JAAlbert From United States of America, joined Jan 2006, 1196 posts, RR: 1 Reply 1, posted (6 years 4 weeks 1 day 20 hours ago) and read 9674 times:
Very interesting. (I think). Those fan blades rotating in opposite directions should have a very effective garbage disposal effect should any bird find its way into the engine!
SEPilot From United States of America, joined Dec 2006, 6260 posts, RR: 39 Reply 2, posted (6 years 4 weeks 1 day 19 hours ago) and read 9652 times:
I am not an expert in jet engines, but just from basic physics and engineering principles the idea is fascinating. The idea of eliminating the need for fixed blades by having contrarotating blades has enormous potential, as well as substantial difficulties in getting it right. If they can do it and get it right it will be a magnificent acheivement. The next step for ultimate efficiency would be a geared contrarotating fan. Anyone seen Rube Goldberg lately? Oh, that's right, he's dead. Summon his ghost, the industry needs him. Seriously, it would be enormously difficult to make a geared contrarotating engine reliable enough, but if it could be done it would be the holy grail of jet engines.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
Dougloid From , joined Dec 1969, posts, RR: Reply 3, posted (6 years 4 weeks 1 day 17 hours ago) and read 9408 times:
You're up early Keesje....a most interesting article on a very timely subject.
On the subject of ultra high bypass fan engines I worked on a few Garrett ATF3s back in the day. They were used on the USCG HU25A and the French Navy equivalent, mating the engine to a modified Falcon 20 airframe. There was an extensive teething process with numerous service bulletins which required some of the mechanics to go to the airplanes and modify the engines. One of our guys spent seven weeks in Tahiti on that show.
The original task was to produce a very efficient engine with very low IR signature for a high altitude pilotless drone that Teledyne Ryan was going to build-which sounds a lot like Global Hawk.
That project got shelved but the ATF3 eventually got built. There was some internal dissension within Garrett as the ATF3 was a Torrance design and all the other engines came out of Phoenix. Well, I could be wrong about that part of it because it has been about 25 years
.
The ATF3 turned the airflow a bunch of different ways and ejected its exhaust into the fan air path midway through stacks. It was said that the ATF3 produced 93-95 per cent of its thrust from the fan, and it was a three spool engine.
Ultimately the ATF3's efficiencies were attained using 70s technology and materials, which was a very expensive way to do it. New materials and processes allowed simpler and less expensive engines to reach the same high degree of fuel economy.
There is a very interesting ATF 3 site that is worth a trip, particularly the part about the Tacit Blue engines and how they disappeared and reappeared..
DAYflyer From United States of America, joined Sep 2004, 3807 posts, RR: 4 Reply 4, posted (6 years 4 weeks 1 day 16 hours ago) and read 9305 times:
A very intersting subject indeed, Keesje.
I work for a company that manufactures high speed turbine impellers for commercial applications. Couter-rotating is indeed possible, but tricky. But let me tell you, the ones we have done here for non-aircraft use move HUGE volumes of air at tremendous speeds. I wonder what engineering problems and success they are having with this at Snecma??
N328KF From United States of America, joined May 2004, 6222 posts, RR: 3 Reply 5, posted (6 years 4 weeks 1 day 15 hours ago) and read 9232 times:
Quoting SEPilot (Reply 2): Seriously, it would be enormously difficult to make a geared contrarotating engine reliable enough, but if it could be done it would be the holy grail of jet engines.
Don't propfans contrarotate?
