PTXMan,

I'll take a shot at that explanation... others feel welcome.

We are talking about the "natural frequency of ocillation" in a system. The natural (or inherent) vibration frequencies are in a escallating order, where you have "focal points" for the vibration which work out to be natural divisions of the length of the member. So, the lowest natural frequency of a member is 1/2 (center), then the endpoints (I think), then the next order is 1/3 and 2/3 (two focal points), then 1/4, 1/2 and 3/4 length, and so on. (sorry, can remember the exact order of divisions, been too long). To avoid excitation of the member, you try to connect at some high-order point (or points) such that it would take a very high frequency (speed) to excite the member into resonant vibration. By connecting at 5/11 or some other odd division of the member's length, you make it far more difficult to excite the member into resonance.

So, this is a sound engineering effort to take a preventative measure to prevent flutter, as we know that the initiation of a flutter event is from some excitation force "matching" a natural frequency. If you avoid the match points (harmonic, or frequencies in harmony), you avoid the flutter. This is why we like a very rigid structure (aileron & wing) because the natural freqiency of vibration goes up with a more rigid member.