A few questions I am curious about regarding Jets.

[LikeABoss]

Hi all.
I am just wondering as to what noise the aircraft actually makes while it is on ground before/after passengers board the aircraft?

I believe the engines start at pushback, but why the noise before that?
I am not 100% sure about this, but I believe the fans on the engines are moving while aircraft is on ground (before start of engines), why is that?

Lastly, when a jet aircraft banks to the right for example, why does aileron barely deflect at all?
Right turn bank, quiet a steep one as well on the flight I was sitting on today, and the right aileron barely deflected up.

Lastly, do the spoilers always automatically go up/down on the fly by wire jets to help bank an aircraft?

Sorry for all the questions.
Thank you in adv

[misd-agin]

Noise? Maybe the APU running?

Why does the front of the engine move before the engines are started? It's free wheeling(can spin anytime). Once the wind gets strong enough it starts the fan(N1) spinning.

In general the faster you're moving the less aileron input you need to start a roll. Once you're in the turn(banked) ailerons are returned to normal.

On all aircraft (that have spoilers) spoilers might deflect(rise) to assist in roll control. It depends upon the amount of control input the pilot makes. In general minor roll inputs do not deploy(raise) roll spoilers while large control inputs cause the spoilers to deploy to assist in roll.

[EW73]

I'll try and answer your questions as best I can for you...

The front of the engine, what you see is the 'fan', as said earlier, it's a freewheeling one that is connected via cocentric shafts to a couple of turbine wheels at the rear of the engine, and they also turn with the fan, though as a passenger you won't be able to see that far up into the rear of the engine. This fan arrangement is simply being spun by the prevailing wind, either forwards or backwards, it doesn't matter, the core engine will start to rotate the fan in the correct direction during engine start.
Again, as mentioned, the additional noise you can hear during boarding, and right up to just after engine start is the APU, which is the auxiliary power unit, on most aircraft it's located in the tail section and provides both electrical power and pneumatic power until the main engines are started. The allows for electrically powering up the entire airplane and running the air cycle airconditioning systems. The pneumatic power is also used to drive air motors to start the main engines...except in the new Boeing 787 Dreamliner, where this job is done with electric starter motors.
The last question has already been answered...

Cheers EW73

[victorc10]

The Hydraulic pumps make a rather loud whine, and to some extent the Fuel pumps also.

[Piltdown Man]

I often wondered about that as well. What you hear is probably a combination of various noises. The two most likely are the airconditioning packs and the Auxiliary Power Unit (APU). Taking the airco. pack first, here is a diagram (http://www.google.co.uk/imgres?q=air+cycle+machine&hl=en&sa=X&biw=1472&bih=959&tbm=isch&prmd=imvns&tbnid=7sKs5qOFQG6gzM:&imgrefurl=http://www.k-makris.gr/AircraftComponents/CoolPack/pack.htm&docid=Cz9eRkxLw9nb6M&imgurl=http://www.k-makris.gr/AircraftComponents/CoolPack/340acm_2.JPG&w=500&h=375&ei=opDLTpHfIIPd8gOnzo3YDw&zoom=1&iact=hc&vpx=179&vpy=500&dur=46&hovh=194&hovw=259&tx=98&ty=91&sig=107403381652702210202&page=1&tbnh=145&tbnw=176&start=0&ndsp=32&ved=1t:429,r:18,s:0). Air from the APU is bled off but it has to be cooled. An aircycle machine does this job. Both the inlet and outlets make a fair bit of noise. The APU is a small jet engine (http://www.google.co.uk/imgres?q=apu&start=41&num=10&hl=en&biw=1472&bih=959&tbm=isch&tbnid=NmYxUExSXP4WmM:&imgrefurl=http://fothesky.********.com/2011/05/auxiliary-power-unit-apu.html&docid=9gB319cKbio59M&imgurl=http://1.bp.********.com/_SzlVkNhb_fI/TP840x8AhzI/AAAAAAAAAEY/j12jCwfADHI/s1600/b737-apu-743273.jpg&w=440&h=550&ei=x5LLTpGJG4e68gOEyNDLDw&zoom=1&iact=hc&vpx=1162&vpy=396&dur=805&hovh=251&hovw=201&tx=84&ty=142&sig=107403381652702210202&sqi=2&page=2&tbnh=131&tbnw=105&ndsp=40&ved=1t:429,r:30,s:41) (well gas turbine to be precise) and its job is to produce air, for airconditioning and engine start and electricity when the engines generators are not running. Not surprisingly, it sounds like a jet engine and again, the noise is generated at both the inlet and outlet.

Ailerons - at speed you hardly need any any control movement and spoilers may be used instead of or as well as 'up' aileron. And yes, some fly by wire aircraft automatically demand the use of spoilers (on the downward moving wind) in turns.

PM