ORIGINAL: Rotaryphile
The taper used in the elevons reduces their mass near the tips, where their mass is most likely to induce flutter because simple wing flexing vibratory excursion is highest near the tips.
Control surfaces should be as light as practical while retaining sufficient strength to do the job. What they need in order to minimize the likelyhood of flutter is high stiffness to weight ratio, not maximum possible stiffness at the expense of weight. I would be strongly inclined to employ mass balancers at the tips of the elevons. I employ them on all of my airplanes that are expected to fly fast enough to make flutter a possibility. The mass balancers, if mounted at the tips, should statically balance about a third of the static unbalance of the elevons.
Excessively heavy mass balancers can be more dangerous than none, since they may induce flutter a flutter mode where the wing or stab flexes in a more complex manner than simple flexing of the tips up and down.
Such higher harmonics usually only appear at rather high airspeed, where flutter can be extremely brutal, and break up the airplane in a fraction of a second.
I have found that models built from EPP -cut foam- will flutter -but this stuff simply refuses to break- I have been playing with it - recently, doing overpowered ,extremely light aerobatic designs
I wish this stuff had been around years ago - - with a little carful use of carbon fibre rods and tubes and strips - you canmake areally GOOD model which will fly nice straight aerobatic sequences .
The beauty of it is IF you can see flutter - simply strengthen or brace the offending section and go back to flying.
The foam has a slightly spongy texture and the beads are bonded together far more solidly than the stiff foams such as expanded styrene bead or the Depron type stuff.
The rigid materials we have all used for years, will ALL flutter- then fracture or break given the right circumstances