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Airbus: Open Rotor A320-replacement Prior 2025  
User currently offlinerheinwaldner From Switzerland, joined Jan 2008, 2213 posts, RR: 5
Posted (2 years 2 months 9 hours ago) and read 25387 times:

Sorry, the source is again in German (closer sources are often written in one of the EADS languages but tend to catch more news):
http://www.ftd.de/unternehmen/indust...eues-flugzeugkonzept/70041830.html

Summary:
- Open Rotor trial flights on an A340 would be realistic in 2016

- The on-going A30X project would draw benefit from those tests

- An Open Rotor A320 replacement could be launched with EIS between 2020-2025.

- Rotor size: about 4.2 meters. So the configuration would require fuselage mounted engines.

- Time from launch to EIS: 7 years


Other interesting news:
- A new laminar flow wing mounted on an A340 testbed could fly in 2014 and bring 10% fuel reduction.

- There is a pressure to bring new technologies quicker on the market than today. Certification efforts have become too much of a burden.

- A reserach center in Bangalore will be established to catch the Asian spirit and ideas for future programs.

89 replies: All unread, showing first 25:
 
User currently offlineptrjong From Netherlands, joined Mar 2005, 3906 posts, RR: 19
Reply 1, posted (2 years 2 months 9 hours ago) and read 25269 times:

Why are propfans suddenly called 'open rotors'?    Helicopters have open rotors.


The only difference between me and a madman is that I am not mad (Salvador Dali)
User currently offlinebtblue From United Kingdom, joined Mar 2004, 578 posts, RR: 4
Reply 2, posted (2 years 2 months 8 hours ago) and read 25178 times:

I wonder if it will look anything like this...

http://www.youtube.com/watch?v=Yo0Rp6TQPXo



146/2/3 737/2/3/4/5/7/8/9 A320 1/2/18/19/21 DC9/40/50 DC10/30 A300/6 A330/2/3 A340/3/6 A380 757/2/3 747/4 767/3/4 787 77
User currently onlineBMI727 From United States of America, joined Feb 2009, 15719 posts, RR: 26
Reply 3, posted (2 years 2 months 8 hours ago) and read 25158 times:

Quoting rheinwaldner (Thread starter):
Summary:
- Open Rotor trial flights on an A340 would be realistic in 2016

- The on-going A30X project would draw benefit from those tests

- An Open Rotor A320 replacement could be launched with EIS between 2020-2025.

- Rotor size: about 4.2 meters. So the configuration would require fuselage mounted engines.

- Time from launch to EIS: 7 years

Do the engine manufacturers have anything to say about this? Because that might be a little bit important at some point.

Furthermore, it is hard to read the partnership of Rolls-Royce with Pratt and Whitney on the GTF as anything other than a tacit admission that open rotor will not be ready in the near future.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlinePM From Germany, joined Feb 2005, 6870 posts, RR: 63
Reply 4, posted (2 years 2 months 7 hours ago) and read 24831 times:

Quoting rheinwaldner (Thread starter):
The on-going A30X project

Is this a new narrowbody or something else?

Quoting BMI727 (Reply 3):
Do the engine manufacturers have anything to say about this?

I'm guessing that RR, for one, will not be displeased.

Quoting rheinwaldner (Thread starter):
A reserach center in Bangalore will be established to catch the Asian spirit and ideas for future programs.

I'm moving to Bangalore in seven weeks. Looking forward to lots of aerospace activity!   


User currently offlinescouseflyer From United Kingdom, joined Apr 2006, 3381 posts, RR: 9
Reply 5, posted (2 years 2 months 7 hours ago) and read 24740 times:

Quoting PM (Reply 4):
Quoting rheinwaldner (Thread starter):
The on-going A30X project

Is this a new narrowbody or something else?

It's the new build NB plane, I think that they've also called it the NSR

http://www.flightglobal.com/blogs/fl...irbus-outlined-future-a30x-co.html


User currently offlineparapente From United Kingdom, joined Mar 2006, 1548 posts, RR: 10
Reply 6, posted (2 years 2 months 7 hours ago) and read 24740 times:

Here is another 2 examples of 'future aircraft'
http://www.youtube.com/watch?v=XKncIxPZIHQ&feature=endscreen&NR=1

http://www.youtube.com/watch?v=WGBLRNrZN1U&feature=related

There were examples of Boeing patent designs posted not long ago on this forum.Again they were very similar (an extra small tail on the fuse as I recall for blade out/noise reasons.
However all the designs have roughfully come to the same conclusion of 3 lifting surfaces,FSW and double (triple) tails with or.Lower cruising speeds with thicker laminar flow wings.BUT

The NEO and MAX have now been launched. They will want at least a 15 year production run,there is no real competitive pressure, so I don't see it happening in the time frame suggested.


User currently offlinejustloveplanes From United States of America, joined Jul 2004, 1040 posts, RR: 1
Reply 7, posted (2 years 2 months 7 hours ago) and read 24529 times:

Sounds like a sonic cruiser type of lead in.

User currently offlinerheinwaldner From Switzerland, joined Jan 2008, 2213 posts, RR: 5
Reply 8, posted (2 years 2 months 5 hours ago) and read 23921 times:

Quoting BMI727 (Reply 3):
Do the engine manufacturers have anything to say about this? Because that might be a little bit important at some point.

This is true of course (if flight tests should start in 2016). The article mentions ongoing discussion between RR, Safran and Airbus.

Quoting BMI727 (Reply 3):
Furthermore, it is hard to read the partnership of Rolls-Royce with Pratt and Whitney on the GTF as anything other than a tacit admission that open rotor will not be ready in the near future.

And the article is an open announcement that the open rotor could be ready for flight test in 4 years and ready for operation in 8 - 13 years. Possibly your interpretation (which was shared by me until yesterday) has to be revised.

B.t.w. Boeing killed the 7J7 in 1987 not because the prop-fan would not have been ready in the near future (at that time!), but because the pressure due to high fuel prices was gone.


User currently online76er From Netherlands, joined Mar 2007, 511 posts, RR: 1
Reply 9, posted (2 years 2 months 5 hours ago) and read 23832 times:

Quoting rheinwaldner (Reply 8):
the pressure due to high fuel prices was gone.


And the noise problem..


User currently onlineflipdewaf From United Kingdom, joined Jul 2006, 1562 posts, RR: 1
Reply 10, posted (2 years 2 months 5 hours ago) and read 23763 times:
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Quoting BMI727 (Reply 3):
Furthermore, it is hard to read the partnership of Rolls-Royce with Pratt and Whitney on the GTF as anything other than a tacit admission that open rotor will not be ready in the near future.

Maybe you could look at it like that or maybe (this is my view) pratt realised that the GTF is only the short term solution and needs longer terma cash flow which they see getting from the open rotor while RR didn't want to lose narrow body revenue in the medium term.

Fred


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 11, posted (2 years 2 months 4 hours ago) and read 23545 times:

Quoting rheinwaldner (Thread starter):
- Rotor size: about 4.2 meters. So the configuration would require fuselage mounted engines.

Wow...that's gonna put the engine centerline about 8' away from the fuselage...that's a loooooong strut. This seems like a great application for the HondaJet over-wing style mounting.

Quoting rheinwaldner (Reply 8):
And the article is an open announcement that the open rotor could be ready for flight test in 4 years and ready for operation in 8 - 13 years.

The A350 and 787 didn't face nearly open rotor level configuration/engine issues and they still took more than 8 years to get to operation from conception...I don't see this one going faster, even if they commit today.

Tom.


User currently offlineRevelation From United States of America, joined Feb 2005, 12350 posts, RR: 25
Reply 12, posted (2 years 2 months 4 hours ago) and read 23450 times:

Quoting justloveplanes (Reply 7):
Sounds like a sonic cruiser type of lead in.

There aren't too many similarities.

SC was about burning fuel to go faster, OR is about saving fuel and going slower.

SC came out of nowhere, OR has decades of research behind it.

SC claimed to have launch customers lined up (IIRC it was AA, no?), OR is about using a testbed to prove out a technology.

Quoting 76er (Reply 9):
And the noise problem..

To me, the biggest problem is safety, in particular the blade failure scenarios.

Second is market acceptance: will the fuel burn savings be enough to make it so customers accept longer flights?

Third is community acceptance, i.e. the noise issue.

I'm also told a variable pitch mechanism is desired, and doing this is challenging.



Inspiration, move me brightly!
User currently offlinePlaneAdmirer From United States of America, joined Jul 2009, 561 posts, RR: 0
Reply 13, posted (2 years 2 months 4 hours ago) and read 23339 times:

How can this possibly make sense in light of the NEO? Airbus has over 1,000 orders for a plane that they will render outdated in under 10 years?

User currently offlinenasula From Finland, joined Sep 2010, 47 posts, RR: 0
Reply 14, posted (2 years 2 months 3 hours ago) and read 23176 times:

To me this is the really interesing tidbit:

Quoting rheinwaldner (Thread starter):
- A new laminar flow wing mounted on an A340 testbed could fly in 2014 and bring 10% fuel reduction.

Any more information on this? A new wing for the A330/340 family? Or some other target just being flown on an A340?

If this happens for the A330 and gives a 10% reduction + the additional reductions from the engine optimisations being talked about for the A330 sound VERY interesting indeed. That would make the A330 a tough competitor for the 787 and sound like killing off the 350-800?

Or am I missing something?


User currently offlineBurkhard From Germany, joined Nov 2006, 4387 posts, RR: 2
Reply 15, posted (2 years 2 months 2 hours ago) and read 22475 times:

Quoting PlaneAdmirer (Reply 13):
How can this possibly make sense in light of the NEO? Airbus has over 1,000 orders for a plane that they will render outdated in under 10 years?

OR and A320 could live together very well for decades. OR means lower speed and that is optimized for distances below 1000 or 1500 miles, while the NEO we know to be targeted for a range extended compared to the current A320s - where OR slower speed would really start to make a difference.


User currently offlineKC135TopBoom From United States of America, joined Jan 2005, 12128 posts, RR: 51
Reply 16, posted (2 years 2 months 2 hours ago) and read 22425 times:

This sounds a lot like the 1980s GE-36-UDF, P&W/Allison-578-DX, Progress D-27, and the RR RB-3011 programs. The GE-36 actually flew demo flights at the FAS aboard an MD-81 demo aircraft, and flew flight testing in the US aboard a B-727.

The GE-36 was chosen to power both the B-7J7 and the MD-94X, both programs were canceled.

The Progress D-27 is available on the An-70.

