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CRJ Loud Noise When Parked: What Is It?  
User currently offlineLemmy From United States of America, joined Dec 2004, 258 posts, RR: 0
Posted (9 years 6 months 3 weeks 11 hours ago) and read 5429 times:

I flew from SBA to PHX the other day on a CRJ-200 and, as I was waiting at the bottom of the stairs, I heard an extremely loud noise that sounded like high-pressure air being released. This has happened the last few times I've flown on a CRJ. In all cases, the engines weren't running, but the APU was.

Any ideas what this noise is? It's not a big deal, but my ears are pretty sensitive from years of unprotected rock and roll, so I've taken to walking up to the airplane with my fingers in my ears, which looks kinda funny (about par for the course with me, though).


I am a patient boy ...
29 replies: All unread, showing first 25:
 
User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 1, posted (9 years 6 months 3 weeks 11 hours ago) and read 5299 times:

This sound comes from the APU. The APU electronic control unit (ECU) operates the load control valve (LCV) to close, if bleed air is selected and the EGT reaches a predetermined level. As the EGT drops, the ECU commands the LCV to open again. This pulse action from the ECU is done by the LCV for modulating purposes.

In other words: this sound is normal when the APU runs on ground and the air conditioning packs are selected to "on". By the way, I noticed that noise on CRJ´s only. Never heard it on other aircrafts.




This job sucks!!! I love this job!!!
User currently offlineLemmy From United States of America, joined Dec 2004, 258 posts, RR: 0
Reply 2, posted (9 years 6 months 3 weeks 4 hours ago) and read 5160 times:

Any idea what pressure the bleed air is at when the LCV opens? Sounds pretty high to me.


I am a patient boy ...
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 3, posted (9 years 6 months 2 weeks 6 days 22 hours ago) and read 5110 times:

Where is the outlet of the LCV located.
regds
MEL



Think of the brighter side!
User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 4, posted (9 years 6 months 2 weeks 6 days 21 hours ago) and read 5105 times:

Lemmy:
If I remember right, the APU bleed air pressure is somewhere around 41 PSI. My training manuals are at work, maybe someone here may correct me if I´m wrong with this.

Hawk:
The LCV is installed on top of the APU. It opens the APU bleed port to the bleed duct to supply the aircraft system.



This job sucks!!! I love this job!!!
User currently offlineWoodreau From United States of America, joined Sep 2001, 1038 posts, RR: 6
Reply 5, posted (9 years 6 months 2 weeks 6 days 14 hours ago) and read 5058 times:

Before the LCV opens and the engines aren't running the 10th stage bleed air manifold pressure should be 0 psi. But after the LCV is open it's should be at least 40psi. That's the minimum pressure for an engine start utilizing the APU as the starting air source.


Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 6, posted (9 years 6 months 2 weeks 5 days 22 hours ago) and read 4957 times:

Thanks Troubleshooter.
regds
MEL



Think of the brighter side!
User currently offlineCRJ200Mechanic From United States of America, joined Feb 2005, 204 posts, RR: 2
Reply 7, posted (9 years 6 months 2 weeks 3 days 19 hours ago) and read 4860 times:

Quoting Troubleshooter (reply 4):
If I remember right, the APU bleed air pressure is somewhere around 41 PSI.


I've always seen it around 43 to 46psi

You should hear it when its cold outside and the apu intake has sucked in some ice!



Always remember the responsibilies you hold with an A&P license
User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 8, posted (9 years 6 months 2 weeks 3 days 9 hours ago) and read 4800 times:

CRJ200Mechanic:

I stand corrected. The 41 PSI were just a guess out of my memory. I´ve seen no CRJ from inside for about 6 months now and I have actually no access to my training manuals or the AMM.



This job sucks!!! I love this job!!!
User currently offlineCRJ200Mechanic From United States of America, joined Feb 2005, 204 posts, RR: 2
Reply 9, posted (9 years 6 months 2 weeks 3 days 4 hours ago) and read 4780 times:

Troubleshooter

My applause for such a close guess. I thought about it later and do remember some of the older CRJ's showing about 41

I have access to the manuals if you are ever interested



Always remember the responsibilies you hold with an A&P license
User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 10, posted (9 years 6 months 2 weeks 3 days 3 hours ago) and read 4771 times:

I´ve worked on CRJ100/200. They are "very" old, because they are operated by the CRJ launch customer. Maybe this explains it.


