl the cost will be enormous. It's also important to not forget that there are still many communities spread out beyond just the metorpolitan areas. As a result I forsee demand in fuel efficient or alternative fuel personal transport in the long term. Say hydorgen cars become widely available and practical, then I wouldn't be surprised to start seeing mass transit and rail fall by the wayside again. It's hard to beat the flexibility of having one's own automobile. Speed and comfort were the big advantages that kept airplanes in business vs. cars and trains. At least right now the future for aviation propulsion looks more optimistic. GTF, UDF, heck even Aerodiesels that run on JetA and get better fuel economy than Avgas engines in the GA arena are on the horizon and will soon dominate the market.

 airplane B4e-Forever New Frontiers airplane 


User currently offlinePlaneWasted From Sweden, joined Jan 2008, 516 posts, RR: 0
Reply 13, posted (6 years 2 months 1 week 6 days 15 hours ago) and read 15911 times:

Quoting Boeing4ever (Reply 9):
A GTF is as its name implies...a turbofan jet engine with a gearbox essentially.

But that applies to a turboprop also. But the turboprop is without a duct and therefore the 'fan' is optimized for no duct, giving us a...propeller?

[Edited 2008-06-11 13:05:26]

User currently offlineWingscrubber From UK - England, joined Sep 2001, 848 posts, RR: 0
Reply 14, posted (6 years 2 months 1 week 6 days 14 hours ago) and read 15881 times:

The geared turbofan is the future design, the inducted turbofan is essentially a re-configuration of a turboprop. In my eyes the UDF is just a high-output turboprop, there's nothing futuristic about it, the GTF will be more efficient on all fronts except low altitude regional flights, also, the public reaction to UDFs will not be good, I don't think anybody will want to fly on a UDF powered plane and nobody will want one noisily flying over their house either, IMHO.


Resident TechOps Troll
User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 15, posted (6 years 2 months 1 week 6 days 12 hours ago) and read 15868 times:

The most innovative engine of the last 20 years is a turbofan with a gearbox.

Hopefully OW gets it reliable.

I think when fuel cost kep rising passenger comfort ^& noise will move down the priority list.

If you have to fly, you'll have to go to airports that aren't constrained by noise limitations and higher By Pass Ratio engines will reclaime they place in more modern forms.

UDF seems to way forward for medium sized aircraft.

For short haul probably little beats a TP400 for the next 10 yrs..



and the polar bears don't die because of noise..


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17017 posts, RR: 67
Reply 16, posted (6 years 2 months 1 week 6 days 10 hours ago) and read 15847 times:



Quoting DocLightning (Reply 3):
Stop right there. I have come to the conclusion that you could hit Americans with "Build High-Speed Rail or the aliens will invade" and provide good evidence...and no HSR would be built.

Hehe. So true. I don't get the reason but it's true.

I've lived in the US for 5½ years. House, cars, commute, the whole nine yards. Now I live in Hong Kong, which is more compact than any US city. We have no car. Public transport including taxi is cheap, reliable, and frequent. Sprawl in the American sense is nonexistent. I live in a townhouse and thus obviously very close by my neighbors, which means my kids always have someone to play with. The quality of life of our family has gone up dramatically despite the smaller space and the perceived crowding.

Quoting Boeing4ever (Reply 4):

Why not mount them above the wing a la Hondajet HA-420?

Because that's just plain wrong.  Wink



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineDfwRevolution From United States of America, joined Jan 2010, 968 posts, RR: 51
Reply 17, posted (6 years 2 months 1 week 6 days 9 hours ago) and read 15835 times:



Quoting DocLightning (Reply 3):
Stop right there. I have come to the conclusion that you could hit Americans with "Build High-Speed Rail or the aliens will invade" and provide good evidence...and no HSR would be built.



Quoting Starlionblue (Reply 16):
Hehe. So true. I don't get the reason but it's true.

1. Upfront cost - building dedicated rights of way for high-speed rail requires tens of billions of dollars. Operational cost typically don't reach break-even for several years either. Not too many in the DOT are eager to spend that kind of cash when low-cost airlines are willing to operate shuttle's on their own dime.

