airlinereporter
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Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 5:46 pm

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
 
LoveJT8D
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 6:55 pm

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?
 
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Stitch
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 7:04 pm

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...
 
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ER757
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 7:09 pm

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
 
airlinereporter
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 7:11 pm

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
 
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DocLightning
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 7:17 pm

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.
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817Dreamliiner
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 7:22 pm

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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cargolex
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 7:23 pm

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.
 
airlinereporter
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 7:49 pm

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
 
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clickhappy
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 8:40 pm

It is for sure the RAM prop. It has a distinctive metallic whirl to it.
 
BMI727
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 8:53 pm

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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N766UA
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 10:20 pm

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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connies4ever
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RE: Boeing 787 Sounding Like Prop?

Mon Oct 01, 2012 10:37 pm

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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AmericanB763ER
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RE: Boeing 787 Sounding Like Prop?

Tue Oct 02, 2012 10:21 am

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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