RE: Covering hinge lines?
Ok kids, let's go to school.
First, make a flag by gluing a piece of paper to a stick. Now hold it out the window of a moving car. There is no gap, yet the flag waves.
Why???
There is no gap to create an oscillating force!
This is impossible!!!
The flag waves due to aerodynamic forces.
Now, EVERYTHING in the world vibrates at a certain frequency - Right?
Ok, so now make your flag by hinging a stiff piece of wood to your stick (let's call this a rudder) and seal the gap. It is very possible that at some precise speed, and depending on the shape of your stick, and the relative humidity, and the phase of the moon, etc. that the rudder is going to flutter - right?
Or are you saying that this is impossible?
Ok, if you agree that this rudder CAN indeed flutter (And you should) then you can also see that while there must be certain critical conditions to MAKE it flutter, changing any of those conditions can also stop it.
Unsealing the gap will change those conditions. It will no longer flutter AT THOSE CONDITIONS.
But of course, flutter can NOW occur at other conditions, such as a different speed, humidity, etc, etc.
It's like a guitar string: Tune it to an "A" an it will vibrate at 440hz. IF you play an "A" on another instument, the guitar string will magically vibrate by itself (These BTW are aerodynamic forces acting upon the string). Now tune the string a little sharp, say 450hz Now if an "A" is played by another instrument, the string will NOT vibrate. However, play a note at 450hz and the string will again vibrate.
THEREFORE: Sealing a gap is NOT a good method of preventing flutter. It won't. All that does is move the flutter to another condition (Like another speed).
IF you have a gap, and you want more positive control, seal the gap.
IF you are looking to prevent flutter, make sure your connections are solid and your servos are strong enough.