2. Population density - there are probably only 5 corridors in the U.S. that would support high-speed rail and one already has it (New England). The California coast, central Texas, central Florida, and part of the Midwest would be the other four. Otherwise, our major cities are spaced too far apart for rail to even be an economical option. High-speed rail wouldn't significantly shift the nature of domestic aviation.


User currently offlineBoeing4ever From , joined Dec 1969, posts, RR:
Reply 18, posted (6 years 2 months 1 week 6 days 8 hours ago) and read 15827 times:



Quoting PlaneWasted (Reply 13):
But that applies to a turboprop also. But the turboprop is without a duct and therefore the 'fan' is optimized for no duct, giving us a...propeller?

Are you sure we're on the same page? I think you're asking what the difference is between a UDF and a turboprop...

Illustrations might help, maybe I'm just misreading you...

GTF...



UDF...



I guess to put it in really simple terms, yes, if you take the duct off of say a CFM56, then the fan is like a "propeller". A conventional propeller has performance limits as the blade tips approach the speed of sound.

 airplane B4e-Forever New Frontiers airplane 


User currently offlineTangowhisky From United States of America, joined Jun 2006, 910 posts, RR: 7
Reply 19, posted (6 years 2 months 1 week 6 days 7 hours ago) and read 15806 times:



Quoting DfwRevolution (Reply 17):
ot too many in the DOT are eager to spend that kind of cash when low-cost airlines are willing to operate shuttle's on their own dime.

It is not always about cost, but strategic and environmental reasons need to be considered. When SNCF in France opened over the last decade many new TGV routes, was it on the premise that it would be profitable immediately? No of course not. It is strategic to make the nation less dependent on foreign oil, more sustainable by supporting its nuclear power generation and rail industries (Alstom). And as they did this, they put many regional and trunk airline routes out of business. Guess what? Less planes in France are using the sky as a sewage.

Quoting DfwRevolution (Reply 17):
opulation density - there are probably only 5 corridors in the U.S. that would support high-speed rail and one already has it (New England). The California coast, central Texas, central Florida, and part of the Midwest would be the other four. Otherwise, our major cities are spaced too far apart for rail to even be an economical option. High-speed rail wouldn't significantly shift the nature of domestic aviation.

I totally disagree. On the eastern part of the US there are numerous examples where high speed rail can be used like in France with similar distances and population densities. France don't just pair Paris to Nice, but they pair Paris to Dijon, or Valence where small populations live in these later cities. The same needs to be applied here in the US. Furthermore not all needs to be high sped rail. There are tons of opportunities for commuter, suburban, and inter-city rail systems.

It all requires leadership and a will to change.



Only the paranoid survive
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17017 posts, RR: 67
Reply 20, posted (6 years 2 months 1 week 6 days 7 hours ago) and read 15806 times:



Quoting DfwRevolution (Reply 17):

2. Population density - there are probably only 5 corridors in the U.S. that would support high-speed rail and one already has it (New England).

New England doesn't have high speed rail. Not really. Acela may be a high speed train set but it runs mostly on old tracks and mixed in with other traffic. Slow. Not even close to TGV or Shinkansen.

I will agree that the US only has a few places that would justify HSR. I would say that a "real" HSR service Washington-Baltimore-New York-Boston would be a big success. It might take 10-15 years to break even but it doesn't seem reasonable to continue with the problem prone current rail/road/air system.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 21, posted (6 years 2 months 1 week 6 days 6 hours ago) and read 15795 times:



Quoting Tangowhisky (Thread starter):
1) It has been documented that a UDF will have speed and altitude limitations. It will not fly even close to today's narrowbody cruise speeds, and will not be capable of climbing to high altitudes. These are due to the fact that there is very little jet thrust, and almost all the thrust is generated by the fan blades (like a turboprop).

Almost all the thrust is generated by the fan blades on today's turbofans too...this isn't a show stopper.

