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777-300ER Waffling Engine Sound

Sat Feb 13, 2016 9:54 pm

I've noticed in cold weather that the GE90s make sound similar to a distant police/fire/ambulance siren when climbing out. Why are they effect in this way?
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RE: 777-300ER Waffling Engine Sound

Sun Feb 14, 2016 3:00 pm

I've never noticed it from the inside, but I guess those fans are big enough that small differences in rotation speed might induce rythmic accoustic resonances the way it happens on 'unsynced' twin turboprops.
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RE: 777-300ER Waffling Engine Sound

Tue Feb 16, 2016 9:54 am

Quoting francoflier (Reply 1):
....small differences in rotation speed might induce rythmic accoustic resonances the way it happens on 'unsynced' twin turboprops.

That is what you call "beating", but it has nothing to do with a resonance.

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RE: 777-300ER Waffling Engine Sound

Thu Feb 25, 2016 11:47 am

Its noise abatement procedure. From what I know, in the United States of America, the FAA Federal Air Regulations states that any commercial aircraft must NOT exceed 250 knots (x 1.151 = 287 mph) below 10,000 FT ASL. So if you check out you can watch those videos. The pilots pull back on the throttle that's what that whining noise is from the engines. Have you noticed on the Boeing 707, 727, and MD-80 and MD-90 jetliners the engines spool very loudly, I love it very nice  . Also because of wear and tear, the pilots hardly ever use full maximum power because its like driving your car at maximum RPM. From the videos I've seen, I haven't heard any sirens or anything, that's very unusual. Each GE engine on the Boeing 777 can produce up to 110,000 lbs of thrust on take off. Man o man, these are the biggest engines on any of the Boeing jetliners. It has ETOPS too. General Electric is very good at making engines, however their terrible at making HDMI cables.....   

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