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I don't think it was brought up before.

The tags x120 and x51, don't they mean the same thing?

Should one be a synonym of the other? Note that the latter has no usage guidance as of writing this. Perhaps one is a subset of the other, topic-wise. Also, given the tag guidance of the former...

Flight dynamics is the study of the physics driving the performance, stability, and control of aircraft ...

... shouldn't x197 be a synonym of it? It appeared 183 times out of 197 without it. In other words, the grouping meant to be achieved by the tag system, has been broken here.

Note that SE's tag system is not hierarchical:

Jeff has stated there will never be hierarchical tags ...

— Hierarchical Tags

See help center for tag usage: https://aviation.stackexchange.com/help/tagging

To consider based on replies so far:

  • A new clear tag for steady-state questions; retagging is easy
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shouldn't stability x197 be a synonym of it? It appeared 183 times out of 197 without it. In other words, the grouping meant to be achieved by the tag system, has been broken here.

I don't agree with the premise of the question. ("It" apparently referring to the flight-dynamics and/or flight-mechanics tag.) I'd say that the failure that has taken place here is not that stability is a synonym of some other tag, but rather that users have simply failed to select a broader "umbrella" tag such as flight-dynamics and/or flight-mechanics, in addition to the "stability" tag.

Stability should definitely not be viewed as a synonym of "flight-dynamics" or "flight-mechanics". The "stability" tag needs to be kept, regardless of what happens to the "flight-mechanics" tag. It is useful to be able to find questions that only deal with stability and not with other aspects of flight-dynamics and/or flight-mechanics. And yet this is in no way indicative that the flight dynamics and/or flight mechanics tags wouldn't serve a purpose, if properly used (i.e., if used more often.)

This answer is not meant to weigh in on the question of whether or not "flight-mechanics" is adequately covered by other tags. Just was concerned that the discussion might be turning in a direction that threatened the "stability" tag.

The "stability" tag is certainly a subset of the "flight-dynamics" tag (and probably also a subset of the "flight-mechanics" tag), but losing the finer-scale categorization afforded by the "stability" tag would be a mistake.

Here is an example of a question that should be considered within the scope of the flight-dynamics and/or flight-mechanics tag-- arguably both-- but is not really strictly a question about any aspect of "stability", since the aircraft is simply presumed to be in a steady-state climb -- Does lift equal weight in a climb? The point is a little bit obscured because the asker of the question does go into some detail about what would happen if the forces were not appropriately matched to the flight path, which does touch on stability dynamics-- but the question is answerable without getting into that at all.

Here's another question about forces, where the fact that the aircraft is in a steady-state situation is simply a "given", without getting into "why"-- What produces thrust along the line of flight in a glider?

A question about stability, on the other hand, would look at the balance of torques generated by the wing versus the tail, or would look at the "phugoid" oscillation generated when lift is temporarily larger or smaller than it "should" be for the instantaneous direction of the flight path, etc. All of which would be a subset of flight-dynamics and/or flight-mechanics.

It has been suggested to create a new tag labelled "steady-state". The current answer is not weighing in on that either for or against (though that would seem to go against the guidance here (" Even if you have sufficient reputation, you should only create new tags when you feel you can make a strong case that your question covers a new topic that nobody else has asked about before on this site."), but regardless of whether or not that is done, the current answer supports keeping the "stability" tag as a useful tag.

This related ASE meta answer should give a clearer picture as to where I'm coming from about why it should be ok to have tags that are subsets of other tags-- https://aviation.meta.stackexchange.com/a/4194/34686