Quoting Tangowhisky (Thread starter):
4) If the UDF engines are not on the wings, then it brings back a whole host of systems engineering issues when it is located at the back of the plane. For example, the high temperature engine bleed lines for wing deicing have to be longer, require more sensors for leak detection, and will increase weight and maintenance costs. This is just one of many such systems design issues.

This issue has already been addressed. The 787 doesn't have bleed ducts for wing anti-icing.

Quoting Tangowhisky (Thread starter):
GE and RR are downplaying the GTF and talking up the UDF.

Naturally...because GE and RR are decades behind on the research needed to build a GTF. Market what you can do.

Quoting Cpd (Reply 2):
The UDF I doubt will be accepted by the travelling public, we don't like slower speeds than what we already have.

The travelling public has nearly zero knowledge of how fast the aircraft is actually going, nor do they care. They care about gate-to-gate time. Intelligent ATC could more than make up for the relatively small loss of cruise speed and give us the same overall block times.

Quoting Boeing4ever (Reply 4):
Why not mount them above the wing a la Hondajet HA-420?

The Hondajet is an *extreme* case of point design, much more so than a typical airliner. Although possible in theory, I doubt it's attainable in practice on an airliner.

Quoting Tangowhisky (Reply 11):
The UDF as I understand it has variable pitch allowing for constant speed operations of the blades like a turboprop.

Some UDF incarnations had variable pitch, but not all. It's not an essential component of the technology.

Tom.


User currently offlineWN700Driver From , joined Dec 1969, posts, RR:
Reply 22, posted (6 years 2 months 1 week 6 days 6 hours ago) and read 15795 times:



Quote:
But that applies to a turboprop also. But the turboprop is without a duct and therefore the 'fan' is optimized for no duct, giving us a...propeller?

GTF is much more similar to traditional T-fan than a T-prop. Really, the big difference is that the speed reduction from N2 to N1 is accomplished via planetary gear sets instead of multiple spools. I don't know what the efficiency #s are, but obviously someone thinks very highly of it.

A T-prop has no N1, just the prop. As well the turbine section is centrafugal, not axial flow. It's a basic, but huge difference. T-props offer virtually no thrust from their N2 section, hence the exhaust being mounted at any angle the engineers come up with to facilitate efficient design. Or where they feel like.  Wink Add to that the fact the T-props are constant speed, and must change blade angle to function at all, and from what I've read, no such animal on the Compressor section of the GTF. Hope that helps!

As for the topic, I agree with pretty much everyone else. UDFs may very well have their uses eventually, but getting an STC for swapping a traditional T-fan out for a GTF seems very doable. One won't have to design an entire new a/c around it. Hell, such a thing could breathe all kinds of new life into existing 737/A320 designs. Might just turn out to be a huge blessing for A & B, who knows.


User currently offlineTangowhisky From United States of America, joined Jun 2006, 910 posts, RR: 7
Reply 23, posted (6 years 2 months 1 week 5 days 23 hours ago) and read 15735 times:



Quoting Tdscanuck (Reply 21):
Almost all the thrust is generated by the fan blades on today's turbofans too...this isn't a show stopper.

Today's turbofans still have jet thrust. A UDF is an ultra, ultra bypass. It is not the same and it comes down to fluid mechanics that will limit the UDF in achieving adequate thrust to climb and deliver thrust for high altitude operations.

Quoting Tdscanuck (Reply 21):
This issue has already been addressed. The 787 doesn't have bleed ducts for wing anti-icing.

Apparently from some of the publications I read, more electric systems like on a 787 can not be applied to the same extent on smaller jets dues to space limitations. But perhaps you are right and that on future NB replacements, the technology will develop fa enough to make it happen. Also I read that more electric systems are heavier, but they pay off in maintenance and reliability aspects.



Only the paranoid survive
User currently offlinePlaneWasted From Sweden, joined Jan 2008, 516 posts, RR: 0
Reply 24, posted (6 years 2 months 1 week 5 days 23 hours ago) and read 15731 times:

Quoting Boeing4ever (Reply 18):
Are you sure we're on the same page? I think you're asking what the difference is between a UDF and a turboprop...

