MissedApproach
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Aircraft Electrical Systems- Types?

Sat Jul 21, 2007 11:52 am

Most aircraft I know of operate with either a 110v AC 400Hz electrical system or a 28v DC system. I read in another thread however that the Caravelle & Comet used a112v DC system, at least for engine start. What other electrical systems have been or are used in aviation?
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SilverComet
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RE: Aircraft Electrical Systems- Types?

Sat Jul 21, 2007 1:15 pm

On the A320 series: 115v AC / 28v DC.

On the ATR: 115v AC / 26v AC / 28v DC / 115/200v ACwild.

ACwild is a network supplied by propeller-driven generators where frequency is not regulated. Used in applications where a fixed frequency is not necessary (probe/window heating, prop anti-ice, HYD pumps, some cabin lights, landing lights and some others I forget).
 
411A
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RE: Aircraft Electrical Systems- Types?

Sat Jul 21, 2007 2:00 pm

L1011, 115VAC/400 cycles, 26VAC , 28VDC, 5VDC.

F.27, 28VDC, 115VAC/400 cycles (via either static or rotating inverter), 28VAC.

B707, 115VAC/400 cycles, 28VAC, 28VDC.
 
MissedApproach
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RE: Aircraft Electrical Systems- Types?

Sun Jul 22, 2007 3:29 am

Quoting SilverComet (Reply 1):
ACwild is a network supplied by propeller-driven generators where frequency is not regulated.

I think a lot of wind-driven generators use this as well, converting it to DC, then inverting back to AC with a 60Hz frequency (in North America anyway).

With the 26/28VAC, is this also at 400Hz?
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SilverComet
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RE: Aircraft Electrical Systems- Types?

Sun Jul 22, 2007 4:47 am

Quoting MissedApproach (Reply 3):
I think a lot of wind-driven generators use this as well, converting it to DC, then inverting back to AC with a 60Hz frequency (in North America anyway).

In the case of the ATR, it is not converted to DC and back. It remains AC and the frequency fluctuates between 341 and 488 Hz, depending on the propeller speed. Fixed frequency AC is obtained on a seperate network by converting the DC thru static inverters (the engine driven generators deliver only DC).

Quoting MissedApproach (Reply 3):
With the 26/28VAC, is this also at 400Hz?

Yes.
 
flynavy
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RE: Aircraft Electrical Systems- Types?

Sun Jul 22, 2007 5:09 am

F/A-18 Hornet - 115VAC 400Hz, 28VDC.
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wrldwndrer
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RE: Aircraft Electrical Systems- Types?

Tue Jul 24, 2007 1:20 pm

Always wondered why is 28VDC used in aircraft systems. Anyone know ?
 
NoWorries
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RE: Aircraft Electrical Systems- Types?

Wed Jul 25, 2007 1:24 am

Quoting Wrldwndrer (Reply 6):
Always wondered why is 28VDC used in aircraft systems. Anyone know ?

I believe it's historical. Any sort of DC system with a rechargeable battery will have two voltages of interest -- the discharge voltage (for example 12V in your car) and a charging voltage (approx 14V in your car). Around the time of WWII (if not earlier) the increasing electrical systems demands prompted airplane designers to opt for a 24V discharge voltage (28V charging). By doubling voltage the wires could carry twice the power without any extra copper. Don't ask me why the auto industry standardized on discharge voltage (12V) and the airplane industry standardized on charging voltage (28V). The 28V bus became a de facto standard perpetuated by the rapid development of avionics during the cold war. Design experience and commonality of parts pushed out into commercial aviation and even aerospace (the Apollo command module had 28V busses; the space shuttle has 28V main busses). Probably won't change anytime soon without a really good reason.

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