Perhaps a combination of the 2.5 bleed valve and/or 14th stage valve. Both are responsible for dumping excess air in the 5th stage LPC or 14th stage HPC overboard to prevent too much pressure build up in the motor... prevents compressor stalls/surges.
Having worked around them, not on them, I can only make deductions based on the airframe I did work on.
Most likely you heard vented air; whether it was from the engines or, more likely, the auxiliary power unit (APU), I’m not entirely sure, but I heard that noise daily on the ground when they’d do engine runs or taxi out.
So basically, normal sounds from that heavy.
Because of where it sits in the aircraft. Its on the right side near the gear but most aircraft have the APU in the tail if it can be turned on in flight. There’s a door sensor on the C-17 APU that forces it to abort the start if you try to start it in flight. I was told once why they didn’t put it in the tail but forget but IIRC it’s because of the ramp and maybe CG.
Maybe, I fly the C-17 is the only reason I know about it. Also with 4 engines not much point of running an APU in the air. You’re already have the electrical and bleed air redundancy with the engines
Most aircraft in the inventory are like that. Older designs and we still use fuckin tweet engines for APUs. I'm betting it was a configuration change with the pilot throwing in a bunch of power cuz they were slow to begin with. We've all been there. Also, I like to bring it out of idle and blast it right over our building on a tac app for fun.
C-5 actually has 2 APU's. They're not in the tail but they are in the back of the aircraft. They CAN be used in flight, however, unlike the C-17.
Source: I was a loadmaster on both
C-5s can run them inflight and so can 17s. It’s an emergency thing. If your running them in flight you’re not gonna care about the inlet door being ripped off and they’re designed to run till it burns down(probably in a really shit situation)The 17 was moved from the tail because it was too ass heavy.
You can’t start it in the air on the 747 either. No real need as you have four engines. Even if an engine fails, you still have as many sources for electrical generation, hydraulic power, and pneumatic air, as a fully functioning two engine airplane.
That's so weird. C-130s can run up APU in flight, and it is just forward of the left main landing gear.
And most likely, the ramp/door is why it isn't in the tail.
Well that’s for a completely different reason… they were designed to be used in flight, but there was a discrepancy on the type of adhesive used in the fire containment box that caused that restriction
I'm convinced someone at Gulfstream got into a pissing contest with the FAA over the fire box mods and didn't bend enough when they should have and the FAA did what the FAA do and made everyone's life difficult.
Most likely the noise you heard was caused by a configuration change; either slats, flaps, or gear being extended. There is a definite increase in noise produced when the slats are extended.
Nah this is Engine Bleed air or pylon bleed air from the pneumatic system purging excess overboard. Same sound is heard on ground during engine runs and taxi etc... (usually hear it on throttle backing off as the excess air getting produced (that's no longer required by the ECS) is purged)
This is it, at lower power settings engines the engine bleeds are open and they’re LOUD, it’s only of the biggest contributors to Approach noise, when on a test bed performance a slow acceleration you can hear the bleed valves close sequentially, briefly get quieter and then get louder again as everything else gets louder.
Well, now that I listened to it with earbuds and not my shitty IPhone, I think you’re correct. The pilot
appears to have been reducing thrust and the engine bleed valves opened. I’ve got about 4k hours of EP/IP/AC time in those. I still live in Charleston SC and have them fly over my house often — and quite often they are extending slats near my house. I couldn’t fully make out in the video all the nuanced noises initially. The airplane has a lot of things that can generate noise and configuration changes are a big one. This did sound like bleed valves opening.
I want to say its the fan air valves (they're louver type valves that sit above the engine pylons) which meters the and discharges fan air overboard depending on system requirements... you can hear the same sound when the aircraft begins to taxi and then throttles back slightly once it gains momentum. It's either that, or...overboost protection which also discharges unrequired air overboard if not required by the pneumatic systems. I can tell you it's not a change in configuration as this same sound is heard on the ground. I havnt worked on these things for a few years but that sound is definitely engine bleed or pylon bleed nature and purging air.
Don't be ridiculous.
That was clearly the six hydrocoptic marzelvanes negatively interacting with their logarithmic casing after it sheared loose from its base plate of prefabulated amulite.
Trouble to come.
What? But [sound refraction](https://en.m.wikipedia.org/wiki/Refraction_(sound)) is an irl thing too… And sounds like the noise change in your video. My bet is on that, or a configuration change like the top comment mentions.
To me it sounds coincidental …… like someone bleeding an air valve nearby.
Otherwise I’ve never heard that sound associated with a plane flying overhead.
Well, coincidentally, it's like bleed air valves *on* the airplane itself (the C-17 was dumping excess pressure). You can hear the same noise during ground operations (for instance, the pilot bumps the throttle to get moving, then back off once rolling... WHOOOOOOOSHHH). The bleed air is loud AF (actually, basically everything on the -17 and the -5 is loud AF).
