Richard Riley wrote:
Here are a couple of quotes from the cri-cri mailing list.

The Zenair tube is made from thin steel tube, maybe 19mm diam. It is
flexible and acts like a tuning fork. Any induced deflection of one
flaperon is amplified into the other flaperon, and you get a flutter that
continues until some connection between the flaperons breaks OR until
something ELSE on the airplane breaks and it becomes uncontrollable...
cut

The Columban tube is too stiff to transmit any induced deflection from
one flaperon to the other.

Nitpick (I realize it is not your statement, Richard, but from the
mailing list) about flutter:

A technically more correct statement about the Columban tube is its
increased stiffness eliminates the flutter tendency of the Zenair tube.


Anyway...

A layman's explanation is the larger tube still vibrates, but its
resonant frequency is much higher. Since the airflow over the flaperons
is the source of the vibration, you would have to fly much faster before
the vibrations reach that higher frequency (and the flaperons
destructively "sing" to each other through the tube, and the tube
"sings" along, or resonates).

Both tubes transmit vibrations, just not particularly well when the
vibrations are not at their own resonant frequency (think of one tube
like an "A" tuning fork and the other like a "C"). In most flight
regimes it is irrelevant. The problem is they respond a little too well
to their resonant frequency.

Flutter- a really really complicated branch of aerodynamics.