I don't know why, but for some reason Rakan's W ability doesn't airborne opponents randomly
look at Lux
on that GIF
Rakan's airborne doesn't have a stun component so its just for interrupting channeled abilities (ults and the like) or stoping basic movement, you can still roll, dash, or blink out of it and if you notice lux started casting her ult before the airborne effect applied, in lux's case her ult CANNOT be stopped once cast, even by death (but depends on where in the cast animation it was at before she died).
Again unlike most knock ups rakan's has NO stun component so ALL abilities that are instant cast (do not have a wind up, or can be used while moving without interrupting movement), and all movement abilties can be used while airborne, just like any displacement effect. if you displaced her to another location (like when she flash ults to change the area her ult hits BUT KEEP THE ANIMATION of where she fired it the same(but the area of effect being in the new direction she flashed to!) instead of stationary her ability wouldn't have "hit" is the upside of displacements.
Looking more closely at it, it looked like your charmed her at the same moment your would have displaced her as well, CHARMED is a forced movement effect which do not stack the way you hope they would (they interact unintuitively) so she was walking forward. for the record she was CC'd longer from the charm than if they airborne effect had applied and she landed, a charmed unit cannot be stopped from walking toward the charmer's location at application unless there is forced stopped movement component(nami E debuff with 1200 ap, amumu ult, etc, morg Q etc will allow them to keep moving forward then they will be rooted after the charm/displacement wears off in their new location). This was a BAD rakan play as you applied all your CC simultaneously instead of pacing, so you got 1 second of CC instead of the full 2-2.5 seconds possible.
If you look closely your airborne effect would have applied had you waited 0.25-0.5 seconds longer, instead it applied just before charm fell off while lux was still being forced to move invalidating the knock up (which again ONLY displaces it is not a "stuns and knocks up" effect like alistar Q), this is nuance of rakan seperating those that have mastered him to those that havent (though actually this is a basic mechanic you should pick up from co op vs ai in your first few games with a champion with 2 or more hard CC abilities or for champions with CC/displacement combos, incidentally if Alistair's QW combo was modified to precisely interact and ensure Q applies EXACTLY when W ends if queued properly in the spell buffer(something that separated skilled alistar players from unskilled ones, or those with over 29 MS, etc. But no other CC chain or displacement combo champions have been modified in this way (though malphites/WREQ WORKS because his E buffers to hit EXACTLY when the airborne effect ends so the damage from his E applies (ground targeted spells CANNOT hit airborne enemies during specific windows of the airborne, this was just something shipped as is, and is partly to due with him being unstoppable during ult, aside from that only a few champions can cast spells at the same time as other spells so this interaction isn't too important (lissandra W, etc) in game except in some very niche cases, where its okay because it shows player skill))
INCIDENTALLY rakan's W is a ground targeted spell so it will have some interactions with trist E and certain other movement abilities, and be useless when trying to chain airborne effects (it will not apply to a zac coming in for a landing, etc).
