On May 20, 8:17 am, Eric Greenwell wrote:

trim tab). In his 1989 article on increasing performance, Peter Masak
talked about reducing drag by filling in this bottom concavity. No
mention of the expected drag savings, but lots of words about flutter
concerns.

Not to mention changing the pressure distribution on the aft section
of the wing/tail - thus changing its Coefficient of Moment (i.e. its
desire to rotate/torque around the center of lift). That effect is
less critical on the tail than on the main wing (doing so on the wing
might require an increase in tail volume to control the added moment);
but the bottom line is that you're essentially making a custom airfoil
when you fill that cusp. It isn't necessarily a bad thing, but if you
don't know what you're doing you could just as easily make it perform
worse...

--Noel