Next Generation Engines :: GE-36 UDF

Today, everything seems to be about going green. This applies to the aviation industry more and more everyday as it is not just environmentalists who want to cut down on carbon dioxide and nitrogen oxide emissions but also aircraft operators. Airlines are looking for the next generation of engine that will be the jack of all trades. Higher efficiency, noise reduction, and low operating costs. Engine designs have come a long way in efficiency compared to the first turbojets, which have all but disappeared from commercial airliners; replaced by the turbofan. These turbofans continue to grow more and more efficient however the more efficient these engines are the slower they become, a turn off to airlines who need to get passengers from point to point, so it seems that maybe turbofans are peaking as they are today. Perhaps the answer to the question of next generation aircraft engines is actually something designed in the past.

The GE-36 UDF affixed to its Boeing 727 Test Aircraft.

In 1988 General Electrics, one of the largest aircraft power plant producers in the world, launched the 'Unducted Fan' design, what was known as the GE-36 UDF. The base of this engine was actually a military F404 turbofan also produced by General Electrics. In the engine itself there were no noticeable differences except for the absence of a gearbox which is usually used to turn the compressors at different speeds than the turbine through gear reduction. The use of a gearbox was not needed because GE replaced the conventional higher speed turbine with a low speed, 14 stage turbine. After this the changes made to the engine became more noticeable. Scimitar shaped fan blades were attached to 2 counter rotating turbine stators. Effectively creating a bypass ratio of 5 to 1. (The F404 without the UDF modifications was a bypass ration of 0.34 to 1) The idea behind bypass ratios is that the higher the bypass ratio the more like a turboprop the engine is and the more efficient it can travel, but the trade off is the slower the engine can go. This high bypass ratio created an engine that boasted high fuel efficiency and General Electric Engineers claimed the engines could go up to .75 mach, a speed close to what most domestic flights cruise in. When this engine was uncovered General Electrics engineers were confident; "It's not a case of if it's a case of when." said General Manager of Commercial Operations Ron Welsch at the Farnborough airshow in Paris of 1988, when the engine was officially revealed. However if it was so efficient why is it the project never got off the ground?

Well the roots of the project can actually be traced as far back as the 1970's OPEC (Organization of the Petroleum Exporting Countries) oil embargo. This infamous oil embargo was a wake up call for the United States and began to bring light to the vulnerability the US has to foreign oil suppliers. At that time around 64% of oil was supplied by OPEC. Prices on jet fuel rose from what was once 12¢ a gallon to $1 per gallon. The budget for fuel went from 25% of an average airline's expenses to 50%. General Electrics, looking to move in on the now relevant efficiency market, began work on the UDF project with goals to reduce fuel usage by 30% of the turbofans of the day. General Electrics published a fuel lb/payload lb ratio of .5 versus .8 for the CFM56 (CFM International) and 1.3 for the JT8D-217. (Pratt & Whitney) That is why when engineers unveiled the GE-56 hopes were high. However one factor affected the marketing of this engine. In 1989 the world had changed, oil prices were down and still falling and the airlines found no justification in switching to the UDF, which still had not been completed in development and increased noise pollution in the cabin. Airlines no longer showed any interest and therefore neither did aircraft manufacturers which ultimately put the nail in the coffin for the Unducted Fan design until recently. Interests in Unducted Fan engines have recently been renewed with the oil prices fluctuating and growing in the past years. Higher environmental concerns have also begun to push this design back into the spotlight for smaller domestic aircraft. Maybe Mr. Welsch (see quote above) wasn't thinking of 30 years down the line but it could still be a question of when for the Unducted Fan.

Thanks for reading, more to come in the next few days, rigt now the next topic is planned to be AF447. If you found this interesting don't forgot to comment, they are always welcome. Also if you found it interesting feel free to follow this blog and I'll get some more articles up.  -Consaofise