Ingineer said:
I guess this is a good argument for having an APU that can start fast, thus needing a beefy battery pack. (If your engine-derived electrical fails) I know my little teeny tiny 30kW (by comparison) Capstone turbine takes a couple of kW to start, and it takes a couple of minutes before it's ready to load.
Here, check out this Airbus A320 APU limitations link:
http://www.inral.com/Atto/limitations/apu.htm" onclick="window.open(this.href);return false;
... and see how much a 90KVA APU gets derated in the thin high altitude air, with less O2 to burn and make power -AND- less air to cool the equipment.
90KVA versus 450KVA... eek!!!
NOTE: the term ISA is an
"International Standard Atmosphere", a definition of pressure, temperature, humidity and so forth, under the SI convention. Generally speaking, standard temperature at sea level is 15C ISA, and decreases 2C per thousand feet. Air pressure at lower altitudes loses 1" of Hg per thousand feet, from sea level standard of 29.92" (1013.3mb/hPa).
NOTE 2: The following was the absolute largest APU in service, on the Airbus A380, before the Boeing 787:
A380 Fact Sheet_June 2011.pdf
"
The [Airbus 380] APU comprises the Auxiliary Power Unit (APU), the electronic control box
(ECB), and mounting hardware. The PW 980A APU is the world's most powerful APU [ya, before the B787],
providing 1,800 horsepower... The primary function of the APU is to provide air to power the AGS on the ground and to start the engines. The APU also provides auxiliary electric power to the aircraft via two 120 kVA electric generators. The APU received type certification on Dec. 5, 2006."
The A380 uses four 150KVA electric generators, one on each of the four engines. Its final AC generator is the RAT/ADG emergency air powered unit, rated at 70KVA (yes, you could charge a LEAF with a CHAdeMO port on just the Ram Air Turbine / Air Driven Generator)
For DC, there are
four 50ah NiCad batteries on the A380 (world's largest passenger plane); one for the APU, one for each of the following busses, DC1, DC2, and DC Essential.
It's actually quite amazing how much bigger the B787 stuff is:
There's only two engines, but it has four 250KVA starter/generators VARIABLE frequency (about 400hz), two on each motor, plus the two 225KVA starter/generators on the APU. The reasons are the electrically pressurized cabin takes.... 500KVA to power four motor pumps. Wing anti-ice takes 100KVA. The only bleed air is the engine cowl de-ice. This is the only plane with 230VAC, 3 phase, as all "legacy" AC power is 115VAC @ 400Hz. Therefore, the B787 is required to have 230VAC and 115VAC, plus a normal 28VDC system.
No hydraulic pumps are on the propulsion motors, and are also electrically driven; four EDMP's take a total of 400KVA. The control surfaces are still hydraulic, as would be the landing gear.
The engines do not use bleed air to start, therefore it takes 180KVA to start them.
And that is why those APU starter/generators are so f-ing big!!!
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http://en.wikipedia.org/wiki/Boeing_787_Dreamliner" onclick="window.open(this.href);return false;
This is the first time that the FAA has grounded a passenger airliner since 1979. The FAA also announced plans to conduct an extensive review of the 787's critical systems. The focus of the review will be on the safety of the lithium-ion batteries[294] made of lithium cobalt oxide (LiCo). The 787 battery contract was signed in 2005, when LiCo batteries were the only type of lithium aerospace battery available, but since then newer types (such as LiFePO), which provide less reaction energy during thermal runaway, have become available. On January 20, the NTSB declared that overvoltage was not the cause of the Boston incident, as voltage did not exceed the battery limit of 32 V.
B787 has two lithium cobalt oxide (LiCo) batteries by GS Yuasa. One of the two batteries weighs 28.5 kg and is rated 29.6 V, 76 Ah, giving 2.2 kWh.
That's actually less total power than the four NiCads on the A380.