The TP-400 and NK-12 are turboprops, not UDFs.


User currently offlineB777LRF From Luxembourg, joined Nov 2008, 1308 posts, RR: 3
Reply 17, posted (2 years 2 months 2 hours ago) and read 22305 times:

Quoting nasula (Reply 14):
Any more information on this? A new wing for the A330/340 family? Or some other target just being flown on an A340?

Airbus use their A340 testbeds for all kinds of weird and wonderful stuff, and just because whatever it is they're testing is hanging off, or is bolted on to, a A340/330 family aircraft doesn't mean that's where it's going to end up. If Airbus are going to bring laminar-flow anything (wings sounds a tad ambitious) to the market, they'll probably do it on their newest and shiniest - why sink the money into the old dog, when there's a new one on the block with a hefty R&D bill in need of servicing?

The A330 will receive minor dusting offs from now on. No new engines, no new wings, no new primary structures. But a properly directed bit of polishing can gain those incremental 1.5 or 1.6% that'll keep the sun shining for a bit longer on the old girl.



From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove
User currently offlineStitch From United States of America, joined Jul 2005, 30618 posts, RR: 84
Reply 18, posted (2 years 2 months 2 hours ago) and read 22189 times:
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As they're off the A320neo and 737 MAX, Rolls-Royce has a seriously vested interest in making Open Rotor work for the Airbus NSR and Boeing NSA because it's their way back onto the most important part of the commercial aviation market (just as the GTF was Pratt's).

I think 2025 might be a bit ambitious, but we shall see.


User currently offlineAirbusA6 From United Kingdom, joined Apr 2005, 2011 posts, RR: 0
Reply 19, posted (2 years 2 months 2 hours ago) and read 21816 times:

The A340 has the necessary ground clearance for testing such an engine, whereas the A320 would be too low.


it's the bus to stansted (now renamed national express a4 to ruin my username)
User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 20, posted (2 years 2 months 2 hours ago) and read 21618 times:

Quoting rheinwaldner (Thread starter):
Certification efforts have become too much of a burden.

OEM's spend too much time in the cert process helping the regulators along, educating them in order to avoid the inevitable conservatism which results from not understanding how a design works. Delegated authority was intended to help this, but when someone at the ACO overrides the DER because they have failed to grasp the underlying design, the OEM has little choice but to take their top talent away from designing and turn them into teachers. Worse yet, the education process is not always successful, causing redesign or unwarranted constraints on the design. The cumulative impact of this happening hundreds of times over the course of a program is absolutely crippling. I agree 100% with Airbus on this point - it is something they are undoubtedly struggling through with the A350 at this moment.


User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 21, posted (2 years 2 months 1 hour ago) and read 20136 times:

Re the agreement PW and RR if I am not mistaken it is for "future geared engine technology" or something to that meaning. An open rotor really needs a good gear technology, me think PW and RR have covered both bases with this agreement, not just the shrouded fan case   .


Non French in France
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 22, posted (2 years 2 months ago) and read 19739 times:

Quoting nasula (Reply 14):
If this happens for the A330 and gives a 10% reduction +

They're not going to fit a laminar flow wing to the A330 in production. Laminar flow would be relofting the wing. That would probably mean a new static test and would certainly mean new flutter and stability and control testing, as well as requiring all new wing tooling. There's no way that business case closes.

Quoting ferpe (Reply 21):
An open rotor really needs a good gear technology

Not necessarily; some of the prototype open rotors back in the 80's were direct drive off the turbines with no gearing.

Tom.


User currently offlineEPA001 From Netherlands, joined Sep 2006, 4705 posts, RR: 38
Reply 23, posted (2 years 2 months ago) and read 19449 times:
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Quoting tdscanuck (Reply 22):
some of the prototype open rotors back in the 80's were direct drive off the turbines with no gearing.

Would that type of open rotor also be the most promising type? Or are gearboxes to be expected?


User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 24, posted (2 years 1 month 4 weeks 1 day 23 hours ago) and read 18846 times:

Quoting EPA001 (Reply 23):
Would that type of open rotor also be the most promising type? Or are gearboxes to be expected?

Assuming the noise from a open-rotor engine can be solved at all, gearing the fan seems almost certain. The direct drive UDF engines tested 20 years ago by GE/Boeing were exceedingly loud.

http://www.youtube.com/watch?v=zxVAa...IY&feature=player_detailpage#t=92s

The open-rotor engines tested by PW/McDonnell-Douglas used geared rotors which were quieter (but still very loud by today's standards) and much heavier.

http://www.youtube.com/watch?v=1BMNaXc1rL8

In either case, the forthcoming Stage 5 noise requirements are likely to represent a huge barrier to entry for using this technology versus current high bypass ratio engines which are many dB quieter, yet have little margin against the new Stage 5 noise requirements.


User currently offlineJoeCanuck From Canada, joined Dec 2005, 5408 posts, RR: 30
Reply 25, posted (2 years 1 month 4 weeks 1 day 23 hours ago) and read 19335 times:

The EU especially is going ape about the least bit of airline noise...the open rotor is DOA. The closest we'll see is perhaps a ducted contra rotating fan and/or a variable pitch fan but I'm willing to bet their ain't no way that a pair of open supersonic fans will ever be made quiet enough to meet noise standards...and that doesn't even touch the lost blade scenario.

If fans get any bigger, we may see some more high winged jets, instead of fuse mounted engines.

That being said, I'm all for experimentation...there's lots of stuff that isn't intuitive that just plain works.



What the...?
User currently offlineStitch From United States of America, joined Jul 2005, 30618 posts, RR: 84
Reply 26, posted (2 years 1 month 4 weeks 1 day 23 hours ago) and read 19033 times:
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GE claims the GE36 UDF did meet Stage III noise limits, but it was still a fair bit louder than a turbofan both inside and outside the aircraft.

As such, I do believe that a UDF engine will need to use the fuselage and control surfaces as baffles, like in the Boeing "Fozzie" concept, EasyJet's EcoJet design or one of Airbus' A30X design.


User currently onlineRoseflyer From United States of America, joined Feb 2004, 9510 posts, RR: 52
Reply 27, posted (2 years 1 month 4 weeks 1 day 23 hours ago) and read 19034 times:

It looks like Airbus is continuing to do investment in new technology. That’s no surprise. I am glad to see propfans get more attention.

With fuel prices where they are, propfans and open rotor will be talked about. There are still problems with them such as noise, but investment is still warranted.

I think proposing timelines is a bit premature with the level of maturity of the technology. I am surprised Airbus would float numbers about such technology when it is just in the R&D phase and no one knows where it would go.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlineSemaex From Germany, joined Nov 2009, 823 posts, RR: 2
Reply 28, posted (2 years 1 month 4 weeks 1 day 23 hours ago) and read 18700 times:

One thing I wonder is: I hear talks about those OR designs using counter-rotating propellers for efficiency purposes - but aren't they by laws of physics a lot louder than 'one-spool' propellers?


// You know you're an aviation enthusiast when you look at your neighbour's cars and think about fleet commonality.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 29, posted (2 years 1 month 4 weeks 1 day 22 hours ago) and read 18144 times:

Quoting EPA001 (Reply 23):
Quoting tdscanuck (Reply 22):
some of the prototype open rotors back in the 80's were direct drive off the turbines with no gearing.

Would that type of open rotor also be the most promising type? Or are gearboxes to be expected?

Personally, I expect a gearbox. The big advantage of the gearbox-less designs was...the lack of gearbox. But now that P&W has proven you can do a gearbox with acceptable weight, power density, and reliability, I don't really see why you wouldn't do it. Otherwise you're seriously underrunning the turbine (or overrunning the prop).

Quoting JoeCanuck (Reply 25):
The EU especially is going ape about the least bit of airline noise...

The EU is also going ape about carbon emissions and fuel consumption...they're going to have to give somewhere.

Quoting Semaex (Reply 28):
I hear talks about those OR designs using counter-rotating propellers for efficiency purposes - but aren't they by laws of physics a lot louder than 'one-spool' propellers?

Basically, yes, since the second fan is running in the wake of the first. There are lots of tips and tricks to try to minimize this but it doesn't work against you from a noise standpoint. On the up side, with counter-rotating fans you don't need as large a diameter for the same thrust so you can keep the tip speeds down, which helps with noise.

Tom .


User currently offlinelightsaber From United States of America, joined Jan 2005, 12903 posts, RR: 100
Reply 30, posted (2 years 1 month 4 weeks 1 day 22 hours ago) and read 18065 times:
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   But I want to be clear, the speed penalty is going to keep them in the 70 to 150 (maybe 180) seat range.

Everyone should remember an unshrouded fan has a lower optimal cruise mach number than a shrouded fan. Just to be clear, the openrotor is an unshrouded fan and a GTF is a shrouded fan. So the best engine will be mission dependent. The cruise mach number penalty is on the order of 0.1. In other words, cruise at Mach 0.7 vs. 0.8 of a turbofan/GTF.

Open rotors are for
Quoting Roseflyer (Reply 27):
With fuel prices where they are, propfans and open rotor will be talked about. There are still problems with them such as noise, but investment is still warranted.
Quoting ptrjong (Reply 1):
Why are propfans suddenly called 'open rotors'?

Company based terminology. NASA and Douglas liked the propfan name. Not many others did...
Whatever sells better. Heck, it might go to market as 'GreenFan' or 'GreenRotor.'  


Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently onlinebikerthai From United States of America, joined Apr 2010, 2070 posts, RR: 4
Reply 31, posted (2 years 1 month 4 weeks 1 day 22 hours ago) and read 17826 times:

Quoting Revelation (Reply 12):
To me, the biggest problem is safety, in particular the blade failure scenarios.

Which makes me want to ask . . .

Ever since GE introduced the composite fan blade in the GE90 for the 777, have there ever been an incident of blade failure for that engine? If yes, what was the result? Were there any major blade failure due to bird strike?

I was told by GE (way back when) that the failure of the composite blade is different from a metal blade and any failure would result in smaller pieces flying off instead of large chunks. Were they proven right after all these time?

If the failure mode for a composite blade is different than a metal blade, then maybe we can re-think open rotor failure scenarios.


bt



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlinerampart From United States of America, joined Aug 2005, 3109 posts, RR: 6
Reply 32, posted (2 years 1 month 4 weeks 1 day 22 hours ago) and read 17608 times:

Quoting tdscanuck (Reply 11):
This seems like a great application for the HondaJet over-wing style mounting.
Quoting JoeCanuck (Reply 25):
If fans get any bigger, we may see some more high winged jets, instead of fuse mounted engines.

