SonexBuilders.net

I've seen some commentary about the ability to remove the aft fuselage lower skin for maintenance and inspection. As I'm currently assembling the aft fuselage I can see the potential advantage for access to rudder pulleys and other control linkages. Has anyone looked into doing some or all of the lower skin using rivnuts and screws in place of rivets?

Since the skin is considered a structural part of the airframe, I'd be concerned whether rivnuts and screws have the same strength specs as SS pop rivets.

I hate Rivnuts. On the 1946 C140 I restored they used them to hold on the tank cover. The hole in the base metal is large and the threads are aluminum. When the bolt corrodes to the threads the rivnut will spin. There was a tap stuck in a rivnut which had been hammered through and left in the tank bay.

If I was going to make a skin removable, nutplates and screws would be the way to go. I would much rather add a structural access panel than remove the whole skin.

Even better, leave out the panel. If you are at a point where you absolutely need it, you can cut it out after the fact. Since the panel is not there you may be more motivated to deal with the slight inconvenience and figure out how to maintain without it.

Interesting question, and I would definitely ask Sonex first. Of course steel screws and platenuts are stronger than rivets, but might not lock the parts together as well. If I were doing it, I'd probably consider flush screws, with dimpled skins for a better physical lock.

Cheers,
Rusty (not a structural engineer)

Just a thought, you might want to take a look at the underside of a Waiex. They have a removable access panel held in place with nut plates and machine screws. This is to give access to the control mixer system for the "Y" tail flight controls. I suspect something similar could be accomplished on a Onex.

Many thanks for the good observations. I'm thinking I'll put the bottom skin on per the plans (after everything else is checked out) and if I ever have to get at something that can't be gotten through the design access panels, I'll cross that bridge when I come to it! :D