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ERJ145 "Hairdryer" Noise During Taxi  
User currently offlineCMH From United States of America, joined Jul 2010, 3 posts, RR: 0
Posted (4 years 1 week 3 days 6 hours ago) and read 4580 times:

I've wondered for years what this noise is - Embraer RJ-145, and just after coming into ORD yesterday, I hear the captain shut down one engine during taxi, and then I hear a hairdryer-like noise somewhere in the belly, but it changed pitch up and down quite a bit - think of a hairdryer with some massive voltage fluctuation. I thought it might be the APU, but it was clearly coming from underneath instead of the back, and an APU wouldn't change pitch so wildly. All of the flaps and slats were already returned, so it wasn't that either. Ideas?

12 replies: All unread, jump to last
 
User currently offlineCitationJet From United States of America, joined Mar 2003, 2425 posts, RR: 3
Reply 1, posted (4 years 1 week 3 days 4 hours ago) and read 4536 times:

Quoting CMH (Thread starter):
then I hear a hairdryer-like noise somewhere

It must have been an A340 taxiing by.......
     


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User currently offlineMadDogJT8D From United States of America, joined Oct 2009, 397 posts, RR: 1
Reply 2, posted (4 years 1 week 3 days 4 hours ago) and read 4533 times:

LOL CitationJet, that was awesome!  

User currently offlineDashTrash From United States of America, joined Aug 2006, 1520 posts, RR: 2
Reply 3, posted (4 years 1 week 3 days 4 hours ago) and read 4527 times:

That's an aux hydraulic pump.

User currently offlinebri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 4, posted (4 years 1 week 3 days 3 hours ago) and read 4509 times:

Quoting DashTrash (Reply 3):
That's an aux hydraulic pump.

   Yup,
Because

Quoting CMH (Thread starter):
the captain shut down one engine during taxi

and so some of the hydraulic system has to be powered by an electric pump.



Position and hold
User currently offlinewestern727 From United States of America, joined Jan 2007, 743 posts, RR: 4
Reply 5, posted (4 years 1 week 8 hours ago) and read 4180 times:

Sorry to go somewhat OT but I've noticed a high-pitch noise in the MD-80 (incl. the -88) and the DC-10 while at the gate, though the MD-80's seemed to be of a higher pitch. Electric hyd pump? Thanks in advance.


Jack @ AUS
User currently offlinemrocktor From United States of America, joined Jan 2005, 1668 posts, RR: 50
Reply 6, posted (4 years 6 days 8 hours ago) and read 4048 times:

Quoting western727 (Reply 5):
Electric hyd pump?

Very likely, if not the APU itself.


User currently offlinepilotpip From United States of America, joined Sep 2003, 3149 posts, RR: 11
Reply 7, posted (4 years 6 days 5 hours ago) and read 4013 times:

The captain shut down the #2 engine. The result is the electric driven hydraulic pump for the #2 system turning on to power the nose wheel steering. Quite annoying isn't it?


DMI
User currently offlinejetdoctor From United Kingdom, joined Aug 2001, 257 posts, RR: 0
Reply 8, posted (4 years 6 days 3 hours ago) and read 3973 times:

Indeed it is the #2 hydraulic pump, and the fluctuation in sound is the demand on the pump, either being the nose wheel steering or brake operation.
I personally find the noise very annoying, and often wonder if the fuel savings from single engine taxi outway the additional hours on an electric backup pump. #2 pumps are always going bad and have to be replaced.

Regards,

Jetdoctor



Break ground, and head into the wind. Don't break wind and head into the ground.
User currently offlineThePinnacleKid From United States of America, joined Feb 2005, 724 posts, RR: 8
Reply 9, posted (4 years 6 days 2 hours ago) and read 3965 times:

Quoting pilotpip (Reply 7):
The captain shut down the #2 engine. The result is the electric driven hydraulic pump for the #2 system turning on to power the nose wheel steering. Quite annoying isn't it?

Ummm... actually, that should be the #1 that was shut down... Most people that commute will single engine taxi on #1 because it is quieter in the back for the people because the engine driven hyd. pump would be running and not the elec. pump under the cabin... it is the #1 hyd. system that controls the nose wheel steering and also the culprit with the noise around mid cabin on the 145...

That said, a lot of guys like to single engine taxi on #2, and #2 is started first (during pushback) because when the engine is turning and the eng. driven hyd. pump is running it does NOT power the steering, there by allowing for simultaneous pushback operations... unlike starting #1 which must be done AFTER pushback... when on a towbar type push (non-electro)



"Sonny, did we land? or were we shot down?"
User currently offlinepilotpip From United States of America, joined Sep 2003, 3149 posts, RR: 11
Reply 10, posted (4 years 6 days 2 hours ago) and read 3943 times:

It's been a while. That's one of the things that's different on the 170.


DMI
User currently offlineThePinnacleKid From United States of America, joined Feb 2005, 724 posts, RR: 8
Reply 11, posted (4 years 5 days 23 hours ago) and read 3901 times:

Quoting pilotpip (Reply 10):
It's been a while. That's one of the things that's different on the 170.

I figured as such... hehe... just had to harass a fellow Jungle Jet driver =P safe flyin' mr.



"Sonny, did we land? or were we shot down?"
User currently offlineN243NW From United States of America, joined Jul 2003, 1628 posts, RR: 20
Reply 12, posted (4 years 5 days 15 hours ago) and read 3836 times:

ThePinnacleKid has it spot-on. I've heard the noise many times from the rear of the 145 series, and often I'll try to book a seat farther forward simply to avoid it. Sometimes even a couple rows can make a huge difference.

And yes, it appears that the protocol with many pilots is to taxi out on #2 to enable engine start during pushback and to taxi in on #1 to reduce passenger annoyance.



B-52s don't take off. They scare the ground away.
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