Engine noises on take-off

[JohnnyRocket]

Might seem like a silly question, but on take-off, the engine noises on some jets, like A330 or B757 are very loud and you can alsmost hear a "vibration" in the noises that can be heard.

This noise soon calms down and fades away after about 10 to 12 minutes, even though the aircraft is still climbing.

Can someone tell me what is this noise and why does it just gradually fade away - almost without noticing?

[Bullethead]

G'day Johnny,
I fly a B767 and climb thrust is normally set at 1000' above the runway elevation, so you get a reduction in engine noise then and as the airspeed builds the engine noise tends to get left behind and is muffled by increasing airspeed noise.
The 'vibration' could be a resonance caused by slightly different rpms of the two engines.
Regards,
BH

[Chris777]

"Climb thrust"...??

In the cabin, some of these jets really sound like they're going to dismantle on the runway they rattle so much. I mean brand new 737-800s too.

Can I add my own question?

There is often a palpable bumping noise all the way along the run way on take-off roll. Is this the centre-line being tracked perfectly?

Thanks!
Chris

[PaperTiger]

Are you by chance referring to the growl or "buzzsaw" noise ?
There's a long thread in the Tech Log about it.
It diminishes as the power is reduced during climb. (Takeoff is a higher setting of course).

[AR1]

There is a certain amount of resonance experienced, and its prominent in the A319/320 series. Dont recall it in my 2 757 flights nor 767.

I do recall having a near ****ng myself expeirence on an A320 out of Minneapolis, when a meal trolley came loose and made an 'inappropriate' bang on climb out** - of course it could have been worse, I could have been on a DC9.

** Cheapskate was sat in the seats backing on to the galley.

[chiglet]

It's the cats eyes in the centreline.

C'mon Rainboe they are called Runway Certreline Lights....Cats Eyes are what you get:-
a, in a cat
b, Reflective Glass held ib a rubber/plasticised covering to reflect the beams of "Motor Vehicle Lights" to enhance safety,[ie marking lanes] on the Queens Highway.
I made that lot up.......
watp,iktch

[AlphaWhiskyRomeo]

Aren't most runway centreline lights to one side of the white centreline to allow nosewheels to track the white line without bumping over the lights?

[Raven30]

They wouldn't be centreline lights then though, would they!

......and ours ARE on the centreline!

[chiglet]

The Trident was the most civilised a/c.......offset nose wheel
watp,iktch

[Chris777]

Is this why pilots sometimes line up "just right of the centre line"? (Those of you who've seen the Cathay Pacific 747-400 DVD might remember Capt Don Grange explaining this to his F/O) I always assumed it was to do with the weather, but then I'm a PAX.

I did wonder if they were really called cats eyes in aviation speak, but didn't want to annoy Rainboe by saying anything...

[chiglet]

Chris,
Say "Nowt"....Rainboe gets annoyed
Say "Owt".....Rainboe gets VERY annoyed........[I have heard that it "could be PMT", but I find that hard to believe.....
watp.iktch

[Chris777]

I noticed, chiglet
By the way, was my assessment of lining up just off the centre-line correct?