A hercules pre "J" anyway is powered by a single-spool type gas turbine engine..that simply put is either "on" or "off" other than when being operated at low-speed ground idle mode (civilian version, not too sure about military engines) for taxiing about, this engine basically runs at one speed...twhen power is desired, pushing the power levers forward simply adds fuel...this would tend to cause an increase in rpm, but the propellor senses this, and increases it's blade angle "bite" causing increased thrust..and vice versa when the power lever is retarded...some fixed shaft engines TPE-331 for example are fixed shaft single spool as well, but are provided with an rpm lever to allow small changes in rpm for passenger comfort..by small 3-4% reduction...twin-spool turboprops as in pt-6 engines have a gas producer (n1) section that is controlled by the power lever, and a power-section (n2) that is connected through the reduction gear to the propellor..since the connection between the n1 and n2 is gaseous, and not mechanical, a bit of efficiency is lost...the fan section on all large hi-bypass fan engines on airliners are configured this way as well...since the fan is nothing more than a many-bladed propellor...so some turboprops have 3 controls...pt6 power...prop...condition (which turns on and off fuel for starting and shutting down, and adjusts idle speed), Garrett, honeywell whatever power, and (speed/ rpm lever which controls engine rpm using prop pitch during flight mode, and uses fuel to control rpm during ground ops(beta) and the good old t-56/allison501 early herc's cv580, l electra..which has one set of levers..power...anybody want to take a stab at the dart/tyne/kunetsov???
