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Prosealing elevator skin stiffeners

NorthernRV4

NorthernRV4

Well Known Member
I'm at the point of back riveting my stiffeners to the .016" elevator skins and I read of a lot of issues with cracks propagating from the last rivet hole at either end but most often the trailing edge end. I will be following all the usual recommendations; proper bend radius, glob of RTV. I plan on doing the proseal mod too but I'm wondering if those who have gone this route would recommend doing the entire length of the stiffener or just the ends, maybe an inch or so? Seems like it could be unnecessarily messy to do the whole length and add time/weight.
 
Proseal stiffeners

NorthernRV4 said:
I'm at the point of back riveting my stiffeners to the .016" elevator skins and I read of a lot of issues with cracks propagating from the last rivet hole at either end but most often the trailing edge end. I will be following all the usual recommendations; proper bend radius, glob of RTV. I plan on doing the proseal mod too but I'm wondering if those who have gone this route would recommend doing the entire length of the stiffener or just the ends, maybe an inch or so? Seems like it could be unnecessarily messy to do the whole length and add time/weight.
Click to expand...

I did mine. It's not flying yet so I can't comment on the long term or how much weight was added. I doubt it was much. It was not messy compared to fuel tanks!
 
I did mine, too, full length. I'm doing that for all the .016 control surfaces in the slipstream.

Dave
RV-3B, (very) slow build, now on ailerons, out of the slipstream
 
When I worked at Columbia Helicopters, the policy for the sheet metal department to reduce cracking and working rivets, was to seal every riveted joint, and use solid rivets wherever possible. I believe Erickson had the same policy, except the reason for it was to prevent cracks, working fasteners, and the tail falling off and everyone dying.
 
I have never seen cracks along the length of the stiffeners, only at the end rivets. Flexing of the skins beyond the stiffeners is the problem.

What I do- shape the stiffeners with a small 90deg tab at the spar end, apply a small blob of proseal at the trailing edge to tie the 2 converging stiffeners together, also apply proseal blob to those little bent tabs to fglue the stiffeners to the spar. This takes care of all that nasty flexing. I've not had a crack show up on any surfaces built using this process.
 
Thanks fellas! I will pro seal the entire length, if anything it's good practice for when I get to the tanks.

Ralph, I like the idea of a blob at each end, I hadn't considered the end where the stiffener meets the spar. A little tough when it comes time to close the ctrl surface, no? Having never used pro seal, when it cures where is it on the scale of hardness? JB Weld -> RTV silicone?
 
If the trailing edge bends are properly done, there shouldn't be any problems. My -6 has been flying since early 1993 with .016" skins, no pro-seal, no RTV, and no cracks whatsoever.
 
Proseal

NorthernRV4 said:
Thanks fellas! I will pro seal the entire length, if anything it's good practice for when I get to the tanks.

Ralph, I like the idea of a blob at each end, I hadn't considered the end where the stiffener meets the spar. A little tough when it comes time to close the ctrl surface, no? Having never used pro seal, when it cures where is it on the scale of hardness? JB Weld -> RTV silicone?
Click to expand...

It's a little harder than RTV.
I wouldn't op it on like tanks. A thin coat on both surfaces should suffice then a glob about the size of a piece of chewing gum at the intersection of each pair.
Buy the small size from Vans. It's enough to do the control surfaces.
 
May be coincidence, not sure, but I see more cracking on planes with 360s & bigger more often than on 320 planes.
Proseal, or RTV fine to use. RTV definitely easier. The little flange I bend at the front end of the stiffeners is to have a surface the blob can hold to while sliding the spar in for riveting.
Note if gluing the whole stiffener- keep it light as these surfaces have to be balanced later.
 
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