Hey Fellas, seems there are some likely very suitable engines out there experimental class helo's but most never make it to production, I guess the returns just aren't there. So I found http://www.rotronuav.com/ a UK based company who has gone all the way to production of some very sweet rotarys. The twin rotor 600XE rated at a max of 100hp & constant 70hp is a tiny powerhouse. Unlike many of the other engine guys out there Rotron will talk to you. The only downside I can see so far is the cost... yes, take a seat, it's going to be brutal!! The 600XE complete is a staggering 24'700 UK pounds... oouchh!!! but it is really out there by it's self for a up to date, all modern engine & if you have the $$$ it could be a winner. I'm very tempted for my next build.