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Unducted Fan Should Have Been Used!  
User currently offlineNWDC10 From , joined Dec 1969, posts, RR:
Posted (9 years 1 month 1 week 6 days 20 hours ago) and read 11482 times:

I know the unducted fan wasn't wanted by the airlines and it was loud, but they could have worked on it and made it quieter. Should the engine developers continue working on the engines to fine tune them and convince the airlines the engines were "reliable" to be used? Robert NWDC10

21 replies: All unread, jump to last
 
User currently offlineWhiteHatter From , joined Dec 1969, posts, RR:
Reply 1, posted (9 years 1 month 1 week 6 days 20 hours ago) and read 11479 times:

There are other issues to consider beyond noise, unfortunately.

An unducted fan throws up many other problems such as safety and fuel consumption. A ducted fan has a casing which contains the blades should there be a failure. On an unducted engine there would not be that same barrier and an engine failure could turn into an extremely nasty accident.

The blades turn a lot faster than the prop on a turboprop engine and therefore have a lot of kintic energy in them which would need to go somewhere.


User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 2, posted (9 years 1 month 1 week 6 days 18 hours ago) and read 11376 times:

Quoting NWDC10 (Thread starter):
I know the unducted fan wasn't wanted by the airlines and it was loud, but they could have worked on it and made it quieter. Should the engine developers continue working on the engines to fine tune them and convince the airlines the engines were "reliable" to be used? Robert NWDC10

I remember seeing the "propfan" MD80 test mule hauling in and out of Long Beach....seems to me that must have been in the early eighties when I was working at Garrett over by the terminal. It was quite noisy, but I believe what killed the project was the high level of vibration transmitted to the airframe structure...it was causing fatigue cracks or so it was said. That was the rumor on the airfield.

At the time fuel economy was not as critical as it is now...No reason to think that it would have been any less safe than any other turboprop....

In fact, the only airplane I ever saw that was damaged by a prop blade was a Metroliner-in fact, it was the fourth one built, and it had round windows...one gear leg collapsed, the right hand prop ( a Hartzell) struck, a blade came off ( a weakness on that model prop anyway) and went through the fuselage and broke the gearbox on the the left engine....I had some fun with those engines!

Just remember.....stay out of the plane of rotation and you'll be fine...had anyone been in the seat at that station they woulda lost their legs.


User currently offlineCorey07850 From United States of America, joined Feb 2004, 2528 posts, RR: 5
Reply 3, posted (9 years 1 month 1 week 6 days 17 hours ago) and read 11353 times:

Some interesting notes on the GE/NASA UDF.... Has a Bypass ratio of 35:1 (designs up to 80:1!!), 11.7' blade diameter, and supposedly had a 25% decrease in fuel consumption compared to similar models.

User currently offlineLightsaber From United States of America, joined Jan 2005, 13271 posts, RR: 100
Reply 4, posted (9 years 1 month 1 week 6 days 17 hours ago) and read 11330 times:
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Quoting NWDC10 (Thread starter):
I know the unducted fan wasn't wanted by the airlines and it was loud, but they could have worked on it and made it quieter.

Why not just use a geared turbo-fan. Faster cruise, less noise, safer (blade containment), etc. Sorry, but noise is being regulated more and more; its become one of the criteria in the trade studies all new engine designs undergo. Look at the Cheverons on the CF-34; they cause a 0.25% fuel burn penalty but they reduce noise quite a few dB. SNA, LGB and other airports all have noise caps. Thanks to nimbys, noise will continue to be an issue.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineSllevin From United States of America, joined Jan 2002, 3376 posts, RR: 6
Reply 5, posted (9 years 1 month 1 week 6 days 17 hours ago) and read 11323 times:

Quoting Dougloid (Reply 2):
but I believe what killed the project was the high level of vibration transmitted to the airframe structure...it was causing fatigue cracks or so it was said.

Not just the vibration of the battering of the airframe was a significant issue; aircraft using UDF's would require some significantly different metals and design in the fuselage near the fans.

Steve


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 6, posted (9 years 1 month 1 week 6 days 17 hours ago) and read 11291 times:
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How are UDF's affected by icing?




2H4





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User currently offlineBoeing7E7 From , joined Dec 1969, posts, RR:
Reply 7, posted (9 years 1 month 1 week 6 days 16 hours ago) and read 11217 times:

Quoting 2H4 (Reply 6):
How are UDF's affected by icing?