What advantage or disadvantage is there with 8 ft of strut above a wing (a scaled up Hondajet) or 8 ft of strut out the side of the aft fuselage (I'm envisioning a wider MD80 strut, right?). Or if it does happen, is it likely to fit between twin vertical stabilizers as has been illustrated frequently (which some have said has a maintenance access issue, but something will have to fall back in priority)?

And a high wing/low slung engine configuration would not help with shielding noise or controling uncontained failures, correct?

-Rampart


User currently offliner2rho From Germany, joined Feb 2007, 2584 posts, RR: 1
Reply 33, posted (2 years 1 month 4 weeks 1 day 21 hours ago) and read 17245 times:

Airbus has long been interested in OR for the A30X, however a while ago they deemed the techonology immature today, while at the same time being impressed by the GTF demonstrator that they got to test one of their famous A340 testbeds, so they launched the NEO. But precisely because of that, they now need a return on investment on the NEO, so I don't expect OR before 2027, even if from a technological standpoint I consider it feasible earlier (assuming no NEO and full R&T resources dedication, which is not the case). I'm sure Airbus wants to give OR a second chance sometime though.

Quoting tdscanuck (Reply 29):
Quoting JoeCanuck (Reply 25):
The EU especially is going ape about the least bit of airline noise...

The EU is also going ape about carbon emissions and fuel consumption...they're going to have to give somewhere.

The EU does not know the word trade-off. For example, with existing tech, you could decrease CO2 emissions tomorrow morning by simply tweaking the combustion, but at the expense of emitting more NOx, which is also emissions-restricted. But you can also consider it a great technological challenge - to reduce noise, CO2 and NOx, all by considerable quantities and despite

Quoting rheinwaldner (Thread starter):
- A new laminar flow wing mounted on an A340 testbed could fly in 2014 and bring 10% fuel reduction.

As others have said, they will not be rewinging the A340 (or A330); being a testbed I would assume that one or several sections of the A340 wing would be substituted by laminar flow sections to evaluate the technology, which could also feed into the A30X.


User currently onlineBMI727 From United States of America, joined Feb 2009, 15719 posts, RR: 26
Reply 34, posted (2 years 1 month 4 weeks 1 day 21 hours ago) and read 16815 times:

Quoting rheinwaldner (Reply 8):
And the article is an open announcement that the open rotor could be ready for flight test in 4 years and ready for operation in 8 - 13 years.

You'd have a pretty hard time getting a new airframe with today's state of the art flying in 8 years, let alone with a change as big as open rotor engines. Plus with the pressure of continuing A350 development, I think we're talking at least 10 years, before you consider engine development.

Quoting rheinwaldner (Reply 8):
but because the pressure due to high fuel prices was gone.

There are also some nagging technical issues.

Quoting tdscanuck (Reply 11):
This seems like a great application for the HondaJet over-wing style mounting.

...until it sheds a blade anyway.

Quoting PlaneAdmirer (Reply 13):
How can this possibly make sense in light of the NEO?

For that matter, if you really thought that you could have this open rotor narrow body flying in 2020-2022, you probably wouldn't have launched the NEO at all.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3392 posts, RR: 4
Reply 35, posted (2 years 1 month 4 weeks 1 day 20 hours ago) and read 16360 times:

Quoting lightsaber (Reply 30):

Company based terminology. NASA and Douglas liked the propfan name. Not many others did...
Whatever sells better. Heck, it might go to market as 'GreenFan' or 'GreenRotor

I honestly think its only hope to get past regulators is to approch it from "advanced turboprop" direction instead of "green turbofan". Blade out and noise are going to be thier own circles of hell, and that much worse when compared to something that is nice and shrouded in comfy kevlar wraps. I just don't see it happening unless the bribe money flows like a river if they keep pushing it for the 737/A320 market. Smaller market, but so much easier if they pushed for a model slightly bigger than the Q400 for the small, then move up into the 73G size in the "future" stretch if the "market" demands with a baseline in the middle. The smallest model is there mostly to help keep everyone on the idea that this is the 21st centrury turboprop of the future with more speed, and less noise.


User currently offlinefcogafa From United Kingdom, joined May 2008, 772 posts, RR: 0
Reply 36, posted (2 years 1 month 4 weeks 1 day 20 hours ago) and read 16013 times:

Quoting XT6Wagon (Reply 35):
...until it sheds a blade anyway.

Why is the risk of that different to a Dash 8 or ATR today?


Another problem with this proposal is passenger resistance to props, as they are seen as less safe than jets.


User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3392 posts, RR: 4
Reply 37, posted (2 years 1 month 4 weeks 1 day 20 hours ago) and read 15744 times:

Quoting fcogafa (Reply 36):
Why is the risk of that different to a Dash 8 or ATR today?

Well thats why I think its a total mistake to only mention the 737/A320 or that market in everything you say about the planes for these open rotor engines. It *should* lead the regulators to compare the safety to the current turbofans on the current narrowbodies.


User currently offlinelightsaber From United States of America, joined Jan 2005, 12903 posts, RR: 100
Reply 38, posted (2 years 1 month 4 weeks 1 day 20 hours ago) and read 15687 times:
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Quoting BMI727 (Reply 34):
For that matter, if you really thought that you could have this open rotor narrow body flying in 2020-2022, you probably wouldn't have launched the NEO at all.

   They will in effect be different markets just as the Q400 compliments the CR7/9. The slower cruise speed of the open rotor won't matter on the 1 hour mission, but for any mission over 2.5 hours... We're talking adding significant time.

Quoting r2rho (Reply 33):
For example, with existing tech, you could decrease CO2 emissions tomorrow morning by simply tweaking the combustion, but at the expense of emitting more NOx, which is also emissions-restricted. But you can also consider it a great technological challenge - to reduce noise, CO2 and NOx, all by considerable quantities and despite

It is quite a challenge. A higher pressure ratio will cut CO2, but it will be with higher NOx. But it often isn't done as the maintenance costs will exceed the fuel savings. At least on shorter missions. There is a reason widebody engines are so different than narrowbody engines. They average fligth time is longer and thus the tolerated compromises are different.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 39, posted (2 years 1 month 4 weeks 1 day 19 hours ago) and read 15359 times:

Quoting bikerthai (Reply 31):
Ever since GE introduced the composite fan blade in the GE90 for the 777, have there ever been an incident of blade failure for that engine?

No failure due to any blade/engine issues. Blades have been replaced due to FOD damage (bird strikes and so on) but I don't believe one has ever actually failed (i.e. come off or come apart). GE likes to bring this up on a fairly regular basis.

Quoting bikerthai (Reply 31):
I was told by GE (way back when) that the failure of the composite blade is different from a metal blade and any failure would result in smaller pieces flying off instead of large chunks. Were they proven right after all these time?

Composites don't crack into chunks like metals, that's true. They tend to split (think a tree trunk breaking) or turn into loose assemblages of fibers and powdered resin.

Quoting rampart (Reply 32):
What advantage or disadvantage is there with 8 ft of strut above a wing (a scaled up Hondajet) or 8 ft of strut out the side of the aft fuselage (I'm envisioning a wider MD80 strut, right?).

Because if it's over the wing you don't need an 8' strut. You hang the fan off the back (or front) edge of the wing. The engine core is over the wing (or slightly forward or slightly aft). Then you just need to make sure the centerline is 8' from the ground...the core could be snuggled right up against the wing like the 737-100 or Sonic Cruiser.

The only way to do that with a fuselage mounted engine is to have it so far aft (or forward, hypothetically) that the fans clear the end of the fuselage and, even then, you need to keep them separate from each other. That's fairly clearly a non-starter.

Quoting rampart (Reply 32):
And a high wing/low slung engine configuration would not help with shielding noise or controling uncontained failures, correct?

True.

Quoting fcogafa (Reply 36):
Why is the risk of that different to a Dash 8 or ATR today?

More energy per rotor. The thrust ranges we're talking about here are only barely approached by even the largest turboprops in existance. You also have way more blades, making them more likely to interfere with each other during a failure.

Tom.


User currently offlineSemaex From Germany, joined Nov 2009, 823 posts, RR: 2
Reply 40, posted (2 years 1 month 4 weeks 1 day 19 hours ago) and read 15355 times:

Quoting Revelation (Reply 12):
To me, the biggest problem is safety, in particular the blade failure scenarios.

  Do open-rotors or propfans run faster than props mounted on a Dash-8 or an Avanti, or where does this fear come from? Besides, if the propellers are mounted quite aft, I don't see how this could be more dangerous to the airframe or passengers than the propellers mounted right next to my head in the 8th row of an ATR.



// You know you're an aviation enthusiast when you look at your neighbour's cars and think about fleet commonality.
User currently offlinetom355uk From United Kingdom, joined Nov 2007, 336 posts, RR: 3
Reply 41, posted (2 years 1 month 4 weeks 1 day 19 hours ago) and read 15304 times:

Quoting lightsaber (Reply 30):

Just like a Q400?? I can't believe that no one has seriously considered a 120 seat turboprop - or have they and we just haven't heard about it?

These UDF's being discussed, are they 'puller' or 'pusher' units? All I can imagine at the moment is a CF6 or similar without the nacelle! How far away is this from the reality?



on Twitter @tombeckett2285
User currently offlineKC135TopBoom From United States of America, joined Jan 2005, 12128 posts, RR: 51
Reply 42, posted (2 years 1 month 4 weeks 1 day 18 hours ago) and read 13868 times:

Quoting tdscanuck (Reply 22):
Quoting nasula (Reply 14):If this happens for the A330 and gives a 10% reduction +
They're not going to fit a laminar flow wing to the A330 in production. Laminar flow would be relofting the wing.

Actually, to get accurate inflight test readings, they will probably mount the 'wing' as a canard, or something on their test bed A-340. The 'wing' will of course be scaled down, but its shape will be accurate.

This has been done on B-707s, B-720s and B-747s by several companies, including Boeing.


User currently offlinelightsaber From United States of America, joined Jan 2005, 12903 posts, RR: 100
Reply 43, posted (2 years 1 month 4 weeks 1 day 18 hours ago) and read 13767 times:
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Quoting fcogafa (Reply 36):
Another problem with this proposal is passenger resistance to props

There is some. But the higher speed will prevail.

Quoting tom355uk (Reply 41):
Just like a Q400?? I can't believe that no one has seriously considered a 120 seat turboprop - or have they and we just haven't heard about it?

Ok, bad analogy as the open rotor is significantly faster than a turboprop.   

