Tangowhisky
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GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 1:53 pm

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.
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Burkhard
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 2:05 pm

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.
 
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cpd
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 2:11 pm

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?
 
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 2:23 pm



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.
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Boeing4ever
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 2:25 pm

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.

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Tangowhisky
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 2:50 pm



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.
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Boeing4ever
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 3:48 pm



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.

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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 3:51 pm

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
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planewasted
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 3:58 pm

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]
 
Boeing4ever
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 4:02 pm



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.

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Boeing4ever
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 4:04 pm



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 

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Tangowhisky
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 4:28 pm



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.
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 5:22 pm



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.

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planewasted
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 8:03 pm

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]
 
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 9:47 pm

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.
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keesje
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RE: GTF Or UDF Which Is The Engine Of Future?

Wed Jun 11, 2008 11:24 pm

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..



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Starlionblue
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 12:59 am



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
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DfwRevolution
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 2:00 am



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.
 
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 3:21 am



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.

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Tangowhisky
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 4:16 am



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.
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Starlionblue
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 4:19 am



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.
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 5:06 am



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.

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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 5:29 am



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.
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Tangowhisky
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 12:12 pm



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.
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planewasted
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 12:21 pm

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]
 
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 1:27 pm



Quoting Tdscanuck (Reply 21):
Some UDF incarnations had variable pitch, but not all.

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 engine. (And yes it had variable pitch blades.)

The current name used within the advanced design community for non-ducted high bypass turbofans is Open Rotor. Let's try that instead of using GE's proprietary UDF as a catchall.
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keesje
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 2:29 pm



Quoting WN700Driver (Reply 22):
A T-prop has no N1, just the prop.

TP400 has 3 axes & 1 gearbox..

Quoting WN700Driver (Reply 22):
As well the turbine section is centrafugal, not axial flow. It's a basic, but huge difference.

Not all, e.g. the TP400 axial turbine..

Quoting WN700Driver (Reply 22):
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!

TP400 will have 3 constant speeds / blade angles for various flight stages.



I think the RR/Snecma/MTU TP400 is the only state of the art engine promising over 20% SFC reduction over existing engines, is able to power aircraft over 150 seats in a twin configuration and has come into production. It has been a militiary program so far, I think OEMS will take a closer look.

"Never mistake motion for action." Ernest Hemingway
 
Boeing4ever
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 2:57 pm



Quoting PlaneWasted (Reply 24):
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?

Ok, just making sure.  Smile

Good question. A propfan (since UDF is proprietary...I'd hate to "Kleenex" the technology  Wink ), essentially combines the performance of a jet engine with the economics of a turboprop. What's better than a turboprop is some of the solutions to the performance limitations of a propeller blade. UDF's use scimitary shaped blades, and more of them, allowing them to use a lower rotational speed while still having a decent amount of power.

Generally speaking a propfan has better performance in terms of speed over a turboprop.

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

I'm still waiting to see if bleedless becomes an industry standard. But I forgot about the 787's bleedless technology. D'oh!

Quoting Tdscanuck (Reply 21):
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.

After reading up on the design of the HondaJet (there's some really juicy technical papers posted on their website Big grin ), I won't disagree that it would be harder to attain on an airliner. However, I can't help but feel that with a good nacelle design and an optimized wing it could work. Quoting the paper on over-the-wing-engine mounting, so long as "the engine front face is located, and the vertical distance between the wing and nacelle is 1/3 to 1/2 is max. height of the nacelle" the drag divergence characteristics are favorable when a pylon is added. True though that this is an *extreme* case of point design.

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Tangowhisky
Topic Author
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 3:44 pm



Quoting Starlionblue (Reply 20):
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.

Without the investment in proper trackwork, TGV speeds can not be achieved.

Quoting Starlionblue (Reply 20):
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.

Take a look at the map below. The TGV runs through small cities. Smaller than Boston and Baltimore. There are far more TGV opportunities in the US than what we are led to believe. Airlines in the US will fight tooth and nail to keep TGV out of the US.

