Connor's reassurance that the batteries aren't used in flight isn't right?
What starts the APU in the air?
Also, the 787 also has electric brakes, no power, no brakes, yeah I know that the brakes aren't used in flight but I'd consider them a vital part of aircraft equipment.
The APU will be started in flight if power is lost in one engine by the power available from the remaining engine.
Battery will only be used to start the APU in flight if ALL electrical power is lost. EG Double engine failure.
The brakes are only powered by the main battery IF all other normal power sources are lost. IE both engine generators fail AND APU generators fail.
Connor is correct.
With 150 batteries replaced, and something like 100 aircraft in service
Only 50 a/c in service.
I havent seen the data, but given this aircraft is virtually all electric...what happens if you were dispatched APU non-op, and went engine out?
I suppose this is a very real scenario for testing...but the concern from the way the batteries in the front and back are linked together, it just make one wonder.
The two batteries are not linked. (Or shouldn't be
)
If APU is inop and you lose one engine you still have two good generators producing 500KvA.
If you lose that you are down to the RAT and (Main) battery only. Good luck with that.
Correct me if I'm wrong, but the RAT needs airspeed to provide the force to spin the blades to create the electrical energy. The job of the brakes is to slow the aircraft upon landing - if airspeed (groundspeed?) and power generation are being reduced once the aircraft is on the runway, where is the energy that keeps the brakes applied? As the aircraft slows the RAT rotation slows ergo the power output decreases. Or are the brakes of the type that when engaged will 'lock' onto that position?
In that situation the main battery provides the power for emergency brakes.
In a traditional hydraulic system the emergency brakes are provided by a compressed gas accumulator. The main battery serves the same function on 787 electric brakes.