Quoting tom355uk (Reply 41):
All I can imagine at the moment is a CF6 or similar without the nacelle! How far away is this from the reality?

Take a CF34 with triple the fan diameter, and you have the idea. The CF6 derived open rotor would be for a HUGE platform.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineRevelation From United States of America, joined Feb 2005, 12350 posts, RR: 25
Reply 44, posted (2 years 1 month 4 weeks 1 day 16 hours ago) and read 12703 times:

Quoting Semaex (Reply 40):
Do open-rotors or propfans run faster than props mounted on a Dash-8 or an Avanti, or where does this fear come from?

Seems you and Tom were writing at the same time, see his #39 for the answer.

Quoting Semaex (Reply 40):
Besides, if the propellers are mounted quite aft, I don't see how this could be more dangerous to the airframe or passengers than the propellers mounted right next to my head in the 8th row of an ATR.

I can guarantee you I would not want to be in an ATR if it had a prop blade failure.

You take a system with that much weight spinning at that rate and destabilize it with a prop failure, and all hell can break loose.

Here's some input on the blade-out issue from two folks who know an awful lot about designing airplanes:

http://seattletimes.nwsource.com/htm...ge_on_radical_airplane_design.html has some concerns:

Quote:

The pod that encases an engine today, called a nacelle, must by regulation be capable of containing any parts that break off in operation, including fan blades.

With no nacelle covering the propellors, a nightmare scenario is a blade flying off into the fuselage or wing, something referred to as a "blade-out."

In a discussion last year, Boeing engineering legend Joe Sutter dismissed the open rotor as unrealistic because this problem is insurmountable. (See this blog entry from last year, at the bottom.)

"If I were chief engineer, what would scare the hell out of me is the first day I lose a blade and lose an airplane," Sutter said then.

Now, apparently Boeing has concluded that Sutter is right.

Bair in his Paris presentation ruled out the open rotor option as an alternative he had to think about.

"Those are 14 feet to 16 feet in diameter, very large blades that spin very fast," said Bair. "We cannot envisage an engineering solution for a blade-out."


It'd be interesting to see what kind of data there is today about turboprop blade-out causing hull loss.

Can you imagine if you spend $billions developing open rotor, and you do have a hull loss due to blade-out? One bad event could wipe out that investment, IMHO.



Inspiration, move me brightly!
User currently offlinerampart From United States of America, joined Aug 2005, 3109 posts, RR: 6
Reply 45, posted (2 years 1 month 4 weeks 1 day 16 hours ago) and read 12522 times:

Quoting Revelation (Reply 44):
Can you imagine if you spend $billions developing open rotor, and you do have a hull loss due to blade-out? One bad event could wipe out that investment, IMHO.

OK, how about a ducted prop? Why are ducted props limited so far to blimps, RC aircraft, and the occasional experimental homebuilt? Perhaps it would diminish the effeciency?? But if it's a minor diminishing, the safety allowance may be worth it.

-Rampart


User currently offlineDocLightning From United States of America, joined Nov 2005, 19415 posts, RR: 58
Reply 46, posted (2 years 1 month 4 weeks 1 day 16 hours ago) and read 12415 times:

Quoting Revelation (Reply 12):
To me, the biggest problem is safety, in particular the blade failure scenarios.

I'd wager that the propellers on a Brazilia are just as dangerous. If anything, these are less dangerous because they will be mounted aft of anything important.

What I don't get is the love affair with canards. I understand the aerodynamic benefits and the benefits in controllability, but how are you supposed to taxi into a gate with a jet ramp there? Most jet ramps angle up once they leave the aircraft. Most jet ramps will obstruct the canard from entering (or be at risk for hitting it when put into position). Why do designers keep putting them on concepts?


User currently offlinelightsaber From United States of America, joined Jan 2005, 12903 posts, RR: 100
Reply 47, posted (2 years 1 month 4 weeks 1 day 16 hours ago) and read 12387 times:
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Quoting rampart (Reply 45):
OK, how about a ducted prop?

That's a GTF. Seriously.

The advantage of an open rotor is:
1. Weight (no duct/shroud)
2. Larger fan (due to drag/weight optimization shifting to a greater diameter fan blade)

The disadvantages:
A. Blade tip losses (its why all turbofans have the nacelle surrounding the fan)
B. Lack of stators after the fan (straighten out the airflow for best propulsion efficiency)
C. Lack of a nozzle (A variable nozzle is even better as take-off, climb, and cruise are best at different expansion ratios due to the different mach # of the aircraft.)

Point #1 means the Open Rotor benefits aircraft less than 200 seats the most (above that, the disadvantages might outdo the weight advantage).

Point #2 means a nice bypass ratio. This means a more efficient take off and a far more efficient cruise.

Point A means that the speed of the blades must be backed off below what would be optimum for a shrouded fan (GTF). This is part of the reason for a lower cruise speed. Its also an efficiency hit that is overcome by the propulsion efficiency of the large diameter fan.

Point B is an efficiency loss. Because of B, the large fan (#2) must be taken advantage of or there is no reason doing an open rotor. Hence why we look at body mounted or above wing (a la Hondajet) placement of the engines. In other words, unless the fan diameter is large, don't bother with an open rotor.

Point C means both an efficiency loss (overcome by the large diameter), but also a lower optimum cruise speed (hard to separate from Point A).

As soon as the shroud (duct) is put on, one wants a nozzle to improve cruise efficiency and that is a GTF. For blimps or RC aircraft, their top Mach # is low enough that a nozzle isn't warranted (in a blimp) or affordable. (Note: I've seen RC aircraft with proper nozzles to optimize thrust. But I'm sure my old RC crowd was on the geeky side...) A blimp shrouds the propellers for noise control (brought by managing the blade tip losses...). RC aircraft are trying to simulate jet engines. Now that RC jet engines are far cheaper, the number of shrouded props flying seems to be declining, but that is just my impression.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlinedfwrevolution From United States of America, joined Jan 2010, 962 posts, RR: 51
Reply 48, posted (2 years 1 month 4 weeks 1 day 15 hours ago) and read 12060 times:

Quoting DocLightning (Reply 46):
Most jet ramps will obstruct the canard from entering (or be at risk for hitting it when put into position). Why do designers keep putting them on concepts?

Because airlines/airports consistently find work-arounds for ground facilities when there are substantial economic gains offered by an inconvenient design feature. Examples:

- 777 wingspan is a category higher than DC-10, airlines opted for larger gates rather than the folding wingtip
- 787 wingspan, airlines again were not dissuaded by being pushed into a larger category.
- 737NG winglets, AA initially declined to add winglets because of gate spacing, but retrofit them when the fuel savings cost was compelling


User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3392 posts, RR: 4
Reply 49, posted (2 years 1 month 4 weeks 1 day 15 hours ago) and read 11734 times:

Quoting Revelation (Reply 44):
Here's some input on the blade-out issue from two folks who know an awful lot about designing airplanes:

The only way I can see it is if they are mounted pusher with no critical systems inline with the fan. Bonus points if you put them 2-3 degrees off axis so that the fans don't intersect. Ruin your gains from open rotor, but might be better than having an armored vertical stabilizer between the two to prevent a blade out from removing the other rotor.


User currently offlineGAIsweetGAI From Norway, joined Jul 2006, 933 posts, RR: 7
Reply 50, posted (2 years 1 month 4 weeks 1 day 14 hours ago) and read 11526 times:

Quoting lightsaber (Reply 47):
B. Lack of stators after the fan (straighten out the airflow for best propulsion efficiency)

In the standard slightly-ahead-of-the-wing configuration, you do have a huge stator right behind the fan.  
(Although I'd tend to agree if you say that the efficiency doesn't increase dramatically.)

  



"There is an art, or rather a knack to flying. The knack lies in learning how to throw yourself at the ground and miss."
User currently offlinedavs5032 From United States of America, joined Sep 2010, 388 posts, RR: 0
Reply 51, posted (2 years 1 month 4 weeks 1 day 14 hours ago) and read 11000 times:

Quoting DocLightning (Reply 46):
What I don't get is the love affair with canards. I understand the aerodynamic benefits and the benefits in controllability, but how are you supposed to taxi into a gate with a jet ramp there? Most jet ramps angle up once they leave the aircraft. Most jet ramps will obstruct the canard from entering (or be at risk for hitting it when put into position). Why do designers keep putting them on concepts?

Couldn't a canard be designed to fold up @ the gate rather easily? (I know nothing about their design, but would think this could be done given their relatively small size.)


User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3392 posts, RR: 4
Reply 52, posted (2 years 1 month 4 weeks 1 day 13 hours ago) and read 10517 times:

Quoting davs5032 (Reply 51):
Couldn't a canard be designed to fold up @ the gate rather easily? (I know nothing about their design, but would think this could be done given their relatively small size.)

easier to cantilever the gate so the canard goes under the gate arm. Much cheaper to put the money and wieght into the gate than the planes

[Edited 2012-05-31 21:38:05]

User currently offlinetrent1000 From Japan, joined Jan 2007, 553 posts, RR: 2
Reply 53, posted (2 years 1 month 4 weeks 1 day 12 hours ago) and read 10035 times:

Wouldn't such mounted fans suffer more from bird strike than engines now?

Any fan blade separation would be uncontained, possible affecting the other engine.

How about effects from lightning strike to the mounted fans?

Would the fans be geared in any way?


User currently offlinegigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 54, posted (2 years 1 month 4 weeks 1 day 11 hours ago) and read 9767 times:

So can someone educate me on how often a turboprop actually throws an entire blade?

NS


User currently offlineDocLightning From United States of America, joined Nov 2005, 19415 posts, RR: 58
Reply 55, posted (2 years 1 month 4 weeks 1 day 11 hours ago) and read 9540 times:

Quoting dfwrevolution (Reply 48):
- 777 wingspan is a category higher than DC-10, airlines opted for larger gates rather than the folding wingtip
- 787 wingspan, airlines again were not dissuaded by being pushed into a larger category.
- 737NG winglets, AA initially declined to add winglets because of gate spacing, but retrofit them when the fuel savings cost was compelling

Gate spacing is relatively easy to fix with respect to coming up with an entire new design for a jetramp that can dip under the canard.


User currently offlinegigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 56, posted (2 years 1 month 4 weeks 1 day 11 hours ago) and read 9460 times:

Quoting trent1000 (Reply 53):
Would the fans be geared in any way?

This i can answer. Apparently, technically a propfan is defined as an direct drive engine.

However, there's no reason at all why the GTF's gearbox couldn't be appropriate for these speeds.

