The overlap between aerodynamics and flight is far too small to link these categories as synonyms. Only a small subset of things which fly (in fictional worlds) rely on a subset of aerodynamic principles (lift and drag). I think it’s pretty clear that racing haulers across the arctic tundra, racing hovercraft, and land yachts, as well as a supertall, 5,000 km, or 100 mile high building are going to need some expertise from the field of aerodynamics, but are very unlikely to be concerned with really much of anything to do with flight such as stall speeds, wing musculature, glide slopes, aerial maneuvers, hitting aircraft or birds, and vertical climb rates. It’s also likely that spiderlings, ginormous bumblebees, witches on moonless nights and trying to balance on their brooms or protect themselves, people walking on air, others with Superman-like powers, and floating islands should be very concerned with all those challenges associated with flight, but don’t need much if any help from aerodynamics. Monica approved the aerodynamics > flight synonym assignment back in 2019 but I can’t find anything for a discussion about it. That was a mistake, this is now the discussion.
Recommended definitions of the two tags:
Aerodynamics: For questions about the interaction of air moving around objects, particularly in relation to the forces and motion they experience as a result. The tag encompasses the principles and theories that govern the behavior of air and its effects on various objects, such as buildings, aircraft, automobiles, ships, organisms, and sports equipment. Use this tag when concepts like lift, drag, thrust, downforce, turbulence, boundary layers, flow separation, and weight, are crucial in designing efficient and stable objects within an atmosphere or gaseous medium.
Flight: For questions about things within the air in opposition to gravity. This may be by any means such as aerodynamic lift, jet propulsion, buoyancy, magical flight seen in folklore and mythology, a superheroe's power of flight through innate abilities, or any technological advancements. Also included are concepts such as dispersal of seeds through the air, "ballooning" transportation of spiderlings, avian flight, or any other organism traveling through the air.
My primary reason for taking on this site correction (which I really believe it is) derives from the extraordinary answer posted to my navigation question by @William. This user is not a frequent participant in this exchange with merely 5 answers spanning 5 years however, as I think this answer shows, it is a mistake to rate users by their volume. There is no logic in the strategy of achieving highest quality by throwing more... things... at the wall and seeing what sticks, as we do in deciding what topics are in demand on here.
My secondary reason is a personal vested interest in ground effect vehicles—things which actively avoid flight—which will have little benefit from experts in flight (I know, I have asked pilots. Ground effect is an evil they want to be rid of). If there is another "William" in the fringes watching an aerodynamics tag, I want that user's input, and so I want that user to have a home here even if they only contribute once per year, or less.
Quality is NOT improved by volume; noise is. And my decision to make the correction post was driven by precedent. But despite the circular logic—you have prevented questions from using that tag, the synonym clearly is at cause for some of that loss—per some comments, let's talk about numbers. For reference, I will use a community-elected moderator Monica's decision to remove the [tactics] synonym from [warfare] in 2019. That separation resulted in 23 auto-retagged queries getting the [tactics] tag. There are currently 62 questions about aerodynamics that exclude the [flight] tag, including high speed trains, high speed "chasers" evolved from caterpillars, and telekenetic land ships. A closer look will find some of these are involving flight—mostly ballistic, such as my own. But what is important to note here is that this community elected moderator never once mentioned the number of queries using the tags as a justification. The very last statement under the decision to break [tactics] away from [warfare] was this: "I’m focusing on the smaller issue of this one IMO incorrect synonym."
Aerodynamics is, as even my esteemed detractor has admitted, an incorrect synonym for flight. It is a perfectly good sub-category for flight, if this were that other forum. But we do not have sub-stacks or sub-categories. We have two things which are defined as the same: synonyms. [aerodynamics] is very simply not a synonym for [flight]. Thus, the choice is to either delete the tag, or to separate the tags; but I see no logic in treating them as equals on a community resource striving for excellence.