At what point is does a creation based on some else's creation no longer a copy and is considered a variant or new creation? Is there a precentage thingy or is it up to the moderators discreation? Here Compared to this. In my opinion Just changing the wheels and adding car engines with a lack really trying to make it different or stand out from the original is a copy. Am I wrong? Especially when it be changes I would have done myself being I made the original.
What you did is add better wheels right. Tell me if you added anything more. In you case it is an improvement so it can be considered a new varients.
When you add weapons and a new color scheme it's not considered a new varients. You need to add things that will make the plane fly better or add more detail to the plane. But I may stand corrected.