These items should be double-checked before you attempt to fly your new helicopter. These items should be checked for both helicopters you have built yourself, and also for prebuilt ARF kits.
The main rotor blades should be mounted for the correct rotor head rotation. For most helicopters this is clockwise. For the Corona this is counterclockwise.
The tail rotor blades should be mounted for the correct rotation. Turn the main gear by hand so the main rotor blades are rotating in the correct direction, and the tail rotor blades should be rotating in the correct direction also. If the tail rotor blades are rotating in the wrong direction:
Make sure the tail blades are not mounted backwards.
If the heli uses a belt-driven tail, then ensure the tail belt is twisted in the correct direction.
If the heli uses a gear driven tail, then ensure the the tail drive gears is meshing at the correct point on the main gear.
Check the meshing of all gears, and ensure they are not too tight. If your gears (including bevel gears and motor pinions) are meshing together too tightly, you will lose a lot of power and your flights will be very short.
Make sure that the gear teeth only mesh together by about 3/4 of a tooth. This can be easily set by putting a plastic bag between the gears and squeezing the gears together, then removing the bag. You can check the mesh by holding one gear and rotating the other. If the gear mesh is correct, there should be some free play. This will allow the gears to transfer power more efficiently.
If using a tail belt drive, make sure it's not too loose nor too tight.
The flybar paddles should be parallel to each other. If you have the KSJ-624 paddle gauge set, then you should use these to align the paddles. (Not applicable to the Corona.)
The flybar should tilt very smoothly and easily. If you blow on the flybar paddle, the flybar should tilt. If the rotor head is built absolutely perfectly, then the flybar paddle should tilt down, then bounce and come back up. You should be able to keep the flybar paddle bouncing by blowing on it with the right timing.
If the flybar does not tilt easily, then you will have very little cyclic control, which is dangerous. This problem must be fixed before you attempt to fly the model. To fix this, you may need to:
Loosen some ball links using a pair of pliers or ball link sizing tool
Lubricate the flybar pivot with powdered graphite