Timeline for Why does an elevator deflection (step) result in a nonzero short-term-steady-state response in pitch rate?
Current License: CC BY-SA 4.0
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| Sep 7, 2018 at 12:47 | history | edited | Sanchises | CC BY-SA 4.0 |
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| Sep 7, 2018 at 12:44 | comment | added | Sanchises | @Zeus True. I was reasoning from the idea that the error dynamics are unstable when using the short-term model as an observer precisely because the conditions (the system matrix) do not remain constant in general. I will edit the answer to be a little bit more precise. | |
| Sep 7, 2018 at 7:04 | comment | added | Ben | I truly appreciate all the comments. I was afraid people would give replies on things I already knew and not address the real issue, but that second paragraph was exactly what I was looking for. Thanks! | |
| Sep 7, 2018 at 0:38 | comment | added | Zeus | Sorry, @Sanchises, my point was that the term short-period does not mean 'short term'! It means 'considering the states with quick response' (i.e. short period / high frequency). It is possible and valid to use a short-period-only linear model for quite a long stretch of time, as long as the conditions remain valid (V, H ~ const). For example, the airplane may exhibit pitch oscillations (being underdamped), while not departing the trajectory significantly. Or a simulator for the task of aiming a gunsight at a distant target might use a short-period model successfully. | |
| Sep 6, 2018 at 10:12 | comment | added | Sanchises | @Zeus I meant to say that the name implies that it only predicts short-term effects and is invalid in the long run. Of course, the model was created with the reason to get a simple estimate of the short-term behaviour, not the other way round. Thanks for your comment. | |
| Sep 6, 2018 at 7:06 | comment | added | Zeus | Excellent answer! The only minor note is that the name 'short period' is not because the model is just 'oversimplified'. It rather happens that when we linearise the full model, for typical airplanes the states ɑ and q (in pitch) change much faster than the others (altitude and speed), and thus it makes (some) sense to analyse them separately - always, as you note, keeping in mind the limitations. But for very small airplanes, and particularly models, the frequencies are much closer, and it may become incorrect to consider 'short-period' motion for them separately at all. | |
| Sep 4, 2018 at 12:18 | vote | accept | Ben | ||
| Sep 4, 2018 at 12:02 | history | answered | Sanchises | CC BY-SA 4.0 |