When they call the roll in the Senate, the Senators do not know whether to answer 'Present' or 'Not guilty.' T.Roosevelt
Contrarotating is not that difficult as far as shafts/bearings are concerned; what is difficult is the blade contours. Contrarotating between a prop and a turbine is easy; it is geared anyway. The difficulty starts when you gear between the fan and turbine within the engine; first, where do the gears go and second, how do you make them reliable enough? That is what P & W is working on, and as I understand it it is not easy. Then add a contrarotating shaft in there that also needs to be gearded and you have just squared or cubed your problems. I'm not at all sure that it can be done.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
TristarSteve From Sweden, joined Nov 2005, 3694 posts, RR: 34 Reply 8, posted (6 years 4 weeks 1 day 15 hours ago) and read 9133 times:
[quote=SEPilot,reply=7]Contrarotating is not that difficult as far as shafts/bearings are concerned; what is difficult is the blade contours. Contrarotating between a prop and a turbine is easy; it is geared anyway. The difficulty starts when you gear between the fan and turbine within the engine; first, where do the gears go and second, how do you make them reliable enough? That is what P & W is working on, and as I understand it it is not easy. Then add a contrarotating shaft in there that also needs to be gearded and you have just squared or cubed your problems. I'm not at all sure that it can be done.[/quote
Why not have two HP turbines, with two stages on each, each driving one fan. Then you don't need any gears.?
Justloveplanes From United States of America, joined Jul 2004, 872 posts, RR: 1 Reply 9, posted (6 years 4 weeks 1 day 14 hours ago) and read 9110 times:
why are so few prop applications counter-rotating?
SEPilot From United States of America, joined Dec 2006, 6260 posts, RR: 39 Reply 10, posted (6 years 4 weeks 1 day 14 hours ago) and read 9077 times:
Quoting Justloveplanes (Reply 9): why are so few prop applications counter-rotating?
In a nutshell, cost and complexity. Howard Hughes's plane that crashed (I forget what the model was) had counter-rotating props, and the failure of one of them is what caused the crash.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
DfwRevolution From , joined Dec 1969, posts, RR: Reply 11, posted (6 years 4 weeks 1 day 14 hours ago) and read 9059 times:
Quoting Keesje (Thread starter): Snecma is looking at contrarotation fan as an option for next generarion Narrowbody aircraft. Wonder how GE thinks about it.
What must really be on their mind is the future of the CFMI partnership...
Lightsaber From United States of America, joined Jan 2005, 10695 posts, RR: 100 Reply 12, posted (6 years 4 weeks 1 day 14 hours ago) and read 8974 times:
Quoting Keesje (Thread starter): RR (3 spool) and Pratt (GTF) are also testing the water.
Pratt proposed one for the Sonic Cruiser.
Quoting SEPilot (Reply 2): Seriously, it would be enormously difficult to make a geared contrarotating engine reliable enough, but if it could be done it would be the holy grail of jet engines.
Hence why Pratt is focused on the simple GTF. But is this a concept of high merit? Yes!
Quoting TristarSteve (Reply 8): Why not have two HP turbines, with two stages on each, each driving one fan. Then you don't need any gears.?
But that is effectively a triple spool without the benefit of getting the turbine's mach number into its optimal range. The current triple spool has higher efficiency than your proposal. Why? By having the intermediate spool turbine and compressor spinning at their optimal mach number (which must be at a higher RPM than the fan based on diameters and temperature increases to compression heating) the engine gains in efficiency.
Should this be done long term? Yes! But we're talking engines in the 2020 timeframe. This is pretty far out technology.
Short term I'm still a fan of the GTF. This concept is far more complicated than a two shaft GTF.
You miss the point. The idea is to have a gear reduction between the fan and the turbine, and then have contrarotating fans/turbines as well. That is what I was getting at.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
Lemurs From United States of America, joined Mar 2005, 1439 posts, RR: 4 Reply 16, posted (6 years 4 weeks 1 day 10 hours ago) and read 8640 times:
Lightsaber, why couldn't this just be a 3 spool design? I saw your response to TristarSteve, but I didn't quite follow what the problem would be...if you were hooking up the two fans to their own spools and making the core the a single spool, it could work and still be fairly conventional and simple, no?
