PPRuNe Forums - View Single Post - Performance on Jets vs. Turbo Props
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Old 11th July 2001 | 11:40
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Crossunder

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Joined: May 2001
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From: Norveg
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'Ello Nick!

Think of it this way:

In a straight jet engine, fuel is sprayed into the chambers, combusted and expelled out in the back. This means that (for all practical purposes) all fuel is used for thrust production (thrust producers)

In a prop, after the fuel is ignited, a lot of the heat energy is wasted throught gears/transmissions etc before it is transferred to the propeller disc (which isn't realy that efficient either) which in turn produces thrust, hence it is more convenient to talk about power (Watt)!

So, it is convenient to relate fuel flow to thrust output in a jet, and power output (internally) to fuel flow in a prop.

It is difficult to know exactly how much thrust a propeller generates, but for a jet engine it is quite simple.

Since FF is important for endurance/range calculations, drag (thrust required/FF) curves are used when talking about jets and power curves (FF) is used for props!

Fanjets have thrust curves that look like combinations between straight jets and props, because of the huge bypass fans that act as proopellers.

Are you inbound ENDU Aug.11???
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