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Boeing 787 Sounding Like Prop?  
User currently offlineAirlineReporter From United States of America, joined Jun 2010, 78 posts, RR: 0
Posted (1 year 11 months 3 weeks 6 days 1 hour ago) and read 11629 times:

I live in the flight path of Paine Field and have the privileged of having new 787s flying over my home. Yesterday was the third time where one flew over and at just the correct angle, it sounded EXACTLY like a prop engine. I thought for sure there was a prop plane by the 787, but all three times, no other plane.

Have any of you experienced this at all? I have never heard another jet engine sound like that before. It lasts maybe 3-5 seconds before going back to sounding like the GEnx or Trent1000 engine.

Thanks,
David

13 replies: All unread, jump to last
 
User currently offlinelovejt8d From United States of America, joined Sep 2010, 55 posts, RR: 1
Reply 1, posted (1 year 11 months 3 weeks 6 days ago) and read 11358 times:

I have never had the privilege to listen to the 787 fly overhead or spot it at an airport yet, so I think it's cool you've had a chance to hear engine sounds that are unique to the aircraft. As far as my observation goes from shuffling through a variety of 787 Youtube videos, I find the engine sound inside the cabin sounds very comparable to the GE-90 series. I hope to be able to listen to this plane fly over and hear the engines externally. Maybe you were in a direct angle to briefly pick up the acoustics from the fan blades clearly.

Was the 787 taking off, of landing?


User currently onlineStitch From United States of America, joined Jul 2005, 31007 posts, RR: 86
Reply 2, posted (1 year 11 months 3 weeks 6 days ago) and read 11274 times:
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I've only heard the Trent 1000 (Package A) fly overhead and while it is very much a unique sound, I don't recall it sounding like a prop...

User currently offlineER757 From Cayman Islands, joined May 2005, 2529 posts, RR: 7
Reply 3, posted (1 year 11 months 3 weeks 6 days ago) and read 11232 times:

Quoting Stitch (Reply 2):
I've only heard the Trent 1000 (Package A) fly overhead and while it is very much a unique sound, I don't recall it sounding like a prop...

I love the sound of the Trents - just awesome! I think the GEN-X's sound different and not as cool, but never noticed either sounding like a prop


User currently offlineAirlineReporter From United States of America, joined Jun 2010, 78 posts, RR: 0
Reply 4, posted (1 year 11 months 3 weeks 6 days ago) and read 11214 times:

Quoting lovejt8d (Reply 1):
Was the 787 taking off, of landing?

In all three cases, the 787 was coming in to land. Now, I have heard it plenty of other times with out it sounding like a prop.

David


User currently offlineDocLightning From United States of America, joined Nov 2005, 19727 posts, RR: 58
Reply 5, posted (1 year 11 months 3 weeks 5 days 23 hours ago) and read 11159 times:

It's a soft buzzing sound, not dissimilar from a prop. The A380 sounds similar.

These new ultra-quiet engines still have blade tips breaking Mach 1 at takeoff power. That's going to make a noise as those shockwaves are emitted. It can be muffled, sure, but not silenced. The buzz used to be louder on the prior generation of engines (those powering the MD-11, 767, 747, and A330/40). Also, on the newer engines, you can barely hear the noise made by the core, so all you hear is the fan.

So yes, it starts to sound not entirely unlike an Embraer Brazilia flying over.


User currently online817Dreamliiner From Montserrat, joined Jul 2008, 2396 posts, RR: 1
Reply 6, posted (1 year 11 months 3 weeks 5 days 23 hours ago) and read 11107 times:

Ive only heard the Trent 1000 version when it came to MAN, I dont recall it sounding like a prop, sounded like nomal jet engines to me though a hell of a lot quieter.


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User currently offlineCargolex From United States of America, joined Apr 2010, 1271 posts, RR: 8
Reply 7, posted (1 year 11 months 3 weeks 5 days 23 hours ago) and read 11106 times:

My first question is, was the Ram Air Turbine deployed? Because that can sound like a prop.

Some test flights do deploy the RAT to test.