This job sucks!!! I love this job!!!
User currently offlineCRJ200Mechanic From United States of America, joined Feb 2005, 204 posts, RR: 2
Reply 11, posted (9 years 6 months 2 weeks 3 days ago) and read 4757 times:

wow, you were working on some of the very first. Did they still have the tail skids installed?


Always remember the responsibilies you hold with an A&P license
User currently offlineTito From United States of America, joined Feb 2001, 125 posts, RR: 1
Reply 12, posted (9 years 6 months 2 weeks 2 days 23 hours ago) and read 4754 times:

The sound is definitely a result of the LCV closing, however it appears as if the LCV closes in response to the EGT rising momentarily FIRST (you can observe the EGT rise followed by the corresponding noise and resulting EGT decrease). My guess is that the EGT rise is a result of the variable inlet guide vanes being modulated (intentionally?), the LCV is just doing what it's supposed to do to keep the combustion cooler. I haven't heard this happening with any other aircraft so perhaps this guidevane cycling is unique to this APU. Is this a result of system logic exercising the guide vanes or just modulating the guide vanes as a way to induce modulation of the LCV?

User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 13, posted (9 years 6 months 2 weeks 2 days 22 hours ago) and read 4752 times:

CRJ200Mechanic:
Yes, the tail skids are still installed. Some of the first CRJ100 will be returned to Bombardier. Retired from service with Lufthansa CityLine.

Tito:
The variable guide vanes are commanded to open when bleed air is extracted. This allows a higher mass flow through the compressor caused by the higher air demand. As more air is available, the EGT will not rise above the given limits. The only modulating part in this circuit is the LCV. The variable guide vanes are simply commanded open or close.



This job sucks!!! I love this job!!!
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 14, posted (9 years 6 months 2 weeks 2 days 22 hours ago) and read 4748 times:

Quoting Troubleshooter (reply 13):
Yes, the tail skids are still installed.


Any Pics of these Tail Skids.
regds
MEL



Think of the brighter side!
User currently offlineCRJ200Mechanic From United States of America, joined Feb 2005, 204 posts, RR: 2
Reply 15, posted (9 years 6 months 2 weeks 2 days 21 hours ago) and read 4744 times:

Quoting Troubleshooter (reply 13):
The variable guide vanes are commanded to open when bleed air is extracted. This allows a higher mass flow through the compressor caused by the higher air demand. As more air is available, the EGT will not rise above the given limits. The only modulating part in this circuit is the LCV. The variable guide vanes are simply commanded open or close


right on the money troubleshooter



Always remember the responsibilies you hold with an A&P license
User currently offlineCRJ200Mechanic From United States of America, joined Feb 2005, 204 posts, RR: 2
Reply 16, posted (9 years 6 months 2 weeks 2 days 20 hours ago) and read 4739 times:

HAWK21M

I found some pictures for the tail skid. I accidently posted them under the topic lightening diverters. Sorry about the mistake



Always remember the responsibilies you hold with an A&P license
User currently offlineTito From United States of America, joined Feb 2001, 125 posts, RR: 1
Reply 17, posted (9 years 6 months 2 weeks 2 days 12 hours ago) and read 4718 times:

Quoting Troubleshooter (reply 13):
The variable guide vanes are commanded to open when bleed air is extracted. This allows a higher mass flow through the compressor caused by the higher air demand. As more air is available, the EGT will not rise above the given limits. The only modulating part in this circuit is the LCV. The variable guide vanes are simply commanded open or close.


Thanks troubleshooter. What puzzles me is that the EGT spikes (to the top of the green arc) momentarily which sets this whole thing into motion, and every CRJ i've seen does this constantly. What causes this spike? This is just sitting there with a constant AC and air load. I've tried timing it but there seems to be no discernable pattern to its frequency, and some airplanes are worse than others, but they all do it.


