B747 onboard systems
Hi, I am reading PMDG's operating manual for their B747.
I am at the chapter about aircraft systems and since I am a bit more interested in engineering and since the PMGD manual are not very detailed and in some chapters the manual has huge gap or the explanation isn't really understandable I am asking those on this forum who are experts when come to aircraft technics.
HYDRAULIC SYSTEM
Manual says that B747 has 4 independant hydraulic systems. It has 4 engine driven demand pumps (one per engine), 4 hydraulic reservoars and 4 air driven pumps. Then it says that engine 4 has also AC electric driven AUX hydraulic pump - used only to power brakes durring ground towing usage. Then in the next statement it comes to a bit contradictious statement with previous one (each engine has air driven pump) as manual says that engine 1 and 4 have bleed air driven AUX hydraulic pump and engine 2 and 3 have AC electric driven AUX hydraulic pump.
Logicaly stated I'll say that there are 4 engine driven pumps, 4 AUX pumps (bleed air driven in engine 1,4 and AC driven in engine 2,3) + additionaly AC driven AUX pump for brakes.
Now I don't know if APU has aslo mechanicaly driven hydraulic pump, but I gues that it can run anyone of four engine AUX pumps via bleed air or AC electric (in case all four engines are malfunctioning).
ELECTRICAL SYSTEM
Manual says that each engine has 115V, 400Hz, 90kVA AC generator driven via constant speed drive, and all four generators can be paralled if they all works well (providing 400Hz). Then there are additional 2 AC generators driven by APU of the same characteristics as those on engines, but they aren't paralled. Then manual says there are also 2 nickel-cadmiun batterys onboard and if I understood they can only be charged via external power source. But on the next side manual says that there are 4 battery busses. Then manual says that there are automatic SSB that split left/right side of the plane (this is needed if sides are not powered via paralled generators).
What I don't know here how many batterys are on board and what they can power (manual says all standbay systems). I predicts that this is just avionics. AUX hydraulic pumps are AC powered and I guess there are no inverters that will invert battery DC to AC?
And how is with DC busses manual talks about. Can you separare DC busses manualy via overhead panel?
I aslo don't know what is AC and what is DC powered.
PNEUMATIC SYSTEM
Provides pressure air for air cycle machine found in AC packs, start up engine, wings & engine anti ice, tank pressurization....
The question is if the bleed air from the engine for anti ice flows through wings leading edge and then return to the engine or is this one way path and bleed air blows through small holes in the leading edge?
Then another question is where is location of catalistic converter (to remove ozone). Then next question is how many heat exchangers are there. As manual says there are primary located before the compressor of air cyle machine and secondary after it. But manual also mentioned that there is air to air heat exchanger mounted in the engine bay so that airstream from the fan cooles the bleed air.
Last edited by flybik; 15th Nov 2009 at 21:49.