747400sp From United States of America, joined Aug 2003, 3181 posts, RR: 3 Posted (4 years 7 months 3 weeks 4 days 11 hours ago) and read 16728 times:
In September of 2007 Airliner World, on P. 60, there an article about Easyjet's Ecojet airliner. This aircraft has large unducted fans at the rear of it's fuselage. I believe the article was saying that this could be the direction Boeing and Airbus could go with the Y-1 and NSR. So do you see the Y-1 and NSR with unducted fans?
KELPkid From United States of America, joined Nov 2005, 5609 posts, RR: 5 Reply 1, posted (4 years 7 months 3 weeks 4 days 11 hours ago) and read 16756 times:
Not fully unducted, no.
There's a reason the GE UDF prototype never went beyond the prototype stage, something about 16+ fan blades (really prop blades?) moving at supersonic tip speeds and making ungodly amounts of noise in the process, not to mention what would happen should a birdy find it's way into the blade (prop?) arc and one of them should come loose...
I think that, should the concept move forward, we will see the "fan" (prop) blades ducted for both of the reasons above...I understand that P&W's GTF (geared turbo fan) concept is a move in this direction.
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
747400sp From United States of America, joined Aug 2003, 3181 posts, RR: 3 Reply 2, posted (4 years 7 months 3 weeks 4 days 10 hours ago) and read 16704 times:
There's a reason the GE UDF prototype never went beyond the prototype stage, something about 16+ fan blades (really prop blades?) moving at supersonic tip speeds and making ungodly amounts of noise in the process, not to mention what would happen should a birdy find it's way into the blade (prop?) arc and one of them should come loose...
I think that, should the concept move forward, we will see the "fan" (prop) blades ducted for both of the reasons above...I understand that P&W's GTF (geared turbo fan) concept is a move in this direction.
They also mention geard turbo fans for the aircraft. Anyway, with the high sales both the 737 and A320 has been getting lately, it could take another ten years before we see the Y-1 or NSR .
Dougloid From , joined Dec 1969, posts, RR: Reply 3, posted (4 years 7 months 3 weeks 3 days 18 hours ago) and read 16567 times:
Quoting KELPkid (Reply 1): There's a reason the GE UDF prototype never went beyond the prototype stage, something about 16+ fan blades (really prop blades?) moving at supersonic tip speeds and making ungodly amounts of noise in the process,
I used to see the MD80 test bed come in and out of Long Beach on a regular basis. The noise was awful, and the project was ended with the MD80 at least because the structure back there couldn't tolerate the vibration levels.
RoseFlyer From United States of America, joined Feb 2004, 7613 posts, RR: 51 Reply 4, posted (4 years 7 months 3 weeks 3 days 18 hours ago) and read 16546 times:
Quoting KELPkid (Reply 1): There's a reason the GE UDF prototype never went beyond the prototype stage, something about 16+ fan blades (really prop blades?) moving at supersonic tip speeds and making ungodly amounts of noise in the process, not to mention what would happen should a birdy find it's way into the blade (prop?) arc and one of them should come loose...
Other than there being more blades, how are these fears that you point out different from those expected with a turboprop?
If you have never designed an airplane part before, let the real designers do the work!
SEPilot From United States of America, joined Dec 2006, 5901 posts, RR: 39 Reply 5, posted (4 years 7 months 3 weeks 3 days 17 hours ago) and read 16533 times:
Quoting RoseFlyer (Reply 4): Other than there being more blades, how are these fears that you point out different from those expected with a turboprop?
Speed; turboprop blades do not go supersonic, and consequently turboprops do not approach the speeds that jets do. A 737 or A320 replacement would have to match current speeds or it will be DOA.
Quoting 747400sp (Reply 2): Anyway, with the high sales both the 737 and A320 has been getting lately, it could take another ten years before we see the Y-1 or NSR .
I expect Boeing to jump on Y1 just as soon as they can (provided the engines are available or will be) because they are now in a position to regain their dominance. Airbus will be heavily involved in developing the A350 for a number of years after the 787 push is over, and Boeing would be just stupid to sit on their hands. And the market for planes smaller than the 787 is much bigger than for larger ones, so that is the one to tackle first.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
JayinKitsap From United States of America, joined Nov 2005, 761 posts, RR: 1 Reply 6, posted (4 years 7 months 3 weeks 3 days 13 hours ago) and read 16470 times:
Would it make any sense to add a rotating duct to what is currently an unducted fan. I would think it would eliminate a lot of vibration and provide much better airflow. There would still be the supersonic issues.
