Boeing 747 Engine Power: Realistic or Not?

[MalachiK]

Hi there

I'm writing a problem sheet for a class that I teach and I'm trying to use as many real world examples as I can. I'm writing simple questions about the power output of engines that are moving vehicles at constant speeds. I've used cars and boats, but now I want to use aircraft.

From information on the internet I've researched that a Boeing 747 has a max thrust of around 1184 kN and a max speed of 274 m/s. This gives me a max power output of 324 MW. Err, I know this is a maximum value and all, but I don't believe the result. To my simple physics teacher's mind it seems far too big. Can someone give me a hint if my value is reasonable?

 

[SteamKing]

You might want to read this article:
http://www.aerospaceweb.org/question/propulsion/q0195.shtml

The max. rated thrust of a jet engine is required when the plane is taking off fully laden under adverse conditions (i.e., hot day, airfield at high altitude, low humidity, no headwind, etc.) Once the plane has climbed to cruising altitude and accelerated to cruising speed, only a fraction of the rated thrust is required to maintain level flight.

 

[russ_watters]

Not just not required, but also not possible. For a turbofan, the ability to generate thrust drops as speed increases.

 

[MalachiK]

Thanks for the link. I get much more believable values now!