Rc helicopter won't lift off

SOURCE: Yiboo ch-47 rc helicopter: Rear

If you twist its rotors a little more then the lift can increase. But try to twist then only if they could be else you may become minus them and I would hate it.

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: My helicopter won't take off,

This issue is the "Drive Gear Unit" It is the small gear just above the motors which is attached to the very large gear. You will have seen several posts indicating that sometimes this gear shifts and does not engage the larger gear. In my case I looked and say that it was indeed trying to engage the larger gear, however the gear is stripped (the teeth are nearly gone). The sound that you are hearing is the sound of the gear slipping against the Bigger gear. I have a UJ365 which is a newer model. To my disappointment I cannot find a "Drive Gear Unit" anywhere on line. The copter will not function without it. This issue is that it takes the lift of both rotors to lift the copter into the air. There are two motors (one for each rotor) and each motor has one of these drive gear units. Each of these attach to the larger gears which turn the rotors. The rotors each turn in the opposite direction. This is what keeps the copter from continually turning in one direction. When one of the "main Gear Units" becomes damaged it seems to have three noticeable effects. (1) There is a noise that is the gear grinding against the bigger gear. (2) Because many of the teeth are stripped the drive gear engages the bigger bear only some of the time, this causes the rotor to turn slower and in-turn causes there not to be enough lift from the rotors to lift the copter. And finally (3), someone noted that copter wants to spin in one direction. Understanding the above, you can now understand that if one of the rotors is not reaching its full potential to turn, it is also not reaching its full potential to counter act the other fully functioning rotor. Thus the fully functioning rotor is forcing the copter to spin in its direction and the malfunctioning rotor is not spinning fast enough to stop the spin.

So this is the answer to your questions, hopefully on the older models there will be parts available for you to replace it. The copter cannot work until the part is replaced.