Wednesday, June 24, 2009

Do Not Work Around Our Bugs!

For most of its beta run, X-Plane 930 beta 14 didn't handle engine power limiting very well*. Here's the short version of the saga.
  • Real planes sometimes have systems to limit total power output, because the power output of the engine (whether torque or internal temperature) can exceed safe operating limits at sea level).
  • With X-Plane 9.00 you could set a critical altitude for an airplane - below this altitude, X-Plane would limit the power output of the jet. The idea is (roughly) to simulate these limiters by derating the engine's power output below this "critical altitude".
  • This feature was really only meant for reciprocating engines - when Austin discovered in 9.20 that people were using this for turbines (understandable, given that there was no alternative) he simply disabled the feature for turbines. That wasn't so good.
  • To resolve the situation a little bit more cleanly, X-Plane 9.30 has a setting per airplane called "FADEC - automatically keep engines from exceeding max allowable power or thrust" that, when checked, gives you version 9.00 style behavior.
Now this was mostly good except for one problem: the betas would default this setting to "off" when loading an old plane. Since version 9 always acted as if the "FADEC"** was on, this meant that old planes would need to be edited.

Finally with beta 14 we switched things: beta 14 and newer default old planes to have the FADEC checkbox on, so that planes match their old behavior - you can turn the check-box off if you don't want this behavior.

There is one final hitch: if you already went in and edited your airplanes for the earlier betas, you will find that they are now set wrong. You will have to reset the check-box. If you go back to the original, unedited, 920-compatible airplane you will find they "just work".

I mention all of this to make two points:
  1. File formats for new features are subject to change during beta. In this case, the file format for the new FADEC check-box (introduced in 930) changed at beta 14. The OBJ syntax for dynamic lighting changed during beta too. Don't do "bulk" work (e.g. change a large number of planes in the same way ) on your fleet based on betas - you might have to redo that work again! Wait until the sim goes final. That's when the file formats are locked up.
  2. Don't work around bugs in the sim. I have seen so many forum posts where there is a trivial bug in the sim (e.g. the sim is just screwed up in a simple way) and authors go in and update scenery to work around the bug. File a bug, then wait! If you work around the bug, we can't fix the bug, and if we don't fix the bug, then the bug just bites other users.
* Disclaimer: I don't do systems, I don't know anything about airplanes, so this whole discussion will be heavily simplified. The point of this post is not to get into a discussion of FADECS - in fact, don't even bother to post about FADECs, I'm not going to approve them. If you want to talk about FADECs and engine modeling, email Austin. The point of this post is one about file formats and compatibility.

** FADEC isn't a very good name for this feature - the feature generically limits power, without specifying a mechanism. My understanding is that some airplanes have mechanical limters, like a pressure valve on a turbo. Some planes have no limiters at all...ask a pilot "can you cook the engine by pushing the throttle too far" he will say "I'm not going to be the one to find out."

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