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Guest BrianC

Dumb question - turbo prop vs. turbine?

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This has plagued me for awhile now and I'm finally going to swallow my pride and ask the question. What's the difference between a tubocharged piston, a turbo prop, and a turbine? I thought a King Air (turbo prop) was probably a turbine but I've seen other things that have led me to believe a turboprop is not a turbine engine. My brother flies a Malibu which is turbocharged but I've never heard it referred to as a turboprop. He is trading up to a TBM, which I know is a turbine and is supposed to be much safer. The Cessna 421 is differentiated from a turboprop in some of Stoenwork's stuff, yet I know the Conquest is the turbine version. Aaaaahhhhhhh! It's very confusing! If you can help - I'd love to hear it. THanks!David

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David,Abbreviated answer - but more responses to follow, I'm sure.Simply, a "turbine" engine has no pistons - it is in fact, a spinning turbine that uses the combination of compressed fuel / air mixture to form combustion, and that exploding mixture, within the turbine sections (several layers of increasing mechanical force vanes) - accelerates the turbine itself, which propels the aircraft via the "forced airflow" exhaust - low pressure on the intake - very high pressure on the exhaust side. A turbine uses compressed air to start the turbine spinning - before fuel is added. When the compressed air pre-start gets the turbine up to a min. speed - the fuel is added / ignited - make sure you have the brakes on !!A "turbo-charged" engine - is a piston engine that is enhanced by the compression of the air - in the intake manifold channel. This process creates increased performance via the increaased (forced) air-flow, subsequently being mixed with fuel - and the compressed mixture is then "forced" into the cylinders. The intake fuel/air mixture is thus under pressure - which increases it's explosive power - ie: more "performance". The 'turbo-charge" compression is a function of the engine itself - similar to the turbine compression. The turbo-chrager works off the energy (spinning) of the engine components once fired up. The turbo-charger uses energy from the engine - to create a compression of the air intake stream - to create even more energy from the engine output....... ie: Uses a little energy - to create "bigger" energy....... The turbo-charger itself - is like a "turbine" - in that it takes low pressure air in the intake - and compresses the air - via a turbine (very small) - forcing the mixture into the manifold. Again - higher pressure / more air/fuel = more power....... When a turbo "blows" - like on top-fuel dragsters - it is this spinning turbine that let's loose - very dangerous - as the turbine is spinning extremely fast - sometimes above 9,000 rpm ! Most conventional turbo-chargers are limited in performance - to prevent such an explosion.......A turbine (jet) or turbo-prop (turbine engine driving a propeller) are the same - bascically - in function & operation. Turbine jets - use the exhuast itself as propellant...... the turbo-prop uses a propeller connected to the spinning turbine (geared down) to create the propellant force.......Hope that helps......Ron

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>What's the difference >between a tubocharged piston, a turbo prop, and a turbine?>David The difference between a piston (turbocharge or not) and real turbine engine is at least $500,000 !! :-)Michael J.

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Ron,Thank you for the well thought out response! In some of the Stoenworks info on the Cessna 421 he mentions that turboprops are pretty much limited to 12,000-18,000 ft altitudes while the 421 does better in the mid-20s. I would think turboprops -being turbines would have enhanced performance over a turbocharged piston. THat said though, is the King Air a turbine (turboprop) or a turbocharged piston? Do turbines have magnetos and some of the other things we associate with normal piston engines? Thanks againDavid

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The King Air is a turboprop... and how anybody could say that a turboprop is limited to FL180 or thereabout baffles me. The service ceiling on a King Air is somplace in the neighborhood of 35,000 feet.

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>Do turbines have magnetos and some of the other things we >associate with normal piston engines? Thanks again No. These are completely DIFFERENT engines costing millions. They are essentially jet engines. They have spark plugs to initiate ignition but after that combustion is self-sustaining. Does your car's engine look like a jet engine ??Turboprops are NOT limited to FL180. Jetstream 41 which is a turboprop can reach FL370.Michael J.

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I think the following quote from Hal Stoen, a 421 pilot for many years, is what is causing the most confusion for me."Unlike most turbo props, whose engine limitations restrict power settings above 15,000 feet, the 421 liked to operate above FL200 (20,000 feet). From 15,000 to FL200 was pretty much King Air country. From FL200 to FL250 the 421 pretty much owned the airspace. Those altitudes were too high for most turboprops, and too low for the pure turbines. "David

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What can I say ? I have no clue what he is talking about unless he talks about some ancient chapter from history of aviation. Even Piper Malibu (piston/turbocharged) can reach FL250. King Air 350 have a ceiling of FL180 with one engine shut down ! The other thing that just appeared to me - he is using term "turboprop" for turbocharged piston. But this is incorrect.Michael J.

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Michael,I think you're right since the 421 is a turbocharged piston.I have no idea what he's talking about with the King Air, since as far as I know it's always been a TP.Speaking of price. Yeah, the difference between piston and turbine is amazing, especially since the turbine has one heck of a lot fewer moving parts. Go figure.

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>turbine is amazing, especially since the turbine has one >heck of a lot fewer moving parts. Go figure. Apparently this is because of very exotic alloys needed in turbine engines (the temperatures in turbine engines are much higher).Michael J.

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>Apparently this is because of very exotic alloys needed in turbine >engines (the temperatures in turbine engines are much higher).Speaking from experience (18yrs or Turbofan Overhauls) the temperatures in turbine engines can reach in excess of 2000F degrees. A piston engine rarely exceeds 400F. The materials used to build turbines still are a mystery with names like "Hard as hellium" and "Oh My Godnium" and "I can't affordium"Ken

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Blowhole mentions but doesn't describe the turbofan engine, which uses a turbine (jet) engine to drive a fan. Most of the thrust from this setup is produced by the fan. I believe this is the most widely used type of jet engine for civilian aircraft.David

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What he probably means by 15-20k being King Air country is that this is where you will find them. True that the King Air has a ceiling up in the 30's, but in practicality, you won't find them up that high. It's just too much work getting there. In fact, our 1900Ds were always filed at either 15 or 16.

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I always really liked this web site to learn about about as many kinds of engines as one might want to. http://www.keveney.com/Engines.htmlThe "Jet Engines" section describes rocket, turbojet, turboprop, and turbofan engines in full animated glory.I know you'll enjoy it.

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>When a turbo "blows" - like on top-fuel dragsters...;)

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