Because of the bad weather on Saturday, I did not get to see the 3DNT in action ... and according to weather reports, this weekend does not look any better [&o]

Thierry,
According to the designer of the 3DNT (Jan Henseleit), you don't need any nitro when using an OS91 motor. The power is obtained by using a gear ratio specific to that engine(7,7:1), and also because of the unique design of the heli(it is a very light heli).