The FlightGlobal article points out that the front fan has noticably fewer fan blades than the rear one. That hints at a simple 3 spool, but different than what RR is doing. Standard HP core, fairly standard LP driving the rear fan and lead stage(s) and another LP (VLP?) beyond that driving the lighter front fan only. It would certainly reduce the complexity of the problem down dramatically from any kind of geared solution, no?
There are 10 kinds of people in the world; those who understand binary, and those that don't.
Lightsaber From United States of America, joined Jan 2005, 10695 posts, RR: 100 Reply 17, posted (6 years 4 weeks 1 day 8 hours ago) and read 8525 times:
Quoting Lemurs (Reply 16): Lightsaber, why couldn't this just be a 3 spool design? I saw your response to TristarSteve, but I didn't quite follow what the problem would be...if you were hooking up the two fans to their own spools and making the core the a single spool, it could work and still be fairly conventional and simple, no?
It could be a 3-spool.
But by using two of the spools to turn the fans, you limit each spools Mach number at the fan (Feel free to think RPM). Thus, you lose the benefit of RR's triple spool of having the low compressor and low turbine spinning fast enough to be efficient.
I've read a bit more about this offline, and am now convinced that the added complexity of the 2nd part of the gearbox wasn't as bad as I feared. So move the EIS up by 5 or so years.
I still think a geared solution is simpler. But that's me. I've been exposed to the ugly sides of GTF's and haven't been scared off.
Lemurs, love the quote in your signature.
So now I'm in favor of this as a 2nd generation turbofan. You really need to get the low turbine Mach number (again, feel free to think RPM) up. Dramatically! There is too much efficiency being thrown away in a low Mach number turbine.
Lemurs From United States of America, joined Mar 2005, 1439 posts, RR: 4 Reply 18, posted (6 years 4 weeks 1 day 8 hours ago) and read 8472 times:
Quoting Lightsaber (Reply 17): But by using two of the spools to turn the fans, you limit each spools Mach number at the fan (Feel free to think RPM). Thus, you lose the benefit of RR's triple spool of having the low compressor and low turbine spinning fast enough to be efficient.
Ah right, I always lose sight of that. Low pressure systems in current turbofans are inherently about picking the least ugly tradeoff, aren't they? I don't suppose the configuration of the fan would dramatically change the optimal rotational speed for a given diameter, would it? There's only so fast the outer edges can go before they stop doing their job well, right? (i.e. would that front fan with fewer blades have a higher optimal RPM than a conventional fan, allowing for a less painful tradeoff?) Still obviously not as good as letting everyone spin at their most efficent speed, like a gearset would allow, I realize.
Quoting Lightsaber (Reply 17): Lemurs, love the quote in your signature.
Thanks! It's both fun and practical. It sort of acts as a self-selection mechanism. I know almost without fail that I will enjoy talking to anyone who "gets" it without me having to explain. I have a large body of experience using it, so I know it works. Let's just say I am not shocked you got it.
There are 10 kinds of people in the world; those who understand binary, and those that don't.
RayChuang From United States of America, joined Jun 2000, 7696 posts, RR: 5 Reply 19, posted (6 years 4 weeks 1 day 6 hours ago) and read 8174 times:
Combine this with the upgraded CFM56 engine core and we could see 8-14% fuel efficiency improvements without having to go to a new airframe for a 737 or A320 Family replacement. That could make the A320 Family viable for the next 25 years.
XT6Wagon From United States of America, joined Feb 2007, 3133 posts, RR: 4 Reply 20, posted (6 years 4 weeks 1 day 5 hours ago) and read 8064 times:
Quoting RayChuang (Reply 19): That could make the A320 Family viable for the next 25 years.
NO
The MX benefits of the construction methods used for the 787 make the 737RS unbeatable given that any existing engine could very well be used on the 737RS if it works on a A320. Not to mention the 737RS will be cheaper to make than the 737NG despite having more toys stuffed in it.
The A320 dies the day the 737RS enters service, the only question is how long does the body keep twitching.