My general sense is the GTF is the way to go.
A slight loss of speed for much better efficiency might be tolerated for the shorter range Y1 craft but I agree that with transcon flights there would be a desire to have higher speeds.
N231YE From , joined Dec 1969, posts, RR: Reply 7, posted (4 years 7 months 3 weeks 3 days 12 hours ago) and read 16463 times:
Quoting Dougloid (Reply 3): I used to see the MD80 test bed come in and out of Long Beach on a regular basis. The noise was awful, and the project was ended with the MD80 at least because the structure back there couldn't tolerate the vibration levels.
I remember reading that the paint started to bubble and flake off of the airframe, due to the shockwaves of the blades beating against it.
KELPkid From United States of America, joined Nov 2005, 5609 posts, RR: 5 Reply 11, posted (4 years 7 months 3 weeks 3 days 11 hours ago) and read 16435 times:
Quoting RoseFlyer (Reply 4): Other than there being more blades, how are these fears that you point out different from those expected with a turboprop?
Well, let's take the GE UDF prototype: worst case, where will a blade that breaks loose go? Through the fuselage I know that in a turboprop, that's a pretty rare occurence, however you are slinging a lot more of them a lot quicker (and in some cases, closer to the fuselage) than a turboprop slinging a prop. Also, when birds go through props, the usual result is minced bird (you might have a ding in the prop that will need to be addressed ASAP...).
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
No, at current cruise speeds. Maybe, if they back off the speed.
Quoting SEPilot (Reply 5): A 737 or A320 replacement would have to match current speeds or it will be DOA.
Not really. The vast bulk of 737 and A320 flights are short/medium range. Dropping 10% in cruise speed will cost you something like 12 minutes...a drop in the bucket compared to normal delays.
Quoting SEPilot (Reply 5): I expect Boeing to jump on Y1 just as soon as they can (provided the engines are available or will be) because they are now in a position to regain their dominance.
They already have regained dominance...I'm not sure that's much of a motivator for them anyway. Dominance, by itself, doesn't mean profitability.
Quoting SEPilot (Reply 5): And the market for planes smaller than the 787 is much bigger than for larger ones, so that is the one to tackle first.
Not necessarily. The volume is far higher, but the profit margin is a lot thinner.
Quoting JayinKitsap (Reply 6): Would it make any sense to add a rotating duct to what is currently an unducted fan. I would think it would eliminate a lot of vibration and provide much better airflow.
Aerodynamically, that would probably work, but balancing it would be kind of tricky. It would make for some very cool testing.
SEPilot From United States of America, joined Dec 2006, 5901 posts, RR: 39 Reply 13, posted (4 years 7 months 3 weeks 3 days 8 hours ago) and read 16384 times:
Quoting Tdscanuck (Reply 12):
They already have regained dominance...I'm not sure that's much of a motivator for them anyway.
I wouldn't say that; I would say they've regained parity. I doubt very much that they do not desire dominance; I do not know of any company in any industry that had it in its grasp that did not seek it.
Quoting Tdscanuck (Reply 12):
Not necessarily. The volume is far higher, but the profit margin is a lot thinner.
True, but the A320 is what gives Airbus their bread and butter. By knocking that out from under them they are applying extreme pressure to Airbus, and if you say Boeing doesn't want to do that (in spite of all their kind words) I have such a deal for you on a bridge in Brooklyn.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
Lehpron From United States of America, joined Jul 2001, 7028 posts, RR: 25 Reply 14, posted (4 years 7 months 1 week 5 days 11 hours ago) and read 16288 times:
Quoting Tdscanuck (Reply 12): Quoting JayinKitsap (Reply 6):
Would it make any sense to add a rotating duct to what is currently an unducted fan. I would think it would eliminate a lot of vibration and provide much better airflow.
Aerodynamically, that would probably work, but balancing it would be kind of tricky. It would make for some very cool testing.
Too much extra inertia for the engine. IMO, any fuel saved by the idea is lost just trying to run it up and down.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
KELPkid From United States of America, joined Nov 2005, 5609 posts, RR: 5 Reply 15, posted (4 years 7 months 1 week 4 days 23 hours ago) and read 16205 times:
Quoting Lehpron (Reply 14): Too much extra inertia for the engine. IMO, any fuel saved by the idea is lost just trying to run it up and down.
