Post by Tom/CalClassic on Mar 31, 2021 13:49:16 GMT -5
RR has announced development of what they call the Ultra Fan turbine engine, with fan almost 12 feet in diameter. Isn't this "fan" really an 18 blade ducted propeller? That would make it a turboprop engine.
If it's "ducted" (i.e. inside a casing) it's considered a "ducted fan" even if the fan blades themselves actually change pitch to perform better and save fuel. In engines like the AE3007's from Rolls that we had on our E-145, the fan blades had a fixed pitch, but the intake air went through "stators" that had a variable pitch down the line in the turbine section which gave the engine it's fuel mixture ratio, and hence, it's efficiency. The stators were controlled via computers (i.e. Full Authority Digital Engine Control = FADEC), which is why the FADEC's had to function or the thing would command a shutdown and no more engine. Since the blades for the fans themselves were fixed, then they could call that particular engine a "ducted fan" as opposed to whatever this thing is supposed to be.
If there is no casing per say (like on a Beech 1900 or Twin Otter), then it's a turboprop since you now have a traditional propeller instead of a fan, regardless if the pitch stays constant (like a CV-580) or if the thing changes pitch (like the Beech 1900).
I'm with you on this one, Tom, since it seems these new engines are basically ducted versions of that fan McDonnell-Douglas came up with many years ago for the MD80/90 series I believe? Except that particular one was outside with no ducting and pushed instead of pulled. That one was considered a turboprop-type aircraft, right?
Also, it would be interesting if this would be the next generation of ducted fans, like the variable pitch was the next generation of propeller after the fixed pitch but before the constant pitch. There really isn't much in that article to go into the details of how the thing operates, but I'm guessing that's under the whole business intelligence thing where you don't want proprietary things to go out in the open too soon.
Considering almost all -- if not all -- the engines of today are operating with FADEC's (even some GA gasoline ones), I'm wondering if things will just be all auto in the near future with only the minimal of intervention by us mere mortals.
Don't know what the diameter is of today's largest turbo fan engine, but an even larger diameter engine leaves less clearance between the ground, which is already very small. Engineers will have to redesign engine mountings\ wings\landing gears, in order to accommodate this.(Only a guess)
The technical name is Geared Turbofan. Marketing name is "Ultra Fan". BTW, they are the last to the game (again). Every Pratt & Whitney 1000G turbine installed on an A220, Mitsubishi MRJ, Embraer E-Jet v2, and A32Xneo is a Geared Turbofan. Every Garrett TFE731 installed on thousands of business jets are Geared Turbofans. Every Lycoming ALF 502 or LF 507 installed on the Avro RJs is a Geared Turbofan. It's not new technology. The concept is simply that there is a limit on bypass ratio with a normal turbofan engine because the blade tips go supersonic. By introducing a gearbox on the bypass fan (N1) shaft, you can run larger bypass ratios because the fan is running at a slower, more efficient rate for its size. It also allows for simpler fan blade design.
Also, doing a quick lookup, IAE had a "Super Fan" that was supposed to go on the A340, but got cancelled in 1987, when Rolls Royce was still part of the alliance. The engine was to take a V2500 engine core, add a Tyne-technology gearbox, and drive an RB.211-sized fan to give a 20:1 bypass ratio (later revised to 17.5:1). The project ended up only being a paper exercise, but it also had a big effect on the A340 because Airbus announced it as a primary option to the aircraft and Lufthansa actually made their initial order with the engine before it was "indefinitely delayed" in 1987, a year after its announcement.