DO NOT BUY THE UJ377 HELICOPTER FROM YIBOO!!!! I HAD 2 OF THEM AND BOTH AFTER A COUPLE OF DAYS WILL NOT FLY ANYMORE!!! WITHOUT A CRASH!! THESE ARE JUNK AND FOR THE $ ITS NOT WOTH A COUPLE OF DAYS OF PLAYING TIME!!!!!

SOURCE: Yiboo AH-64 3D RC Mini Apache Helicopter

There is a small set screw on the bottom gear that holds in the upper shaft. You can see these gears through the belly of the helicopter. I had the same problem with the top rotors, and had to go in and re-insert the rotor shaft and tighten the set screw. I applied locktite to the threads to prevent it from backing out. It works now, but one problem I notice is that there must have been a spacer bushing between the two gear wheels. Without the bushing, it will still fly, but I can feel some play in the upper shaft and wonder if over time that the counter spinning gear wheels will start to wear against eachother.

SOURCE: my helicopter won't fly, it just spins around.

i had the same problem took it back to dealer it work 4 about 10 mins they are prone to this problem i bought a different 1 same problem stick to scalextric at least it works

SOURCE: my rc helicopter can not fly it spin in floor

Hi
This type of helicopter uses a fixed pitch blade. Have you recently replaced one or all the blades? If the blades are correctly positioned then once the motor comes to speed, the pitch of the blade creates enough lift to overcome the force of gravity. The problem you're having can only be that the motor is not coming to speed or the blades have been replaced but the pitch is now at the wrong angle.

SOURCE: remove and replace balance bar?

Were you able to find a replacement balance bar? I broke mine and can't find one? Thanks!

SOURCE: I have a Yiboo UJ4705 RC Helicopter that I need

http://www.ujtoys.com/4703-Mini-Metal-Gyro-3-5D-Assorted-Parts-Set-p/uj4703-3.htm