I guess to put it in really simple terms, yes, if you take the duct off of say a CFM56, then the fan is like a "propeller". A conventional propeller has performance limits as the blade tips approach the speed of sound.

That was what I was talking about.
But I still don't understand how the UDF is better than a turboprop. Because it has the same speed disadvantages, right?
Is it that it is easier to make a powerful UDF than a powerful turboprop?

I believe the GTF is the future, it combines turboprop economics with torbufan speed. We just need to be able to make them powerful enough.

[Edited 2008-06-12 05:25:19]

25 F14D4ever : We need to be more accurate with our acronyms. There was and is only one UDF, the GE Unducted Fan, a trademarked name for the GE36 demonstrator engin
26 Post contains images Keesje : TP400 has 3 axes & 1 gearbox.. Not all, e.g. the TP400 axial turbine.. TP400 will have 3 constant speeds / blade angles for various flight stages. I
27 Boeing4ever : Ok, just making sure. Good question. A propfan (since UDF is proprietary...I'd hate to "Kleenex" the technology ), essentially combines the performan
28 Post contains images Tangowhisky : Without the investment in proper trackwork, TGV speeds can not be achieved. Take a look at the map below. The TGV runs through small cities. Smaller
29 Post contains links and images A342 : The Tu-114 and its military ancestors suggest otherwise. View Large View MediumPhoto © Joop de Groot - CRMAP Admittedly, it was a commercial fai
30 Tdscanuck : N1 and N2 are, by definition, the spool speeds. The GTF still has two spools. The gearbox gives you a reduction between N1 and fan speed, not between
31 XT6Wagon : UDF isn't going anywhere. Low speed applications will continue to use inexpensive and reliable turboprops Higher speed commercial applications will co
32 Dougloid : I worked for Douglas in Long Beach when they were testing the UDF demonstration aircraft. It was a noisy SOB, but the main reason it was never develo
33 Post contains images Keesje : Don't know if it has been officially released "20% more efficient" then comparable turbofans is what the marketing folks say. Maybe SFC ~0.4 ? Specs
34 Thegeek : That's the way I see it too. The UDF will never see commercial success. Not even after my lifetime. So there. As for the GTF, why is it making a gear
35 Dougloid : The only two I am familiar with are the TFE731 and the ALF502, both were planetary gears and both consumed a lot of engineering hours because buildin
36 Tangowhisky : One of the problems with any open rotor engine is that the pressure pulses created by the rotating blades are no longer absorbed by the nacelle, but
37 Dougloid : If it is, it is a heckuva achievement. The best SFC I've ever heard of was the Curtiss Wright Turbo Compound R3350 which could attain a SFC of 0.36.
38 Tangowhisky : Hey Dougloid When are you going to write a book? I always enjoy reading your posts, especially the endless tales and aerospace history facts you bring
39 A342 : Most props have their SFC given as lb of fuel per horsepower. Did you convert these figures to lb of fuel per lbf of thrust, with a prop on it? Only
40 Tdscanuck : Because the power is a whole lot higher but the weight/size constraints are basically the same. I believe that's what he meant as well, but it's not
41 Dougloid : Ahhhh, but we weren't comparing turbofans to turboprops, me and the bruthah were talking about turboprops and big radials.
42 Boeing4ever : I wonder how GE and RR will answer the vibration problem. Suddenly my HondaJet style mounting idea looks less favorable. Cracking issues should have
43 Tdscanuck : With a HondaJet style mount, you'd have to hang the fan over the trailing edge of the wing. That would save the wing from the worst of the vibration.
44 Thegeek : Wouldn't the NK-12 of the Tu-95 have a similar sort of shaft power as a CFM-56 sized GTF? That's the way I calculated in my head anyway. Since no one
45 Tdscanuck : I should have caveated that by adding that the Russians are a whole different ball game when it comes to high power gearboxes. There are some other t
46 Boeing4ever : Yeah, I messed up... I don't have an answer for the noise and vibration on the fuselage, but I'm assuming the mounts were where the cracks took place
