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4 Answers

Turbojet – Thrust producer //// Prop-power – Power producer

Asked by: 5862 views , , ,
Aerodynamics, Aircraft Systems

Why is a turbojet known as a thrust producer, but a piston-prop is known as a power producer?

 

My ground instructor was unable to give any explanation at all, but there must be a good scientific reason why?

 

Maybe a turbojet's thrust increases linearly with throttle, but a piston-prop's power increases linearly - some good reason like that...?  But I'm only guessing...

 

Thanks.

 

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4 Answers



  1. lo_fly on Mar 17, 2013

    Honestly i’ve never heared that.
    Both turbojet and piston prop produce thrust and power because

    Power = Force (thrust) x Velocity

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  2. Best Answer


    Nathan Parker on Mar 17, 2013

    As lo_fly says, turbojets and props both have thrust and both have power; it’s a necessity because of the way in which those concepts are defined mathematically. The only real justification in drawing the distinction is that fuel burn is related linearly to thrust in a jet, whereas it’s related to power in a prop.

    Actually, another reason for maybe saying that is that with a turbojet, thrust is relatively constant with velocity, but with a prop (constant speed prop), it’s power that’s constant with velocity, with thrust decreasing the faster you go.

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  3. Joseph Leonard Platt on Mar 17, 2013

    http://www.aerospaceweb.org/question/propulsion/q0195.shtml

    I’m a retired Flight Engineer not a Flight Instructor, but perhaps the above link would help.

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  4. Jon on Mar 17, 2013

    Everyone above is correct in that both produce power and thrust. The distinction comes from how the output of an engine is measured. Turbojets and turbofans engines are measured by the thrust (force) that they produce, because that’s the easiest way to measure it – you put it on a stand, turn it on and see how hard it tugs on the stand. Reciprocating engines, on the other hand, produce thrust by turning a propeller, but there are a lot of variables that affect how much thrust a propeller produces from a given amount of power. To make measurement easier, and more consistent, reciprocating engines are measured at the propeller shaft. You might noticed that turboshaft and turboprop engines are also measured in power (horsepower) because that’s what you get out of the _engine_.

    Hope that helps.

    Jon

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