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Guest Mr Chips

Turbo-props

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Could someone explain to me what a turbo-prop is?,....is it a jet engine with propellers on the front?,if so what about the response time to the throttle"is it more immediate like a prop-piston engine?,or does it still lag behind like a pure jet?

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Hi CaptainVic!You're pretty much on the ball there...For a more detailed description try Google or your favorite search engine and type turboprop definition... that will give you plenty of places to start...or try http://en.wikipedia.org/wiki/Turboprop...And yes, there is a response lag associated with spool up, as in turbofans in jet aircraft... no immediate response to throttle inputs... that can take some getting used to, particularly on final approach...Andrew

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A turboprop is a "jet" engine only insofar as you mean that a basic component involves continously compressing and rapidly expanding air by igniting it. It deoesn't provide jet ptopulsion as a means of thrust--instead it is fundamentally a propeller engine. Just to be clear. Your short description as a "jet engine with a propoeller on the front" could be misleading.

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I would check that statement of not providing thrust. The Cessna Caravan is an example.

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>A turboprop is a "jet" engine only insofar as you mean that a>basic component involves continously compressing and rapidly>expanding air by igniting it. It deoesn't provide jet>ptopulsion as a means of thrust--instead it is fundamentally a>propeller engine. Just to be clear. Your short description as>a "jet engine with a propoeller on the front" could be>misleading.the beech 1900d gets 15% of its "thrust" through turbine exhaust, so yes it's 15% a "jet". the turbine exhaust nozzles are angled due to windows melting if the airplane was stationairy and they both were straight out.

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I was simplfying things for the sake of argument. You both are correct, I should have said "primary source of thrust" or something similiar.

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I think the distinction between a turbo prop and a jet is getting blurred by the high-bypass turbofans prevelant on just about all modern airliners. Something like 75% of the thrust is generated by the low pressure compressor (also called N1, the big fan that the sexy short skirted stewedesses are usually photographed against) - that fan, is by any other name, a propeller!

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>I think the distinction between a turbo prop and a jet is>getting blurred by the high-bypass turbofans prevelant on just>about all modern airliners. Something like 75% of the thrust>is generated by the low pressure compressor (also called N1,>the big fan that the sexy short skirted stewedesses are>usually photographed against) - that fan, is by any other>name, a propeller!well technically, the N1 high bypass fan is directly connected to the N1 shaft and exhaust turbines. some turboprops the prop is tied to a turbine which is NOT directly connected to an exhuast turbine. there is a small gap between the engine exhaust turbine and a reverse flow turbine which drives the prop (it is tied to the prop usually through a gearbox). the reason for this is ease of maintenance on the free power turbine section (the section tied to the prop).you can tell these type of turboprops simply by looking at the engine when it is shut down. the prop will be feathered, of which the beech 1900d is a good example. the direct drive turboprops (ie where the prop is directly connected to the hot section) will not feather when shutdown, of which the jetstream 31 is a good example.but i understand the point you are making. the high bypass engines are nice as they reduce noise, reduce fuel consumption, and generally keep the engines cooler.

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>some turboprops the prop>is tied to a turbine which is NOT directly connected to an>exhuast turbine.Fun to watch a King Airs PT6A turbine section get inspected by a mechanic holding the prop in place while the turbine section spools up :-eek

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Fun! The simple point I was trying to make to the original poster is the distinction between an engine designed to produce thrust by jet propulsion (i.e., by accelerating hot exhaust gas through a nozzle--like a rocket) and one designed to produce thrust by driving a conventional propeller. His originl post ("a jet engine with a propeller on the front") was ambiguous since "jet engine" is sometimes used loosely to refer to any engine that has compressors, turbines, etc. I was ignoring that turboprops do utilize their exhaust gas as propulsion to some extent and fanjets do utilize bypass air accelerated by "fans" to some extent. But on the whole, a turboprop is a propeller driven aircraft.

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i think most pax see a turboprop and they think, "contact!".personally, a "jet" a/c is easier to fly than a "prop" a/c.

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>i think most pax see a turboprop and they think, "contact!".>>personally, a "jet" a/c is easier to fly than a "prop" a/c.Contact as in hand propping? :-lol

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>>Fun to watch a King Airs PT6A turbine section get inspected by a >>mechanic holding the prop in place while the turbine section spools >>upA sort of manual hotel mode: "Not long now Bill, PAX nearly all on board" - LOL!

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