Bryan,

I would be grateful for your comments on my particular setup. The model is a Sazuki designed Hybird bipe built by Oxai. Respected designer and top flyer so I'm assuming this model falls into the catagory of a "good" design.

I don't know where the designer's datum is for this design but taking the bottom wing as 0, the top wing is at around -0.2, the tail adjustable but currently at 0 and the thrust line -1. A contra is installed. I started with the model balanced at Suzuki's recommendation which according to all the calculations we have done puts the neutral point well in front of 25% mac. The model tracked well, went dead straight vertical up and very nearly dead straight vertical down. Only major problem was a significant pull to canopy on both knife edges. So using your trimming methods which have worked well for me in recent years I started to move the CG back by temporarily adding lead to the tail. With the CG back well over an inch the pull was still aparent but slightly reduced and here's the problem, the lateral stability was greatly reduced so this line of correction appears limited for this contra equipped design anyway. My current thinking is to add the dreaded tail drag inducing element to restore some of the lost lateral stability robbed by the contra and then continue to move the CG back.

My question Bryan is, does this seem a sensible approach or is there something other more productive to try, bearing on mind that major changes with a bipe are doubly difficult!

Malcolm