Heli Invasion - shoot helicopt

Stop helicopter invasion! 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. 
-Upgrade weapons`s rate of fire and amount. 
-Using box2d physical engine to simulate the collision, flying,exploding. 
-Support all android devices.