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Old 31st Dec 2005, 03:51   #1 (permalink)

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Q: Turbofan rpm at N1 100% for a CFM56-5B4

Just curious...

For a CFM56-5B4 engine (typical for an A320):

What would be the approx. rpms of the turbofan at a N1 of 100% ?

Thanks in advance.

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Old 31st Dec 2005, 05:25   #2 (permalink)

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I managed to answer my own question:
5200 RPM (max N1 at 104%).

Source:
http://www.aftd.com/TCDS_PDFS%5CE37NE_10.pdf
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Old 1st Jan 2006, 17:26   #3 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Only 5200 RPM at max power? I'm very suprised. Considering cars do that with a significant engine rev.
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Old 1st Jan 2006, 20:23   #4 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Quote:
Originally Posted by Tonic Please
Only 5200 RPM at max power? I'm very suprised. Considering cars do that with a significant engine rev.
The difference is that the CFM56 N1 shaft is probably about similar in size to this entire car
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Old 1st Jan 2006, 20:44   #5 (permalink)

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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Plus the tips of the blades at 5200 RPM are going very fast (supersonic).
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Old 1st Jan 2006, 22:26   #6 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

So its the middle of the fan going 5200? Or something else? What is used to come up with the speed?

A-FLOOR, made me chuckle Supersonic speeds on the tips? Bloody hell.
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Old 1st Jan 2006, 22:45   #7 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Middle, centre or tips; they're all rotating 5200 times in one minute!
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Old 1st Jan 2006, 22:46   #8 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Exactly, so how can the tips be going "supersonic"?
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Old 1st Jan 2006, 23:11   #9 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Quote:
Originally Posted by Tonic Please
Exactly, so how can the tips be going "supersonic"?
They are revolving at 5200rpm, but towards the centre is travelling a smaller circumference (ie distance) than the tips, which are travelling much further in the same amount of time, hence in terms of mph/kph/m/s etc etc, the further from the rotational centre the faster they are travelling. Try it by putting a disc of card on a pencil. Mark a point on the edge and a point near the centre. Turn the disc slowly and see how much faster the mark on the edge has to go to cover one rotation of the disc......

Revolutions per minute may be the speed the shaft is turning at, but it is not the speed through the air that a point on a disc on that shaft is achieving.

PP
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Old 2nd Jan 2006, 00:33   #10 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

The numbers say:

Fan diameter is 67" or 5.6 feet. The state of Arkansas has legislated that pi=3, so I'll use that to find the circumference is 16.8 feet. And the blade tips travel 16.8 feet every revolution.

Speaking of revolutions, if we do 5200 in a minute, that's 83 in a second.

So - 16.8 feet in revolution, and 83 revolutions in a second, so it's about 1400 feet per second, without even considering the vector addition of incoming flow.

Sound travels 1100 feet per second on a standard day, so yes, the tips are supersonic. About 1.3 times the speed of sound.

I need a beer.
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Old 2nd Jan 2006, 12:25   #11 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Thanks people Enjoy your beers.
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Old 2nd Jan 2006, 13:02   #12 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Quote:
Originally Posted by barit1
The numbers say:

The state of Arkansas has legislated that pi=3,

That figures, them hicks are trying to go metric down there
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Old 2nd Jan 2006, 15:43   #13 (permalink)
 
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Re: Q: Turbofan rpm at N1 100% for a CFM56-5B4

Nope, it was long before that evil communist plot.

And I found a source postulating it was Indiana, not Arkansas:http://arshermeneutica.org/besieged/...the_Vaue_of_Pi

(WHOOP WHOOP thread creep detected!)
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