Here are some ideas about modeling electrical systems that are general
enough to handle most airplanes.  The base object will probably need to keep
a list of suppliers and another list of users.  If the state of any
component changes it will then be resposible for notifying all of its users.
The alternative method, by which every user would check its power supply at
every sim-cycle seems wastefull, especially when you have 300+ users.  AC
components can have any number of suppliers, but generally only use one at a
time.  DC components can use all their suppliers at the same time.

Here are some objects to be derived from the base object:

1)  CSD  (constant speed drive), which exists between an engine and its
generator.  The CSD has one supplier, the engine, and one user, a generator.
The CSD's function is to spin the generator at a set speed regardless of
engine rpm.  CSD parameters to monitor are Oil Quantity, Oil Temperature
going in from the cooler, and Oil Temperature going out to the cooler.  The
measure of the CSD's health is the oil temperature Rise (out - in).  The CSD
has a cockpit switch which can physically disconnect it from the engine in
order to protect the engine.  The switch is for emergency use only, as once
it is used the CSD clutch can only be engaged by a mechanic.

2) Battery, nominally 28 Volt, which will last about 30 minutes if it is the
only power source available.  It is normally supplied by the battery
charger, so if the charger is powered the battery is transparent.

3) Ground Power, supplies 115 Volt, 400 cycle AC power to a "Ground Power
Bus".  This is plugged into the side of the airplane, and is either there or
it isn't.  A light in the cockpit advises if its there.

4) APU (auxilliary power unit), which could be derived from a turbine
object, but I think that would be a waste.  It supplies 115V/400Hz
electrics, and usually supplies pneumatics as well.  It has a Start/On/Off
switch in the cockpit, and an EGT gauge.  It burns fuel from one of the
airplanes main tanks.

5) EPU, similar to an APU except that it only works (automatically) when
regular electrical sources fail.  The F-16 EPU has its own hydrazine fuel
supply.  I don't know if EPU's can supply hydraulics as well.

6) Generator, which supplies 115V/400Hz power to a bus.  Supplier is a CSD.
You could model the APU generator as an independent object using the APU as
a supplier, or you could incorporate the APU generator into the APU model.
Generators generally have two switches. The field switch turns the generator
on/off.  The breaker switch connects/disconnects the generator from its bus.

7) RAT (ram air turbine), like the EPU it usually comes on atomatically,
although it can also be activated by a cockpit switch.  The RAT falls down
into the airstream and supplies 155V/400Hz power.  In some airplanes it also
supplies hydraulics, or only hydraulics.

8) HPG (hydraulic powered generator)  uses a hydraulic motor to spin a
generator.  This is purely a backup source, used for ETOPS certification,
and comes on automatically.

9) Bus, a simple component which only keeps a list of suppliers and a list
of users. AC or DC.

10) TR (transformer/rectifier) converts AC to DC.  Supplier is one of the AC
buses.  User is one of the DC buses.

11) Static Inverter converts DC to AC.  Used by the battery bus to supply
the Standby AC bus.  In the event the battery is the only source operating,
the Standby AC bus is the only source of AC power.  Only essential users are
on this bus.

12) Battery charger, supplied by an AC bus (with a backup AC bus also), user
is the battery and everything the battery powers.

I'll soon draw up a diagram of a typical Boeing electrical system and send
it to whoever wants it.

Dave Culp

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