Eh? A diver driver that I have tons of respect for, he is top dog in the Swedish Air force (I could kill for his job, some of the time), anyway he feathers the prop (DHC-Singel Otter, turbo prop) when loading jumpers. Darn the thing turns so slowly you can count the blades!
Have a question(s) about turbines and turbo-props. I know how a gas-generator work but how do you transfere the energy produced to the prop? In thrustor jets I understand the concept, but it gets a bit hazy for me when a prop is involved.
-Helicopters, is the main rotor shaft, power turbine and gas generator physicly connected to each other or is the gas generator rotating freely supplying gas to the power-turbine which via a reduction gearbox supply power to the rotorshaft? Is the gas-generator and powerturbine on the same rotating spindle or are they not joined?
-Turbo-props, same question really?
-Are there any instances where the powerturbine is hanging on the same shaft as the gasgenerator? Not jets...
I am not a turbo prop of much of a fixed wing guy but our SEAT's here at the base (single engine air tankers) run turbo props and one of them (the one with the Pratt&Whitney engine) puts his props into feather when he is idling and getting loaded with retardant to not blow the ground crews away when they load him. I am assuming that's what your buddy is doing when he is loading jumpers.....
There is no real problem with the feathering since the engine is not direct drive. It might get warm a little because the power turbine might turn a lot slower than the gas producer.
On helicopters the gas producer and the power turbine is not mechanically connected as well (you couldn't start it unless you'd put in a seperate clutch) and they link up later at full speed only by what is called "gas coupling" when the essentially turn the same speed or close to it.
The gas producer and the power turbine are usually two drive shafts with one of them being hollow and the other one turning inside the first one without any mechanical connection between eachother.
That way you don't need a clutch when you start the engine. You speed up the gas generator with its compressor wheels and its turbine wheels and the power turbine is just another wheel you "hang" in there to drive something with it (in case of the helo, the gearbox that drives the rotor).
I hope I explained that ok.
Sorry for responding so late. I can't always check out all the threads. If you have any more questions, fire away!
I am ready!
