Unducted fan or propfan:
Propfan - Wikipedia, the free encyclopedia
The excerpts below are from an article by Bill Sweetman, the premier aviation journalist:
The Short, Happy Life of the Prop-fan | History of Flight | Air & Space Magazine
... Airbus’ chief planner, Adam Brown, still believes that Boeing hyped the 7J7 in a bid to disrupt the A320 program. At the 1985 Paris show, Airbus faced the inevitable question: Was the company still confident in the A320’s future? “We can go up against the ‘magic aeroplane,’ ” Brown answered, “and we can beat it.”
...
Airbus stuck to its guns, Brown says today, because its studies showed that aft-engine aircraft were heavy, and maintenance costs would be higher.
...
At the end of August 1987, Boeing announced that the 7J7 had been postponed a year. (And Monty Python’s dead parrot was “just resting.”)
McDonnell Douglas tried to carry on with prop-fan development. It had the rear-engine MD-80, but it was losing ground to the A320 and 737. MDC fitted a UDF engine to an MD-80 in late 1987 and wanted to launch the UDF-powered MD-91 and -92 by July 1988. The company even saw a 300-aircraft market for a Navy patrol version of the MD-91. But GE wanted to see 100 to 150 airline orders before committing to the program. Recalls Conboy, “If people aren’t going to buy it, there’s not much you can do.” ...
Russia’s Tu-95 bomber and its airliner derivative, the Tu-114, were designed in the 1950s and had jet-like swept wings. The turboprop-powered Tupolevs could sprint at Mach 0.78, but had to cruise at around Mach 0.7 for best range. Their 15,000-hp engines drove 18-foot counter-rotating propellers, requiring tall landing gear to keep the tips off the runways.
The Ukrainian Antonov An-70 and the yet-to-fly Airbus A400M cruise at up to Mach 0.72, about as fast as the jet-powered C-17 airlifter, but slower than commercial jets. They use large-diameter propellers, not prop-fans.
There is little interest in true high-speed propellers today. The latest conventional turbofans are more efficient than the engines of the mid-1980s, thanks to new fan aerodynamics and materials, so there is less to be gained by a move to a UDF-type engine. It’s also questionable whether the prop-fan could meet current international noise rules.
Last edited by Modern Elmo; 8th Apr 2011 at 17:09.