Eric has kindly uploaded the most recent release of the Spitfire model to
cvs. If you haven't already noticed, this  release adds a fuel system with
Upper and Lower tanks (which are interconnected), priming pump, fuel cocks,
and a fuel gauge.

Unfortunately, there are three problems with this release:

1. With both fuel cocks open, when the fuel in the Upper tank runs out, the
engine stops, despite the lower tank having fuel available and being
selected. This is, I believe, due to a bug at line 67 of the script
~/data/nasal/fuel.nas which improperly sets the tank property
"kill-when-empty". This problem is not unique to the Spitfire model, but
affects all YASim models. This can readily be demonstrated by taking any
such model, and using the drop-down dialog to reduce the fuel in one tank.
With the engine running you can watch the fuel in that tank run out and the
engine stop.

2. If both fuel cocks are moved to the "off" position and back to the "on"
position the engine will not start or restart, even if fuel is available in
all tanks. The Simulator has to be restarted to overcome this problem. This
problem is caused by the logic of fuel.nas, and is not a bug.

3.  When a tank is empty, the tank is de-selected by fuel.nas. Thus the
position of the fuel cock levers on the Spitfire panel do not necessarily
reflect the state of the tank. Again, this is not a bug, but a consequence
of the logic of fuel.nas and of the operation of the levers.

Solutions:

1. Short term. 

A. Use only the Lower Tank. Although this is contrary to the POH, it works
perfectly well.

B. Avoid setting both fuel cocks to "off".

C. Move the fuel cocks through their full range to realign them

2. Medium Term.

I attach a script - fuel-new.nas which is a minor modification of fuel.nas
that works around the bug at line 67 and modifies the logic so that problems
1 & 2 above are corrected. Problem 3 remains. You can use this script to
replace fuel.nas if you want, or perhaps, if accepted, it could be uploaded
to cvs as a temporary replacement for fuel.nas. I believe that it will work
for all YASim models, and has no adverse effects on non-YASIM models: don't
throw fuel.nas away just in case!!!! (But don't leave both in ~/data/nasal).


3. Longer term.

It would be a better solution if the problem with line 67 could be
investigated so that it can be made to work correctly. Similarly, the logic
of fuel.nas could be reviewed to correct problems 2 & 3 above. I am well
aware that Andy is very busy right now, but perhaps he could spare some
time? On the other hand, this is not a show-stopper.

Melchior Franz has been most helpful in helping me with testing the problems
and the replacement script. I think  that he may be in a position to confirm
both my findings and the efficacy of the new script.   

Regards,

Vivian

Attachment: fuel-new.nas
Description: Binary data

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