Electric power consumption onboard

[PK-GDU]

I understand that big jet airliners generated its own electricity for its in-flight operation. I assume the electric power is a must to run;


Cabin lighting and cabin entertainment system
Cabin heating
Galley food preparation system
Hydraulic pumps or actuators
Flight controls
Navigational system and radio communicaton
External lights, strobo-light, spotlight to tail fin.
Any other electrical devices (?)
I am just curious about how much kilowatt required for B747 , B 777, A340 or smaller B737, A320 ?

If compared to the airplane propulsion power, how many percent this electric power will consume the energy from burned fuel?

[forget]

Selamat pagi PK. If you have a general interest in aircraft electrics try this, excellent 737 site -

http://www.b737.org.uk/electrics.htm

[PK-GDU]

Good afternoon, ..thanks.. gee the B737 electric pages are really comprehensive. Last year ,as pax in a B734 I got an experience of having to get off the a/c when all electricity suddenly gone in that night . It happened in only a couple of seconds after pushback started. The plane was towed back to gate, door re-opened and with the help of F/A flashlight all pax alighted . From a good distance I saw pool of liquid formed in the tarmac apparently made by dripping jetfuel aft the wing. Burst fuel line to APU ?, surely had stopped the only generator running. If my assumption was right , should the battery powered static inverter automatically replace the lost AC power?. I remember very well, of how the F/A could not instruct anything to pax through the P/A.
Thanks again,
PK-GDU

[Intruder]

I am just curious about how much kilowatt required for B747 , B 777, A340 or smaller B737, A320 ?
The 747 has 4 60 KVA (54 kilowatt) generators. On a 747F, a nominal load is around 20% with all generators running, or about 40 KW. This will vary with fuel pump configuration and use of galley and emergency loads like alternate flap drives.

Passenger galleys and entertainment loads will raise this significantly.

[chornedsnorkack]

So, aircraft engines usually provide thrust, and also power 3 types of systems: bleed-air pneumatic, hydraulic, and electric. Correct? With exceptions, like 787 which has no bleeds.

How do the power requirements of those four compare?

Bleeds are commonly shut down deliberately in lower levels to gain thrust.

Now, as for the systems listed:


* Cabin lighting and cabin entertainment system
Agreed (really no way to do it by bleed air or hydraulic)

* Cabin heating
As mentioned, usually a bleed-air system. But how do they heat or cool air as needed? In any case, 787 has no bleeds, so this would be suited to electric rather than hydraulic application.

* Galley food preparation system
Agreed. I do not think there is any actual fire in galleys.
* Hydraulic pumps or actuators
* Flight controls
Are those electrical, or hydraulic?

I think most planes where all hydraulic systems drain will lose all flight controls except throttles, like 747, DC-10 and A300. However, VC-10 has some kinds of local hydraulic pumps - how are those powered? And A380 has 2 general hydraulic systems plus local hydraulic pumps - powered by what?
* Navigational system and radio communicaton
* External lights, strobo-light, spotlight to tail fin.
* Any other electrical devices (?)

Like black boxes.

A MD-11 famously flew for several minutes after the black boxes stopped recording because their electric supply was broken by fire.

However, each engine has a generator, the auxiliary power unit in the tail has an identical generator.

Identical in capacity? So, 3 generators in total.


However, capacities like this are irrelevant for pilots. They load shed automatically if load is excessive.

Do pilots have any discretion, about which systems they plan on using and which they think unsafe to power up?


all fuel pumps off, all electrics off, all carbon life forms off, move away from machine as soon as possible! Sounds sensible with loose fuel around!

On ground, yes...

In air... you presumably would not want to shut down all engines and ditch at a heavy weight and with most of fuel still in tanks because some of the fuel is loose around the plane.

and emergency loads like alternate flap drives.

A 747 has no rat. Do windmilling engines provide as much electricity as working ones? Can the flaps be driven solely by windmilling engine electricity?

Generally, are there any electric systems on a plane which should never intentionally be shed or switched off before the plane has come to rest on ground or water?

[Intruder]

A 747 has no rat. Do windmilling engines provide as much electricity as working ones? Can the flaps be driven solely by windmilling engine electricity?
No electricity below idle, so none from a windmilling engine. Normal flaps are run by hydraulics and air. Trailing edge flaps will run on hydraulics from windmilling engines. If all 4 engines are dead, no leading edge flaps.

[llondel]

A 747 with all engines dead is either on the ground, in deep doodoo or in a volcanic dust cloud. So what did power the electrics on that BA flight? Battery power? The PA was allegedly working if the captain was able to make that wonderful announcement to the cabin.

[PK-GDU]

Two more little curious questions;

1. Airbus main gear brake cooling fans, almost sure electrically driven and presumably automatically switched on and off based on brake temp sensors feedback. Is there any pilot manual override control on this ? and is it possibly only run while the a/c is on ground?

2. Weather radar , is it consume large current of electricity ? will it be first to shed during certain a/c electrical problem?

Thank you All,

PK-GDU

[apaddyinuk]

Ever so slightly off the point. On some aircraft (in this case a 777) there are little plugs in the loos which can be used for electric razors. Please dont think you can plug in your mobile phone to charge if you have an adapter. And if you are that stupid please dont leave it there unsupervised!!!

Some numpty did this once upon a time and when I came to do my toilet checks (apparently only 12 minutes or so after he plugged it in) I found the adapter had melted into the plug and was nicely smoldering... would have been no time before the facial tissues which are stowed directly above the plug would have ignited and then we would have had a lovely little situation over the Atlantic Ocean in the middle of the night!

[Intruder]

2. Weather radar , is it consume large current of electricity ? will it be first to shed during certain a/c electrical problem?

No. Galley loads and certain redundant fuel boost pumps go first.

[tom775257]

Airbus brake fans are just controlled by the pilot by a switch, not automatic at all (at least on the 320 series). They are electrically driven. I don't know whether you can switch them on in the air, I have only flown a jet once with them fitted.


A320 has 3x 90KVA generators, one on each engine and one on the APU. I would guess if only one was running it would be around the 50-60% load.
Tom.

[PK-GDU]

Another Q on aircraft electrical system, trivial one, as long as it is permitted.

Q: Are there auxiliary electrical supply points which ready at typical cargo jet planes, to energize any specific requirement may arise from unusual package unit of machinery ( which need constant supply of electricity ) or to operate an important portable equipment ? ( medical equipment related...as an example ) just as in a medical evacuation flight ?

If am not totally wrong, the voltage and frequency generated by the aircraft generator is specific ( 400 cycles / min ?) so conversion through inverters will be necessary.

Thanks again..,
PK-GDU