Woudn't it also introduce problems similar to what World War I rotary engines had, like only being able to turn effectively in one direction? That pesky problem with (too much) rotating mass
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
2H4 From United States of America, joined Oct 2004, 8936 posts, RR: 65 Reply 16, posted (4 years 7 months 1 week 4 days 23 hours ago) and read 16198 times:
AIRLINERS.NET CREW HEAD DATABASE EDITOR
Quoting KELPkid (Reply 15): only being able to turn effectively in one direction?
Boy, that would make for some interesting new logic in TCAS RAs......
KELPkid From United States of America, joined Nov 2005, 5609 posts, RR: 5 Reply 17, posted (4 years 7 months 1 week 4 days 22 hours ago) and read 16190 times:
But seriously, folks,
What it is to stop an engine manufacturer from putting, say, a fixed, ring-shaped duct (non-rotating) around an "unducted" fan and thereby making it ducted? (This is kind of what I had in mind waaay back in reply #1...). Would it hurt effeciency? Boats do this all of the time around propellers for various reasons It would help with noise containment and loose blade containment.
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
KELPkid From United States of America, joined Nov 2005, 5609 posts, RR: 5 Reply 18, posted (4 years 7 months 1 week 4 days 22 hours ago) and read 16189 times:
Quoting 2H4 (Reply 16): Boy, that would make for some interesting new logic in TCAS RAs...... biggrin
2H4
On the plus side, it would greatly reduce the mental gymnastics needed to compute a hold entry... You'd eliminate 50% of the possiblities
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
SCAT15F From United States of America, joined Feb 2007, 318 posts, RR: 0 Reply 19, posted (4 years 7 months 1 week 4 days 22 hours ago) and read 16185 times:
The UDF cruise speed is actually the same as the current 737NG. I think this engine is definitely the way to go. As efficient as it was in the '80s it could be that much more so now: Imagine GEnx technology mated to a counter-rotating UDF!
Tdscanuck From Canada, joined Jan 2006, 11029 posts, RR: 72 Reply 20, posted (4 years 7 months 1 week 4 days 14 hours ago) and read 16114 times:
Quoting KELPkid (Reply 17): What it is to stop an engine manufacturer from putting, say, a fixed, ring-shaped duct (non-rotating) around an "unducted" fan and thereby making it ducted?
I think that's called a turbofan.
The line between fan and prop gets very blurry in the realm you're talking about. The latest engines are all heading for wide-chord blades, which pretty much makes them fixed pitch props or ducted "unducted fans".
XT6Wagon From United States of America, joined Feb 2007, 2845 posts, RR: 4 Reply 21, posted (4 years 7 months 6 days 16 hours ago) and read 15952 times:
I don't think you will ever see an "unducted fan" in service.
Not only do the obvious downsides rule against it, I think the FAA would in the end just say "unless you can prove a blade out won't bring the plane down, you can't use it" at which point the impossiblity of proving that jumps out and makes the whole idea just one huge trainwreck.
WingedMigrator From United States of America, joined Oct 2005, 1944 posts, RR: 57 Reply 22, posted (4 years 7 months 6 days 16 hours ago) and read 15941 times:
Quoting KELPkid (Reply 1): not to mention what would happen should a birdy find it's way into the blade (prop?) arc and one of them should come loose...
Here's a hybrid design solution for your consideration...
One could mount two propfan units at the very rear of the aircraft, with a slight cant about the yaw axis (inward toward the CG). Using a design canted by 5 or 10 degrees, one would not lose any significant propulsive efficiency (by virtue of the cosine law) and, more importantly, the geometrical plane of either propeller would not contain anything-- be it airplane structure or the other engine. There would be no hazard from an uncontained blade failure.
Then, you could have a very short, lightweight composite duct, possibly co-rotating with the propeller, without the requirement for containing a blade failure. This would suppress the noise and perhaps make it look less like the propeller that it is, hopefully without driving up the mass or adding too much drag.
Tdscanuck From Canada, joined Jan 2006, 11029 posts, RR: 72 Reply 23, posted (4 years 7 months 6 days 12 hours ago) and read 15919 times:
Quoting XT6Wagon (Reply 21):
Not only do the obvious downsides rule against it, I think the FAA would in the end just say "unless you can prove a blade out won't bring the plane down, you can't use it" at which point the impossiblity of proving that jumps out and makes the whole idea just one huge trainwreck.
Why would that be impossible to prove? It would basically be like showing that you can't loose the aircraft from a rotor burst today. You just need to show that no single path through the airframe in the plane of the propeller would compromise a system and it's redundant backup.
