Didier
Thomas says the model tends to be tail heavy thats why he has a fairly large component tray in front
All batteries , pump ECU etc go up front.
We have only one viper flying here so far and this on is balanced as per the recommended CG and is a pleasure to fly.
Bear in mind that this one has lights etc and the electric retracts , so there are 2 additional 2500mA lipos so is a little heavier.
Xantos