ORIGINAL: CraigG

Matt,

As Morne says, your analysis it exactly right. With ''slotted'' or gapless control surface attachments like this, you have to calculate the geometry and intstall your hinges accordingly. This includes removing material from the rudder to allow hinge movement as you have descriped. The install is complicated somewhat when the control surface is tapered, like your fin, because the distance to each hinge pivot point from the leading edge is different. It's also hard to ''test'' your hinge placement and lack of interference prior to gluing them in place, after which they can't easily be moved. It all takes some time, careful measurements and trial and error. The good news; it doesn't have to be perfect but the more accurate, the better.

Another issue to consider is that the hinge on the fin side is unsupported where it protrudes in the leading edge of the rudder. This can cause the hinge to flex and potentially cause flutter. You need to make sure the trailing edge of the fin supports the hinges as close to the leading edge of the rudder as possible. With my Viper, I needed to add small blocks of hard balsa of varying widths at each hinge location to better support the hinges and to minimize the unsupported sections. Take a look at the pictures in post #102 on page 5.

And I will say this one more time, the supplied hinges look like Robart's but are inferior and not up to the task. The pivot pins are of softer material and have play in them and the hinges themselves will break/fail easier. Compare them side by side with a Robart's and then replace them!

Craig