On Mon, Feb 17, 2014 at 5:09 PM, Onno Meyer <[email protected]> wrote: > Steam turbines can also be combined in different configurations, > e.g. two turbines on two shafts for flank speed and a different > turbine driving both shafts for cruise.
There have been multiple ways of doing this for ships. The first, with turbines that were on the propeller shaft, was simply to have more than one turbine set on a shaft. This was inefficient because the best speeds for turbines are a few thousand RPM, while propellers need to be kept down to a couple of hundred. The next was to have the turbines turn generators to drive an electric motor on the shaft. This worked fairly well, but was heavy and vulnerable to flooding. The third was to gear the turbines together. This wasn't practical until about 1920, but was the best solution, and remains in use for gas turbine ships. It's probably easier to gear turbines (steam or gas) together than reciprocating engines, because turbines turn smoothly and with far less vibration. There were lots of attempts to make powerful piston aero engines by gearing smaller ones together: http://en.wikipedia.org/wiki/Heinkel_He_177#Engine_difficulties http://en.wikipedia.org/wiki/BMW_803 http://en.wikipedia.org/wiki/Allison_V-3420 But none of them worked reliably. Piston engines with more than about 14 cylinders seem to get harder and harder: http://en.wikipedia.org/wiki/Junkers_Jumo_222 http://en.wikipedia.org/wiki/Rolls-Royce_Vulture There were a few that worked well, after a lot of development: http://en.wikipedia.org/wiki/R4360 http://en.wikipedia.org/wiki/Napier_Sabre Although there weren't many geared-together paired gas turbines, they seem to have been easier than the piston engines. The tank engine that started this example has the advantage of being a tank engine, and thus less weight-critical than an aero engine. John _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
