Kugerand

Jack GG stands for Gas Generator, which is the High Pressure Spool or sometimes called the core. It has the HP compressor, combustor and HP Turbine (HP = horsepower). It provides the high pressure air and temperature + combustion to power the low pressure or power turbine as those gases expand and transmit torque - much like a dam. The LP (low pressure shaft goes then goes thru a speed reduction gearbox and out to a shaft for the propeller. Here is a link to an engine cut away. In the picture - Compressor Turbine = HP turbine, Centrifugal Compressor = HP compressor. Power turbine = LP (low pressure turbine) http://www.bing.com/images/search?q=pratt+and+whitney+pt6a+engine&view=detailv2&&id=4B590A4D827FACEE914DB16BDF941758DB8D1BA7&selectedIndex=9&ccid=wwHDYv59&simid=608016079654423462&thid=OIP.Mc301c362fe7da531705c1c45425f312do0&ajaxhist=0