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CRJ700 family goes canvas

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Re: CRJ700 family goes canvas

Postby tdammers » Tue Nov 27, 2018 8:22 pm

it0uchpods wrote in Tue Nov 27, 2018 7:46 pm:Hi tdammers,
you are still missing this commit in master: https://github.com/tdammers/CRJ700-fami ... 1a4323f8ac

Merging from nl256 or cherry picking into master will work.

J


It appears that you are right. I think I forgot to pull in the nl256 branch from github before merging into master. Should be fixed now.

Now putting my teeth into the standby instrument; it's kind of useless right now because it drifts way too fast, and I want the "CAGE" button to do the right thing (set the attitude indicator to "level").
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Re: CRJ700 family goes canvas

Postby it0uchpods » Tue Nov 27, 2018 9:34 pm

Are you sure that the CAGE button should do that? then it would be off, as the CRJ does not sit level on the ground. In the Airbus, it aligns it to current attitude when pull the knob. (in the old AI at least, the new IESI automatically aligns to current att)

Josh
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Re: CRJ700 family goes canvas

Postby tdammers » Wed Nov 28, 2018 12:38 pm

it0uchpods wrote in Tue Nov 27, 2018 9:34 pm:Are you sure that the CAGE button should do that? then it would be off, as the CRJ does not sit level on the ground. In the Airbus, it aligns it to current attitude when pull the knob. (in the old AI at least, the new IESI automatically aligns to current att)

Josh


I don't actually know what it does in the real aircraft; the current behavior seems wrong in any case.

A comment in the documentation mentions that in the real CRJ, you have to keep the aircraft level while caging the standby gyros, so from that I concluded that the CAGE button will simply calibrate the attitude indicator to a level position. This makes sense in that it would allow you to still calibrate the standby instrument after a main instrumentation failure, as long as you have a visual horizon reference available.

Further googling unearths this: https://www.studyblue.com/notes/note/n/ ... k/11048093

Assuming that the standby instruments in the 700 and 200 are more or less the same, this would suggest that the CAGE button would align with the horizon as indicated by the other attitude indicators, but because the standby gyros are subject to acceleration-induced errors, the calibration should be done in level, unaccelerated flight. So you are probably right; CAGE should just reset the attitude indicator.

So the question is what a realistic error model would be. Apparently the standby instrument uses piezoelectric gyros, not vacuum-driven mechanical ones, so I guess it might not drift significantly. It will, however, be off in accelerated or decelerated flight; and depending on the types of electrical failures, it might stop working anywhere between 0 and 11 minutes.

So maybe what we should do is this:

- A property rule that applies the acceleration-based error on the fly (add scaled longitudinal acceleration to pitch and roll indications)
- A Nasal job that periodically adds a small amount of drift to the standby gyros
- A binding for the CAGE button that resets the standby instrument's drift to negative acceleration error (simulating what would happen if you cage the instrument during accelerated flight)

And on top of that, we might want to model electric failures for the gyros, treating the standby instrument separately (i.e., keeping it available longer than the PFDs).
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