Re:Unducted fans?

From:         h andrew chuang <>
Date:         06 Jan 94 01:54:00 PST
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Karl Swartz wrote:

| >what happened to unducted fans?
| The biggest appeal to the UDF was fuel economy.  When fuel prices
| retreated a bit, so did the appeal of the UDF.  Compounding this
| was the risk/cost of the new technology, noise and vibation problems,
| and potential image problems of what some might view as a "prop"
| plane.

Just to clear up some terminologies.  UDF is a registered trademark of GE.
The engine, GE36, had the counter-rotating fans.  (Coincidentally, in
Cincinnati, where the GE Aircraft Engines headquarters is, there is a chain
of convenient stores called UDF---United Dairy Farmers.  I wonder if the
store name inspired GE's naming scheme! :-)  If I remember correctly, Pratt's
counterpart was a single-stage, gear-driven propfans that did not really had
a special name like the UDF.  Garrett was a partner and its main function was
designing the gearbox.  Pratt's current Advanced Ducted Prop (ADP) also uses
gear-driven fans.  Pratt is currently working on an ADP application for the
growth A340.  Few years back, Lufthansa was very disappointed when Airbus
decided not to offer the A340 with a proposed UHB (ultra high by-pass) V2500.

| Delta's MD-90 launch order actually included the option to convert
| some of the orders to a UDF version, but everyone else lost interest.

Correct me if I'm wrong.  Both GE and Pratt practically halted their
propfan efforts after the cancellation of the 150-seat B7J7 program.  I
seem to remember that the current V2500-powered MD-90 was launched after
the B7J7 cancellation.  Therefore, I seriously doubt that Delta's order
included options for a UDF version.  It was proposed to put the UDF on the
MD twins, but I don't recall an actual offer of MD90/UDF to any customers.

| >I seem to recall that somebody even bolted a prototype onto one side
| >of a DC-9 and flew it around.
| The prototype MD-80, actually.  I once saw it at Mojave, with an
| extra-long pylon but no #1 engine at that point.  Boeing did the
| same thing with a 727.  Seems to me the MD-80 had a GE engine while
| the 727 had a Pratt, but I wouldn't bet on it.
I believe Karl is right.