Flutter!!*&4##!?

Sooner or later, this word and its effects become the topic of the day so let’s talk about flutter BEFORE it destroys your airplane.

Flutter is the oscillation of the control surface (normally the ailerons). The aileron starts oscillating up and down as the air traveling over its surface moves it back and forth. It may start as a dull buzz and can easily end up with the aileron flying off the wing within a few seconds. So what creates the opportunity for flutter to occur? Here are the possible choices:

1.      Your airplane is overpowered and the construction of the wing and tail are insufficient to keep the aileron centered due to the very high speed flow of air over and under the surfaces.

 2.      The servo attached to the surface is not strong enough to hold the aileron at neutral.

3.      The control rod coming out of the servo output arm is too far from the center of the servo thereby reducing any leverage.

4.      The control rod is too thin and flexible.

 5.      The control rod is installed too close to the surface of the aileron, again eliminating the leverage that should exist.

 6.      The hinging is loose and weak with too much gap from the TE of the wing. 

7.      The hinge gap is not sealed.

8.      The aileron is not balanced.

 9.      The servo output arm and or control horn are too flimsy for your application.

 10.  Etc, I am sure there are more. 

Now, what can be done to eliminate the potential for flutter. Just look at the list and do the opposite! Here is what I believe are the main culprits.

1.      Position your control rod in the closest hole to the center of the servo control arm as possible. This provides greatest leverage and servo strength.

2.      Position your control rod in the furthest hole in the control arm from the surface as possible. Again, this provides the greatest amount of leverage.

3.      Keep the control rod as short and rigid as possible. Never use all threaded rods as they are weak. Never place excessive bends in the control rod as this adds weak spots in the rod.

4.      Make sure all pieces in the linkage are heavy duty for your needs. I believe 4/40 should be a minimum on all aircrafts.

5.      Choose a high quality servo that can hold the control service in the desired position.

6.      Keep the hinge gap as slight as possible and use a sufficient number of quality hinges.

7.      Using your covering material or a tape designed for this purpose, completely seal all gaps on the control surfaces.

8.      There are many articles available regarding the static balancing of control surfaces. Refer to these and balance the control surfaces whenever possible. Some surfaces are dynamically balanced by their very design.

9.      Use motor sizes that are recommended by the manufacturer. Extra speed places extra stress on your airframes. If you want to go real fast, build a Quickee or a jet.

If you can easily wiggle any control surface of your plane when your radio is turned on, you are on the road leading to flutter and destruction of your plane. I hope these comments have been helpful and you will never experience the devastating and dangerous effects of control surface flutter.

Written by Mark Weiss for Giantscaleplanes.com