Big version: Width: 960 Height: 720 File size: 50kb
TGV Routes Frnace
Only the paranoid survive
 
A342
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RE: GTF Or UDF Which Is The Engine Of Future?

Thu Jun 12, 2008 4:38 pm



Quoting Tangowhisky (Thread starter):
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)

The Tu-114 and its military ancestors suggest otherwise.

Quoting Tdscanuck (Reply 21):
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.


View Large View Medium
Click here for bigger photo!

Photo © Joop de Groot - CRMAP



Admittedly, it was a commercial failure.




I think that putting open rotor engines on a BWB will significantly reduce the noise. On the ground that is. But how could one make the cabin quiet enough?

Finding proper designations for certain engine types is almost impossible. Most people consider the Progress D-27 a propfan, whereas the NK-12 is supposed to be a turboprop. Where do we draw the line?

Now what kind of engine is this? It has variable pitch, it is contra-rotating - and ducted!

http://www.kmpo.ru/hke.htm
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tdscanuck
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 12:56 am



Quoting WN700Driver (Reply 22):
Really, the big difference is that the speed reduction from N2 to N1 is accomplished via planetary gear sets instead of multiple spools.

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 N1 and N2.

Quoting WN700Driver (Reply 22):
A T-prop has no N1, just the prop.

N1 is just the LP spool speed...any multi-spool turboprop still has an N1 speed.

Quoting WN700Driver (Reply 22):
As well the turbine section is centrafugal, not axial flow.

Really depends on which engine you're talking about.

Quoting PlaneWasted (Reply 24):
But I still don't understand how the UDF is better than a turboprop. Because it has the same speed disadvantages, right?

Not quite. It's faster than a turboprop, but slower than a turbofan (which is slower than a turbojet, which is slower than a ramjet, which is slower than a scramjet...)

Quoting Boeing4ever (Reply 27):
Quoting Tdscanuck (Reply 21):
This issue has already been addressed. The 787 doesn't have bleed ducts for wing anti-icing.

I'm still waiting to see if bleedless becomes an industry standard. But I forgot about the 787's bleedless technology. D'oh!

Fair point that bleedless hasn't been proven yet, but at least the technology exists. I think it will be a winner. Pneumatics are a perpetual pain in the a$$...even if electric is heavier, I think bleedless will pay off.

Tom.
 
XT6Wagon
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 5:24 am

UDF isn't going anywhere.

Low speed applications will continue to use inexpensive and reliable turboprops

Higher speed commercial applications will continue to use ducted fans until we can use a ramjet or scramjet based technology to move current "high" speed applications to needing "highsubsonic" to correctly label the speed.

UDF just has huge downsides and minimal benifits over the continued evolution of the current high bypass axial flow jet engine.

UDF faces the same when compared to a turboprop. Its a answer with no question in sight.
 
Dougloid
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 8:16 am



Quoting Boeing4ever (Reply 4):
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.

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 developed further was that the vibration was too high for the structure, there were cracking problems because of it and nobody really had an answer for an uncontained fan failure.

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

The line's gone, the building's gone. The only people who could bring this off are the Chinese as they're producing a DC9 lookalike mostly based on what they learned at SAIC in the eighties. For someone who spent a lot of time sightseeing at Douglas, the resemblance is more than coincidence.

Quoting Keesje (Reply 15):
The most innovative engine of the last 20 years is a turbofan with a gearbox.

The idea is a lot older than that, Keez. I spent a fair amount of time working on Garrett TFE731s (high bypass geared fan) and that design originated in the 1960s. The devil's in the details though-as Lightsaber could tell you about the Pratt GTF. Making a planetary gearset that has the kind of dead ass reliability on the airframe of, say, a CFM56 would require a lot of testing and modifications. The TFE731 came out in the sixties and I came on the shop floor in 1980 and we were still doing planetary gear set service bulletins. Matter of fact, one of the last ones I remember was a special washer for detuning vibrations on the sun gear, which I was issued a special tool for and still have, I think.