From what I understand it's minimal because heat exhaust from the turbine is expelled around the blades.

The idea isn't dead and may very well show up on a T-Tail 50-90 seat RJ. If they can cut 20-30% of the fuel burn off those aircraft they become money makers again. They're a tad slow but fast enough for regional routes.


User currently offlineApathoid From , joined Dec 1969, posts, RR:
Reply 8, posted (9 years 1 month 1 week 6 days 2 hours ago) and read 11009 times:

There was a resonance issue with it that to the best of my knowledge was never resolved. It was feared it would induce fatigue cracking in the airframe.

MD 80's have had uncontained failures that have cause injury to passengers as well.

L-188's have had prop separations where the prop came thru the cabin.

It can happen to any aircraft component that spins really fast and has some mass.

Best rule is don't sit anywhere near the props or the fan or any of the t-wheels. Bad mojo happens when that shit comes apart.


User currently offlineTheunclesam From United States of America, joined Feb 2005, 55 posts, RR: 0
Reply 9, posted (9 years 1 month 1 week 6 days 2 hours ago) and read 10965 times:

Quoting Dougloid (Reply 2):
I remember seeing the "propfan" MD80 test mule hauling in and out of Long Beach.

Wasn't this plane on that Discovery show "Beyond 2000"? They made it sound like unducted fans were the best thing since sliced bread. I remember the aircraft having counter rotating blades too, am I correct?



"So what's your robot do?" "Collects data about the surrounding enviroment. Then drives into walls."
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 10, posted (9 years 1 month 1 week 6 days 1 hour ago) and read 10909 times:

Quoting Lightsaber (Reply 4):
Why not just use a geared turbo-fan.

Well, it was tried twice that I know of and in both instances the teething process was long, painful, and far more expensive than a lot of people have a stomach for.

What am I talking about?
Why, the TFE731 and the ALF502.

When I started in the shop at Garrett there were still planetary gear mods being done....after that, there was a mod to detune the sun gear with an anti vibration washer....it cost Garrett a LOT of dough.

Then, Avco Lycoming goes and gets a similar bright idea with the ALF502....gearbox failures a plenty. It pretty much sunk the BAE146 and nearly killed the CL600


User currently offlineWhiteHatter From , joined Dec 1969, posts, RR:
Reply 11, posted (9 years 1 month 1 week 6 days 1 hour ago) and read 10861 times:

There was also the IAE V2500 Superfan proposal for the original A340 as well. Luckily CFM had an alternative available.

Quoting Apathoid (Reply 8):
MD 80's have had uncontained failures that have cause injury to passengers as well.

L-188's have had prop separations where the prop came thru the cabin.

It can happen to any aircraft component that spins really fast and has some mass.

yes, but with a UDF the problems are magnified. The blades would be totally uncontained when the engine decides to digest itself, and the shorter blades would be running at much higher speeds than a turboprop.

It would be a shrapnel bomb going off next to the fuselage of an airliner rather than prop blades carving into the fuselage, as happens when a conventional propeller breaks up (which they admittedly rarely do).


User currently offlineIRelayer From United States of America, joined Jul 2005, 1073 posts, RR: 2
Reply 12, posted (9 years 1 month 1 week 6 days 1 hour ago) and read 10837 times:

I'd say leaps and bounds in engine technology will come about under two circumstances:

1) If the military wants it and thus pays for its development.

2) A joint venture between two of the big boys for a next-generation engine design.

Right now I see stagnation. The biggest development in engines is the GE-90 series and the GENx. Both of these are pretty high technology, but they are evoluationary, not revolutionary.

IMO, Unducted is a cool concept, but prop-fans are too wild and crazy to risk-averse airlines right now.

-IR


User currently offlineRayChuang From United States of America, joined Jun 2000, 8018 posts, RR: 5
Reply 13, posted (9 years 1 month 1 week 6 days ago) and read 10798 times:

Quoting WhiteHatter (Reply 1):
A ducted fan has a casing which contains the blades should there be a failure. On an unducted engine there would not be that same barrier and an engine failure could turn into an extremely nasty accident.

I think that was probably the biggest reason why propfans were never adopted for single-aisle airplanes. Indeed, before Boeing shelved the 7J7 program they were supposedly redesigning the plane to accommodate the IAE V2500 engine and uprated CFM56 engines.