NS


User currently offlineRevelation From United States of America, joined Feb 2005, 12350 posts, RR: 25
Reply 57, posted (2 years 1 month 4 weeks 1 day 11 hours ago) and read 9419 times:

Quoting DocLightning (Reply 46):
I'd wager that the propellers on a Brazilia are just as dangerous. If anything, these are less dangerous because they will be mounted aft of anything important.

According to stuff already posted, you'll lose that wager. The open rotor blades are just a lot bigger and spin a lot faster, and no one has come up with an acceptable way to dissipate that amount of energy before the thing hits something important like the cabin, the tail feathers, or the other rotor.

Quoting XT6Wagon (Reply 49):
The only way I can see it is if they are mounted pusher with no critical systems inline with the fan. Bonus points if you put them 2-3 degrees off axis so that the fans don't intersect. Ruin your gains from open rotor, but might be better than having an armored vertical stabilizer between the two to prevent a blade out from removing the other rotor.

I imagine that when Bair and Sutter made the statements above, they had done the numbers to enough precision to convince themselves that such approaches were non-starters.

Quoting gigneil (Reply 54):
So can someone educate me on how often a turboprop actually throws an entire blade?

Me too.

I know I saw one episode of an air disaster type show where a commuter turboprop was lost because of a blade-off. It didn't throw the whole blade, it was because the blade snapped 1/3rd down its length because it was weakened due to corrosion starting from the inside of the blade growing out. The issue had to do with the procedure used to balance the blade unintentionally introducing a corrosive to the inside of the blade.

However I too would like to know how often blade-out has happened on a turboprop, and how often it has resulted in a hull loss.



Inspiration, move me brightly!
User currently onlineBMI727 From United States of America, joined Feb 2009, 15719 posts, RR: 26
Reply 58, posted (2 years 1 month 4 weeks 1 day 11 hours ago) and read 9337 times:

Quoting lightsaber (Reply 38):
They will in effect be different markets just as the Q400 compliments the CR7/9. The slower cruise speed of the open rotor won't matter on the 1 hour mission, but for any mission over 2.5 hours... We're talking adding significant time.

Who's going to design and build it? For that matter, if Airbus had really thought that open rotor would be ready in the early 2020s, they wouldn't have gone down the NEO route. They would have built the A30X as they showed it: with both turbofan and open rotor engine versions. As it stands I think that Airbus would have problems bringing any completely new design to market in that timeframe, let alone one with likely a completely new configuration. Conventional wisdom for getting programs run correctly dictates one miracle per plane so one has to wonder how many questions are left with scaling down composite intensive airlines.

And for that matter, is Boeing not talking to engine manufacturers too? What has changed in the past year that has pushed up open rotor to the pre-2025 timeframe? Boeing might have been completely caught out if this is true, considering that they could have designed an all new narrowbody based as a hybrid of Fozzie and the Kermit Kruiser with a GTF/LEAP-X powered version entering service in 2018 or so and the open rotor version in the early 2020s.

Frankly, I tend to doubt all of it. Airbus says they can have an open rotor plane in service by 2025, but the actions of them and everybody else seems to say the opposite. Airbus launched the NEO, Boeing launched the MAX, and Rolls-Royce signed on with the GTF. None of that screams "open rotor by 2025."



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineDocLightning From United States of America, joined Nov 2005, 19415 posts, RR: 58
Reply 59, posted (2 years 1 month 4 weeks 1 day 11 hours ago) and read 9296 times:

Quoting Revelation (Reply 57):
According to stuff already posted, you'll lose that wager. The open rotor blades are just a lot bigger and spin a lot faster, and no one has come up with an acceptable way to dissipate that amount of energy before the thing hits something important like the cabin, the tail feathers, or the other rotor.

If the rotors are mounted way aft on the fueslage, then it can be arranged that no such structures are located aft of the rotor. Unless the aircraft is stopped, any blade flung free will probably pass behind the other rotor.

Nobody here has explained why a turboprop blade is "less dangerous." It may not be spinning as fast as an OR, but if one comes loose, it will slice clean through anything it touches short of a thick, solid concrete wall.


User currently offlinelightsaber From United States of America, joined Jan 2005, 12903 posts, RR: 100
Reply 60, posted (2 years 1 month 4 weeks 1 day 10 hours ago) and read 9142 times:
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Quoting BMI727 (Reply 58):
As it stands I think that Airbus would have problems bringing any completely new design to market in that timeframe, let alone one with likely a completely new configuration.

It would be tough, but possible. However, Airbus would have to drop one of their current projects. Obvioulsy the NEO and the A350 variations will go through. That would mean cancelling the A389. Note: I know of no work being done on the A389, but if Airbus launched another project soon (they would have to start soon to meet the timeframe), they wouldn't have the resources to launch the A389.  
Quoting BMI727 (Reply 58):
And for that matter, is Boeing not talking to engine manufacturers too? What has changed in the past year that has pushed up open rotor to the pre-2025 timeframe?

Nothing that I know of. However, Airbus is more interested in the concept than Boeing. Boeing has some serious concerns with the noise and vibration. I believe the open rotor is about 12 years from service (at best). However, since I'm not a fan of the concept, I'm willing to accept its going to go ahead and I've just chosen to ignore my timeframe estimates.   

Quoting DocLightning (Reply 59):
Nobody here has explained why a turboprop blade is "less dangerous."

No one could. The only difference is weight. Each "OpenRotor" blade will weight 2X to 6X as much as today's turboprop blades. Current turbofan blades may be made lighter as instead of extra strength at the blade root, the shroud has layers of Kevlar that allow more aerodynamic fan blades; the fanblades are lighter as the 'safety factor' is the proven 'blade out' performance of the shrouded engine.


Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineBurkhard From Germany, joined Nov 2006, 4387 posts, RR: 2
Reply 61, posted (2 years 1 month 4 weeks 1 day 9 hours ago) and read 8410 times:

Quoting r2rho (Reply 33):
so I don't expect OR before 2027, even if from a technological standpoint I consider it feasible earlier

If Airbus now considers an EIS in 2025, we know that even 2027 is optimistic once reality steps in.

Quoting tdscanuck (Reply 39):
No failure due to any blade/engine issues. Blades have been replaced due to FOD damage (bird strikes and so on) but I don't believe one has ever actually failed (i.e. come off or come apart). GE likes to bring this up on a fairly regular basis.

What about the Air Canada 77W a few days ago?


User currently offlinejporterfi From United States of America, joined Feb 2012, 438 posts, RR: 0
Reply 62, posted (2 years 1 month 4 weeks 1 day 8 hours ago) and read 8118 times:

This seems like a really interesting concept. However, it seems to be very expensive to develop, and the cost of it may offset fuel savings. I hope that is Boeing chooses to pursue this, they well test the new engine on the 747 testbed. That would be a sight to see: a 747 with 3 turbofans and 1 propfan! I hope this moves relatively quickly and that Boeing, Airbus, Embraer, and Bombardier all become interested in developing these aircraft.

User currently offlinesturmovik From India, joined May 2007, 509 posts, RR: 0
Reply 63, posted (2 years 1 month 4 weeks 1 day 8 hours ago) and read 8100 times:

Quoting davs5032 (Reply 51):
Couldn't a canard be designed to fold up @ the gate rather easily? (I know nothing about their design, but would think this could be done given their relatively small size.)

View Large View Medium
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Photo © Boyan Georgiev
View Large View Medium
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Photo © Alberto Storti



Something like the Tu-144, perhaps? The purpose there was different (canards folded up in flight, as opposed to on the ramp), though, and I don't believe the 144 used gates. Canards certainly can fold up, but I don't know what the weight penalty will be like (or any other risks, for that matter).



'What's it doing now?'
User currently offlineDocLightning From United States of America, joined Nov 2005, 19415 posts, RR: 58
Reply 64, posted (2 years 1 month 4 weeks 1 day 8 hours ago) and read 8048 times:

Quoting lightsaber (Reply 60):
No one could. The only difference is weight. Each "OpenRotor" blade will weight 2X to 6X as much as today's turboprop blades.

So I don't understand why Mr. Sutter seems to be unable to come up with safety solutions that Embraer and Saab came up with decades ago. This is like arguing that standing on the surface of the Sun is safer than standing on the surface of Betelgeuse because Betelgeuse is hotter.


User currently onlineN14AZ From Germany, joined Feb 2007, 2695 posts, RR: 25
Reply 65, posted (2 years 1 month 4 weeks 1 day 8 hours ago) and read 8017 times:

Stupid question of mine: could it be that Airbus is just talking about this plans right now because of tactical reasons?

User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3392 posts, RR: 4
Reply 66, posted (2 years 1 month 4 weeks 1 day 7 hours ago) and read 7931 times:

Quoting DocLightning (Reply 64):
So I don't understand why Mr. Sutter seems to be unable to come up with safety solutions that Embraer and Saab came up with decades ago.

Risks acceptable yesterday are not acceptable today. For example the doors on a 737 couldn't be certified on a new design plane.

Turboprops are grandfathered in as far as risk goes. They are higher risk than a turbofan for many reasons, most unrelated to the prop, yet its an area for extra risk.

If the airframe maker markets a new open rotor aircraft as a replacement for a current turbofan plane then the regulators SHOULD be looking at the risks the passengers will be facing from the transition from 737/A320. As we saw with the A380, you do NOT want to be playing the lotto with high velocity bits of metal. Even with good design, you really don't want to come up with the jackpot. The open rotor adds a whole new level of danger not present in current aircraft.


User currently onlineflipdewaf From United Kingdom, joined Jul 2006, 1562 posts, RR: 1
Reply 67, posted (2 years 1 month 4 weeks 1 day 6 hours ago) and read 7718 times:
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I don't kow if I'm just being stupid here but I know what a turbojet is and i know what a turbofan is and I know what a turboprop is but the open rotor is just a big turboprop is it not?

Fred


User currently offlineDocLightning From United States of America, joined Nov 2005, 19415 posts, RR: 58
Reply 68, posted (2 years 1 month 4 weeks 1 day 6 hours ago) and read 7698 times:

Quoting XT6Wagon (Reply 66):
Turboprops are grandfathered in as far as risk goes. They are higher risk than a turbofan for many reasons, most unrelated to the prop, yet its an area for extra risk.

So how did the Q400 get certified?


User currently offlinetom355uk From United Kingdom, joined Nov 2007, 336 posts, RR: 3
Reply 69, posted (2 years 1 month 4 weeks 1 day 6 hours ago) and read 7643 times:

Quoting flipdewaf (Reply 67):
but the open rotor is just a big turboprop is it not?