Avco Lycoming thought they could sling a quickie GTF together with the ALF502 and its unreliability nearly sunk the Canadair Challenger.

P&W has spent a huge amount of money developing am airline size GTF and with every increase in the price of fuel and no end in sight it looks better and better from a fuel economy standpoint and from its low noise signature.

I've got some research material I put together and I'll find a link for it. Garrett was far ahead of their time.

Quoting Keesje (Reply 26):
I think the RR/Snecma/MTU TP400 is the only state of the art engine promising over 20% SFC reduction over existing engines, is able to power aircraft over 150 seats in a twin configuration and has come into production. It has been a militiary program so far, I think OEMS will take a closer look.

It's certainly the only engine around in its horsepower class, that's for sure and it's at the beginning of its development cycle. What kind of sfc is it producing?
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
keesje
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 9:35 am



Quoting Dougloid (Reply 32):
What kind of sfc is it producing?

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
• Type of engine: three-shaft turboprop
• Power output: approx. 11,000 shp at sea level
• Pressure/compression ratio: 25
• Weight: approx. 1,860 kg (dry)
• Length: 3.5 m engine overall length
• Propeller*: Ratier-Figeac FH386 propeller

Architecture
• Intermediate Pressure Compressor
- pressure ratio 3.5
- 5 stage unit with no variables
• High Pressure Compressor
- pressure ratio 7
- 6 stage unit
• Combustor
• High Pressure single stage Turbine
• Intermediate Pressure single stage Turbine
• Low Pressure three stages uncooled Turbine (Power Turbine)
• Offset Propeller Gear Box* compliant with two senses of rotation for the propeller

For Civil use it would have to be shaved. It has a lot of militairy redundancy, a bit too "bullit prove" for civil use.

"Never mistake motion for action." Ernest Hemingway
 
thegeek
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 9:46 am



Quoting PlaneWasted (Reply 24):
But I still don't understand how the UDF is better than a turboprop. Because it has the same speed disadvantages, right?



Quoting XT6Wagon (Reply 31):
UDF just has huge downsides and minimal benifits over the continued evolution of the current high bypass axial flow jet engine.

UDF faces the same when compared to a turboprop. Its a answer with no question in sight.

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 gearbox with the required reliability is so difficult when it's been done for years for turboprops? If the problem is caused by it being a planetary gearbox, is that essential?
 
Dougloid
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 1:11 pm



Quoting Thegeek (Reply 34):
As for the GTF, why is it making a gearbox with the required reliability is so difficult when it's been done for years for turboprops? If the problem is caused by it being a planetary gearbox, is that essential?

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 building such things is more or less of a black art. There were multiple service bulletins before the gearset became dead ass reliable.

My old man worked on planetary gearsets when he was at Curtiss Wright and he said they were problematic. Of course, on your large round engines there was a centerline thrust consideration as well.

My guess is that spur gearing probably takes up too much space lengthwise and does not yield an end product with fan thrust on the centerline.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
Tangowhisky
Topic Author
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 2:58 pm



Quoting Dougloid (Reply 32):
the main reason it was never developed further was that the vibration was too high for the structure,

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 start pounding on the structure. I believe this is one of the main sources of noise and discomfort for a turboprop without active noise and vibration suppression system. I wonder if the structure needs to be beefed up for the vibration aspects of open rotor engines versus those with a shroud.

Quoting Thegeek (Reply 34):
As for the GTF, why is it making a gearbox with the required reliability is so difficult when it's been done for years for turboprops?

The other issue is that the gearbox of a UDF is in a much hotter section, where as on a turboprop it is not.

Quoting Tdscanuck (Reply 30):
The gearbox gives you a reduction between N1 and fan speed, not between N1 and N2.

Correct.

