at what height above the ground does a heli (T-Rex) escape ground effect?

over five feet and you should be fine...If you are trimming your heli, you need a big open enclosed garage or building.

Kind of depends on what you are flying over. Smooth surfaces like garage concrete are going to have more compared to a grass or a rough surface that will disperse some of the wind.

5 feet - yeah you're probably pretty well out of it. After a few feet you're starting to feel a lot less of it.

thanks guys

Typically, and I'm speaking from a full size helicopter point of view, the ground effect distance is equal to the diameter of the main rotor system. Don't know if that applies to RC helis because of the incredibly increased head speed or not.

I'll check the book I read when I get home but I think it is either half of the main rotor diameter or full rotor diamiter, meaning 25 in main rotor your heli should be out of ground effect at 25 in.

You learn to 'feel' it regardless of where it's 'supposed' to be. It's usually 1-2ft off the ground for my heli.
Once you learn to hover well, you won't notice it enough for it to bother you anyways.

whtmex you are right in r/c is exactly as ful size helicopter. Why do you think is different? The theory of rotatry wing in r/c & full size heli are same theoty. So in r/c is also the distance is equal to the diameter of the main rotor system

I usually get the heli going into ground at 60mph effect, which ain't pretty.