This is the way I see it (as explained above in response to my earlier question).

More accurately, I'm seeing a small turbofan core (CF34 was mentioned above) with something like a GE90 Fan on the front (or back, depending on config)?

Or am I still way off? When does a 'Prop' become a 'Fan'? 10 blades? 50 blades? 100 blades?



on Twitter @tombeckett2285
User currently offlineEPA001 From Netherlands, joined Sep 2006, 4705 posts, RR: 38
Reply 70, posted (2 years 1 month 4 weeks 1 day 4 hours ago) and read 7467 times:
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Quoting CM (Reply 24):
Quoting EPA001 (Reply 23):
Would that type of open rotor also be the most promising type? Or are gearboxes to be expected?

Assuming the noise from a open-rotor engine can be solved at all, gearing the fan seems almost certain. The direct drive UDF engines tested 20 years ago by GE/Boeing were exceedingly loud.

Thanks for your reply and the links you have placed in your post.  
Quoting tdscanuck (Reply 29):
Quoting EPA001 (Reply 23):
Quoting tdscanuck (Reply 22):
some of the prototype open rotors back in the 80's were direct drive off the turbines with no gearing.

Would that type of open rotor also be the most promising type? Or are gearboxes to be expected?

Personally, I expect a gearbox. The big advantage of the gearbox-less designs was...the lack of gearbox. But now that P&W has proven you can do a gearbox with acceptable weight, power density, and reliability, I don't really see why you wouldn't do it. Otherwise you're seriously underrunning the turbine (or overrunning the prop).

Thank you as well Tom. Not only for this reply, but for so many good posts you have written here.   It is highly appreciated.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 71, posted (2 years 1 month 4 weeks 1 day 4 hours ago) and read 7434 times:

Quoting trent1000 (Reply 53):

Wouldn't such mounted fans suffer more from bird strike than engines now?

In the sense that they're bigger, so have more area to hit, yes. But the blades will necessarily be stronger (since they don't have containment) so when they do get hit the effects may not be as bad.

Quoting trent1000 (Reply 53):
How about effects from lightning strike to the mounted fans?

I doubt the fan is an attractive target for lightning attachment. It's moving too fast and not particularly pointy (or conductive, if CFRP) in the way that lightning likes.

Quoting trent1000 (Reply 53):
Would the fans be geared in any way?

Maybe, maybe not. Geared and ungeared have both been demonstrated. I lean toward geared but there's no technical requirement for that.

Quoting gigneil (Reply 54):
So can someone educate me on how often a turboprop actually throws an entire blade?

Rarely. Less rarely than a jet engine throws a non-fan blade.

Quoting Revelation (Reply 57):
I imagine that when Bair and Sutter made the statements above, they had done the numbers to enough precision to convince themselves that such approaches were non-starters.

This is almost certainly true. However, you have to be careful about those kinds of predictions because they're sometimes predicated on a bad assumption about technology. The "guru" of British aviation engine design in the early 20th centure proved, conclusively, that the jet engine was impossible. He was the equivalent of a Bair or Sutter in our time. Most of the industry believed him, which was largely responsible for Whittle's difficulty getting his jet engine designed, built, and accepted.

Turned out he'd made a hugely inaccurate prediction about compressor performance by failing to take into account new technology and designs. He was right...if his assumptions were correct. But they weren't.

Quoting DocLightning (Reply 59):
If the rotors are mounted way aft on the fueslage, then it can be arranged that no such structures are located aft of the rotor. Unless the aircraft is stopped, any blade flung free will probably pass behind the other rotor.

It should actually go ahead of the other rotor. The blades have a tremendous forward force on them (they're generating thrust). Liberated from the hub the blade will want to go forward (thrust) until it aerodynamically twists back to zero AoA.

Quoting DocLightning (Reply 59):
Nobody here has explained why a turboprop blade is "less dangerous." It may not be spinning as fast as an OR, but if one comes loose, it will slice clean through anything it touches short of a thick, solid concrete wall.

The consequences of a blade out, should it occur, are just as bad in either case. The likely hood of a blade-out, however, is different. The open rotor blades are under a lot more load, moving faster, and there are more of them.

Quoting Burkhard (Reply 61):
Quoting tdscanuck (Reply 39):
No failure due to any blade/engine issues. Blades have been replaced due to FOD damage (bird strikes and so on) but I don't believe one has ever actually failed (i.e. come off or come apart). GE likes to bring this up on a fairly regular basis.

What about the Air Canada 77W a few days ago?

The original question was about fan blades; the AC 777 didn't throw a fan blade. Failure of internal engine blades is, compared to fan blade or turboprop failures, must more common. But the engine typically has very little problem containing internal blades (their energy is far lower, per blade, than the fan).

Quoting DocLightning (Reply 64):
So I don't understand why Mr. Sutter seems to be unable to come up with safety solutions that Embraer and Saab came up with decades ago.

Well, if Lightsaber's measure of 2x-6x heavier is correct, coupled with the higher speed of an open rotor, then we're talking about 10x the kinetic energy of the blade. That, right there, could overcome existing turboprop armoring.

Quoting flipdewaf (Reply 67):
the open rotor is just a big turboprop is it not?

Basically, yes.

Quoting tom355uk (Reply 69):
When does a 'Prop' become a 'Fan'? 10 blades? 50 blades? 100 blades?

It's fuzzy. There is no solid definition.

Tom.


User currently offlineflyglobal From Germany, joined Mar 2008, 573 posts, RR: 3
Reply 72, posted (2 years 1 month 4 weeks 1 day 3 hours ago) and read 7336 times:

Quoting N14AZ (Reply 65):
Stupid question of mine: could it be that Airbus is just talking about this plans right now because of tactical reasons?



As far as I know, there is some 'green Planet' research money from EU looking into new fuel efficient engine programs.
Talking about a 2025 plan for introduction may release such money to European engine makers and probably as well some to Airbus studying plane integration of open rotors.

I think they have to start using available funds now - and they do that with SOP 2025 in mind, then probably they need more funds for continued studies when first research resut are available.

I believe this is the main reason for talking 2025.

Eventually getting Boeing slightly nervous with a game changer theme could be a nice welcomed side effect for Airbus, before Boeing adds more and more changes to the 737-MAX and it sets a contrapoint to Boeing moving out a potential Max successor.

My 2 Euro & US$ Cents

regards

Flyglobal


User currently onlinebikerthai From United States of America, joined Apr 2010, 2070 posts, RR: 4
Reply 73, posted (2 years 1 month 4 weeks 1 day 3 hours ago) and read 7329 times:

Quoting Revelation (Reply 57):
The open rotor blades are just a lot bigger and spin a lot faster

But the construction/cross section of an open rotor would be much different than a prop or a fan for that matter.

Where as a prop is have a narrow cord with respect to the aspect ratio, the open rotor blades would have a much wider cord and would be more beefy at the root. You would less likely get a complete blade failure, most likely a partial blade failure.

Were as the fear is that you would loose the entire blade (and all that mass). You would more likely lose only a portion of the blade. And as Tom has pointed out, you would more likely get delamination and splitting of a blade if a composite rotor is use than if would get a complete blade break off. With the delamination the blade will more likely stay attached until you can shut down the engine.

In the bird strike test on the GE90 composite blade. The blade did not failed in a regular way. Where as the metal blade would deform and or break, the energy from the bird cause a shock to go down the composite blade and snapped off a small portion of the tip of the blade. You don't get a complete blade failure.

bt



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlineSEPilot From United States of America, joined Dec 2006, 6834 posts, RR: 46
Reply 74, posted (2 years 1 month 4 weeks 1 day 3 hours ago) and read 7329 times:

Quoting DocLightning (Reply 46):
I'd wager that the propellers on a Brazilia are just as dangerous. If anything, these are less dangerous because they will be mounted aft of anything important.
Quoting Revelation (Reply 57):
According to stuff already posted, you'll lose that wager. The open rotor blades are just a lot bigger and spin a lot faster, and no one has come up with an acceptable way to dissipate that amount of energy before the thing hits something important like the cabin, the tail feathers, or the other rotor.

The danger of a blade loss is not just the danger of a loose blade damaging something else, it is the guarantee that with the departure of a blade the engine will depart the airframe due to the remaining unbalanced rotor still spinning at very high speed. If the structure is strong enough to withstand that amount of unbalance it will be so heavy as to outweigh all advantages. This is why Joe Sutter says that he sees no solution to the problem. Having flown prop planes for 25 years, one fact that I have always recognized is that if the prop breaks the plane is coming apart. Hence I have always taken extremely good care of my prop. As to the difference in the OR and a turboprop, the big difference is speed and number of blades, as tdscanuck explained above. There is also the perception that large airliners simply do not crash. This means that a known weakness that is guaranteed to bring the plane down is simply unacceptable in this day and age. Smaller turboprops have been around for a long time, and therefore the risks they pose are accepted, but a new large airliner with greater risk I do not think will be accepted.

I actually see three problems that I believe will doom the OR. The safety issue is the first, the noise issue is the second, and the speed issue is the third. The one thing that the OR can offer, substantially better fuel economy, must compete against those issues. The one factor that could bring it to predominance, substantially higher fuel prices, could also bring the whole world economy to a screeching halt, stopping all new plane development. Also, it is a political, not a supply problem. The GAO has officially pronounced that the US has more petroleum reserves than any other country in the world, and if we muster the political will to exploit them the prices will plunge. This will also render the OR uncompetitive. Remember that conventional fanjets are becoming quieter and more efficient all the time, and so the OR is aiming at a moving target. I just do not see the particular alignment of factors that would make the OR viable for large airliners as very likely, and justifying the tens of billions of dollars necessary for its development. I see the expansion of the geared fan as being a much more likely scenario.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlinerheinwaldner From Switzerland, joined Jan 2008, 2213 posts, RR: 5
Reply 75, posted (2 years 1 month 4 weeks 1 day 3 hours ago) and read 7262 times:

Quoting Roseflyer (Reply 27):
With fuel prices where they are, propfans and open rotor will be talked about.

The 7J7 was drafted to undercut A320 fuel burn per seat by 50%.

I can tell you, for these kind of incentives airlines would sacrifice anything else...

Is that realistic? Hardly, as Boeing seems to have been in the business of fabricating PR stunts at that time as today...

But the 50% gains don't have to be accurate at all. It suffices to note, that a fantastic gain potential does exist. Airbus has stated 30% for the A30X.


Quoting tdscanuck (Reply 11):
The A350 and 787 didn't face nearly open rotor level configuration/engine issues and they still took more than 8 years to get to operation from conception...I don't see this one going faster, even if they commit today.