Quoting Tdscanuck (Reply 30):
Quoting WN700Driver (Reply 22):
As well the turbine section is centrafugal, not axial flow.

Really depends on which engine you're talking about.

Perhaps what he meant was a turboprop turbines are centrifugal and axial for turbofans and turbojets as the later are designed to produce a certain amount of core jet thrust.
Only the paranoid survive
 
Dougloid
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 4:18 pm



Quoting Keesje (Reply 33):
Quoting Dougloid (Reply 32):
What kind of sfc is it producing?

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 ?

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. The best I could get my 331s to do was about 0.48.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
Tangowhisky
Topic Author
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 4:37 pm

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 back.
Only the paranoid survive
 
A342
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RE: GTF Or UDF Which Is The Engine Of Future?

Fri Jun 13, 2008 9:02 pm



Quoting Dougloid (Reply 37):
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. The best I could get my 331s to do was about 0.48.

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 then we can compare turbofans to props.
Exceptions confirm the rule.
 
tdscanuck
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 12:25 am



Quoting Thegeek (Reply 34):
As for the GTF, why is it making a gearbox with the required reliability is so difficult when it's been done for years for turboprops?

Because the power is a whole lot higher but the weight/size constraints are basically the same.

Quoting Tangowhisky (Reply 36):
Perhaps what he meant was a turboprop turbines are centrifugal and axial for turbofans and turbojets as the later are designed to produce a certain amount of core jet thrust.

I believe that's what he meant as well, but it's not true that all turboprop turbines are centrifugal.

Tom.
 
Dougloid
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 1:00 am



Quoting A342 (Reply 39):
Quoting Dougloid (Reply 37):
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. The best I could get my 331s to do was about 0.48.

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 then we can compare turbofans to props.

Ahhhh, but we weren't comparing turbofans to turboprops, me and the bruthah were talking about turboprops and big radials.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
Boeing4ever
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 5:23 am



Quoting Dougloid (Reply 32):
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 developed further was that the vibration was too high for the structure, there were cracking problems because of it and nobody really had an answer for an uncontained fan failure.

I wonder how GE and RR will answer the vibration problem. Suddenly my HondaJet style mounting idea looks less favorable. Cracking issues should have no place on the wings.  no  I also wonder what that would do to the flutter characteristics of the wing.

On the uncontained fan failure, I wonder how big of a regulatory issue it is. What happens if say an ATR-72 or Q400 suffers an ejected blade?

Quoting Tangowhisky (Reply 36):
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 start pounding on the structure. I believe this is one of the main sources of noise and discomfort for a turboprop without active noise and vibration suppression system. I wonder if the structure needs to be beefed up for the vibration aspects of open rotor engines versus those with a shroud.

It will probably depend on how much noisier it would be compared to a turboprop and if a beefed up structure would increase weight enough to cancel out any efficiency advantages over using say a GTF.

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tdscanuck
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 5:41 am



Quoting Boeing4ever (Reply 42):
I wonder how GE and RR will answer the vibration problem. Suddenly my HondaJet style mounting idea looks less favorable. Cracking issues should have no place on the wings.

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. Still have a problem at the side of the fuselage.

Quoting Boeing4ever (Reply 42):
I also wonder what that would do to the flutter characteristics of the wing.

Not much...flutter is a coupling between the wing aerodynamics and the wing stiffness. Unless you were crazy enough have a wing resonance mode near the UDF vibration frequency, it shouldn't have a flutter impact. The HondaJet-style mounting is certainly going to have a major flutter influence, but that's just because of the mass and mounting position, not particularly because it's a UDF.

Tom.
 
thegeek
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 6:30 am



Quoting Tdscanuck (Reply 40):
Because the power is a whole lot higher but the weight/size constraints are basically the same.

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.

Quoting WN700Driver (Reply 22):
As well the turbine section is centrafugal, not axial flow.

