DA 42 accident

Recently, Mike Isaksen posted:

"C J Campbell" wrote ...
Jose said:
I don't know the system, so I can't second guess the engineers
intellegently about it. However, it does seem to be a serious
oversight that the engines themselves can't supply their own juice.

They do -- with an alternator on each engine. There is also a
generator. How predictable is the failure of two alternators, the
batteries, etc?

Chris,
I do not see the Generator to which you keep refering.

On the schematic you're referencing, the Generators are the circular
symbols with the 'G' and labeled as such. However, as the relay in the
Generator circuit is labled "Alternator Relay", and there is an excitation
circuit I suspect that the terms are being used interchangeably. Not
technically correct, but...

Each engine
has a Starter Motor and an Alternator. The Airframe has a single Main
Battery (10 amphour rated) and a series up Alternator Excitation
Battery (1.3 amphour) used "in the event of a main bat failure"
(Diamond quote in POH). From the article's diagram the magazine
editor marked the excitation battery in RED. I am not good enough
with technical German to read the article, maybe another reader can
summerize the reason for the red highlight.

http://img.edsb.airworkpress.com/red/da42/esys_big.gif

http://www.pilotundflugzeug.de/artik...12/DA42_Unfall

I am a bit confused how that excitation battery is normally charged
and how the battery is monitored.

The excitation battery has a direct feed from both generators (really
alternators). If the fuse isn't blown, either alternator may be able to
charge this battery from excitation feedback. There is no indication of
how the battery condition would be monitored, but if neither alternator
operates, the excitation battery would be highly suspect.

Neil