47 A342 : Keesje was, or at least I think so: The GEnx and Trent 1000 have a SFC of about 0.5 lb of fuel / lbf of thrust / hour. I assume this was the base for
48 Tdscanuck : My guess is lighter, if for no other reason that not having to pack around a fan case. They're heavy. Tom.
49 Post contains links and images Keesje : If you google for TP400 and SFC c=values of .4 or .42 come up. Seems reasonable. Props are useally about 20% more efficientr then same technology tur
50 A342 : Again, we cannot directly compare the SFC for a prop to that of a jet, because they are given in different units.
51 Boeing4ever : It's a little hard to see in that picture you're referring to, but are you talking about that strut going from the engine to the C-130 gear fairing?
52 Nomadd22 : Maybe I'm a little slow here, but it seems like everybody is comparing fuel consumption of one engine to another engine at different speeds. If a UDF
53 Tdscanuck : Not all open rotor versions have a gearbox. Some are directly coupled to the turbine, so they should be in about the same weight as a turbofan minus
54 Baroque : Or in some cases of centrifugal compressors because the engine or its ancestors was designed by Frank Whittle!
55 Tdscanuck : Good point. They've got a mockup (at least, I assume it's a mockup) of the first Whittle engine at the Museum of Flight in Seattle...the fact that it
56 Dougloid : We had a GE I-16 in the lab at the tech school I got my aircraft mechanic's training at and it was an interesting piece of gear. That was a first gen
57 Baroque : That seemed to be the main reason he used them. I think he was well aware of the theoretical benefits of axial flow, but as Ted comments, he was fair
58 Dougloid : The materials science of the war era is phenomenally interesting, B. The squareheads had been effectively shut off from strategic materials that sugg
59 Baroque : I get the feeling that you could persuade them to use up the whole ten hours with one good shove on the throttle. What seems to be missing in this th
60 Starlionblue : I had read that. In some ways it must have sucked to go from a late mark FW-190 or Bf109 into a Me-262. - Throttle response: much poorer. - Possibili
61 Keesje : I think the earlier (proto) engines were much more reliable, having longer TBO's. As dougloid explained the right alloys were no longer available, st
62 Post contains links and images Dougloid : I'd like to see that stuff if we get this dollar business under control, and that's likely going to be some rough sledding for us yanquis. In particu
63 Tangowhisky : Good point Baroque. It would be great to see comments on why this option is not talked about. I think the variable pitch has quite an effect. It is c
64 Post contains images Keesje : dougloid, nice pics of your old man, may he rest in peace. Years ago I organized a similar photo shoot in a new engine shop, bribing the mechanics to
65 Tdscanuck : It's talked about, but it's a mechanical furball. Variable pitch on big turboprops is already something of a voodoo art and, for a UDF, you're talkin
66 Post contains links Starlionblue : While the reasons are understandable, it is a bit of a shame. German engineering during the was was probably second to none and there is so much inte
67 Dougloid : An interesting video. It's probably been said before but the problems in German armaments were not materials or advanced technology but fragmentation
68 Baroque : It reminded me of the story about the test after the end of the war in the UK of an ME 262. It rolled and rolled down a heavy bomber airfield runway
69 Starlionblue : Indeed. There was also an unfortunate obsession with "the best weapon" even if that meant introducing shortages. Case in point: tanks. The Germans ha
70 Dougloid : The Panther was a case in point. Essentially when the Germans were faced with the T34 and the T34/85 they knew that when (not if) the Soviets learned
71 Nomadd22 : A lot of good. What you pay to acquire a tank is only a small part of it's expense. Five Shermans would cost five times as much to transport, operate
72 Baroque : Arguable, you could consider tracks as the ultimate in ducts?
73 Starlionblue : You have a good point. However the amount of resources used to move those Panthers weren't insignificant either. The Sherman was much lighter and thu
