Good morning/afternoon/evening gents

A topic that’s been spoken about a few times on these forums are that of the CSeries (A220) and it’s Pratt and Whitney GTF PW1000G engines. For those who haven’t heard these wonderful engines yet I’ll describe their quirky sounds. Upon spooling up you hear a low deep howling noise similar to that of the all time classic Vulcan howl (of course not as loud) You can also hear this sometimes on the approach, its when ever the engine is spooling up from idle.

Ever since I first spotted a CSeries aircraft that howling noise intrigued me. I wanted to find out exactly what causes it as it’s so unique. Over the years I came up with a few ideas of what caused it but have more less debunked each one. My thirst thought was the fact the fan has a 1:3 gear box meaning the 1st stage fan spins 1/3rd slower than the LP and HP compressors. I debunked this after hearing the PW800 engine found on new G500 and 600 business jets. The PW800 made an identical howl but does not use a gear system. One folk who commented on one of my Youtube videos said its the VSV (variable stator vanes) Before he mentioned that I had no idea what they were, essentially they’re guide vanes in the compressor which pivot depending on the power/air flow. He said that when these VSVs move that creates the difference in tone (the howl). I then found that VSV is a pretty common feature among Turbofan engines which brought me back to why does the GTF make the howl and no other engine does? Any way I found one more feature that could cause this noise. I read that the PW800 and PW1500G share the same core (hence the howling noise on both engines) I then read that these engines have a TALON Combustor. Which I later read the PW4000 also has, on some PW 777s you can hear a similar howl noise during the drop spool. So I thought being that these 3 engines create some kind of howl when spooling up could this be linked with the TALON combustor? Does the TALON combustor creat a unique howling noise when fuel is added?

I appreciate this is a long post folks but I hope you guys can help me one my quest for the howl haha! So yes if anyone knows for sure what actually causes the GTF’s and PW800’s spool up howl that would be greatly appreciated! Many thanks!

I haven't been on the A220 yet, so I don't know exactly what howling you're talking about. But when an engine is at idle or approaches idle or accelerates from idle, in addition to the aforementioned VSV, the VBV, the variable bleed valves, control the air flow through the compressor. When these valves open they can produce a quite noticeable deep hissing or growling sound. I found this to be quite noticeable on the A330 with PW4000 engines at idle. Maybe that's the sound you're referring to?

Here's a video I made which shows the howl I'm talking about; https://www.youtube.com/watch?v=XQTmLN2zZdg

It could possibly be like you say a mixture of the VSV and VBV, the larger variants of the PW4000 like on the 330 and 777 do make a similar deep howling noise when they spool up so it could also be the same with the GTF. Have a look at the video I linked and see what you think, I also wondered if it could just be the air being compressed a fair bit more than say a CFM 56 or IAE.

That's an interesting sound. I would still put my money on the VBV. The howl is getting louder when the engine accelerates out of idle and then stops. This could be the result of an increasing amount of excess air leaving through the wide open VBV until they close.
But maybe someone who has worked with these engines has a better idea. That's just my guess.

It is the harmonics of the associated pressure changes within the combustor structure during the phase from idle to higher thrust settings that cause the distinctive sound you are hearing.

nuke wrote:

It is the harmonics of the associated pressure changes within the combustor structure during the phase from idle to higher thrust settings that cause the distinctive sound you are hearing.

Yep, this was brought up a few weeks ago and someone linked to a podcast, towards the end of which, the Program Manager for the PW GTF indicated that it's the harmonics unique to the engine, within the lower thrust ranges as they change power settings.

Cheers fellas, so would it be a safe bet that it's Pratt and Whitney's TALON combustor that's responsible for this noise? Being that the PW4000, PW1000G (GTF) and PW800 all make a similar howling noise as they spool and they are also (to my knowledge) the only 3 engines to have the TALON combustor.

I LOVE that sound. That, and the GE90 growl on start-up. Like the buzz-saw on an accelerating CF-6 too of course!! Oh, and the Vulcan howl!
Oh and the whine of a spooling up RB211 naturally!!! ..and the high-pitched shrill of a RR Dart!! ..and the crazy racket of the old RR Spey, how could one note!..and coming to think of it, the racket of the Soloviev D-30 on the IL-62... and and and... oh, wait....

It sounds ruddy awful in the cabin.

oldannyboy wrote:

Oh and the whine of a spooling up RB211 naturally!!! .

everybody knows that theres no better sound in aviation than the RB211 spooling up

nuke wrote:

It is the harmonics of the associated pressure changes within the combustor structure during the phase from idle to higher thrust settings that cause the distinctive sound you are hearing.

Sure, it is the harmonics. Virtually no natural sound comes without them. More important are the "pressure changes within the combustor structure". I would call that a resonance and the effect is known as combustor howl which destroyed gas turbines before. Fortunately the pressure fluctuations are not that high in the PW1000.


Gruß, masi1157

r6russian wrote:

oldannyboy wrote:

Oh and the whine of a spooling up RB211 naturally!!! .

everybody knows that theres no better sound in aviation than the RB211 spooling up

RB211 spool up is music for the Aviator Soul.
Even the IAEs on the A320 have a little of a sweet note.It was more evident on the older A1s.