User currently offlineCRJ200Mechanic From United States of America, joined Feb 2005, 204 posts, RR: 2
Reply 18, posted (9 years 6 months 2 weeks 2 days 7 hours ago) and read 4695 times:

TITO

the older airplanes tend to do it more often because the APu's are getting tired and worn out



Always remember the responsibilies you hold with an A&P license
User currently offlineUndehoulli From , joined Dec 1969, posts, RR:
Reply 19, posted (9 years 6 months 2 weeks 2 days 7 hours ago) and read 4692 times:

What about the packs??? Those can get awufully noisy with the bleed air running through them, those compressors spinning and all! On the ERJ one pack is located on each side underneath the fuselage just ahead of the wings. Pack 1 is on the boarding side. It's so noisy that a lot of times it isn't even run during passenger boarding. That's why it gets so damn hot in the flight deck - pack 1 supplies 80% of the air for the flight deck and only 20% for the cabin. Pack 2 does the opposite. I am not a CRJ expert but am in the aircraft systems groundschool right now, so hopefully soon I'll know more before long. I do know that on the ERJ the APU bleed valve is either open or closed. I'll have to ask if the LCV has variable settings in the CRJ.

User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 20, posted (9 years 6 months 2 weeks 2 days 5 hours ago) and read 4679 times:

Undehoulli:

The packs of the CRJ are not as loud as the ERJ packs.

Air distribution on the ERJ is as follows:
Pack 1 56% cockpit - 44% cabin
Pack 2 100% cabin
A total of 28% air from both packs is routed to the cockpit and the remaining 72% of both packs supply the cabin.
The operation of the APU LCV on the ERJ depends on the APU type installed. On the "-C11" APU the valve is simply commanded open or close. The air flow is limited by a flow limiter venturi. On the "-C14" APU the LCV modulates bleed pressure and air flow.

I know this answer is not related to the original topic, but I think it is worth to be discussed here.



This job sucks!!! I love this job!!!
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 21, posted (9 years 6 months 2 weeks 2 days 1 hour ago) and read 4647 times:

Quoting CRJ200Mechanic (reply 16):
I found some pictures for the tail skid. I accidently posted them under the topic lightening diverters. Sorry about the mistake


No prob,I've seen them.Thanks.
Have you got any close views Available.
regds
MEL



Think of the brighter side!
User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 22, posted (9 years 6 months 2 weeks 1 day 23 hours ago) and read 4643 times:

Hi Hawk,

this is the closest view I could find. You can see the tail skid on the aft fuselage below the "A" of the tail registration. Hope this helps.

View Large View Medium
Click here for bigger photo!

Photo © Charles Falk




This job sucks!!! I love this job!!!
User currently offlineCRJ200Mechanic From United States of America, joined Feb 2005, 204 posts, RR: 2
Reply 23, posted (9 years 6 months 2 weeks 1 day 16 hours ago) and read 4613 times:

Quoting HAWK21M (reply 21):
Have you got any close views Available



those were the closest views I could find. the A/C I work on are too new and don't have them. Next time I get a comair callout I will take my digital camera with me and see if it has one. Comair is the only operator that flys into Tulsa with them. I will see what I can do.



Always remember the responsibilies you hold with an A&P license
User currently offlineCRJ200Mechanic From United States of America, joined Feb 2005, 204 posts, RR: 2
Reply 24, posted (9 years 6 months 2 weeks 1 day 16 hours ago) and read 4610 times:

Quoting Undehoulli (reply 19):
I'll have to ask if the LCV has variable settings in the CRJ



The CRJ's is either open or closed. The exact ratio's for the packs I don't know. All I do know is that the left pack supplies the flight deck and right pack is for the cabin



Always remember the responsibilies you hold with an A&P license
25 RJ : CRJ: Left pack supplies 70% to the flight deck and 30% to the cabin. Right pack is the opposite, 70% to the cabin and 30% to the flight deck. Thanks f
26 CRJ200Mechanic : Thanks for giving me some info I should already know, since I work on the things. Thanks for the info. I have often wondered
27 HAWK21M : How Vunerable are the CRJ MLGs to collapse. regds MEL
28 CHQIAH : I'm leaning about 99% to the APU, however, just for the sake of boredom, it had about a 1% chance (if the a/p was a line base for the airline's mx) of
29 JoseKMLB : I love that APU in the winter its like a small fire place boy does it keep you warm...
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