ORIGINAL: DaveL322

I figured out ''tweaking'' the stabs in 1989 while trimming a Tipo.....it pulled to the canopy in KE with right rudder, but was dead straight in KE with left rudder. Much of the prevailing wisdom at the time was to shift the CG aft slightly to have a plane that pulled less to the canopy in KE with right rudder, and pitched an equal amount to the belly in KE with left rudder. I found by slightly reducing the incidence of the left stab and increasing the incidence of the right stab an equal amount, I was able to have the airplane pitch an equal amount to the canopy in either KE. I then moved the CG back slightly (resulting in a slight bit of down elevator trim) and the plane had zero pitch coupling in KE. I cut the wing in half 4 times, adjusting the dihedral each time until there was zero roll coupling in KE. Electronic mixing is always the last resort

Every plane I have owned since that time has had some amount of twist in the stabs (or elevators if the stab is fixed) to balance the right/left KE behavior. I've never had to change rudder trim or aileron trim because of twisting the stab, and I've never seen loop tracking suffer from the twist in the stabs.

June 2011, I had 2 Bravos within 1 oz flying weight of each other (#1 being 1 oz heavier than #2), and to the best of my ability to accurately measure incidence, control throw, CG, etc, they planes were identical. Both had the same amount of twist in the stab, and both had the same behavior in KE. I replaced the single prop Neu setup on the #2 plane with a Contra unit, and moved the lipos slightly aft to maintain the CG. The #2 plane now weighed 1 oz more than #1 and in right rudder KE it pitched to the belly, and in left rudder KE it pitched an equal amount to the canopy. I removed the twist from the stabs, and the plane had zero pitch coupling on either side.

My conclusion -
Spiral airflow is real, and twisting the stabs is an effective way to reduce or completely mitigate some of the undesireable effects, and I've found zero down sides to twisting the stabs. I don't advocate twisting the stabs until all other parameters are addressed - proper geometric alignment of all surfaces, all surfaces warp free, etc.

I've flown a number of Hebert designs over the years (including some of his personal planes) and all have flown well.....so I would never suggest that Brians trim methods are BS.....but as with many things, there is more than one way to skin a cat.

Joe - try the stab / elevator tweak, and let us know how it works.

Regards,