Hi all,
I'm surpriced no one has gone in to detail about mass balancing the elevators and rudder. I have to say hello to Stahle from Norway who pointed this out at the beginning of this thread. We are both owners of the first batch of Viper Jet's. Stahle uses mini wing servos from Volz of about 4kg/cm and I am using Graupner 3728 digital wing servos with metal gears for elevators and rudder of similar torque (for elevator and rudders).
The key to success is the mass balancing. As the Viper control surfaces are quite nicely made for this to be done. If I remember correct I added ca 20g of lead in the leading edge of each elevator tip section (protruding in front of the hinge line). This weight resulted in a 100% static balance of the elevators. In the rudder top section (leading edge protruding in front of the hinge line) I put in as much as I could which was 30g resulting in approx 70% of static balance.
This is in total 50g of lead in the tail. I ended up with two receiver battery packs of 150g each in the nose cone and the ECU battery pack above the nose gear.
The new Super Viper is probably a bit heavier in the tail due to the added reinforcements so it may be undesirable to add all that weight in the tail after all. At least if you are installing standard size heavy servos.
The benefit of mass balancing is the drastic reduction of forces transferred to the drive train of the servo if a flutter is induced. And as a fact the tendency of self induced flutter is significantly reduced.
Regards/Johan