Re: [Flightgear-devel] Fg Fuel System Changes
Here’s an overview of the fuel system from the perspective of a user – not a developer, but maybe it helps. Do you need the API documentation? Try here for a start: http://jsbsim.sourceforge.net/JSBSim/classJSBSim_1_1FGTank.html Jon Here's an overview of the fuel handling in JSBSim now. At load-time the propulsion system (FGPropulsion) reads the configuration file and builds a list of engines and a list of tanks. Each engine creates a list of feed tanks using the tag. This list is only created at load-time, but in the future I'd like to see run-time control over this list. The list is owned by each FGEngine and is called SourceTanks. The list is the same size as the number of tanks, and each list item corresponds to a tank. At load-time each list member is set to zero, and when a tag is encountered the list member corresponding to that tank is set to non-zero. The engine will only feed from tanks that have a non-zero value in SourceTanks. The non-zero value happens to be equal to the tank's priority, but it's only treated as a non-zero in the ConsumeFuel() algorithm. It could just as well be zeroes and ones. This is, in effect, a map of all the tanks, representing which ones are allowed to feed this engine. The trick in making this run-time modifiable will be to decide on a scheme to allow one property to modify this map. Each tank has a priority value, with 1 being the highest priority. The default value is 1. The priority is an attribute owned by the tank, and it's exposed to the property tree, so the priority can be changed at run-time. Since the priority is owned by the tank, this means that all engines will see the same priority from a given tank. Setting the priority to zero is like closing a valve "at the tank". So far this is the only valve you have control over in the fuel system. The SourceTanks list, belonging to each engine, can be thought of as a set of valves too. Each engine is connected to all tanks, but a valve "at the engine" is closed for each list member with a value of zero. When refueling is activated (by setting the property "propulsion/refuel" to 1 or true) fuel is added at the same rate to ALL tanks at a total transfer rate of 6000 lbs per minute, hardcoded. This code presently ignores tank priority. It also ignores what fluid is supposed to be in a particular tank, so don't use this with a rocket. The refuel code could use some work. When dumping fuel (by setting the property "propulsion/fuel_dump" to 1 or true) fuel is removed from ALL tanks down to any standpipe level previously defined at load-time for each tank. The dump rate is defined at load-time, and is the rate for the entire fuel system. This code ignores tank priority. If no standpipe is defined, all fuel will be dumped. Default dump rate is zero. Total fuel quantity is calculated in FGPropulsion::Run() and written to the property "propulsion/total-fuel-lbs". Fuel temperature is calculated in FGTank::Calculate(), but only for tanks that had an initial temperature defined at load-time. Fuel quantity is always measured by weight. There is no method in the code for conversion to volume, and there is no tracking of fuel density. FGPiston does provide a gal/hr output, and uses 6.0 lb/gal as the conversion factor. FlightGear manipulates the JSBSim tank quantities by converting gallons to pounds in JSBSim.cxx, using a conversion factor of 6.6 lb/gal. Dave From: Jon S. Berndt [mailto:jonsber...@comcast.net] Sent: Monday, October 22, 2012 7:27 PM To: 'FlightGear developers discussions' Subject: Re: [Flightgear-devel] Fg Fuel System Changes 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 -- Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_sfd2d_oct___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/list
Re: [Flightgear-devel] Fg Fuel System Changes
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; iGetTank(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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Re: [Flightgear-devel] YASim and documentation
On 10/05/2012 05:53 AM, Vivian Meazza wrote: > Andy is still around, but inactive. It might be possible to run stuff by him > once in a while. He even reads the mailing list (but not the forums) on occasion. :) Indeed, I'm busy with other things these days, but am still broadly happy to answer questions if posed (as long as I remember enough to come up with a meaningful answer). Just cc: me if you do, because my latencies here are measured in weeks. > But I would in general worry about mucking about with such a > critical part of FG, unless I was very sure about what I was doing. Bugs can always be fixed. What YASim needs is a maintainer, not really expertise per se. The latter comes from the former. Andy -- Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_sfd2d_oct ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
[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; iGetTank(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
- Original Message -
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