John,
Yes, there were some changes. I’ll try to help out soon, but am limited on time
at the moment. You might search the JSBSim mailing list for the “tank priority”
terms.
Briefly, as I recall, there is now a “priority” element, with priority “1”
being the highest. I forget if “0” means anything. Any tank with the same
priority provides fuel until all tanks of the same priority are empty. Then,
the next priority tanks are used (1, then 2, then …).
The “new” tank system was introduced by one of our developers who is also an
airline pilot. Unfortunately, I don’t think that the features is widely used,
yet – at least in models in the JSBSim repository. I’m using it in one vehicle
model now, but can’t share that.
I hope this helps. You might try cross-posting to the JSBSim developer list,
too. Let me know if you need more help.
Jon
From: castle...@comcast.net [mailto:castle...@comcast.net]
Sent: Monday, October 22, 2012 10:41 AM
To: FlightGear developers discussions
Subject: [Flightgear-devel] Fg Fuel System Changes
HI,
Had been running with fg-2.4 for some time and finally getting around to
upgrading to 2.8. Seems there where some changes to the fuel and tanking
system in JSBSiim starting with 2.6. It "breaks" the mods made to the code to
support the 737/747 full scale cockpits tanking models in 2.4 and prior.
In large aircraft such as the 7x7 types the fuel is NOT drawn equally from all
tanks. Rather, in terms of graph theory, you should think of the tanking
system as a fully connected graph for the tanks, engines, and crossfeed valves.
Such that any feed tank can feed any engine or all engines can draw from one
feed tank. The case where all tanks feed to a manifold that supplies all
engines is just one special case.
At any rate, is there a writeup on the changes? Or might the author find some
time to describe what was changed?
Having trouble understanding how to the "FuelExpended" variable to a specific
tank and how to pass the tank contents onto the flightgear side.
Here is how it works in my 2.4:
this was the mod to the FGEngine::ConsumeFuel(void) in 2.4
if ( Active_Tank >= 0 ) {
Tank = Propulsion->GetTank(Active_Tank);
if (Tank->GetType() == FGTank::ttFUEL) {
//Fshortage += Tank->Drain(CalcFuelNeed()/TanksWithFuel); // SEE NOTE
ABOVE
Fshortage += Tank->Drain(CalcFuelNeed() );
}
} else Starved = true;
where "Active_Tank" was a value passed from the cockpit fuel control panel (via
network controls) to fg and the fg/jsbsim interface in jsbsim.cpp.
and this was the code to transfer fuel in the 737 model to the center feed tank
// Remove equal amount of fuel from each feed tank.
// FuelNeeded = FuelToBurn/TanksWithFuel;
// for (i=0; i<FeedList.size(); i++) {
// Tank = Propulsion->GetTank(FeedList[i]);
// Tank->Drain(FuelNeeded);
// }
Tank_0 = Propulsion->GetTank(0);
double center_fuel = Tank_0->GetContents();
if ( center_fuel < 6000.0 ) transfer = true;
else if ( center_fuel > 9000.0 ) transfer = false;
if ( transfer ) {
Tank_1 = Propulsion->GetTank(1);
if ( Tank_1->GetContents() > 100.0 ) {
Tank_0->Fill( 0.040 );
Tank_1->Drain( 0.040 );
}
Tank_2 = Propulsion->GetTank(2);
if ( Tank_2->GetContents() > 100.0 ) {
Tank_0->Fill( 0.0401 );
Tank_2->Drain( 0.0401 );
}
}
So setting Active_Tank=0 has both engines drawing from the center tank and when
it drops below 6000# the fuel transfer system fills until it reaches 9000# or
the pilot can select, via the fuel control panel, to feed each engine directly
or crossfeed as desired. Setting Active_Tank=-1 starves the engine.
The 747 is much more complex and, in the interest of brevity, is not discussed.
The entire function "ConsumeFuel" is removed and having some difficulty
undestanding how "FuelExpended" is interfaced to draw down the tanks.
Any help would be apprecuated.
John
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