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APU limitations & operating techniques


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In "The Boeing 737 Technical guide" book by Chris Brady I read that there were many different APUs available for the 737. Each model requires, even if slightly, different operating techniques.

I'm wondering which model IXEG ac implements and if correct warm-up, cool-down times, EGT limits, starter limits and so on are implementd.


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We model the Sundstrand APS 2000 APU. It is FADEC controlled - and in our V1.0 it always starts up (below a certain altitude, iirc) and will not "break" if you don´t adhere to the various limits. I feel that this is realistic enough, because in 10 years of flying this plane I only had to refer to the starting limits only a few times (you can start it 3 times without any waiting, but then have to wait 30mins before the 4th and subsequent attempts). Usually the APU starts up just fine. the procedure is: Toggle APU switch to ON. Release. Ta-da!


We plan to have a "wear and tear" model in future updates and versions - but I will vote strongly to not make it a "gamey" model.  If you bust a limit, it usually does not mean that the affected component will fall apart into a 1000 pieces. The limits on operations are usually designed to keep the component running without damaging it in the long run. So if you have a limit of 2 minutes between start attempts, and you only wait 1:55, the starter most likely will not fail right away...


I don´t think we will make this totally "realistic", because then you would have to fly the plane for thousands of hours before you see any "wear", but it will not be a "bust the limit by one degree and the plane will instantaneously combust" model, either. Some middle ground.



Edited by Litjan
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