I saw a TV show on the Travel Channel "Millon Dollar Planes". They showed a PC-12. When going over features and benifits they discussed that the pro was not attached to the Turbine engine rather that the air pulled buy the engine then thus pussed from the forward movment turned the prop. Embassing, well I dont understand the purpose of the prop?Cant put this one together, could someone offer some insight which I am sure will result in me feeling like a real "klutz".Thank you.Thank you.Mark.System:OS:MS Windows XP Professional, Ver 2002 Service Pack 2 Hardware:Intel Pentium® 4 CPU 2.802.84 GHz, 3.00 GB of RAM Radeon X1600 Pro 512MB running a 21/19.6 Sony Flat Screen Tubed Monitorand a 17/16 NEC/Mitsubishi Tubed MonitorGeForce FX 5200 128MB running a NEC/Mitsubishi 18 Flat Panel

>>I saw a TV show on the Travel Channel "Millon Dollar Planes". They showed a PC-12. When going over features and benifits they discussed that the pro was not attached to the Turbine engine rather that the air pulled buy the engine then thus pussed from the forward movment turned the prop. Embassing, well I dont understand the purpose of the prop?Cant put this one together, could someone offer some insight which I am sure will result in me feeling like a real "klutz".Thank you.<

I can't answer that question, but I know a lot of those shows are not entirely accurate with the info they give. I'm not saying they are not correct, but I've seen many shows that give totaly wrong information about scuba diving ( deep sea detectives is one exception to that, those guys are well known in the dive community ). They may be correct about the PC 12, but after seeing a lot of wrong info about diving I always question things like that.

Sorry for the spelling issues.My question is that from what I viewed it seems that the prop is not connected to the engine rather it spins free. This is what I am confussed with. If it spins free then why is there to begin with. If I remeber this correct it is a turbine engine.I apprecate ny input and agian sorry for the spelling oversight. Thank you.Mark.System:OS:MS Windows XP Professional, Ver 2002 Service Pack 2 Hardware:Intel Pentium® 4 CPU 2.802.84 GHz, 3.00 GB of RAM Radeon X1600 Pro 512MB running a 21/19.6 Sony Flat Screen Tubed Monitorand a 17/16 NEC/Mitsubishi Tubed MonitorGeForce FX 5200 128MB running a NEC/Mitsubishi 18 Flat Panel

The PC-12 is powered by the most ubiquitous turboprop in the airline business: the Canadian made, Pratt & Whitney PT6A], and indeed, the constant speed propeller is connected to the output-shaft of this engine.My main reason in replying[/b here is because the Pilatus PC-12 is the most unbelievably beautiful aircraft. For anyone who has not seen one, they know not what they have missed.

Standard turboshaft engine. The compressor and stage 1 turbine are connected by a hollow shaft. The stage 1 turbine's only function is to drive the compressor section. The stage 2 or power turbine sits behind the stage 1 turbine and is connected to the propeller gear reduction by a shaft that runs through the center of the stage 1 shaft.Thrust that would normally be produced by hot gasses exiting rearward (for every action, there is an equal and opposite reaction) in a turbojet engine is for all intents and purposes absorbed by the power turbine and transmitted to the propeller.There is no physical connection between the stage 1 and stage 2 shafts. You could likely hold the prop from turning with your hand during startup and run as long as you didn't allow it to move. Turbine helicopters are often started this way (with the rotor brake initially on).Turbofan engines basically use this same concept, except rather than rotating a propeller, the power turbine rotates a large ducted fan.Just an FYI:The torque gauge in the cockpit reads the torque in ft/lbs being exerted on this power turbine shaft.Jim

Thanks Bill.I was really scraching my bald spot larger than it is. I will try and catch the show agian when it replays. As for the plane as a whole it is indeed a beautiful plane. Do you know of a web site to view the specs, (T/O and Landing requirments ect...). Thank you.Mark.System:OS:MS Windows XP Professional, Ver 2002 Service Pack 2 Hardware:Intel Pentium® 4 CPU 2.802.84 GHz, 3.00 GB of RAM Radeon X1600 Pro 512MB running a 21/19.6 Sony Flat Screen Tubed Monitorand a 17/16 NEC/Mitsubishi Tubed MonitorGeForce FX 5200 128MB running a NEC/Mitsubishi 18 Flat Panel

You are correct Sir! When I was flying Caravans we had to learn the engine inside and out, granted the PC-12 (which I also have a few hours in...) has a PT-6-67 and the C208 has a -114 or -114A they are basically the same. The "jet" or compressor stage is actually pointed backwards, with the exhaust gasses exiting out the "front" of the engine, where they pass over the power turbine, as you said. The airflow through a PT-6 makes no less than three 180 degree turns as it passes through the engine, and again, as stated before, there is NO physical connection between the compressor and power section, other than a common housing... Thats why we call it a Free-shaft turbine!AaronPS, I too have heard that is possible to hold the prop during startup, but I'll watch someone else try that one out first.

OK this is a VERY simplified description of the process. Experts please jump in here!Mark, you are basically correct, the turbine and the prop are not physically connected, BUT the turbine does still drive the prop. Read on...There are broadly speaking, two types of Turboprop engine, a traditional turboprop engine has the prop directly attached to the turbine by way of a reduction gearing, the Garrett turboprops as found on the Metroliner and Jetstream 32 aircraft are an example.See - http://en.wikipedia.org/wiki/TurbopropThe other 'type' of turboprop is more technically known as a turboshaft, where the turbine is not physically linked to the prop. Instead, jet thrust from the turbine is blown through a 'free power turbine' that is geared to the prop and thus turns it.See - http://en.wikipedia.org/wiki/TurboshaftThe type of turboprop engine that the PC-12 has is a PT6A-67B, which is a turboshaft type.Hope this helps!Mark

Thanks all.Mark.

I have held a prop by hand while the engine starts. No big deal. But when you let go that prop takes off like there is no tomorrow. Dont try this at home! Seems to be quite a variance on what people's impression of what a pt6 is.Jack

Whaat? So basically a jet with a prop that turns freely?Sounds... well, quite interesting.

All that and not one person answered Mark's question. :-violin

Obviously you know the answer, what are you waiting for somebody to e-mail you a quarter? :D

what was the PRECISE question again?