Since no one else noticed, I think you are talking about the compressor, not the turbine.
 
tdscanuck
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 2:27 pm



Quoting Thegeek (Reply 44):
Quoting Tdscanuck (Reply 40):
Because the power is a whole lot higher but the weight/size constraints are basically the same.

Wouldn't the NK-12 of the Tu-95 have a similar sort of shaft power as a CFM-56 sized GTF?

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 technologies where they live in their own world (welded titanium, for example). They've been way ahead on the turboprop power curve for a long time. Although, back of the envelope, a CFM56-sized gearbox probably ends up carrying something like 20000 HP, which is higher than the NK-12 (but not much).

Quoting Thegeek (Reply 44):

Quoting WN700Driver (Reply 22):
As well the turbine section is centrafugal, not axial flow.

Since no one else noticed, I think you are talking about the compressor, not the turbine.

You'll also find turboprop engines with full axial compressors. The choice of axial vs. centrifugal doesn't really depend on the type of propulsor, it's got a lot more to do with envelope, RPM, and diameter of the engine itself.

Tom.
 
Boeing4ever
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 8:09 pm



Quoting Tdscanuck (Reply 43):
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. Still have a problem at the side of the fuselage.

Yeah, I messed up...

Quoting Tdscanuck (Reply 43):
Not much...flutter is a coupling between the wing aerodynamics and the wing stiffness. Unless you were crazy enough have a wing resonance mode near the UDF vibration frequency, it shouldn't have a flutter impact.

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 on the MD-94X? The best I can come up with at this moment is reinforcing the structure at the location where the vibration is the highest. With CFRP I wonder if the weight penalty would be reduced.

Quoting Tdscanuck (Reply 43):
The HondaJet-style mounting is certainly going to have a major flutter influence, but that's just because of the mass and mounting position, not particularly because it's a UDF.

Mounting position I'm sure with R&D can be tackled. As for mass, I'm curious, is a Propfan lighter than a conventional turbofan or a GTF?

 airplane B4e-Forever New Frontiers airplane 
 
A342
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 9:00 pm



Quoting Dougloid (Reply 41):
Ahhhh, but we weren't comparing turbofans to turboprops

Keesje was, or at least I think so:

Quoting Keesje (Reply 33):
"20% more efficient" then comparable turbofans is what the marketing folks say. Maybe SFC ~0.4 ?

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 Keesje's assumption. Keesje, can you clarify?
Exceptions confirm the rule.
 
tdscanuck
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RE: GTF Or UDF Which Is The Engine Of Future?

Sat Jun 14, 2008 9:47 pm



Quoting Boeing4ever (Reply 46):
I'm curious, is a Propfan lighter than a conventional turbofan or a GTF?

My guess is lighter, if for no other reason that not having to pack around a fan case. They're heavy.

Tom.
 
keesje
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RE: GTF Or UDF Which Is The Engine Of Future?

Sun Jun 15, 2008 9:18 am



Quoting A342 (Reply 47):
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 Keesje's assumption. Keesje, can you clarify?

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 turbofans. The BPR of above 1:30 plays a rol. Accelerating a lot of air a littlebit is far more efficient then accelerating a little bit of air a lot (straight jets). The CFM56 and V2500 aren't impressive in this respect BPR 1:5.

Quoting Tdscanuck (Reply 48):
Quoting Boeing4ever (Reply 46):
I'm curious, is a Propfan lighter than a conventional turbofan or a GTF?

My guess is lighter, if for no other reason that not having to pack around a fan case. They're heavy.

I think an open rotor is at east as heavy as a turbo fan of the same category.. big fan, enormous gear box etc. As can be seen in the picture in pst 33, they had to add bars to make the engine - prop interface stiff enough. So probably additional structure also compared to a turbo fan..

Picture from the MTU website combining SFC & BPR:

http://i191.photobucket.com/albums/z160/keesje_pics/MTUenginedevlopment2007.jpg?t=1213521398
"Never mistake motion for action." Ernest Hemingway

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