LeeE wrote:
>On Monday 07 January 2008 18:24, LeeE wrote:
>
>
>>On Monday 07 January 2008 11:07, Chris Metzler wrote:
>>
>>
>>>On Sun, 6 Jan 2008 23:00:22 +0000
>>>
>>>LeeE wrote:
>>>
>>>
>>>>Can anyone else confirm this problem on the OSG cvs branch?
>>>>
>>>>
>>>Yes, I see it too, and have for at least a couple of weeks.
>>>
>>>-c
>>>
>>>
>>Thanks - confirms it's not just a local problem here.
>>
>>LeeE
>>
>>
>
>Searching through Aircraft/controls.hxx gives
>
> enum {
> ALL_TANKS = -1,
> MAX_TANKS = 8
> };
>
>but in Aircraft/controls.cxx there's
>
>FGControls::set_feed_tank( int engine, int tank )
>{
> if ( engine == ALL_ENGINES ) {
> for ( int i = 0; i < MAX_ENGINES; i++ ) {
> feed_tank[i] = tank;
> CLAMP( &feed_tank[i], -1, 4 );
> }
> } else {
> if ( (engine >= 0) && (engine < MAX_ENGINES) ) {
>
> CLAMP( &feed_tank[engine], -1, 4 );
> }
> }
> // feed_tank[engine] = engine;
>}
>
>If these bits of code are relevant to the problem MAX_TANKS seems
>too low - many large aircraft will have more than 8 fuel tanks.
>
>If I understand CLAMP syntax correctly, it's limiting the value to
>4, which ties in with the number of tank nodes that are created by
>default.
>
>I didn't find any other occurrences of 'tank' in the FG source code
>that seemed relevant.
>
>LeeE
>
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>
I'm, pretty certain that might be my code for the handling a 747 fuel
system. It has nothing to do with how nasal handles fuel.
In a nut shell, the 747 plumbing feeds the engines from 5 tanks, the
center and four wing tanks through a combination of shutoff controls and
cross-feed valves. In graph theory this can be represented as a fully
connected graph where any engine can "suck" fuel from any one of the
five tanks or any tank can feed all four engines. Reserve tanks
transfer fuel to the main feed tanks, but CANNOT feed the engines via
the fuel manifold. So yes, you can have more tanks than those that
directly feed engines. In the 747 or any large complex system, mess up
your fuel panel and you starve an engine. This is accurately modeled in
the 747 sim.
The 747 FMS model determines which tank is feeding which engine and sets
the value of "tank" accordingly. A "-1" indicates no fuel connection
for the engine. This value in turn is passed to FG via the native_ctrls
protocol/packet and passed in turn to JSBSim via the jsbsim.cxx module.
Unfortunately, the supporting code is not part of the JSBSim baseline so
it is impossible to see how it works , although it has been submitted a
while back. You can see the supporting source changes by downloading the
tar file of the code used at a Mathworks expo and will be usedat the
upcoming Linux show in February. Look at the FGEngine.cxx, jsbsim,cxx
and FGTurbine.cxx modules in the modified jsbsim code.
Personally, I don't like the way fuel is currently modeled in FG and
really don't like using a scripting language to do real-time execution,
but that's just me I guess ;-) Happy to share the code and my ideas,
but not the primary author or responsible agent for that capability so I
live with the problem and update my version of the source as required
with each FG release.
Regards
John W.
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