NWDC10
Topic Author
Posts: 904
Joined: Sat Dec 20, 2003 10:15 am

Unducted Fan Should Have Been Used!

Wed Sep 14, 2005 7:19 am

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
 
whitehatter
Posts: 5180
Joined: Sat Jun 12, 2004 6:52 am

RE: Unducted Fan Should Have Been Used!

Wed Sep 14, 2005 7:23 am

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.
Lead me not into temptation, I can find my own way there...
 
Dougloid
Posts: 7248
Joined: Tue Jul 05, 2005 2:44 am

RE: Unducted Fan Should Have Been Used!

Wed Sep 14, 2005 9:46 am

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.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
corey07850
Posts: 2335
Joined: Wed Feb 04, 2004 4:33 am

RE: Unducted Fan Should Have Been Used!

Wed Sep 14, 2005 9:56 am

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 avatar
lightsaber
Crew
Posts: 11728
Joined: Wed Jan 19, 2005 10:55 pm

RE: Unducted Fan Should Have Been Used!

Wed Sep 14, 2005 10:04 am

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
"They did not know it was impossible, so they did it!" - Mark Twain
 
sllevin
Posts: 3312
Joined: Wed Jan 30, 2002 1:57 pm

RE: Unducted Fan Should Have Been Used!

Wed Sep 14, 2005 10:08 am

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
 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: Unducted Fan Should Have Been Used!

Wed Sep 14, 2005 10:27 am




How are UDF's affected by icing?




2H4


Intentionally Left Blank
 
Boeing7E7
Posts: 5512
Joined: Sat Jul 31, 2004 9:35 pm

RE: Unducted Fan Should Have Been Used!

Wed Sep 14, 2005 11:47 am

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.
 
apathoid
Posts: 887
Joined: Fri Sep 28, 2001 3:19 pm

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 12:57 am

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.
 
theunclesam
Posts: 52
Joined: Tue Mar 01, 2005 5:13 am

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 1:39 am

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."
 
Dougloid
Posts: 7248
Joined: Tue Jul 05, 2005 2:44 am

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 2:05 am

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
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
whitehatter
Posts: 5180
Joined: Sat Jun 12, 2004 6:52 am

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 2:24 am

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).
Lead me not into temptation, I can find my own way there...
 
irelayer
Posts: 929
Joined: Wed Jul 06, 2005 4:34 pm

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 2:38 am

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 avatar
RayChuang
Posts: 7982
Joined: Sat Jun 24, 2000 7:43 am

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 2:58 am

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.
 
Dougloid
Posts: 7248
Joined: Tue Jul 05, 2005 2:44 am

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 3:03 am

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...
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
User avatar
clickhappy
Posts: 9042
Joined: Thu Sep 13, 2001 12:10 pm

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 3:11 am


View Large View Medium
Click here for bigger photo!

Photo © Frank C. Duarte Jr.

 
SBN580
Posts: 374
Joined: Sat Mar 12, 2005 1:55 am

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 3:14 am

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!
North Central: Good People Made Their Airline Great! FLY MD-90 POWER! Keep 'em Flying DELTA Family!
 
gigneil
Posts: 14133
Joined: Fri Nov 08, 2002 10:25 am

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 3:14 am

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
 
AirRyan
Posts: 2398
Joined: Wed Mar 30, 2005 9:57 am

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 3:17 am

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.
 
baw716
Posts: 1459
Joined: Thu Nov 20, 2003 7:02 pm

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 5:41 am

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 avatar
Starlionblue
Posts: 17049
Joined: Fri Feb 27, 2004 9:54 pm

RE: Unducted Fan Should Have Been Used!

Thu Sep 15, 2005 6:53 am

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."
 
N62NA
Posts: 3984
Joined: Sun Aug 10, 2003 1:05 am

RE: Unducted Fan Should Have Been Used!

Sat Sep 17, 2005 12:33 am

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.

Who is online

Users browsing this forum: No registered users and 12 guests