Couldn't make up your mind?
Seriously, control surface balance is important. Adding mass aft of the hinge line, here a lot of glass and bondo, is simply a bad idea. In the case of an elevator, it requires more counterweight after paint. In the case of an RV rudder, the control surface CG shift is permanent, and appears to reduce flutter margin.
Ok, set structural issues aside. As general good practice, you should not mix materials unless really necessary. I have seen unpainted RV's with five or six different fillers. In addition to various adhesion and chemical issues, different sanding densities result in waviness after paint. Polyester body filler over epoxy/micro makes no sense anyway...a filler over a filler.
I had a feeling you might post something like this. You are not getting my full story and maybe didn't go look at the pics either before "publicly roasting"
my
assumed lack of flutter knowledge.
Let me first start by saying your knowledge of fiberglass far supersedes mine, however the method I used is working on many flying RVs out there. As some say, more than one way to skin a cat.
First, I am very aware of flutter and did everything I could to add as little weight as possible. I did not heap a big ole blob of stuff on my parts and call it good. In fact I sanded the gelcoat off quite aggressively down to fiberglass first so that the filler was more of a replacement than an addition.
The cabosil mix only fills the very slight gap between tip and metal. (very little was used, maybe 3-4ml on ALL surfaces) A method I am pretty sure I learned from your endorsement elsewhere on the forums.
The fiberglass I used was ungodly thin and was even sanded afterwards.
The micro was then added as the primary filler. However, there were still a few areas I wanted a better shape or needed to fill ever so slightly. Hence the Rage Gold. Fiberglass is a suitable substrate for Rage Gold and it sands easier than micro and more important to me at the time it is ready for sanding in 30 min.
If you look at the pic below you will see how little and how thin the filler really is, especially aft of the hinge line. (upclose you could see the seam almost the full length under the coat. the thick being where I sanded the gelcoat) This is also the case for the rudder.
20190617_180404 by
Jereme Carne, on Flickr
In the next pic you can see the finished product which in my mind blends quite well and looks professional. Both elevators are also still well overbalanced which indicated I didn't change their balance much which I'm sure also translates to the rudder. I also elected to just use micro on the HS tips. In the end this is what I would do in the future with all surfaces as I know many guys that still don't have any cracks.
20190625_164306 by
Jereme Carne, on Flickr
Now I'm definitely not trying to change the fiberglass masters mind. I do however feel that I needed to point out what I did as well as the fact that many have done it this way too and don't seem to be falling out of the sky. Is it more work than necessary; yes. Does it work; based on the data I have seen it does. In addition, the only case I know of that resulted in tragedy was one example with excess filler on the rudder on the tune of about 1/4" + in places. (the report estimated multiple POUNDS of filler on the rudder if I remember right) He was also WELL above Vne.
All that being said, flutter is no joke and everyone should do what is necessary to not add excessive filler aft of the hing line. I do not feel like I did.