I agree, but we also have to consider that "configuration/engine issues" were not responsible for the long development time. They also represent a comparably small workblock for conventionally configured aircraft. In case of the 787 and A350 the most research clearly was spent for structure&materials. Would the A30X use conventional structures but a revolutionary propulsion, the overall research and development time would not necessarily be longer (assuming CFRP structures to be conventional at that time).

Quoting BMI727 (Reply 34):
For that matter, if you really thought that you could have this open rotor narrow body flying in 2020-2022, you probably wouldn't have launched the NEO at all.

I agree.

About the motivitaion behind this Airbus PR attack, there might be another story (especially behind that 2020/2025 EIS claim).

In an attempt to make look the launch of the MAX dumb and outdated, the stated EIS could indeed be a pure fictional figure. With the MAX EIS in 2017 any talk about a potential A30X in 2020 (!) would make investments into the MAX look quite questionable (the strengths of the MAX and an OR at different ranges factored out).

Airbus is in a position to publish dreams about a rather quick A320 replacement without losing the face. They were first with the re-engined upgrade and can now loudly talk about the next natural step. Boeing on the other hand are hastily trying to make up the lost terrain with the old model (while still losing the production volume of 1-2 years anyway). Before the MAX will be defined fully and the last doubt about it will be dispelled (e.g. in response to SUH), any lack of perceived focus might stir up some unwanted debate.

So this Airbus talk about an Open Rotor A320 replacement (with unrealistic EIS) maybe just should create the impression, that the MAX would be an unmotivated effort between two real pioneers. First follow the forerunner regarding re-engining and second precede the real break-through in Open Rotor technology by just some years.

Ok, I expect that these points might be discussed controversely. Rightfully, I would say.

But I have noted, that most posters support the idea, that the MAX and the NEO will be the unchallenged block busters for 10-20 years to come (coupled with the idea that over that time there will be plenty of harvest to be brought in by both of them). I just sense that once this idea starts to be challenged, Airbus' position would appear a lot better than Boeing's (keeping up the pace by opening a second front in the neck of the MAX in addition to the pressure of keeping contact with the runaway NEO due to the earlier EIS). So Airbus could simply just torpedo the idea of a reestablished duopoly for many years to come. And for sure they have torpedoed the idea, that because of the NEO they would fall into a sort of satisfied/relaxed-mode.

Quoting tdscanuck (Reply 39):
Quoting fcogafa (Reply 36):
Why is the risk of that different to a Dash 8 or ATR today?

More energy per rotor.

But less per blade. Due to higher blade count.

Quoting Revelation (Reply 44):
I can guarantee you I would not want to be in an ATR if it had a prop blade failure.

But the ATR is certified and flying in considerable numbers.

Quoting gigneil (Reply 54):
So can someone educate me on how often a turboprop actually throws an entire blade?

There have been severall cases in the nineties with Embraer 120's:
http://www.nytimes.com/1995/08/26/us...crutiny.html?pagewanted=all&src=pm

Quoting Revelation (Reply 57):
The open rotor blades are just a lot bigger and spin a lot faster, and no one has come up with an acceptable way to dissipate that amount of energy before the thing hits something important like the cabin, the tail feathers, or the other rotor.

The factor that they are bigger and spin faster is not so relevant IMO, because the blades of the turboprops are big enough and spin fast enough that they would be identically dangerous in case of a failure (= fatally anyway). And this factor has not stopped turboprops from being certified and operated.

E.g. the following case would not have looked worse with an Open Rotor:
http://en.wikipedia.org/wiki/1956_Trans-Canada_Air_Lines_accident

As said above, per blade the Open Rotor could be stressed even less, than today propellers.

In the end we have to state, that similar hazards are managed, certified and operated in the form of turboprops. Dealing even with somewhat more stressed blades should not pose an unsurmountable limit vs the turboprops.

Quoting BMI727 (Reply 58):
And for that matter, is Boeing not talking to engine manufacturers too? What has changed in the past year that has pushed up open rotor to the pre-2025 timeframe? Boeing might have been completely caught out if this is true, considering that they could have designed an all new narrowbody based as a hybrid of Fozzie and the Kermit Kruiser with a GTF/LEAP-X powered version entering service in 2018 or so and the open rotor version in the early 2020s.

There have been reports that Boeing indeed has ruled out Open Rotors for their NSA. This would IMO have been quite a gambling, because that Open Rotors would not come to fruition during the 20-30 year career of an NSA, would have been far from a safe assumption IMO.

Let me mention this NASA report from 2005:
http://ntrs.nasa.gov/archive/nasa/ca...asa.gov/20110015875_2011016834.pdf

Broken blades are no topic at all. But noise is and fuel burn gains too.

The report does not raise the sort of concerns that would warrant ruling out Open Rotors for all times, IMO.


User currently offlineRevelation From United States of America, joined Feb 2005, 12350 posts, RR: 25
Reply 76, posted (2 years 1 month 4 weeks 23 hours ago) and read 6907 times:

Very interesting and informative thread!

Quoting DocLightning (Reply 64):
This is like arguing that standing on the surface of the Sun is safer than standing on the surface of Betelgeuse because Betelgeuse is hotter.

Wow, Doc, your ability to go into total geek mode is impressive!  
Quoting DocLightning (Reply 68):
So how did the Q400 get certified?

Because on paper it is a DHC-8-400, just like the MD-8X/9X models are DC9-8X/9X on paper. DHC-8 dates back to the early 80s, and it in turn is a derivative of the DHC-7, and so on.

Quoting tdscanuck (Reply 71):
This is almost certainly true. However, you have to be careful about those kinds of predictions because they're sometimes predicated on a bad assumption about technology.

I wonder if we'll ever find out if Sutter and/or Bair were leaning on a faulty assumption.

Quoting tdscanuck (Reply 71):
The consequences of a blade out, should it occur, are just as bad in either case. The likely hood of a blade-out, however, is different. The open rotor blades are under a lot more load, moving faster, and there are more of them.

Any hints on the difference in max RPMs and tip speeds for proposed ORs vs modern turboprops?

Quoting tdscanuck (Reply 71):
It should actually go ahead of the other rotor. The blades have a tremendous forward force on them (they're generating thrust). Liberated from the hub the blade will want to go forward (thrust) until it aerodynamically twists back to zero AoA.

Thanks, I had a hard time visualizing the right answer.

Quoting bikerthai (Reply 73):
Were as the fear is that you would loose the entire blade (and all that mass). You would more likely lose only a portion of the blade. And as Tom has pointed out, you would more likely get delamination and splitting of a blade if a composite rotor is use than if would get a complete blade break off. With the delamination the blade will more likely stay attached until you can shut down the engine.

I was finally able to google up the accident I was thinking of last night:

http://en.wikipedia.org/wiki/Atlantic_Southeast_Airlines_Flight_529

The most relevant section is:

Quote:

Flight 529 left the ramp area at Atlanta at 12:10, and took off at 12:23. At 12:43:25 and climbing through 18,100 feet, the occupants of the aircraft heard a thud which Matt Warmerdam, the co-pilot, described as sounding like a baseball bat striking an aluminum trash can.[4] One of the blades of the Hamilton Standard[6] propeller on the left engine had failed and the entire assembly had become dislodged, deforming the engine nacelle and distorting the wing's profile.[7]

Although the EMB 120, like all transport category, multi-engine airplanes is designed to fly with one engine inoperative, the distortion of the engine resulted in excessive drag and loss of lift on the left side of the aircraft, causing it to rapidly lose altitude

When I was watching the TV show (Mayday aka Crash Investigation aka Emergency episode "Wounded Bird") I didn't quite grasp how a blade-out was that different than an engine-out scenario. The quote above explains that the failure caused the entire prop assembly to become "disloged", presumably meaning you could not feather the surviving blades, and thus there was a lot more drag than the engine-out scenario which presumes you can feather the blades. Add to that the distortion of the wing profile and distortion of the nacelle and you end up with an uncontrollable aircraft and in this case, a hull loss and sadly, several fatalities as well.

Personally, I don't see how an OR can deal with this issue. You'd have to convince yourself that you could model the blade out scenarios well enough to convince yourself that the cases that result in an uncontrollable airplane happen less often than all the other ways you end up with an uncontrollable airplane, and as pointed out, then you'd have to convince the regulators that you did this right. Then you'd have to convince yourself that the upside of fuel savings is worth the downside of a calamity should you not get it 100% right. I suppose aerospace engineers make these decisions all the time, but as pointed out already as well, the default stance is to be conservative.

Quoting SEPilot (Reply 74):

The danger of a blade loss is not just the danger of a loose blade damaging something else, it is the guarantee that with the departure of a blade the engine will depart the airframe due to the remaining unbalanced rotor still spinning at very high speed. If the structure is strong enough to withstand that amount of unbalance it will be so heavy as to outweigh all advantages

Ahh. In the above case, the engine did not depart, but the resulting configuration just has more drag and less lift than the certified engine out case does.

Quoting SEPilot (Reply 74):
Having flown prop planes for 25 years, one fact that I have always recognized is that if the prop breaks the plane is coming apart.

Very interesting.

Quoting SEPilot (Reply 74):
There is also the perception that large airliners simply do not crash. This means that a known weakness that is guaranteed to bring the plane down is simply unacceptable in this day and age.

It's also true for commuter/regional airliners from what I see. There was a lot of furor over the Colgan crash a few years ago, and saying "well, it's just a regional airliner" is just not acceptable.



Inspiration, move me brightly!
User currently offlineSEPilot From United States of America, joined Dec 2006, 6834 posts, RR: 46
Reply 77, posted (2 years 1 month 4 weeks 23 hours ago) and read 6885 times:

Quoting Revelation (Reply 76):

Ahh. In the above case, the engine did not depart, but the resulting configuration just has more drag and less lift than the certified engine out case does.

But that was a turboprop, not an OR. I suspect that with an OR it would depart because of the much higher rotational speed, and hence the much higher forces on the engine mounts. I think that in the above quoted case the engine was not very far from departing; 10 or 20% more RPM would probably have done it. And while a plane with engines on the wing can survive an engine falling off, a plane with tail mounted engines will have a much harder time-the CG change may well be too much.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently onlinebikerthai From United States of America, joined Apr 2010, 2070 posts, RR: 4
Reply 78, posted (2 years 1 month 4 weeks 22 hours ago) and read 6718 times:

Quoting SEPilot (Reply 77):

But that was a turboprop, not an OR. I suspect that with an OR it would depart because of the much higher rotational speed, and hence the much higher forces on the engine mounts

Yes but don't you have to figure the total amount of rotational inertial when predicting whether or not a nacelle will deform or depart.