74 XT6Wagon : given the mechanical complexity and unreliablity of the later german tanks, I'd be amazed if it wasn't MORE than 5 times the real cost. Shermans were
75 OldAeroGuy : The UDF didn't have a gearbox. Are you talking about the blade pitch control mechanism?
76 OldAeroGuy : Counter-rotation also plays a part in the efficiency increase.
77 Post contains links and images Dougloid : This is the Chrysler A57 Multibank engine from one interation of the Sherman. Reports say it was reliable once it got dialed in. I would guess about
78 Tangowhisky : Sorry, I meant the GTF gearbox is in a much hotter section.
79 Post contains links Tangowhisky : According to Flight Flobal today, P&W will make the GTF as the "building block" of all their future engines including widebody jets going forward. Her
80 Dougloid : Well, seeing as the ones I've worked on have the reduction gearing running off the LP spool on the compressor end, it's nothing that can't be handled
81 TSS : But how much torque? After all, who needs top-end performance in a tank?
82 Starlionblue : Tell that to modern tank designers who build tanks that do 80km/h or more. Mobility is one part of the equation, together with attack and defense (or
83 2H4 : Is the pitch controllable from the cockpit like turboprops? Also, does the variable pitch provide reverse thrust for the UDF (or other open-rotor des
84 Tdscanuck : We've got that today. It's not really a scaling problem, it's an envelope problem. An airliner needs to be able to hold pretty stable peak performanc
85 XT6Wagon : in addition to other points, the structure to place the engine above the wing is higher than below it. Thus making it far cheaper to hang it off the
86 OldAeroGuy : Only in the sense that throttle position controls blade pitch since the open rotors are constant speed devices. Yes
87 Dougloid : the only figure I could come up with was 202 ft/lb of torque, probably at about 2200 rpm or thereabouts.
88 Dougloid : Seems reasonable enough, even without the telemetry.
89 Tangowhisky : I would say that there will be conventional throttles, and its purpose is for thrust demand. The engine control systems will control blade pitch in a
90 Parapente : This is a very interesting subject. However the concensus in this thread is not. If one was to believe the GTF is "everything" and open rotor is "noth
91 Dougloid : The GE UDF project that I was familiar with was dropped a number of years ago because it was too noisy, the vibration levels were tearing up the stru
92 Baroque : And we have not heard the solutions on here either, well not YET.
93 Post contains links PITIngres : Indeed. I was a bit taken aback by a statement in this article: http://www.atwonline.com/news/story.html?storyID=13093 (referenced in a current civ-av
94 2H4 : Presumably, noise cancellation technology could address much of the cabin noise, but not much can be done to appease the NIMBYs. Dougloid - when you
95 Parapente : Sorry re todays article above - not 12%GTF but 15% BUT not 20-25% Open Rotor but 30%!! This is an astoundingly huge figure.No wonder the "big two" are
96 Post contains links PITIngres : I dunno. There was a 1990 BB&N report (abstract at http://adsabs.harvard.edu/abs/1990bbn..rept.....F I haven't read the full report) that apparently
97 2H4 : Depending on configuration, thrust settings on approach might be high (ie: noisy), as well. Does anyone have any idea how an open-rotor engine would
98 Dougloid : The demonstrator was a noisy sonovabitch. When they were taking off from LGB it sounded like some serious blade tip issues were going on and horrible
99 BAe146QT : I have scanned the thread and haven't seen this mentioned but... what happens when a UDF starts shedding blades?
100 2H4 : Ah, so like a Piaggio Avanti on steroids, then? 2H4
101 Tangowhisky : Yes that is the idea. You vary the pitch to get instant thrust and increase fuel flow to maintain rpm. Like a turboprop. Well the first thing that mu
102 Dougloid : Or the aptly named Cessna Mixmaster or Cessna Skysmasher as you prefer.
103 Tdscanuck : This is a very similar control function to what any engine with variable stator vanes is doing today. The algorithm is different, obviously, but any
104 Dougloid : And perhaps the angle of the fan compared to the direction of travel.
105 BAe146QT : Yes, this was the bit I was referring to. LOL Cute. It's just that by definition, any engine failure on these things in the first, er, stage (?) woul
