I've never seen one of those Cox planes make a successful take-off from grass...

You can hand launch it though if you don't have a paved runway available. It flys slowly enough, even though its a bit underpowered for some people's taste. (gotta fly on the wing.. can't just guide the engine around)

The plane can be rough trimmed by holding it up in a breeze appropriate for a kite, and gently tossing, and catching it. (you can probably walk fast enough to keep up) Early todsses, catch it QUICK, and adjust the trim to counter whatever direction it wanted to go. When you can toss it and let it glide forward, landing itself... its trimmed.