KFRG From , joined Dec 1969, posts, RR: Posted (10 years 4 months 3 weeks 2 days 1 hour ago) and read 6026 times:
Can anyone give me a better understanding of what the SuperFan, proposed for the A340, would have been? I also came across someone saying that it would have been a "geared" engine with gearing. That is where I am lost. How could a turbofan have "gears"?
Thanks for any help.
KFRG From , joined Dec 1969, posts, RR: Reply 2, posted (10 years 4 months 3 weeks 1 day 20 hours ago) and read 6004 times:
The IAE engine dubbed the "SuperFan", was originally supposed to power the A340, but was shelved. I guess my question goes deeper into how exactly a gearbox on a jet works, and what it's exact purpose is. But it sounded in referring to the IAE engine, that this "gearing" would be more speicific and unique.
Dynkrisolo From United States of America, joined Feb 2001, 1835 posts, RR: 7 Reply 3, posted (10 years 4 months 3 weeks 1 day 5 hours ago) and read 5951 times:
The proposed geared Super Fan was in essence a larger version of the Lycoming engine mentioned by RMM.
Why do you want to use a gear to drive the fan? It would allow the fan and the low pressure turbine to run at their own optimal speeds. The fan would like to run at a speed slower than the turbine. Because of the different optimal speeds, that's why Rolls use three spools for their big engines. But the additional spool adds mechanical complexity. Also the compression system and the turbines are still not running at their respective optimal speeds.
For a given core engine, lower fan speed means it's more feasible to fit a larger fan. This will increase the bypass ratio which means better propulsive efficiency and lower specific fuel consumption. Lower fan speed also means quieter fan. OTOH, a larger fan means more drag and more weight.
Sounds like a good idea, right? Unfortunately, the gear technology necessary for higher thrust engines is not quite there yet. Reliability seems to be one of the major issues.
Dw747400 From United States of America, joined Aug 2001, 1245 posts, RR: 1 Reply 4, posted (10 years 4 months 2 weeks 6 days 22 hours ago) and read 5865 times:
From what I understand, geared fans have been looked at for years but no one has found a an effective way to build a strong but lightweight gearbox that can withstand the kind of stresses imposed on it.
Regarding the SuperFan, does anyone know what its projected performance was? Or its bypass ratio?
Dynkrisolo From United States of America, joined Feb 2001, 1835 posts, RR: 7 Reply 6, posted (10 years 4 months 2 weeks 5 days 17 hours ago) and read 5786 times:
Oh, puh-leez. It was merely a paper engine that was nowhere being close to be developed. All fans have supersonic tip speed. The proposed superfan would have a lower tip speed than most of the fans out there. What supersonic blade problem? Also, "fan couldn't withstand the heat???" What heat? If you don't know, don't pretend you know.