UDF (unducted fan)
 

I seem to remember in the 80s there where tests with unducted fan engines, and various models where being planned powers by UDFs. Why havent these caught on and there are no commercial planes flying with UDFs today?
Luke

I flew a high-bypass unducted fan for years. It was the Fokker 27, and the power-plant was the trusty Dart.

Because fuel has gotten cheaper and cheaper over time. Not more expensive.

It also had noise issues. Corrected for inflation fuel is pretty much at an all time low.

Cheers
Wino

Nothing quite impedes the progress of science as the right idea at the wrong time.

The UDF idea was cast aside, Luke, because of vibration and uncontained blade failure issues some time ago. Pity, because I thought at the time it had great promise.
Maybe another day.

from a non-engineer, wouldn't a ducted approach for otherwise the same fan produce increased efficiency by reducing/preventing loss of the pressure differential around the tip? :confused:

This was suggested at the time, but was rejected becauce of rather large drag considerations.

Did see and hear the ukrainian An-70 UDF-Transporter flying at the Berlin Air Show ILA. Wasn't too noisy. (4 engs!) Noise can't be the reason for abandoning UDF designs. Low fuel prices like somebody mentioned above is what I think is correct -aside from the unwanted "propeller-appeal" many airlines try to avoid.
That An-70 looked like a good concept to me. However for other reasons they are getting late on starting producing it.