I wrote
> Sent: 25 July 2004 22:32 > To: 'FlightGear developers discussions' > Subject: RE: [Flightgear-devel] Tried the Spitfire > > > > > Andy Ross wrote > > Sent: 25 July 2004 21:07 > > To: FlightGear developers discussions > > Subject: Re: [Flightgear-devel] Tried the Spitfire > > > > Vivian Meazza wrote: > > > I'm just working on the fuel gauge for the Spitfire, when I > > > ralised that I haven't modeled the fuel system correctly. At > > > present both tanks feed into the engine. What should happen is > > > that the upper tank feeds the lower tank which feeds the > > > engine. Is there any built-in way of doing this? > > > > One way to do this is to always make sure the lower tank is > > selected, and the uper one is not. Then have a Nasal timer fire > > at some sane frequency (mayby 5Hz) or whatnot that takes fuel out > > of the top tank and adds it to the bottom one according to the > > current pump configuration. > > > > It's not hard, really. You can look at the existing fuel.nas > > code for examples. The only gotcha I can think of is that the > > frame rate isn't constant: you want to use the time-elapsed > > property to calculate the amount of fuel to transfer, instead of > > assuming a constant amount per iteration. > > > > Thanks Andy. I have already put together a Nasal script, using fuel.nas as > a > model. It wasn't hard, once I had figured out how to make it re-iterate. > Nasal is a delight to use: doing exactly what we want. > > The script tries to model the fuel system. Both tanks are connected to the > engine, and there is an open pipe connecting them, so fuel is transferred > from the upper to the lower whenever there is room in the latter until the > former is empty. So good so far - that bit works. The gotcha is that the > engine stops when either tank is empty, rather than when there is no fuel > in > any tank. I can't see a way around that without tinkering with the logic > of > fuel.nas. That said, the logic of fuel does seem a little odd. Have I got > my > analysis of the logic wrong? Where is "kill-when-empty" set? I can easily > adjust fuel.nas to work for the Spitfire, but of course I don't want to > rot > up any other model. How to proceed? > I think that something is going wrong in the fuel.nas script. At line 72 kill-when-empty is being set to true for tank[0] on the first pass through after it runs out of fuel, thus setting out-of-fuel to true and stopping the engine. I don't think that this is intended in the script, despite the comment at line 53! I attach a revised script which stops this happening, but I had to resort to some pretty inelegant programming to do it. Is this a NASAL bug, or something local? Regards, Vivian
fuel.nas
Description: Binary data
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