Great improvement from the first version.
-Upgrade whole UI graphics.
-Provide “Recovery” item in game.
-Support challenge mode, hard with more fun.

HeliInvasion2 – Survive waves of invading hostile helicopters! Shoot them with your cannon, rocket, rock, wind, and try to make them rotate until they explode. Let them knock into each other to create massive chain reactions of explosions! Earn money with each exploding helicopter to repair and upgrade your cannon.

-Support Multi touch after getting double shell.
-Compete with your friends through online Leaderboard via the GameCenter system!
-Upgrade weapons`s rate of fire and amount.
-Using box2d physical engine to simulate the collision, flying,exploding.
-Support challenge mode.

BTW， no one can last a minute in Challenge mode.