crank
Posts: 1524
Joined: Tue May 22, 2001 11:42 pm

777 Braking Sound

Sun May 25, 2003 1:09 pm

This might sound like a stupid question, but yesterday when I was plane spotting I heard a strange sound coming from 2 777s (MS and BA). Just as the planes were about to exit the runway I could hear something that sounded just like a train when the brakes are applied. The sound lasted for about 5 seconds.

Is this common to the 777? I've never heard it from any other plane. Or could it be something other than the brakes?

Thanks
 
CX Flyboy
Posts: 6026
Joined: Sun Dec 26, 1999 6:10 pm

RE: 777 Braking Sound

Sun May 25, 2003 4:23 pm

Not neccessarily peculiar to the 777 it is not uncommon for aircraft to have squeaky brakes.
 
covert
Posts: 1500
Joined: Sun Oct 21, 2001 1:02 am

RE: 777 Braking Sound

Mon May 26, 2003 11:06 am

I was standing not far from the threshold of a runway once while a SAA 767 was landing and from the sound of the squeal I thought that aircraft was a done deal...

The last time I heard that sound (or -10 times magnification) the 18-wheeler rolled off the bridge....

But ZS-SRB made it... Seemed pretty routine.
none
 
goboeing
Posts: 2429
Joined: Mon Jun 05, 2000 5:31 am

RE: 777 Braking Sound

Mon May 26, 2003 12:17 pm

Here's a similar question: I've noticed several times while spotting, mainly at MHT and DCA near the end of the runways, a loud but low noise as a jet taxied into position for takeoff. Is this brakes being applied? Or is it a slight difference in engine power?

Back on topic, the noisiest brakes I've heard from inside a plane was on a UAL 727 as we went from about 40kts to 10 turning off the high speed taxiway onto the parallel at COS.

Nick
 
rendezvous
Posts: 531
Joined: Sun May 20, 2001 9:14 pm

RE: 777 Braking Sound

Mon May 26, 2003 1:32 pm

The sound you mention sounds similar to what I have heard on 747's as they exit the runway, from what I can tell it's the flaps, but I'm not on that.
 
goboeing
Posts: 2429
Joined: Mon Jun 05, 2000 5:31 am

RE: 777 Braking Sound

Tue May 27, 2003 11:47 am

If you're talking about my post, it's definetely not the flaps. They certainly can't be heard going up or down over 2 or more jet engines, even at idle. It's a loud humming noise.

Nick
 
AussiePete
Posts: 70
Joined: Tue May 27, 2003 10:35 am

RE: 777 Braking Sound

Tue May 27, 2003 12:05 pm

Airplanes with carbon brakes often exhibit a resonance from the brake stack (heat sink) which can be worse if the heat sink is not in the ideal heat range. The B763 fitted with Allied Signal brakes was very bad and in many cases the vibes and noise were bad enough to cause issues with landing gear components. The fix is there, however on all carbon stack airplanes some vibes still exist (ever wondered why carbon brakes aren't on even the most expensive road cars?).

More often than not the brakes are noisy when too COLD. Some operators use idle reverse landings to provide increased brake temps and hence reduced wear and vibes. Also, soem brake stacks run through a resonant frequency which may be what you are hearing (multiple degree of freedom system running numerous natural resonance frequencies - almost unavoidable).

I believe brakes with rebuilt heat sinks (half thickness carbon rotors/stators rivetted together to give second life) tend to be noisier.

Don't know if this is what you heard though...
 
AWspicious
Posts: 2780
Joined: Fri Sep 14, 2001 7:47 am

RE: 777 Braking Sound

Tue May 27, 2003 4:05 pm

I recall the times I was a passenger on BWIA's L1011s. I would hear the brakes making a low humming tone. Seemed normal to me. However, I don't recall hearing it on the AC 727s or the SSV 320 I've been on.
One noise I sometimes hear comes from the 747s... Mostly BA's. It's a quick whiney noise... Like something being activated, but, only moving a small distance. I'd like to know what makes that sound.

Regards
AW
Nevermind political correctness - Envision using your turn signals!
 
747Teach
Posts: 176
Joined: Wed Nov 29, 2000 3:05 am

RE: 777 Braking Sound

Tue May 27, 2003 11:40 pm

Crank, Squealing or groaning brakes are pretty common to larger aircraft. Some other folks here mention hearing a loud "whine" sound. On the 747 aircraft, the whine may be the 4 pneumatic power drive units that drive the four leading edge flap/slat groups up and down. This can certainly be heard above the sound of idling engines. A similar sound comes from the pneumatic drive for the thrust reversers (on aircraft that have pneumatic reversers). Both sounds last for about 3 seconds. Regards,
 
rendezvous
Posts: 531
Joined: Sun May 20, 2001 9:14 pm

RE: 777 Braking Sound

Thu May 29, 2003 3:05 pm

747Teach, that's what I was referring to, not at least I know what /that/ is exactly.
 
AussiePete
Posts: 70
Joined: Tue May 27, 2003 10:35 am

RE: 777 Braking Sound

Thu May 29, 2003 4:27 pm

747 Teach:
You'd be hard pressed to hear the pneumatic operated reversers on most models as they still use pneumatic piston type actuators (I can't remember whether it was GE or PW who was pneumatic but one is air and the other hydraulic). However, RB211 and their Trent cored engines mounted to 747 are noisy as they use the air operated motor driving cables and gearboxes.

I need a refresher on the 777 reversers, however I remember they do not use the RB211 type system and are in fact quite quiet in comparison.
 
747Teach
Posts: 176
Joined: Wed Nov 29, 2000 3:05 am

RE: 777 Braking Sound

Thu May 29, 2003 8:51 pm

AussiePete: I've been around 747's with the JT-9 engines all day, every day, and have been, for about 20 years. I've also worked 747's with the RB-211 engine. I can assure you the pneumatic motors that drive the reversers can be heard, even from some distance, and even with the engines at idle. On the JT-9, the translating sleeve drive motor is pneumatic, and the sleeve is driven by cables and ball screw actuators (AMM 78-30-00, Page 2, Fig. 1), not pistons. Regards,
 
CX Flyboy
Posts: 6026
Joined: Sun Dec 26, 1999 6:10 pm

RE: 777 Braking Sound

Thu May 29, 2003 9:27 pm

I heard the flaps retract the other day on a GE powered 747-200F.
 
AussiePete
Posts: 70
Joined: Tue May 27, 2003 10:35 am

RE: 777 Braking Sound

Fri May 30, 2003 8:44 am

747 Teach:
Sorry you are correct. Given the current market JT9D powered 747s are very rare in my part of the world (i.e. dead). Hence I was referring more to the later PW4000 etc. Plus the original question was related to the 777.

I fondly remember the days of the JT9D coal burners with their low oil usage, lack of oil leaks, easy maintainability....NOT!
 
L-188
Posts: 29881
Joined: Wed Jul 07, 1999 11:27 am

RE: 777 Braking Sound

Fri May 30, 2003 9:30 pm

Hear the surfaces going up on 747's all the time at work. Especially this summer with all the traffic turing off the runway 500 feet out my office window.
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