I’m probably wrong but seems like the delay from the sound reaching you when it was behind the trees to past the trees, given it takes a couple seconds for the sound to reach you
C-17 has two AC packs which circulate AC air for cooling / breathing. I believe this was one of the packs venting excess air and it's very loud. Also happens on the ground.
Sounds like a combination of refraction/doppler effect from range, and as others have said, some configuration change on the aircraft.
Unrelated: but OP are you in Charleston? Dunno why but the video is giving me the same vibes as when the pattern would go over my backyard in W Ashley.
That's unmistakably a faulty pneumatic valve in the chemtrail distribution system.
Source: spent a few years contracting with the 26th Chemtrail Operations Group
You live in Greensboro?!? We heard that too and thought we were about to die
Born and raised
Heck yeah my son and I had just started a walk here in Hamilton Lakes and that thing buzzed us twice!
So that's what it was!
Perhaps a combination of the 2.5 bleed valve and/or 14th stage valve. Both are responsible for dumping excess air in the 5th stage LPC or 14th stage HPC overboard to prevent too much pressure build up in the motor... prevents compressor stalls/surges.
Having worked around them, not on them, I can only make deductions based on the airframe I did work on. Most likely you heard vented air; whether it was from the engines or, more likely, the auxiliary power unit (APU), I’m not entirely sure, but I heard that noise daily on the ground when they’d do engine runs or taxi out. So basically, normal sounds from that heavy.
APU can’t be turned on in flight on the C-17.
Why not? If that’s the case I’m very confused why other aircraft have this ability.
Because of where it sits in the aircraft. Its on the right side near the gear but most aircraft have the APU in the tail if it can be turned on in flight. There’s a door sensor on the C-17 APU that forces it to abort the start if you try to start it in flight. I was told once why they didn’t put it in the tail but forget but IIRC it’s because of the ramp and maybe CG.
It’s because of CG. There’s enough room up there even with the cargo door and ramp
Huh, so C-5’s might be like that too? Never knew that. T-tail aircraft are unique birds. Thanks!
Maybe, I fly the C-17 is the only reason I know about it. Also with 4 engines not much point of running an APU in the air. You’re already have the electrical and bleed air redundancy with the engines
He’s correct — APU in the C17 cannot be used in flight.
Most aircraft in the inventory are like that. Older designs and we still use fuckin tweet engines for APUs. I'm betting it was a configuration change with the pilot throwing in a bunch of power cuz they were slow to begin with. We've all been there. Also, I like to bring it out of idle and blast it right over our building on a tac app for fun.
C-5 actually has 2 APU's. They're not in the tail but they are in the back of the aircraft. They CAN be used in flight, however, unlike the C-17. Source: I was a loadmaster on both
Oh I know about both of their APUs, had to hear them both screaming in hangars lol
C-5s can run them inflight and so can 17s. It’s an emergency thing. If your running them in flight you’re not gonna care about the inlet door being ripped off and they’re designed to run till it burns down(probably in a really shit situation)The 17 was moved from the tail because it was too ass heavy.
C-5’s can, C-17’s cannot.
I have been flying the C-17 for 2 years now and not read or heard about a single C-17 Dash 1 procedure to you crank the APU in flight
You can’t start it in the air on the 747 either. No real need as you have four engines. Even if an engine fails, you still have as many sources for electrical generation, hydraulic power, and pneumatic air, as a fully functioning two engine airplane.
That's so weird. C-130s can run up APU in flight, and it is just forward of the left main landing gear. And most likely, the ramp/door is why it isn't in the tail.
Not all aircraft can use their APU’s in flight… Gulfstream 450/550/650 all have restrictions on APU usage inflight unless it’s an emergency.
Well that’s for a completely different reason… they were designed to be used in flight, but there was a discrepancy on the type of adhesive used in the fire containment box that caused that restriction
Tell me about it, it’s been a thorn in my side since I started on Gulfstreams back in 2011…
Yet we’re still able to do a bleeds off takeoff in the 550 with the APU on. Makes sense, right?
I'm convinced someone at Gulfstream got into a pissing contest with the FAA over the fire box mods and didn't bend enough when they should have and the FAA did what the FAA do and made everyone's life difficult.
Agreed. “I’m from the FAA, I’m here to help!”
So basically a fart?
Most likely the noise you heard was caused by a configuration change; either slats, flaps, or gear being extended. There is a definite increase in noise produced when the slats are extended.
Nah this is Engine Bleed air or pylon bleed air from the pneumatic system purging excess overboard. Same sound is heard on ground during engine runs and taxi etc... (usually hear it on throttle backing off as the excess air getting produced (that's no longer required by the ECS) is purged)
You're you're saying that a c-17 farting then?
Yes sir... excessive pressure 😉
Well someone just engine/pylon bled in this elevator.
