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Aaron747
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Joined: Thu Aug 07, 2003 2:07 am

PW407x/409x Sound Differences

Wed Dec 29, 2010 7:10 pm

This absolutely drives me nuts - what accounts for the difference in sound between these two 777 powerplants? I'm increasingly becoming more and more obsessed with the incredible noise these things make.

PW407X

http://www.youtube.com/watch?v=cXStqK4vDaE

PW4090

http://www.youtube.com/watch?v=Jro_fncM1o8

An additional curiosity...

http://www.youtube.com/watch?v=P5wl3PjoMXs

What accounts for the ‘burble’ heard 1:04 - 1:08 when the throttles are initially moved forward?
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rjsampson
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Joined: Sat Jul 31, 2010 12:00 am

RE: PW407x/409x Sound Differences

Thu Dec 30, 2010 8:26 pm

I don't think the engines sound different in reality.

If I had to take a stab at explaining why they sound so different in the two videos, I'd say it has to do with the distance and angle from which the video is being shot when the engines spool up.

As you know, the sound of an engine varies dramatically relative to the position from which it's being heard. In the second video, the videographer appears much further away and, as the aircraft comes accelerates closer, it seems like it sounds very similar to the first video when the aircraft is in the same position.
 
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Aaron747
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RE: PW407x/409x Sound Differences

Thu Dec 30, 2010 9:20 pm

Quoting RJSampson (Reply 1):
I don't think the engines sound different in reality.

I have to disagree, as I've sat in seats in the same position on both 777-200 and 777-200ER powered by PW4077 and PW4090 respectively, and there are differences in the sounds they generate in the first half of the spoolup phase. From there on at higher power setting they are relatively similar.
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MarkC
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RE: PW407x/409x Sound Differences

Fri Dec 31, 2010 3:55 am

The majority of the parts in a 77k engine are comparable and interchangeable with the 90k engine. However, there is a big difference in the fan case design. The older engines had composite fan exit guide vanes, and the 90k's had aluminium ones. The sound liners were also different.

I can see how this could produce a different sound.
 
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Aaron747
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RE: PW407x/409x Sound Differences

Fri Dec 31, 2010 6:42 pm

Quoting MarkC (Reply 3):
However, there is a big difference in the fan case design. The older engines had composite fan exit guide vanes, and the 90k's had aluminium ones. The sound liners were also different.

It certainly stands to reason that different materials in the same location could account for the differences I hear. Thanks for the information   
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