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Wed May 22, 2002 5:53 am

Is it possible to find out how much horsepower is generated by, say, the engines on a 757 rather than in pounds of thrust?
II Cor. 4:17-18
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American 767
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RE: Horsepower

Wed May 22, 2002 7:36 am

Well, I wouldn't be able to tell you how many horsepowers are equivalent to 1 pound of thrust but I read in a book, how to fly a 747, that the whole power a 747 would generate during flight is equivalent to 500000 horsepowers. So think about it, each 747 engine generates 56-58000 lbs of thrust, multiply by 4, that is over 220000 lbs of thrust. So to simplify, I would say that 1 lb of thrust is equivalent to 2 horsepowers.
So to answer your question, each engine on a 757 generates roughly 80000 horsepowers. Hope this clarifies your query.

Ben Soriano
Brussels Belgium
Ben Soriano

RE: Horsepower

Wed May 22, 2002 10:36 am

Just a side note:

Horsepower is plural...


RE: Horsepower

Wed May 22, 2002 1:30 pm

Actually, this question has been asked by nearly every pilot who has ever flown a jet aircraft. Go back through's archives and you will read some interesting posts. This is a very complex problem with several variables. In reality, we're trying to compare apples and oranges. I've seen viable formulas showing less than a 1:1 ratio and some that show the ratio as high as 3:1.
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RE: Horsepower

Wed May 22, 2002 5:20 pm

It is simply not possible to directly convert thrust to power (measured in Watts by the way).

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RE: Horsepower

Wed May 22, 2002 10:30 pm

I think at cruise altitude and speed today's high-bypass fans produce around a fifth of their static sea-level thrust. So if the 747 is producing 40,000+ lb (total for four eng) at, what, 480 knots? then by the definition of a horsepower that equals around 60,000 hp.

You can say that the engines are actually producing more power than that considering all the air they're churning up, but if you're just asking about useful power then that's it. People like to imagine that power is a difficult concept, and it can indeed be difficult deciding what to measure-- but once you've decided that, then the definition of power is simple.
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RE: Horsepower

Wed May 22, 2002 11:09 pm

I find it fascinating how far we've come in less than a century. From the elementary power of one horse to the thousands of pounds of thrust. What will the next century bring? Have the quantum leaps already been made, leaving us some scant tweaking to improve on them in the decades ahead, or will we continue to surpass current methods with mind-boggling advances? Let's face it - not much has happened since the first flight of the Concorde.
II Cor. 4:17-18
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RE: Horsepower

Wed May 22, 2002 11:29 pm

And the details of the matter:

The work done is the force times the distance.

The power is the work done divided by the time used.

So, here

Power = Thrust * Velocity, as the velocity is already the distance travelled divided by the time used.

As you can see, not only the output thrust but also the velocity affects the power output which is why you can't really translate thrust into horsepower.

I thought I was doing good trying to avoid those airport hotels... and look at me now.
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RE: Horsepower

Thu May 23, 2002 6:16 am

If you look into the site, then you will notice that RR offers the Trent engine also for marine application - rated at 50MW. 50MW is well over 60,000 HP which corresponds quite well with the assumption that a 747 engine produces roughly 100,000 HP at max T/O power at sea level altitude.

Remember a ship engine has no limited duration T/O power rating - it is pure continuous power - and certainly at sea level altitude.  Big thumbs up

A few other things will probably further reduce the marine Trent power output: First of all a very efficient silencer in the chimney, but also the fact that it will run on less energetic and cheaper fuel oil instead of jet fuel.

The fan is exchanged with a gear box to drive the propeller. I don't know if they ever sold a marine Trent, but a proposed application is a large cruise liner in which it will increase comfort by reducing noise and vibration compared to a traditional and more fuel efficient diesel engine.

Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs
Posts: 147
Joined: Fri Mar 01, 2002 9:31 am

RE: Horsepower

Thu May 23, 2002 6:35 am

Here's a link with all of the units, conversions, etc.
And a handy calculator to use (bookmark it)
Enjoy, and Happy teaching,

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