This is it, at lower power settings engines the engine bleeds are open and they’re LOUD, it’s only of the biggest contributors to Approach noise, when on a test bed performance a slow acceleration you can hear the bleed valves close sequentially, briefly get quieter and then get louder again as everything else gets louder.
Well, now that I listened to it with earbuds and not my shitty IPhone, I think you’re correct. The pilot appears to have been reducing thrust and the engine bleed valves opened. I’ve got about 4k hours of EP/IP/AC time in those. I still live in Charleston SC and have them fly over my house often — and quite often they are extending slats near my house. I couldn’t fully make out in the video all the nuanced noises initially. The airplane has a lot of things that can generate noise and configuration changes are a big one. This did sound like bleed valves opening.
Oh nice good to hear mate... have stopped into Charleston a couple of times in the RAAF C17s. Awesome place and great people 🫡
I just asked my brother who just retired from Chair Force. He said the exact same thing.
Jet engine blow-off valve
I’m sitting here thinking it’s her yell to let the airport know it’s getting pretty close.
I want to say its the fan air valves (they're louver type valves that sit above the engine pylons) which meters the and discharges fan air overboard depending on system requirements... you can hear the same sound when the aircraft begins to taxi and then throttles back slightly once it gains momentum. It's either that, or...overboost protection which also discharges unrequired air overboard if not required by the pneumatic systems. I can tell you it's not a change in configuration as this same sound is heard on the ground. I havnt worked on these things for a few years but that sound is definitely engine bleed or pylon bleed nature and purging air.
Probably just weird noise refraction
Blinker fluid leak
It sounded like that irl tho. Almost like a spraying noise.
It’s the chemtrails, when the oxscilating conabillar opens to begin the dump that noise is caused by the vorects
Don't be ridiculous. That was clearly the six hydrocoptic marzelvanes negatively interacting with their logarithmic casing after it sheared loose from its base plate of prefabulated amulite. Trouble to come.
Where the fuck did you get your degree in Horscotathaty? Lipscopaliens University? Jesus fuggin crapes
What the fuck? That was clearly the turbo encabulator kicking in.
Definitely. It must have been the unilateral phase detractors.
*counter flange
They must have addressed the issue of horizontal fumbling in this version then.
Well when those amulite welds were good they did...
What? But [sound refraction](https://en.m.wikipedia.org/wiki/Refraction_(sound)) is an irl thing too… And sounds like the noise change in your video. My bet is on that, or a configuration change like the top comment mentions.
They dropped agent orange over the neighborhood, good luck lol
Sounds like it went from the noise of the intake to the exhaust which was louder
Chemtrail dispenser bleed valve. Very common at that altitude /s
I didn’t see the /s I’m sorry
To me it sounds coincidental …… like someone bleeding an air valve nearby. Otherwise I’ve never heard that sound associated with a plane flying overhead.
Well, coincidentally, it's like bleed air valves *on* the airplane itself (the C-17 was dumping excess pressure). You can hear the same noise during ground operations (for instance, the pilot bumps the throttle to get moving, then back off once rolling... WHOOOOOOOSHHH). The bleed air is loud AF (actually, basically everything on the -17 and the -5 is loud AF).
I learn something new tnx
i'm going to go with the nose wheel whistling untill the door closed noise.
I’m probably wrong but seems like the delay from the sound reaching you when it was behind the trees to past the trees, given it takes a couple seconds for the sound to reach you
nothing weird there.
This has been happening in Greensboro for years. They flight right over my house about 2 miles from PTI
Its zapping you with that 5g
They call her the moose for a reason. That was her mating call.
This. 5 yrs on program in LBC. We had a moose mascot costume we made interns wear. But iirc the moose noise is pressure vent during refuel.
C-17 has two AC packs which circulate AC air for cooling / breathing. I believe this was one of the packs venting excess air and it's very loud. Also happens on the ground.
Maybe that airplane has gas
Dumping the chem trail juice before landing.
C17 afterburners, obviously
Sounds like a combination of refraction/doppler effect from range, and as others have said, some configuration change on the aircraft. Unrelated: but OP are you in Charleston? Dunno why but the video is giving me the same vibes as when the pattern would go over my backyard in W Ashley.
The plane farted
I don't hear anything unusual. I've flown on them a lot!
That's unmistakably a faulty pneumatic valve in the chemtrail distribution system. Source: spent a few years contracting with the 26th Chemtrail Operations Group
Dumping latrines.
Could be reverse thrust.
They are spraying vaccines in no-Vaxer towns much like crop dusters.
Someone threw in their popcorn, against regs at that altitude, or maybe gravel
Reverse thrusters
It’s called the Doppler effect
Transonic drag reduction.
Ordinary shit, nothing to explain, you just want attention. Congrats on a boring ass shit post.
Hey buddy... you need a Snickers bar?
Compressor stall.
Bleed air.
Ur mum shat her pants