User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 14, posted (9 years 1 month 1 week 6 days ago) and read 10785 times:

Quoting RayChuang (Reply 13):
I think that was probably the biggest reason why propfans were never adopted for single-aisle airplanes. Indeed, before Boeing shelved the 7J7 program they were supposedly redesigning the plane to accommodate the IAE V2500 engine and uprated CFM56 engines.

Good point....blade containment is a big issue...The regs have been tightened a few times....speaking of which Rolls has a GREAT Trent 900 video on their site which shows bird strike and blade containment tests.

As I recall the propfan was a noisy bugger too....much noisier than a common garden variety prop bird...


User currently offlineClickhappy From United States of America, joined Sep 2001, 9644 posts, RR: 68
Reply 15, posted (9 years 1 month 1 week 6 days ago) and read 10768 times:
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User currently offlineSBN580 From United States of America, joined Mar 2005, 401 posts, RR: 3
Reply 16, posted (9 years 1 month 1 week 6 days ago) and read 10757 times:

I have a book MD published on this at home. I got to the the MD-87 (?) demonstrator at EDW AFB from time to time when I worked at NASA DFRC. It looked sooooo coool!


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User currently offlineGigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 17, posted (9 years 1 month 1 week 6 days ago) and read 10757 times:

Quoting WhiteHatter (Reply 11):
There was also the IAE V2500 Superfan proposal for the original A340 as well.

The Superfan wasn't a UDF. It was a geared turbofan engine.

N


User currently offlineAirRyan From United States of America, joined Mar 2005, 2532 posts, RR: 5
Reply 18, posted (9 years 1 month 1 week 6 days ago) and read 10740 times:

What advantages would any of these engines have over the tech developed that will result in the GEnX engines for the 787?

On a side note the P&W F119 developed for the F-22 has also lead to the F135 for the JSF, and GE has really got their F110 humming with the -132 version with their own JSF version (with RR) F136 under development.

Suffice to say I don't think we need any sort of new engine tech per se as P&W, RR, and GE all have developed a lot of new ideas as we'll see on these GEnX engines, they are the most fuel efficient and powerful engines ever created.


User currently offlineBaw716 From United States of America, joined Nov 2003, 2028 posts, RR: 27
Reply 19, posted (9 years 1 month 1 week 5 days 22 hours ago) and read 10639 times:

The UDF is an accident waiting to happen. Vibrate the frame just enough and the engine gets vibrated into the frame and a blade gets ripped off at those speeds...
Talk about uncontained engine failure! On the MD87, it would rip off the tail and anybody sitting back there. You could never place one on an under wing aircraft; imagine an uncontained engine failure with blades exploding into the fuselage and center fuel tank. By the time you heard the explosion, the aircraft would be ripped in two along with anyone who happened to be sitting in the middle of the airplane.

No thank you. Uncontained engine failures in a high bypass engine are bad enough. Just thank God the engines are made so well that they almost never happen.

baw716



David L. Lamb, fmr Area Mgr Alitalia SFO 1998-2002, fmr Regional Analyst SFO-UAL 1992-1998
User currently onlineStarlionblue From Greenland, joined Feb 2004, 17069 posts, RR: 66
Reply 20, posted (9 years 1 month 1 week 5 days 20 hours ago) and read 10588 times:

Quoting Theunclesam (Reply 9):
Quoting Dougloid (Reply 2):
I remember seeing the "propfan" MD80 test mule hauling in and out of Long Beach.

Wasn't this plane on that Discovery show "Beyond 2000"? They made it sound like unducted fans were the best thing since sliced bread. I remember the aircraft having counter rotating blades too, am I correct?

Well, now that we are "Beyond 2000" Big grin... Anyway that program, while very good, loved pie in the sky stuff. "In five years, your toilet will wipe your bottom, dry it and screen you for disease!"



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineN62NA From United States of America, joined Aug 2003, 4524 posts, RR: 7
Reply 21, posted (9 years 1 month 1 week 4 days 3 hours ago) and read 10424 times:

In the September issue of Air and Space Smithsonian...


The Short, Happy Life of the Prop-fan

by Bill Sweetman
Meet the engine that became embroiled in round one of Boeing v. Airbus, a fight fueled by the cost of oil.


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