Wednesday, 05 December 2012 15:29

More Electrical

When this gets unplugged - you are on your own in terms of electricity... Then, when the engines and APU generators stop delivering electricity, it's time to get a little worried and play the one single card you have left.  That card is the battery!


When last we worked on the electrical system, we had to stop short of completing it because we were wanting to tie into X-Plane's default battery model, specifically the charge of the battery yet this was unavailable at the time.  Though we use very little of x-plane default features, we do use a few and a few of these feature use the default battery model.  Mostly that model is simplified, for example if the battery goes to zero charge, then some equipment stops working.  So then what we needed is to be able to control the battery variable within x-plane and make it zero when OUR battery discharge model tells it to be zero.   So we got together with Laminar and got them to make that available to developers.

So then we set to work developing our Direct Current (DC) electrical model, which is very significant in emergency situations with engines out.  We modeled a Ni-Cad battery discharge model based on current draw.  The 737 battery is a 36 Amp-hour battery when discharged at what is called a 5-hour discharge rate.  If you load the battery much more heavily though, then the total capacity of the battery drops.   A 36 Amp-hour battery will last nearly an hour with nominal loads on a 737-300, but Boeing only guarantees 30 minutes.  why?  Well that 30 minute guarantee also includes one APU start in a emergency situation.  An APU start really drains the battery good and as we just mentioned, the capacity of the battery drops when loading it very heavily.

In modeling the battery discharge,  we also include voltage drop depending on load and also when the battery is near full discharge.  You can keep an eye on the DC ammeter battery voltage and when it starts to drop, you know you are about to become a powerless glider in minutes.

Also we modeled the battery charger fully, including charge mode, pulse mode and what is called "T/R" mode, or transformer / rectifier mode.  When you do an APU start,  you will drain the battery to the point of it needing to be charged and if you keep a keen eye on the DC ammeter, you will notice a positive current flow into the battery at a slightly elevated voltage to charge the battery after the APU start, but you will only see this if the generators, ground power unit, OR the APU generator itself that you just started is connected.  These are the sources of electricity needed to charge the battery.  If none are connected, you will see a drain on the battery after APU start.

One consequence of this model is that if you choose to simulate a power out standby situation, you can accurately monitor your power situation and make decisions about how to go about managing the flight in such dire circumstances.  We also model the effect of such power loses and controlling a powerless aircraft is not particularly easy.

The good news though is that if you do not care for learning such a complex system, you do not have to.  You can simply fly the aircraft like real airline pilots do and if everything is working fine, then you have no worries.  As time progresses though and you get curious as to what it is like for a real 737 pilot to have to learn aircraft systems inside and out and protect their passengers or perhaps just see what happens when you play with switches, then the IXEG 737 simulation will be ready for you!


IXEG Dev Team

1 comment

  • Comment Link Monday, 28 December 2015 11:54 posted by Federico

    It's exaclty what we, PC pilots (but not only ... even real pilot )wants from a gret simulator ....using it like a simulation until we decide to have a look deeper and use it like a real plane.
    Well done iXEG Team.

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