Fuel.system section in flight_model.config

Hi MSFS Team. I am trying to implement a fuel cutoff switch similar to what is
in the 747. I realized trying to use the xml fuel template switch (
ASOBO_FUEL_Switch_Valve_Template )does not work since I do not have a
fuel.system section in the flight model. If I try and and this section ,
aircraft editor either locks or crashes. Is there any plan to update the
editor to include this section? Was this section for the 747 manually created?
Thanks, Shervin

Doing some more research it looks like the FUELSYSTEM_VALVE_SWITCH variable is
contained in a WASM module? Does that mean I have to create a WASM module for
the fuel system?

Hello Shervin, The section should be named FUEL_SYSTEM as documented here:
https://docs.flightsimulator.com/html/Content_Configuration/SimObjects/Aircraft_SimO/Flight_Model_Definition.htm?rhhlterm=fuel_system#[fuel_system]
This section is not editable through the AircraftEditor at the moment (it will
in the future) but it shouldn’t crash though. Make sure its content matches
what’s specified in the doc. I can investigate on the cause of the crash if
you provide me with your package. Regards, Sylvain

Thanks Sylvain. I did take a look at that section. I’ll have to tinker around
with it some more. I think I may have to draw out the fuel system first then
try and translate into the proper syntax. Would be nice if in the future
implementation in Aircraft Editor , there is some sort of a visual reference
to help debug/analyze the fuel system. Thanks! Shervin

But that documentation simply consists of a bunch of parameter names. There
are no descriptions of the parameters included nor discussion anywhere I could
find of how they are used (e.g., what are allowable triggers?) and interfaced
with other systems. Also, are you aware of the bug in the default A320 fuel
system that causes fuel to disappear if you start cold and dark (no engines or
APU running and satisfy the trigger for the external fuel transfer valves to
open, the fuel transfers out of the outer tanks, but does not transfer into
the inner tanks. It simply disappears.

We know this is not ideal. This section will be documented as precisely as the
electric systems were documented a few weeks ago. In the meantime, this is the
best we can provide. I am personally not aware of the A320 issue but devs
might be. Have you created a zendesk ticket? If you can provide me with repro
steps (in a dedicated question) I can reproduce the problem and make sure it
has been forwarded to the devs. Regards, Sylvain

“Not ideal” is a bit of an understatement, but okay, I’m confident it will get
there. Thanks. As for the A320 issue, I shouldn’t have limited it to the A320.
It is a fuel system issue, so it would affect any airplane that uses this new
fuel system and has fuel transferred from one tank to another based on a
triggering value. I did not create a Zendesk ticket as I had provided this
info to our rep on the Asobo forums to give you all directly. Maybe that did
not take place. I can create a Zendesk issue if it would help. There are
actually 2 issues I’ve found with the new fuel system that would affect any
airplane using the new fuel system. The one I described - Start Asobo A320
cold and dark anywhere. Turn batteries and external power on. Adjust fuel
quantity as follows: no fuel in the center tank, full left outer and inner
tanks, less than 250 gallons (e.g., 216 gallons) in each inner tank. Watch the
outer tank fuel levels drop without the inner tank levels (where the fuel
should be going) changing. Fuel is simply disappearing. Second issue: Any
amount entered as unusable fuel is effectively being added to the total tank
capacity rather than being subtracted from it. Fuel continues to be emptied
from the tank to a negative amount of fuel equal to the unusable fuel. For
example, for a tank with a total capacity of 2 gallons, with 1 gallon being
unusable, the engines would not quit until 2 gallons of fuel is burned leaving
a fuel quantity of -1 gallons. Is this why the unusable fuel quantity was set
to zero for the default airplanes using the new fuel system? To reproduce this
issue, you will need to change the unusable fuel quantity for any given fuel
tank from zero to some positive value in any airplane using the new fuel
system. Put a small amount of fuel in that fuel tank, start the engines and
burn all the fuel in that tank. The engine will not quit due to fuel
starvation until the amount of fuel originally put into the tank plus the
unusable fuel (rather than minus the unusable fuel) is burned.

This is a perfect example of why we need a visual debugger in the Aircraft
Editor. Maybe there is a some fuel line that leads to nowhere? There are so
many lines in the fuel system for the A320 and 747 it’s hard to tell… at
least for me.

1 Like

Both these issues are fixed and will be available with the Performance Plus
update. Looks like your bug report on the forums was considered :slight_smile: Regards,
Sylvain

Thanks! And here I thought this forum was just for discussing the SDK!

