The unducted fan engine was being tested on a 727 as part of the 7J7
development. Boeing was considering developing a plane about the size
of the 737 that would use two of these engines, and it was designated
the 7J7. I worked on this program a bit before it was canceled and
replaced by the 7X7 development which became the 777.

Dean Wilkinson

"DeltaDeltaDelta" wrote in message ...
As I dug up from my old Flight Internationals (7-14 January 1989), there
were two UDF engine models:

1.) General Electric GE36 - recognisable by the fact that the jet exhaust
pipes are in the rear of the engine, like in other jets
2.) P&W/Allison 578-DX - their exhaust pipes are just before the unducted
fan and the engine rear (after the fans) is a sealed cone

The major difference was that the fans on the GE36 were directly linked
to the turbine, which was modified to rotated at low speeds, since the
blades were known to produce a lot of noise if they spun quickly. On the
578-DX however, the turbine rotated at normal gas turbine speed, while the
fans were linked with a gearbox that allowed them to rotate at lower speeds.
Also, the fans were counter-rotating. The DC-9 on the airliners.net picture
was used for both engines, though like on the "mysterious" 727 somebody
mentioned, it was installed only on the port side, with the standard JT8D
retained on the starboard. Modifications to the a/c itself were almost
minimal, except for the modification of the port pylon due to the increased
vibrations of the new engine.

Triple Delta

"Dan Truesdell" wrote in message
...
I was at GE's Aircraft Engine Group when this project was going on. I
could be wrong about the 727, but I seem to recall a picture with one of
the outboard engines replaced with the UDF. That was a while ago. It
may have been a mock-up.

I seem to recall that your marketing assessment is correct. I've
spent many hours explaining to fellow travelers (having just stepped
into a Beech 1900) that the plane was, indeed, a jet. Good opportunity
to pass on some knowledge to a public that gets it's aviation from that
oh-so-accurate source: the press.

John Gaquin wrote:
"Dan Truesdell" wrote in message


This is GE's UDF (for UnDucted Fan) project. Theory was that the high
efficiency blades would add up to better fuel consumption. The program
was never brought to market. The image you posted is one of the flying
testbeds (possible the only, although I think there might have been a
727 used first).


I never heard about a 727 UDF -- possible, but #2 engine would be a
tough
one. I talked to a few folks involved after the project died - I think
around 89 or 90. They said it actually showed a lot of promise, good
efficiency over the jet for short range. But the word was that the
marketing results killed it. It just looked scary. Given a choice,
focus
groups always shied away from "prop planes". They were considered old.
I
used to run into that in commuter lines, too. People would get off a 20
year old Boeing, and board a brand new t-prop and crack jokes about the
props. A mind is a marvelous thing, wasted.

JG




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