diff --git a/docs-mini/README.electrical b/docs-mini/README.electrical index 6cf9f0b0f..e22f7109e 100644 --- a/docs-mini/README.electrical +++ b/docs-mini/README.electrical @@ -4,36 +4,77 @@ Specifying and Configuring and Aircraft Electrical System Written by Curtis L. Olson February 3, 2003 - Initial revision. +June 14, 2005 - Important update + +UPDATE - June 14, 2005 +====================== + +The xml data driven electrical system described in this document has +severe flaws and is (or should be) obsolete. It is still supported +for backwards compatibility, but new electrical systems should not be +modeled with this system. Instead you should make a procedural +electrical system model using nasal, or wait for a better data driven +electrical system model to be developed "some time" in the future. + +Currently the old/depricated electrical system has been made into a +proper subsystem. Most aircraft will load the default "systems" +configuration via the "/sim/systems/path" property which is set in the +top level preferences.xml file and which defaults to a value of +"Aircraft/Generic/generic-systems.xml". The generic-systems.xml file +in turn specifies an electrical system based on the old/obsolete +system. The default electrical system configuration file named in +"generic-systems.xml" is "generic-electrical.xml". This mechanism +provides a generic electrical system to any aircraft that doesn't +define their own electrical system. Also note that you can still +specify a path to an "old" xml config file using +"/sim/systems/electrical" in your aircraft-set.xml file. This is +again for backwards compatibility. + + + +What follows here is a description of the "old" "depricated" +"obsolete" electrical system. + Introduction ============ -The FlightGear electrical system model is an approximation. We don't -model down to the level of individual electrons, but we do try to -model a rich enough subset of components so that a realistic (from the -pilot's perspective) electrical system may be implemented. We try to -model enough of the general flow so that typical electrical system -failures can be implimented and so that the pilot can practice -realistic troubleshooting techniques and learn the basic structure and -relationships of the real aircraft electrical system. +The FlightGear electrical system model is a simplification of reality. +We don't model down to the level of individual electrons, but we do +try to model a rich enough subset of components so that a realistic +electrical system may be implemented (at least from the pilot's +perspective.) We try to model enough of the general flow so that +typical electrical system failures can be implimented and so that the +pilot can practice realistic troubleshooting techniques and learn the +basic structure and relationships of the real aircraft electrical +system. -An electrical system can be built from 4 major components: suppliers, -buses, outputs, and connectors. Suppliers are things like batteries -and generators. Buses collect input from multiple suppliers and feed -multiple outputs. Outputs are not strictly necessary, but are -included so we can name generic output types and provide a consistent -naming scheme to other FlightGear subsystems. Finally connectors -connect a supplier to a bus, or a bus to an output, and optionally can -specify a switch property (either a physical switch or a circuit -breaker.) +The FlightGear electrical system is essentially a directed graph built +of 4 major components: suppliers, buses, outputs, and connectors. +Suppliers are the power sources such as batteries and alternators. +Buses collect input from multiple suppliers and feed multiple outputs. +Outputs are not strictly necessary, but are included so we can assign +current draws, and name generic output types, as well as provide a +consistent naming scheme to other FlightGear subsystems. Finally +connectors connect a supplier to a bus, or a bus to an output, and +optionally can specify a switch property (either a physical switch or +a circuit breaker.) -At run time, the structure specified in the electrical system config -file is parsed and a directional graph (in the computer science sense) -is built. Each frame, the current is propagated through the system, -starting at the suppliers, flowing through the buses, and finally to -the outputs. The system follows the path of connectors laid out in -the config file and honors the state of any connector switch. +At run time, FlightGear parses the electrical system config file and +builds a directed graph (in the computer science sense.). Each time +step, the current is propagated forward through the system, starting +at the suppliers, flowing through the buses, and finally to the +outputs. The system follows the path specified by connectors and +honors the state of any connector switches. + +FlightGear uses a depth first recursive decent algorithm to propagate +the current through the system. As the recursive calls complete, the +current draw of the "leaf nodes" can be summed up and back-propagated +through the system. This allows us to compute the total downstream +current draw at each component of the system. This allows us to +discharge the battery based on actual loads, and allows us to build an +accurate functioning ammeter model. Suppliers @@ -164,7 +205,10 @@ Summary ======= The electrical system has a lot of power and flexibility to model a -variety of electrical systems. However, it is not yet perfect or -finished. One major weakness is that it doesn't yet model degraded -battery or generator power, and it doesn't model the "charge" of the -batteries in case of a generator failure. +variety of electrical systems. However, it is hopelessly flawed and +cannot model a lot of more complex electrical behavior needed for the +advanced electrical systems found on larger and more complex aircraft. +Please consider writing a procedural model for your electrical system +in nasal or wait for a better data driven electrical system model to +be developed. If you know something about electrical systems, please +volunteer to write a better data driven model! :-)