User currently offlineAirlineReporter From United States of America, joined Jun 2010, 78 posts, RR: 0
Reply 8, posted (1 year 11 months 3 weeks 5 days 23 hours ago) and read 10923 times:

Quoting Cargolex (Reply 7):
My first question is, was the Ram Air Turbine deployed? Because that can sound like a prop.

I think this might be it. Someone else suggested that to me as well and I have reached out to Boeing to find out. Because the sound is very distinct and it would make sense to be the RAT.

And since I have quite a few 787s flying over and each one tests the RAT, I would hear it every once in a while.

David


User currently offlineclickhappy From United States of America, joined Sep 2001, 9633 posts, RR: 68
Reply 9, posted (1 year 11 months 3 weeks 5 days 22 hours ago) and read 10634 times:
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It is for sure the RAM prop. It has a distinctive metallic whirl to it.

User currently offlineBMI727 From United States of America, joined Feb 2009, 15745 posts, RR: 27
Reply 10, posted (1 year 11 months 3 weeks 5 days 22 hours ago) and read 10522 times:

Quoting AirlineReporter (Thread starter):
Have any of you experienced this at all? I have never heard another jet engine sound like that before. It lasts maybe 3-5 seconds before going back to sounding like the GEnx or Trent1000 engine.

I don't recall the engine sounding like a prop, however the characteristic roar of a jet engine, which is caused by the shearing between hot, high velocity exhaust and the cooler, slow moving ambient air is very negligible thanks to a high bypass ratio and a well designed nacelle. This leaves mostly the whining of the fan blades interacting with the intake air, which could sound not too different from a turboprop.

Contrast that to fighters which sound completely different since the fan is usually buried within the fuselage while the low bypass engines leaves them with a loud roar rather than the higher pitched whine common with civilian aircraft. Then there's the afterburner, which effectively removes the bypass ratio, and all hell breaks loose.



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User currently offlineN766UA From United States of America, joined Jul 1999, 8273 posts, RR: 23
Reply 11, posted (1 year 11 months 3 weeks 5 days 20 hours ago) and read 10199 times:

I saw it land at Logan once, and it struck me as hugely quiet. Nothing at all sounded like a turboprop. In fact, nothing much sounded like a jet either.


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User currently offlineconnies4ever From Canada, joined Feb 2006, 4066 posts, RR: 13
Reply 12, posted (1 year 11 months 3 weeks 5 days 20 hours ago) and read 10105 times:

Quoting DocLightning (Reply 5):
These new ultra-quiet engines still have blade tips breaking Mach 1 at takeoff power. That's going to make a noise as those shockwaves are emitted. It can be muffled, sure, but not silenced.

It should not be forgotten that a HBR turbofan is in essence a high performance turboprop with a shroud around the prop.

Quoting BMI727 (Reply 10):
I don't recall the engine sounding like a prop, however the characteristic roar of a jet engine, which is caused by the shearing between hot, high velocity exhaust and the cooler, slow moving ambient air is very negligible thanks to a high bypass ratio and a well designed nacelle. This leaves mostly the whining of the fan blades interacting with the intake air, which could sound not too different from a turboprop.

Re the well designed nacelle, I agree. The "chevron" nacelle reduces noise by making the shearing of exhaust air somewhat out of phase.

For both the above, wait to you hear (or not) PW's GTF. Since the fan will be turning slower, less noise, estimated at 2Db.



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User currently offlineAmericanB763ER From Luxembourg, joined Sep 2005, 166 posts, RR: 0
Reply 13, posted (1 year 11 months 3 weeks 5 days 8 hours ago) and read 9270 times:

I have noticed a similiar thing on approaching 772F's ( courtesy of CZ, MU and QR   ) in one or 2 cases I was hearing an approaching aircraft; swearing it was a turboprop and I was quite surprised to find out it was a B772F. But maybe it is limited to a certain point in the thrust setting range because it does not happen every time... (and no my ears were not playing tricks on me...)
These are all GE-powered 772LR/F's I'm talking about, I don't know about the other versions with RR or PW's though...

CV's 748's on the other hand still have a lot of that "classic" jet approaching sound.

[Edited 2012-10-02 03:23:13]

[Edited 2012-10-02 03:23:53]

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