As I understand it, mass balancing to 100% could cause more problems, bear with me.

If the control surface is neutralized by static balance then the servo which has zero torq available in the nuetral position would be throwing the load back and forth thus spiking servo motor amperages +/-. This in effect would be a micro flutter already setup.

My understanding could however be flawed since I buy into the digital servo OEM hype that it takes a movement off of center to develop servo torq, and digitals develop the torq closer to center than do the others.

John, My unequivocal apologies to all concerned. I fear it was more than a couple of glasses which so distorted my judgement. My wife is away with a friend, cooking for myself and well, you know, just another glass of this fine nectar ! Anyway I humbly ask forgiveness.
Regards,
David Gladwin.

This has been known to happen, but usually on large surfaces, like full flying stabs, as the polar moment of inertia is high.

Be aware that as we have seen higher and higher performance servos, we are seeing a SYSTEM limitation due to the fact that the gain settings in the servo cannot be adjusted. This is usually apparent on the flying stabs, I have never seen it even on heavy mass balanced elevators. We had one of the highest performance digital servos (big Volz) that was unusable on a big UAV as we could not adjust one of the gain settings in the servo controllwer software.

Matt,
You are right about that the Viper rudder has a tight taper.....
In solved that by adding some balsa blocks at the hinges holes location.....I think you called that gusset, right?
I the other Viper thead I posted another draw explaining the same problem.....I still have the idea that some of the guys are not getting the picture [] Anyway, for all of you.....here I go again [&:]
Thanks for the complements

See you.-

Moved to build thread

In reply to Woketman, c/f and mr_matt

Regarding flutter:

Flutter is caused by an aero dynamical effect with a flutter frequency depending of the speed of the aircraft.

When this flutter frequency is the same (or very close) to the natural frequency of the control surface system then the flutter amplitude is amplified and the acceleration and forces in to the system will also be amplified. This is typical for a bad case of flutter.

A very rigid linkage and slope free servo transmission will contribute to a high natural frequency of the control surface system.
When you mass balance your control surface you also contribute to a high natural frequency.

Ideally you want a natural frequency of your control surfaces which are way above the aero dynamical flutter frequency at maximum flying speed.

Regarding torsional flutter of the elevators I think you can rule that out quickly by twisting an elevator half in your hand. Then compare the stiffness with the “system”. It should be quite obvious that the torsional stiffness of the elevator is significantly higher compared to the stiffness of the system.

Please correct me if I'm wrong.
/Johan Tinde

When you are right, you are right!

So, you guys are suggesting that mass balancing to 100% will move the natrual flutter freq higher which is a good thing. I'll try it as I have never done so in the past.

The VPII has servo helpers forward of C/G line on tail surfaces so it is very easy to drill a hole and insert some heli blade style round lead (YIKES, a four letter word).


Thanx for your input.........

Certainly the stiffer the system, the better off you are and the higher the speed at which things will go a flutterin'. But I am not so sure that it can be obvious with a twist of the hand that the system is too stiff to get into a torsional flutter mode. Obviously the more torsionally stiff the surface is, the higher the flutter speed and therefore the better off you are, but its still out there somewhere. If you are gonna put weights out in the tip, I'd be real certain to put lots of carbon fiber oriented at 45 degrees in the skin.

Matt, that counterweight is TOO COOL. Was that on the Bandit's (or Stingray???) elevators or ailerons?

I added 2 ounces of weight to each stab in my old Viper.....and worked perfect....
I beleave more weight will be needed for this new stabs....and my concern is that the plane is already tail heavy....keep that in mind too.