For the RC plane mission just shoot up the 3 that are closest first, then fly across to the final two, but go to the furthest one of these first as i find the last one is driving back towards where youve gotta land the plane

For the helicopter in the fuel depot i use a plane and fly high over the depot, then bail out and parachute down commando stylee saves getting shot to death going through the harehouse

And the helicopter on the weed mission should only take one hit to down