Why not have the ENY system perk up planes?
Cost is added to the high ENY planes.
This way players arnt restricted from using a plane in a unballanced stituation but they have to pay up for it. If they dont want to they can use some other plane. Key thing though is that the player has a choise.
Max perk cost for a non perk plane that is ENYed up to perk should be about 15.
In unballanced situation the cost of the perked planes should go up as well.
Tex