Please suggest me which autopilots is best for 600 class nitro helicopter , because there is not available any expert for my training , please help me

Go for a Bavarian demon. Check heli freak for related threads

I assume you are a beginner heli pilot. I would advise you to buy a simulator program instead of buying any particular rescue unit.   Practice for few days (as a learning tool not as a game). Try to avoid crashes and learn different orientations first. Once you are comfortable then you can buy a small size machine or the size you feel most comfortable in. A crash on a 600 size machine might not only be dangerous but also can cause a noticeable dent in your pocket. One saved crash will cover the money you spend in buying a sim. Such crashes and frequent repair costs discourage most new flyers and they abandon this hobby early on. Simulator, on the other hand, will remain useful even when you have mastered basics. You can practice new moves before trying them in real world. Moreover, this might give you some idea if helis are for you or not before you invest yourself further into this. They are not 100 percent realistic but still good enough.

Do you already have this machine with you?

I already have two Bavarian demons. These work well on Nitro as I have heard. I like these units but these days there are a lot more alternatives available. Earlier these worked fine but were pricey. Such units are not really autopilot units as you are still the one responsible to fly the heli. Different units have different features and stabilization modes. Some provide rescue features. In rescue mode, your machine orients itself to predefined orientation and optionally gains altitude just at the flick of a switch.

Hi,

Shakti, nice brief up on the Heli start up for beginners. I too have a TT 50 nitro lying and scared of flying it.
Although have flown multirotors a lot and recently fpv drones added to my experience.
Earlier used to hover the align 450 only, now started to move around a bit, but loose orientation.
Since flying a fpv drone and heli is a lot same except that the drone will self stabilize and heli will not.

I think flying fpv in acro mode should get u closer to heli flying for practice. atleast a crassh on drone is affordable.

regds

Earlier NAZA-H was available for helicopters, dont know if still available.
I think a FBL is more like a quadcopter. if setup properly should be able to get going.

regds

Thanks to all friends for good suggestion
I have already a 600 class helicopter but planning for purchasing a new small heli for training