Date: 21 Mar 98 16:31:29 From: firstname.lastname@example.org (Ptolomy) Organization: Netcom References: 1
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"Campfire" <email@example.com> wrote: >This is my first posting to this apparently nearly deceased newsgroup(is >ANYONE out there? :) >My curiosity was piqued when I read about PW developing a new geared >turbofan. PW put out a news release stating it was the last great >improvement to be made with current technology(paraphrasing here, so I hope >I got it right). Does anyone know what advantages PW expect out of this? >I'm assuming they'll be running a bigger fan and will need to slow it down >from the core speed, and that the bigger size is because this engine would >be for the proposed superjumbo jets. Anyone have any info? Comments? What >about some of their competitor's comments that this is old technology with >no inherent advantages? Dave, The basic idea behind the geared fan is maximum efficiency. (of course) Anyway, in most t-fans, the fan is part of the low pressure spool - there being the fan, several stages of low press. compressor and the low pressure turbine all physically linked by a single shaft, and is separate from the core - or high pressure spool. The problem is that all of the lp components rotate at the same rpm, but have different aerodynamic efficiency ranges; therefore, this set up is a compromise - reducing overall efficiency. The fans best eff. is slower than that of the lpc and the lpt. By introducing a geared fan you can slow the fan while increasing the rpm of the lpc and the lpt, raising overall efficiency. This will allow higher temps to be maintained, and better power extracion by the turbines, having the direct benefit of increased fuel efficiency and ultimately range. The geared fan is not a new concept, and it is applied effectively in some small t-fan engines. P&W's proposal takes the idea a bit further and applies it to larger engines. It's biggest drawbacks are increased weight and maintenance costs. One of the reasons the geared fan idea has not takenoff in the past has been durability problems with the fan drive gearing. Increased efficiency must go hand in hand with durability and relatively low maintenance costs if one wishes to sell engines. Hope this helps. Regards, JCD.