Maptor, I will try to say this one more time. Gravity can be (almost) be perfectly simulated by constant acceleration. That is what gravity is. The mathematical formula for gravity is acceleration. The only difference is that in FE, the earth is coming up to meet us, and in RE, we are going down to meet earth. According to relativity, these are exactly the same. It all depends on your frame of reference.
Regarding UA, it is a mysterious phenomenon that is sort of like a "wind" that pushes the 'flat' earth from the bottom. WE are not directly affected by UA, the Earth is. So UA is not holding the feather up, or trying to, because eventually it will fall. Instead, it is pushing the air on the earth which in turn pushes on the feather. This push by air is not enough to keep the feather floating forever, because eventually it will fall through the air that is less dense than it, and hit the ground.
Good thing to note. Things that are more dense than other things will always try to equalize themselves. More dense things tend to fall towards the ground, which can be seen with oil and water. Feathers are more dense than air. They will always fall towards the ground unless another force is acting on them. This can be a brisk wind or someone picking the feather up.
Anything else, Maptor? I highly suggest you spend your energy on other topics, because hypothetically, if UA existed, it would almost perfectly simulate gravity. Exceptions to this would be experiments proving that gravity is weaker on the equator due to centrifugal forces and gravity being slightly weaker during a solar eclipse.