It is. As the bug you described potentially affected all third party products,
I consider it SDK related.

Don’t most MSFS bugs potentially affect all third party products? For example,
the current issue with the standard pressure vs altitude relationship,
pressure altitude for non-standard pressure, and temperature effect on
airplane altimeter altitude vs actual height above ground level (i.e.,
altimeter error for non-standard temperature)? Is that a topic worthy of this
forum?

Yes it is. The particular issue you’re mentioning has already been reported in
a question and is being investigated:
https://devsupport.flightsimulator.com/t/3137 Every issue of the game that
has a direct impact on how third parties can design their product is worth
mentioning here. Your A320 bug report is actually a good example. If this was
about the A320 fuel system being incorrectly configured, it wouldn’t fit here.
But it’s about the fuel system itself being flawed so that’s an SDK related
issue.

Thank you for the response Sylvain, but that particular altimeter issue is not
what I am referring to. I am referring to an inaccurate standard pressure vs
altitude relationship being used and incorrect implementation of the effect of
temperature on altimeter altitude vs height above ground. The current preview
build, which attempts to fix these issues with the production version, has
made what used to be a fairly benign couple of issues into very serious bugs.
The current status will make it very difficult for anyone to fly on VATSIM or
any other online network.

See, for example, <https://forums.flightsimulator.com/t/instruments-show-more-
incorrect-altitude-the-higher-up-you-go-causing-issues-with-approaches/418896>
and <https://forums.flightsimulator.com/t/high-altitude-altimeter-setting-
wrong/418320> and <https://forums.flightsimulator.com/t/influence-of-non-
standard-temperature-on-true-altitude-accurate/417707/8>

My bad, about this issue, we are aware the situation is still incorrect in
preview. We have a potential fix but we want to test it further as we’re
worried of possible side effects. I’m afraid we won’t be able to fix this in
the Performance Plus release.

Well, I’m afraid it doesn’t appear to have been completely fixed. For example,
with the A320, the APU will burn fuel from the center tank, and if there is no
fuel in the center tank, it will take it from the left main tank. This can be
verified by putting fuel in both tanks and observing that center tank fuel is
used, then just fueling the left main tank and observing that left main tank
fuel is used. When the left main tank gets to the unusable fuel quantity, the
APU will shut down due to fuel starvation. This is all well and good. The
issue is if the APU is burning from the center tank, and then the center tank
gets to it’s unusable fuel quantity (or only the unusable amount is loaded
initially), the APU will quite happily run forever without burning any fuel at
all. If there is initially only the unusable fuel quantity loaded in the
center tank, then the left main tank must have more than its unusable fuel
quantity for the APU to start, but once started, it will run along without
burning any fuel. Note: for this testing no fuel was loaded in any of the
other tanks. (And this testing was conducted using the FBWA320, though I would
expect the same results from the default A320.)

Hi donstim I forwarded the issue to the developer in charge of the fuel
system. Thank you for reporting this.

Two more observations: 1) It can take some time (in the sim) for an engine to
shut down due to fuel starvation, and this time appears to be a function of
the thrust level (and hence fuel flow?). For example, at idle power sitting on
the ground with the default A320 modified to include unusable fuel quantities,
with zero fuel in the center and outer wing tanks and just over the unusable
fuel quantity in the inner wing tanks, once the fuel level gets down to the
unusable fuel amount, it takes a good 2 minutes before the engines shut down
due to fuel starvation. During this time, the fuel quantity SimVar bounces
from zero to some positive fuel amount every so often. At TOGA power on the
ground with brakes on, the engines shut down within a few seconds of reaching
the unusable fuel level. And in level flight at 5000 feet at 250 KCAS with the
default ZFW, it takes about 40 seconds for the engines to shut down. Is this
intended behavior? 2) I wish I had a more detailed report on this, but it
seems that occasionally the trigger to start the transfer of fuel from the
outer wing tanks to the inner wing tanks is being missed, i.e., the transfer
does not begin. I noticed this once when I was changing units through the
options screen at about the level the trigger should have occurred, but it did
not happen. (I don’t know if that circumstance was just a coincidence or not -
I have not yet tried to repeat it.) I only mention this because we are
occasionally getting reports that the fuel transfer did not occur as expected,
causing the airplane to run out of fuel. Is it possible that this trigger may
be “missed” if something else is going on at around the same time?

What do you mean with this new fuel system? Is there some configuration to
switch between some legacy and a new fuel system?