Keesje From , joined Dec 1969, posts, RR: Reply 21, posted (6 years 4 weeks 14 hours ago) and read 7907 times:
Quoting XT6Wagon (Reply 20): Quoting RayChuang (Reply 19):
That could make the A320 Family viable for the next 25 years.
NO
The MX benefits of the construction methods used for the 787 make the 737RS unbeatable given that any existing engine could very well be used on the 737RS if it works on a A320. Not to mention the 737RS will be cheaper to make than the 737NG despite having more toys stuffed in it.
The A320 dies the day the 737RS enters service, the only question is how long does the body keep twitching.
XT6Wagon it seems a bit premature to present a non existing aircraft (not event sketches available) as a winner over another aircraft because of an unproven technology.
Keesje From , joined Dec 1969, posts, RR: Reply 23, posted (6 years 3 weeks 3 days 10 hours ago) and read 7643 times:
Bombardier recently with regards to their C-series:
“Now we’ve got until 2013, this fits in well with geared-turbofan technology. It also fits with Rolls-Royce which is thinking of a new engine and it fits with CFM as well.”
Scott says that Bombardier has been impressed by Pratt & Whitney’s geared turbofan, which has not been mirrored to date by its rivals.
“They’ve been working on this technology for a long time and it’s now matured to a point where we can put it on a new aircraft. It’s a very good option, but it’s not going unnoticed by Rolls-Royce and CFM.”
the pressure on the industry to come up with new smaller turbofan is increasing it seems..
The MX benefits of the construction methods used for the 787 make the 737RS unbeatable given that any existing engine could very well be used on the 737RS if it works on a A320. Not to mention the 737RS will be cheaper to make than the 737NG despite having more toys stuffed in it.
The A320 dies the day the 737RS enters service, the only question is how long does the body keep twitching.
LOL thanks for the outlook XT6...
Will Fly For Food!
25 Boeing7E7: Going out on a limb here.... ie... Beta vs. VHS... They all get together and develop an engine that combines all of their technologies in one way or a
26 Keesje: CFM studies 'open rotor' concept for next generation airliner engine CFM International is conducting preliminary studies of open rotor and other pote
28 Keesje: CFM is also studying different fan options. One off the problems with UDF es if I remember well the charaterictics of the noise it makes (irritating f
29 Stitch: Both the GTF and LEAP56 programs appear to have the fuel savings needed to justify the launch of the 737RS and A320RS programs... And if the GTF can d
30 Strathpeffer: I was really intersted to read the full article that includes this info in this week's printed FI. http://www.flightglobal.com/articles...-for-next-ge
31 MarkC: The airframers are not ready for new tech engines now. They would rather keep selling their narrow body cash makers for the forseable future. An engin
32 JetMech: True, but I think a more realistic scenario would be Airbus or Boeing scrambling to get some sort of exclusivity deal with an engine maker that produ
33 XT6Wagon: Wrong, Boeing wants to do the 737RS ASAP. They will produce the two side by side for a few years like they did with the 737 and 737NG so the "we woul
34 Stitch: I depends on how that tech can be integrated into existing designs. P&W believe their GTF will fit under the wing of the current A320 family (but not
35 Thegeek: At the risk of reviving an old thread, wouldn't this result in effectively a two stage fan and a low bypass ratio? Wouldn't that be counter productive
36 Tdscanuck: Having a two-stage fan doesn't automatically lower the bypass ratio...provided they lower the disk loading accordingly, they could hold the same bypa
Sponsor Message: 
From , joined Dec 1969, posts, 
From United States of America, joined Jan 2006, 1196 posts, 
From , joined Dec 1969, posts, 
From United Kingdom, joined Jul 2003, 11363 posts, 
From Sweden, joined Nov 2005, 3694 posts, 
This is pretty far out technology.
From Germany, joined Jul 2005, 4655 posts, 
From Canada, joined Mar 2005, 180 posts, 
Sponsor Message: 
Printer friendly format
