glugn wrote:Something that has always interested me: the physical differences between single & double reduction geared turbine engines. The US used double reduction gears while Europeans used single. Given the generally better performance of the double reduction geared turbines, how difficult would it have been to replace a single reduction geared engine w/ a double reduction geared engine?
All other things remaining the same, what would the effect be in terms of increased speed & fuel consumption?
glugn wrote:So then there wouldn't be an improvement in speed if SR gearing was replaced w/ DR I take it?
lynn1212 wrote:i used to work for a company that made gear sets for many different uses including ships. we produced the drive sets for the class of LSTs built for the USN back in the sixties and seventies. double sets were smaller both in size and weight as well as having higher power ratings and larger ratios. however they required a better tech base and machines [not to mention machinists]. every set we built had to pass a stall test where the torque levels were measured in foot tons , 2 500 hp dc motors coupled in tandem to the input shaft and a beam with a scale anchored to the output. in other words locked in position. our 250vdc generator sets didn't like it a bit. the advantage of double sets comes from the ability to use smaller gear pairs to get large reductions. two 4 to 1 pairs requires just 3 shafts, six bearings and gives a 16 to 1 reduction. a 16 to 1 single set would be about 4 times bigger since the output gear would have to be 16X the diameter of the input gear instead of the 4x needed in the double set. larger footprint, heavier, much taller, harder to lubricate, case needs to be built heavier, and the whole thing is more apand t to suffer shock damage as well as being much harder to repair in place or to replace. there is also a large difference between the types of gears used. we used a type called a Sykes herringbone gear. it was a double helical gear with a groove between each half and each tooth was curved so the load was spread over 2 or 3 teeth at a time instead of 1 or 2. this resulted in a much stronger gear and it also ran a lot quieter and resulted in a smaller set. we also used tapered bearings with thrust bearings on the output shaft as well. often overlooked are the oil requirements and cooling. water and gunk will screw up a set real quick. as an aside we cut gears up to 27 feet in diameter and up to a 6 foot face. big impressive hunks of steel
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