2H4 From United States of America, joined Oct 2004, 8936 posts, RR: 65 Reply 24, posted (4 years 7 months 6 days 12 hours ago) and read 15915 times:
AIRLINERS.NET CREW HEAD DATABASE EDITOR
Quoting XT6Wagon (Reply 21): I don't think you will ever see an "unducted fan" in service.
All it takes is financial incentive. If there's enough money to be made, some team of engineers and aerodynamicists would get a washing machine certified by the FAA.
Quoting XT6Wagon (Reply 21): "unless you can prove a blade out won't bring the plane down, you can't use it" at which point the impossiblity of proving that
I agree with Tdscanuck.....what makes that so impossible to prove? If a blade can be contained with Kevlar at the cowl, I don't see why it can't also be kept out with Kevlar at the fuselage...
2H4
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25 Tdscanuck: The aerodynamics of a washing machine are probably marginally better than a Dreamlifter anyway... Tom.
26 2H4: Well, I was going to use a certain Irish manufacturer as an example, but six to one, half-dozen to another.... 2H4
27 Starlionblue: Neat idea, but engine toe in or toe out is dictated by local airflow. Engines today are very carefully toed to take advantage of local airflow. For e
28 WingedMigrator: Good point. But you could have the turbine oriented independently of the prop, by suitable choice of gearbox arrangement. I'm not talking about a U j
29 Starlionblue: Sure, but the prop/fan is the part you want oriented with the airflow.
30 2H4: I can think of one configuration where the separation of a prop wouldn't result in fuselage damage: Perhaps Douglas was on to something... 2H4
31 Tdscanuck: The Learfan also qualifies, though it never made it to production: http://en.wikipedia.org/wiki/Image:LearFan.jpg Tom.
32 Tdscanuck: My bad...you said configuration, not aircraft. The Learfan was the same configuration as your Douglas, so no cookie for me. Tom.
33 KELPkid: I Hear EK will have a laundromat installed in the front lounge area of their A380's Good one!!!
34 SEPilot: I do not think the possibilities of a blade departure is a major consideration. How many propeller designs have been approved by the FAA? Quite a few,
35 EA CO AS: Now multiply that 12 minutes per trip over six to eight flight segments per day. Suddenly that 12 minute savings equals the difference between one mo
36 Starlionblue: The difference being that a prop on a "traditional" turboprop or recip is subsonic. The unducted fan designs have supersonic blade speeds, which cons
37 Faro: And what about the out-of-balance condition with a missing blade? Higher, supersonic blade speeds imply higher imbalancing forces about the engine ax
38 KELPkid: Well, the response to a prop becoming dynamically unbalanced in flight, whether in a recip or a turboprop, is to shut down the offending engine befor
39 SEPilot: I believe that if a prop blade departs on any prop powered plane the unbalance will almost certainly tear the engine loose long before it can be shut
40 Jetlagged: Boeing will most likely wait until engine technology brings efficiency savings up to the point where developing a new aircraft is an economic proposi
41 Texfly101: Yep, like the Bear, the noise leveles are untolerable While the logic is correct, it will depend on whether Y3 promises to get the efficiencies that
42 Scbriml: With the 787 challenges, 767 tanker problems, 777F and 748 development ongoing, Boeing has a fair bit on their plate right now. Given the still growi
43 Starlionblue: Very true. However winning sales at the expense of Airbus is in line with the profit motive most of the time. This is not the same thing as "killing"
44 Texfly101: The main criteria is a 15% reduction in SFB, a 20% reduction in O&M and a 20% reduction in capital costs. Those are the targets that the airlines are
45 Tdscanuck: Catastrophic has a specific meaning in FAA parlance. To be certified, you can't have a single failure result in a catastrophic consequence. So, altho
46 DEVILFISH: I'm always reading that the Avanti is pretty fast for a prop. If shrouding the pusher props could take care of the noise and mitigate blade breakout,
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From United States of America, joined Aug 2003, 3181 posts, 
From , joined Dec 1969, posts, 
From St. Helena, joined Mar 2007, 405 posts, 
From Germany, joined Jan 2006, 13864 posts, 
I know that in a turboprop, that's a pretty rare occurence, however you are slinging a lot more of them a lot quicker (and in some cases, closer to the fuselage) than a turboprop slinging a prop. Also, when birds go through props, the usual result is minced bird (you might have a ding in the prop that will need to be addressed ASAP...).
From Canada, joined Jan 2006, 11029 posts, 
You'd eliminate 50% of the possiblities 
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