Geared Turbofan?

Question

I read in the trade sites and on their own web site that Pratt and Whitney is developing something new called a geared turbofan. I'm wondering how it differs from a conventional turbofan, and what are the advantages of it. It looks on the outside like a convention engine. It's not like the designs seen in the 80s with exposed semitar shaped blades.

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Answer 1

Victor beat me to the punch he is spot on correct.  There is a good article about the new pratt and whitney engine in I think the popular mechanics from a month or two ago.

Answer 2

Pure Jets, like the 707, get great performance at cruise altitude but are very inefficient at low altitudes.  That's they seem to take forever for them to get off the ground.  Military aircraft overcame this with the After Burner.  

Propeller Aircraft have great thrust in dense air but lack efficiency in thin air at higher altitudes.   The first Aircraft I crewed on was the P2V-5, Neptune.  It was originally twin propeller but later two jet pods wee hung under the wing.  At altitude, to save fuel we would shut down one Prop engine and cruise on the jets.  (We had to keep one prop going for utility power.)

This was overcome with the 'Turbofan'.  The front blades act as Propellers on takeoff and at low altitudes.  (That's why the fat front duct to direct air around the nacelle.)  At high altitudes the jet does it's thing.  

Typical Jet engine use two stages, one in front for compression and one in the back for fuel ignition.  Look at this site, http://en.wikipedia.org/wiki/Turbofan

You will find the many different methods very well described with excellent pictures and diagrams, descriptions of different ducting and geared type.

I hope you find this helps

Answer 3

A turbofan gets most of its thrust from a large fan at the front that is driven by a jet engine. Conventional turbofans have that fan operating at the same speed as the jet core, which can be innefiecient. A geared turbofan lets the speed of the drive fan differ from the speed of the turbine, which allows both to be operated at their best speed. This is expected to give a great leap in fuel economy. Possibly as much as thirty percent more efficiency.