i know the use of the trim button on the uh-1 helicopter but i just get confused why i heard that i have to "press the trim release and fly the aircraft to a new altitude and then release, the new altitude will then be held."
how do you fly an aircraft to a higher altitude when you depress your trim release button?(on a uh-1 huey) i thought that the trim release button is used to relieve the force on the cyclic?
As John and AC mentioned, we're talking ATTITUDE, not altitude. That appears to be a typo on your part or whatever you were reading from. I believe your setup is probably similar to the IFR setup on the 206L I fly. The trim release is not actually part of the autopilot, it is simply a cyclic centering device.
The cyclic is held in position by springs and magnetic brakes. In order to move the cyclic, you have to hit the trim release button on the cyclic, move the cyclic to change the attitude of the aircraft, and then let go of the button. All the system does is basically hold the cyclic for you. It is not part of the autopilot system.
I hate this system (but it's required for IFR). You can actually move the cyclic enough even with the magnetic brakes engaged to do small attitude changes. However this causes a problem when you reach the limit of the play in the cyclic and you want to go a little further. You're holding a little force at that point, so when you hit the trim release button the cyclic jumps a little, and everybody on board the aircraft can feel it. So the alternative (and what I generally do) is to hit the button every time I move the stick which is basically all the time trying to hold a perfect attitude.
Meanwhile you also have the coolie hat trim on the cyclic. This is a totally different system, and IS part of the autopilot. It allows you to use the coolie hat to set the attitude, and then the autopilot will hold it. This system is very smooth and works well IMC. However, most of the time if I'm going to turn on the autopilot, I just put it in heading or nav mode with altitude hold.
In altitude hold mode, anytime you pitch the aircraft with the coolie hat, it will cancel the altitude hold mode on the autopilot. You pitch to climb or descend, and when you reach your new altitude you can then hit altitude hold again to resume the autopilot altitude hold mode.