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Nutella_BC
18th Feb 2008, 05:35
Flew on an Air Canada 777LR (Toronto-Vancouver-Sydney) and was quite surprised by how loud the engines were during start up. Many passengers were alarmed by the noise. I also notice that the whole plane was shaking during start up as well. Idling is also loud and the engines doesn't seem smooth at all. Remind me of a propeller plane
Yet underway, I was surprised how quiet the engines turned out to be during take off ?
Is that 777 specific ?

TightSlot
18th Feb 2008, 15:11
Was it very cold? - on some occasions, power may be applied and then reduced after de-iceing, and before take-off. I don't know why this happens but assume it is related to clearing the gloop out of the engines?

The African Dude
18th Feb 2008, 16:23
Could be to do with balancing. My university studies didn't cover balancing for aero engines but larger turbomachines (gas turbines and generators for industrial power generation, for example) need to be balanced - i.e. the centrifugal loading along the shaft needs to be distributed in such a way that there is no left-over, or resultant force, which would result in vibration. Balancing is done by adding small masses along the shaft at calculated points.

It could be that the natural frequency of resonance of this particular shaft coincided with the lower running speed, i.e. the shaft is balanced at operational speed but due to the slightly higher flexibility at lower speeds it is not.

As I say it's only a guess, to throw some contribution in there :)

TightSlot
18th Feb 2008, 18:08
Thanks TS6 - that's my 'new thing to learn for the day' - I've noticed it in particular on Santa/Lapland flights, so all that makes sense. Possibly Canada in winter is pretty much the same as Lapland.

Auctionman
18th Feb 2008, 18:17
Interesting, thanks for posting it Nutella

PAXboy
18th Feb 2008, 21:34
On some occasions, engines will be run up for a sustained period - a minute or more. Although, usually, the FD will advise the pax of this.

It is usual (I have been told) on first rotation of the day, particularly when cold or if the machine did not operate the previous day. It is just making sure the engines are all warmed through and that instruments record normal response curves. This is usually done away from the terminal in a 'lay-by' of the taxi way, before heading to the active.

I sit to be corrected.

oz in dxb
19th Feb 2008, 05:59
The engines on the B777 200LR and the 300ER both have the GE90-115B engines. Engine start is quite noisy and usually has increased vibrations compared to other types of engines.

The GE is a larger engine and has a completely different sound during engine start. A low deep growl and starts to rise in pitch as the fuel goes in.
Vibration is normal on these engines particularly if they have a short turn around. The main rotor cools at different rates so they is a slight bow in the rotor. Normally fixes itself once the engine has stablilsed.

Normal but maybe a little alarming if you haven't flown in a GE90 powered aircraft. Again only found on the 777-300ER/200LR

Nutella_BC
19th Feb 2008, 06:28
The engines on the B777 200LR and the 300ER both have the GE90-115B engines. Engine start is quite noisy and usually has increased vibrations compared to other types of engines.

The GE is a larger engine and has a completely different sound during engine start. A low deep growl and starts to rise in pitch as the fuel goes in.
Vibration is normal on these engines particularly if they have a short turn around. The main rotor cools at different rates so they is a slight bow in the rotor. Normally fixes itself once the engine has stablilsed.

Normal but maybe a little alarming if you haven't flown in a GE90 powered aircraft. Again only found on the 777-300ER/200LR

That's exactly what I experienced- Deep growl and vibrations, unlike other 777s- Again it was a 777LR.
Take off was much quieter than other planes though
Thanks oz

PAXboy
19th Feb 2008, 09:27
Topslide6 I think it has happened twice to me. The last time was about five years on a departure from EGLL. I cannot recall a/c type but it was a European hop so would have been a single aisle machine.

We pulled into a 'lay-by' and the information from the flight deck was as stated above. Engines run up one at a time for a sustained period and then off to the active.