Un-Ducted Fan, wheresit now?

[Airpiraterob]

so i remember big fancy work on the ultra-effecient hi-bypass ratio fans....or the Un-Ducted fans..(UDF) remember the big contra rotating scimitar bladed prop-jets tested on the MD-80's back ni the day? (ie: 1996)
http://www.aviation-history.com/garber/images/udf-2.jpg

supposedly gave 20-30% better fuel economy and speeds of .8m to 150-200 seat planes. They were ultra effecient were they? great performance for less fuel burn right? well if they accomplished this...then WE NEED THEM NOW!

so, anyone know what happened? what the conclusion was? and if they really were that effecient? and why the hell we dont have them to solve our fuel problems?

 

[fr0g]

I believe there are UN-ducted fans around today - the turboprop.

 

[Airpiraterob]

you dont get it do you.....yeah its a turboprop in the mostly classic sense.....but its a high-subsonic large airliner sized engine.....not many high-subsonic turboprops out there now xcept teh piaggio avanti....and thats only 400kts.

 

[EagleRJ]

The UDF differed from a turboprop in that the blades were driven directly off of the low-pressure turbine (which was more of a power turbine, I guess). There was no gearbox, except for some planetary gears that reversed the direction of the second fan disk.

The UDF is supposed to give the performance of a modern high-bypass turbofan while giving better fuel economy. It was also supposed to be quieter, but one of the primary reasons the project is on the back burner was the obnoxious howling sound that the UDF's blades made. It remains a good idea, though, and maybe it has a future if the engineers can make it quieter.

 

[fr0g]

everything you could possibly want to read about propellers, both ducted and UN-ducted
http://www.wordiq.com/definition/Propeller

 

[mzaharis]

There is an aircraft which may yet be fielded that uses propfans, a military airlifter - the Antonov AN-70. Also, the Airbus A400M is a turboprop aircraft that has very propfan-like propellors (scimitar-shaped), and is capable of up to mach .72.

http://www.aeronautics.ru/news/news002/news094.htm
http://www.airbusmilitary.com/

With the advent of more scimitar-shaped props which have capabilities of coping with supersonic tip speeds, it seems that the distinctions between traditional turboprops and propfans is blurring. Maybe the distinction is the degree of tip sweep, and whether there are two contrarotating props on one shaft.

The development of ever higher bypass ratio ducted turbofans may mean that the UDF will not ever be seriously pursued again for airliner use.

 

[FN FAL]

you dont get it do you.....yeah its a turboprop in the mostly classic sense.....but its a high-subsonic large airliner sized engine.....not many high-subsonic turboprops out there now xcept teh piaggio avanti....and thats only 400kts.

I remember seeing the test engine mounted on some sort of Boeing type aircraft. To tell tell you the truth Airpiraterob, the concept could prove to save money and provide efficient power, but no passenger monkey is going to want want to ride in a "prop" airplane.

 

[mzaharis]

I remember seeing the test engine mounted on some sort of Boeing type aircraft. To tell tell you the truth Airpiraterob, the concept could prove to save money and provide efficient power, but no passenger monkey is going to want want to ride in a "prop" airplane.

There were two engines built - a GE UDF that was direct drive from its power turbine, and a geared Pratt/Allison one. If memory serves, the GE was tested on a 727 and an MD-eightysomething, while the Pratt/Allison was only tested on the MD.

A search of "UDF" at airliners.net probably would turn up a few photos. I have seen them posted there before.

EDIT

Here's the 727 with the GE engine.

http://www.airliners.net/open.file/001821/L/
http://www.airliners.net/open.file/125332/L/

And the MD-81
http://www.airliners.net/search/photo.search?regsearch=N980DC&distinct_entry=true
http://www.airliners.net/search/photo.search?&regsearch=N980DC&nr_of_rows=21&first_this_page=15&page_limit=15&sort_order=photo_id+DESC&thumbnails=&engine_version=&nr_pages=2&page=


Another problem with propfans is that, ISTR, they were exceptionally noisy. It would be rather difficult to meet Stage III or IV noise requirements with them. If the tips are supersonic, you're going to get quite a bit of shock wave production, no matter how well sculpted they are.

Interesting NASA paper on propfans:
http://history.nasa.gov/SP-4219/Chapter14.html

 

[Kaman]

Hello,
I recall seeing the GE/Boeing test ship in mojave minus the UDF. This was a few years ago, but I have no idea if it was scrapped or converted back into a conventional 727-100.
MD was conducting tests on their UDF MD-80 out of Yuma, AZ and I saw it flying a few times. Unsure of it's whereabouts now, but probably scrapped or reconverted and sold.

Regards,

Ex-Navy Rotorhead

 

[crash-proof]

Any videos on the net with a test flight? Curious to hear the sound. I can imagine an Avanti...times 50!

 

[Airpiraterob]

probably a soft blender now....
if it was ducted tho it would be just a turbofan...but with 2-variable pitch fan sections....and that would still be more efficient. and it would look like a more or less proper turbofan the passengers like to see.

besides, who says this dosent make any more noise than that of a 777 on takeoff. that buzzing hollow-fan noise.......