With a 4 prop rotor, you loose 1/4 of the inertia thus causing a great disparity in balance.

If you have more blades in an OR, and you lose one blade, the the proportion of inertia changes would be less.
Thus the imbalance would be less. (Even less so if you just lose a portion of the blade)

bt



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlineSEPilot From United States of America, joined Dec 2006, 6834 posts, RR: 46
Reply 79, posted (2 years 1 month 4 weeks 21 hours ago) and read 6631 times:

Quoting bikerthai (Reply 78):

If you have more blades in an OR, and you lose one blade, the the proportion of inertia changes would be less.
Thus the imbalance would be less. (Even less so if you just lose a portion of the blade)

But the much higher speed makes the forces that much higher-that is the problem. I believe that the force goes up by the square of the speed. That is why the higher the speed of any rotating object the more critical balance becomes.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlineRevelation From United States of America, joined Feb 2005, 12350 posts, RR: 25
Reply 80, posted (2 years 1 month 4 weeks 20 hours ago) and read 6520 times:

Time to be the devil's advocate...

Quoting bikerthai (Reply 78):
If you have more blades in an OR, and you lose one blade, the the proportion of inertia changes would be less.
Thus the imbalance would be less.

Indeed but above we estimate the inertia magnitude to be 10x the turboprop, and the lateral forces exerted on the engine mount will scale with that, it seems to me, admittedly a rank amateur. If so, comparing one blade out of four with X inertia would equate to comparing one blade out of 40 with 10X inertia, no?

Quoting bikerthai (Reply 78):
(Even less so if you just lose a portion of the blade)

More if that blade or its sheddings takes out its neighbor(s)...

Seems pretty nasty if you have two rows of counter-rotating blades and your composite blade in the front row delaminates and flaps around and gets clocked by the second row.

Some great articles on the efforts in the 80s to deliver ORs:

http://www.airspacemag.com/history-of-flight/prop-fan.html

Very detailed, points out that indeed the fear of blade out was a big concern right from the start.

Who else knew Alan Mullaly was cheif engineer of the 7J7 program?

http://www.flightglobal.com/news/art...tever-happened-to-propfans-214520/

A few more tidbits.



Inspiration, move me brightly!
User currently offlinePW100 From Netherlands, joined Jan 2002, 2372 posts, RR: 11
Reply 81, posted (2 years 1 month 4 weeks 20 hours ago) and read 6408 times:

Quoting gigneil (Reply 54):
So can someone educate me on how often a turboprop actually throws an entire blade
Quoting tdscanuck (Reply 71):
Rarely. Less rarely than a jet engine throws a non-fan blade

Correct.

Although not a direct conclusive answer This is a very good summary:

Quoting SEPilot (Reply 74):
Having flown prop planes for 25 years, one fact that I have always recognized is that if the prop breaks the plane is coming apart

Correct. From a certification point of view, in-flight propeller blade off is equal to loss of vehicle (and all aboard). Therefore there is no blade-off test for turboprops. The OEM must demonstrate that this will not happen, and the onus is on the OEM to provide for sufficient proof of such.

The certification standards / requirements, be it the FAA, TC, EASA etc. all have similar wording for such.
Quoting FAR 33.75 g.2:

The following effects will be regarded as hazardous engine effects:
. . .
(i)Non-containment of high-energy debris;
(vi) Release of the propeller by the engine;
. . .

A hazardous engine effect prevents continued safe operation of the aircraf; iIn other words, the aicraft is no longer able to contine controlled flight.

I suspect that certification requirements / standard would not be any different for an Open Rotor.


One of the theories to help overcome the above problem to Open Rotors / UDF is by applying life limits to (metal) critical parts of the rotor system. Another one is provided by modern CFRP materials with significantly improved cracking and impact damage behaviour. Thirdly, engine placing is going to be critically important, which therefore would probably be a starting point for the initial aircraft configuration design.

PW100



Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
User currently offlineDocLightning From United States of America, joined Nov 2005, 19415 posts, RR: 58
Reply 82, posted (2 years 1 month 4 weeks 18 hours ago) and read 6215 times:

Quoting Revelation (Reply 76):

Wow, Doc, your ability to go into total geek mode is impressive!

I try.  
Quoting Revelation (Reply 76):
Because on paper it is a DHC-8-400, just like the MD-8X/9X models are DC9-8X/9X on paper. DHC-8 dates back to the early 80s, and it in turn is a derivative of the DHC-7, and so on.

So what you are saying is that no new turboprop will ever be certified again?

Quoting SEPilot (Reply 77):
And while a plane with engines on the wing can survive an engine falling off, a plane with tail mounted engines will have a much harder time-the CG change may well be too much.
http://en.wikipedia.org/wiki/Northwest_Airlines_Flight_5

Admittedly a trijet with tail-mounted engines, but still, the crew remained unaware that the engine had departed the airframe (they knew it had failed, presumably) until after landing.

Quoting Revelation (Reply 80):
Indeed but above we estimate the inertia magnitude to be 10x the turboprop, and the lateral forces exerted on the engine mount will scale with that, it seems to me, admittedly a rank amateur. If so, comparing one blade out of four with X inertia would equate to comparing one blade out of 40 with 10X inertia, no?

How do you get 10x the inertia? The tip speeds cannot be supersonic because there would be no way to contain the noise.

http://en.wikipedia.org/wiki/Republic_XF-84H


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 83, posted (2 years 1 month 4 weeks 17 hours ago) and read 6082 times:

Quoting DocLightning (Reply 82):
How do you get 10x the inertia? The tip speeds cannot be supersonic because there would be no way to contain the noise.

It might go slightly supersonic at takeoff (turbofans do this now) but that's not the point. The modern swept scimitar blades can go faster (same reason that swept wings go faster) and the blades themselves have to be heavier (see lightsaber's estimate of 2-10x mass higher up).

Tom.


User currently offlineDocLightning From United States of America, joined Nov 2005, 19415 posts, RR: 58
Reply 84, posted (2 years 1 month 4 weeks 17 hours ago) and read 6043 times:

Quoting tdscanuck (Reply 83):
It might go slightly supersonic at takeoff (turbofans do this now) but that's not the point. The modern swept scimitar blades can go faster (same reason that swept wings go faster) and the blades themselves have to be heavier (see lightsaber's estimate of 2-10x mass higher up).

Turbofans have a shroud that contains the shockwaves. If the tip speeds cannot be made subsonic, then the OR may be a non-starter after all.


User currently offlinepacksonflight From Iceland, joined Jan 2010, 379 posts, RR: 0
Reply 85, posted (2 years 1 month 4 weeks 7 hours ago) and read 5572 times:

Airbus strategy could be to create small aircraft like 100- 120 seater that sits right above turboprop territory to exist initially parallel to the 320 family. Kind of a test platform, not only to test technology but also to see how passengers accept this new concept.

User currently offlinespeedygonzales From Norway, joined Sep 2007, 721 posts, RR: 0
Reply 86, posted (2 years 1 month 4 weeks 5 hours ago) and read 5392 times:

Quoting rampart (Reply 45):
OK, how about a ducted prop?

That's called a Kuznetsov NK-93:
http://www.airwar.ru/enc/engines/nk-93.html



Las Malvinas son Argentinas
User currently offlineaffirmative From France, joined Jul 2009, 350 posts, RR: 0
Reply 87, posted (2 years 1 month 4 weeks 3 hours ago) and read 5190 times:

Not having read up on the technology. Are the OR engines considered free turbines or are the fans bolted on the outside of the turbine stage?

I like the NK-93 idea. This had the fan blades contained and could probably be made either push or pull. Are the blades on the NK-93 variable pitch too?

I was looking at the MIT double bubble design with the three ducted fans mounted on the upper end of the empannage. With the vert stabs on both sides one could think of a CRP reinforcement all around that "tub" surrounding the engines. With this design there should also be enough shrouding for the noise of the Open Rotors or Ducted fans..

http://img.gawkerassets.com/img/17j7pxm3qu79ljpg/original.jpg



I love the smell of Jet-A1 in the morning...
User currently offlinelightsaber From United States of America, joined Jan 2005, 12903 posts, RR: 100
Reply 88, posted (2 years 1 month 4 weeks 2 hours ago) and read 5037 times:
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Quoting affirmative (Reply 87):
three ducted fans

While I like the design
1. It assumes electrical power transmission at weights below current technology.
2. While long term, I believe the trend will be to fuel cells or other 'in body' power sources, we are not there yet.
3. Look closely, that airframe is optimized for Mach 0.6 to 0.7. It is not a mach 0.8 cruiser
4. In production will go to two fans. All university concepts neglect maintenance and manufacturing expenses too much. This drives the optimal airframe to fewer parts.

That said, I like the shape. A lifting body such as that concept is a nice transition to the BWB. Also, far easier to implement today.

Once the engines are way at the back, ducted or free props become less relevant. It is a trade study. However, ducted props, due to blade tip noise issues, will be significantly quieter. But that isn't 'Open Rotor.' Its a GTF.   

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineaffirmative From France, joined Jul 2009, 350 posts, RR: 0
Reply 89, posted (2 years 1 month 3 weeks 6 days 21 hours ago) and read 4752 times:

Quoting lightsaber (Reply 88):
Once the engines are way at the back, ducted or free props become less relevant. It is a trade study. However, ducted props, due to blade tip noise issues, will be significantly quieter. But that isn't 'Open Rotor.' Its a GTF.

Can you really compare the GTF with, what I would call ducted fan engines, the NK-93? The NK-93 is more similar to the OR studies with dual counter rotating N1 fans while the GTF is a traditional turbofan with a single geared N1 fan. While they're both shaft driven in a similar way they don't seem all that similar.. I believe the NK-93 also features variable fanblades. This would make it even more unlike the GTF.

Regarding the double bubble:
Given that the new OR designs are all being optimized for a slowed cruise the 0,65-0,75 range is a pretty good design right? Sure, some properties in the design needs to be adresed but as a start I think it's a good starting point nontheless. While the do talk about hybrid and electrical powerplants I do feel that's way further in the future. Biofuels are more viable and available in larger scale sooner. And no need for a huge leap in technology to use it.

The study by MIT as the picture shows is quite big.. Considering the amount of windows that plane would probably take 350 pax.. But a smaller 100-200 pax version with two fans could be made similar in design..

Cheers.



I love the smell of Jet-A1 in the morning...
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