Crank From Canada, joined May 2001, 1556 posts, RR: 2 Posted (10 years 6 months 3 weeks 3 days 12 hours ago) and read 2634 times:
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?
Goboeing From United States of America, joined Jun 2000, 2662 posts, RR: 15 Reply 3, posted (10 years 6 months 3 weeks 2 days 13 hours ago) and read 2249 times:
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.
AussiePete From Australia, joined May 2003, 72 posts, RR: 0 Reply 6, posted (10 years 6 months 3 weeks 1 day 14 hours ago) and read 2064 times:
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.
AWspicious From , joined Dec 1969, posts, RR: Reply 7, posted (10 years 6 months 3 weeks 1 day 10 hours ago) and read 2021 times:
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.
747Teach From United States of America, joined Nov 2000, 176 posts, RR: 1 Reply 8, posted (10 years 6 months 3 weeks 1 day 2 hours ago) and read 1992 times:
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,
AussiePete From Australia, joined May 2003, 72 posts, RR: 0 Reply 10, posted (10 years 6 months 2 weeks 6 days 9 hours ago) and read 1864 times:
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 From United States of America, joined Nov 2000, 176 posts, RR: 1 Reply 11, posted (10 years 6 months 2 weeks 6 days 5 hours ago) and read 1830 times:
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,
AussiePete From Australia, joined May 2003, 72 posts, RR: 0 Reply 13, posted (10 years 6 months 2 weeks 5 days 17 hours ago) and read 1790 times:
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!