106 Tdscanuck : They definitely do have seats in line with the prop disc, so that's not it. I'm not sure about armouring. However, keep in mind that the second the b
107 XT6Wagon : turboprops are "grandfathered" in by way of thats how people flew thier powered aircraft since day 1. with props. If you were just inventing the prop
108 Post contains links and images Dougloid : Prop failure is very unusual, and I only saw it once in my time as a tech, although some Hartzells had a depressing habit of shucking blades. My one
109 2H4 : Didn't you once post an amazing photo of this happening right in front of you? 2H4
110 BAe146QT : No, probably not. Someone somewhere has no doubt calculated this, involving such factors as; It's moving forward... ...but so is the plane. It's movi
111 Post contains links Dougloid : Not I. although I woulda given a couple dollars to watch them pull the seat out of the Captain's ass with a block and tackle. It was. else someone wo
112 BAe146QT : There but for the grace, etc... The report is succinct and to the point... but I'd love to hear the interview where he explained what he was thinking
113 Post contains links 2H4 : Now I remember. It was L-188. He's still got it in his profile. Have a look. 2H4
114 Tdscanuck : The second it lets go, it stops wanting to move outward because there's nothing forcing it to go in a circle anymore. But yes, the conflicting factor
115 Post contains links Larshjort : At the first SK Q400 incident in AAL the propeller on the right engine struck the ground while running and some of the blades penetrated the cabin ht
116 Airbuske : Can someone please explain to my why UDF's are so much "better" than turboprops?
117 Starlionblue : As I understand it: Much higher blade speeds allowing higher aircraft speeds.
118 Tdscanuck : Higher speed, mostly. A UDF has a very high bypass ratio, giving it turboprop-like fuel economy, but can cruise closer to jet speeds. Tom.
119 OldAeroGuy : Another reason is that the GE UDF doesn't have a gearbox, saving weight and eliminating complexity.
120 2H4 : In your opinion, does the complexity of the open-rotor's variable pitch fan blades add a degree of complexity close to that of the gearbox of the GTF
121 OldAeroGuy : Good question. I was responding to this question though: Turboprops have both gearboxes and pitch controls. The GE UDF eliminates the gearbox, reduci
122 Parapente : Some of you may have read the latest article in Flight Global on this very subject. What you will have noticed was Rolls opening the door -just a litt
123 Airbuske : I thought the limiting problem with prop blades was that even though your air speed was subsonic, blade tip speed was supersonic, resulting in shocks
124 2H4 : Just a reminder, guys...."UDF" is a trademarked name for GE's particular design. "Open Rotor" is a term that is not specific to any one manufacturer.
125 Airbuske : Is GTF a trademarked name for PW's design?
126 Tdscanuck : Given the number of blades, I suspect that the variable pitch on an open rotor is worse than variable pitch + gearbox on a turboprop. High disk loadi
127 Airbuske : Sorry Tdscanuck, but you face a plethora of questions. Really hope you dont mind. If open rotor blades are the way of the future, why aren't they bein
128 Post contains links and images 2H4 : Right, but I was comparing open rotor with the GTF. I suspect the complexity of the variable pitch blades of the open rotor introduce a level of comp
129 Post contains links and images Tdscanuck : If I minded, I wouldn't be posting...ask away! That's a good question. To some extent, they are. The blades on an A400M look an awful lot like open r
130 F14D4ever : Not unfit, just not necessary, as Tom notes ... Right. In the Eurocoptor example, the issue is resonance with the struts which support the rotor hub.
131 2H4 : Wow, very interesting point. Thanks, guys. 2H4
132 Airbuske : Hmm, that certainly makes alot of sense. v = w x r (from centripetal motion) Since radius (r) is smaller for the open rotor fan, for the same tip vel
133 Post contains images Keesje : RR has recently been testing new open rotor concepts in the big low speed tunnel in the Netherlands. Shapes / diameters, number of blades have changed
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