Empennage Stiffeners, Not to plans....

Here is a hint I remembered from building my 6. The plans show the stiffeners as 1/2" material with 2 1/2" taper on the trailing edge end. The stiffeners are actually supplied 5/8". Per plans, there is a rise of 3/8" at the 2 1/2" mark for 1/2" material.
On the 5/8" material provided, to dupicate that same rise, you need to measure out somewhere around 3 1/4". Someone better at math than I can probably calculate this exactly.
This is imporant when it comes to the critical trailing edge bend. As covered before in other threads, that final bend needs to be squished hard. The skin needs to lay on the spar without being forced down. A straight edge should lay on the skin and touch from spar to almost the trailing edge, allowing for the proper radius of the trailing edge of course.
If you follow the 2 1/2" dimmension for the 5/8" material, they will be 1/8" taller than plans at that location. This may interfere with your ability to properly bend the trailing edge.
I am convinced that poor trailing edge bends lead to the .016" skins that develop cracks. I have no cracks on my 6 after 180 hours. Perhaps they will form, but none so far. I have seen just as many high hour .016 skins without cracks as I have seen with them. I believe this bend is the primary reason.
I know others have chosen to glue down the stiffeners. Not a bad idea, but regardless, the proper bend needs to be made.
I will not be gluing mine. I will use a glob of silicone at the trailing edge to bind the stiffeners together at the time of my final bend, just like I did with my 6.

JonJay said:

I am convinced that poor trailing edge bends lead to the .016" skins that develop cracks. I have no cracks on my 6 after 180 hours. I have seen just as many high hour .016 skins without cracks as I have seen with them. I believe this bend is the primary reason.
I know others have chosen to glue down the stiffeners. Not a bad idea, but regardless, the proper bend needs to be made.
I will not be gluing mine. I will use a glob of silicone at the trailing edge to bind the stiffeners together at the time of my final bend, just like I did with my 6.

Click to expand...

Good catch Jon. Of course will all things RV-3 one needs to look at every part with common sense and consider how it will fit "in assembly". That's why these birds are best built by 2nd time builders who know the big picture.

I'm with you in being convinced that .016" skins are completely adequate and will not crack of constructed correctly. If you have some extra Proseal laying around though I think it's good insurance to spread a thin layer on the bottom of the stiffeners before you rivet them. Proseal's vibration absorbing properties serve well here in preventing any cracks from the stiffener rivets.

Build on!