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  • $\begingroup$ Since specific-tags are preferable, can you please expand (in the answer body) on what topics would be covered by flight-dynamics that are not stability related? Question examples from the site would also be of help. $\endgroup$
    – user14897
    Apr 20, 2021 at 14:24
  • $\begingroup$ Re update: looks like a new steady-state tag is needed (perhaps as a suggestion: [steady-state-flight]). This should not however interfere with the topic at hand if stability is merged with dynamics; retagging with a new tag later is very manageable. $\endgroup$
    – user14897
    Apr 20, 2021 at 15:21
  • $\begingroup$ @ymb1-- see last update (at end)-- I support keeping the "stability" tag. $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 15:24
  • $\begingroup$ @ymb1 -- I guess I'm really not on board with the whole concept of trying to reduce the number of tags attached to any given question as long as they are not simply redundant-- having tags that are subcategories of other tags seems very useful to me. Don't necessarily disagree however w/ ideas that 1) flight-physics may be too broad to be useful and b) flight-mechanics may be pretty much redundant w/ flight-mechanics or vice versa, at least as we seem to be using them in actual practice here. $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 15:25
  • $\begingroup$ Seems useful, but unsupported. The main issue remains: "the grouping meant to be achieved by the tag system, has been broken here." If dynamics encompasses stability, dynamics will be the new stability, and if you type stability, it will automatically suggest dynamics. Nothing is lost; what is gained: properly grouping the topics. Kindly mull it over. $\endgroup$
    – user14897
    Apr 20, 2021 at 15:27
  • $\begingroup$ (Was supposed to read-- Don't necessarily disagree however w/ ideas that 1) flight-physics may be too broad to be useful and b) flight-mechanics may be pretty much redundant w/ flight-dynamics or vice versa, at least as we seem to be using them in actual practice here. ) $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 15:31
  • $\begingroup$ @ymb1 -- answer now expanded $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 15:44
  • $\begingroup$ Re I'd say ... users have simply failed to select a broader "umbrella" tag such as flight-dynamics and/or flight-mechanics, in addition to the "stability" tag. -- That's not how SE tags are meant to be used. I thought I mentioned that topic here, but apparently I did not (a note has now been added to the question). Thanks for the clarification to your answer though. $\endgroup$
    – user14897
    Apr 20, 2021 at 15:51
  • $\begingroup$ @ymb1 -- re "That's not how SE tags are meant to be used."-- what exactly do you base that on? I read over the help center guidance carefully (aviation.stackexchange.com/help/tagging). The statement about a tag being able to be the only tag doesn't seem to me to argue against umbrella tags. And the statement about avoiding meta-tags doesn't seem to either, as all the examples of meta-tags provided said essentially nothing about the content of the question at all. (ctd) $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 15:56
  • $\begingroup$ @ymb1 -- but now I've seen you've provided this new link meta.stackexchange.com/questions/11922/hierarchical-tags . I've never seen that content before and I don't really think it is consistent w/ how we are doing things here. But if you really want to take that approach, then I find I tend to be against the creation of a "steady-state" tag, as it would too finely subdivide things; those topics would be better left under "flight-dynamics" and/or "flight mechanics" in my opinion. But why do we have an "airspace" tag and a "class-e-airspace" tag, if hierarchical tags are not allowed? $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 16:01
  • $\begingroup$ @ymb1 -- I think the issue about having or not having hierarchical tags needs to be addressed in a specific question here on ASE meta $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 16:04
  • $\begingroup$ @ymb1 -- I mean, does it really make sense that a) someone searching specifically for questions just about Class E airspace should not be able to have a tag that selects only those things, or b) questions that are given the "Class-e-airspace" tag are automatically ineligible for the "airspace" tag? Not to me-- but-- I've never created any tags as far as I recall so-- $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 16:12
  • $\begingroup$ Briefly: some of the popular tags are a mess, and they can be easily fixed. BTW [class-e] is specific and good, [airspace] is also good for general airspace questions, but pointless to be attached to every class-e question. But now we're going off-topic I think. $\endgroup$
    – user14897
    Apr 20, 2021 at 16:19
  • $\begingroup$ @ymb1 -- "['airspace' is]... pointless to be attached to every class-e question." -- I couldn't disagree more. Who gets to decide these things, anyway? $\endgroup$
    – quiet flyer
    Apr 20, 2021 at 16:23
  • $\begingroup$ I'm in The Hangar $\endgroup$
    – user14897
    Apr 20, 2021 at 16:24
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Flight-mechanics seems to be intended as a label for Newtonian mechanics in flight. The nomenclature for this that I have seen and am familiar with is flight-dynamics.

Flight-mechanics may be confused with flight mechanics -aircraft technicians.

And indeed as @quietflyer states, Stability is a sub-set of flight dynamics. There are many interesting 6-DoF aviation questions involving forces and accelerations in flight, outside of longitudinal and directional stability.

My view on the matter:

  • Questions marked Stability are also automatically candidates for application of the additional flight-dynamics label.
  • Questions marked flight-dynamics should not be automatically labeled Stability.
  • flight-mechanics seems to be the same as flight-dynamics, which is the correct term.
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