Cockpit Bottom Skin

[mwhatley]

I’m trying to think through the best order of events. I’m about to hang the engine on a tri-gear, right now I don’t have the cockpit bottom skins on, so I have free access to finish up the firewall forward items until I actually mount the engine. But I can’t do the wiring until after that, but I’m thinking it’s best to go ahead and rivet the bottom skin as it will be a pain to do this after the engine is mounted (tough to take the wheels and landing gear legs out with that much weight on the airframe). Just curious what others have done?

[mike.smith]

I’m trying to think through the best order of events. I’m about to hang the engine on a tri-gear, right now I don’t have the cockpit bottom skins on, so I have free access to finish up the firewall forward items until I actually mount the engine. But I can’t do the wiring until after that, but I’m thinking it’s best to go ahead and rivet the bottom skin as it will be a pain to do this after the engine is mounted (tough to take the wheels and landing gear legs out with that much weight on the airframe). Just curious what others have done?

I built a tail dragger, so someone else can correct my comment if it doesn't apply to a nose dragger...

Don't do it!!! The best thing you can do when building a Sonex is to leave the bottom skin off until the night before your airworthiness inspection. I can't think of any one single building hint that is more important than waiting to put that bottom skin on. You will need access in there for everything. Once it's closed up you will hate life. And leaving it open will make putting the wings on SO much easier. At least for the tail dragger version.

[peter anson]

I did it all the wrong way and riveted the bottom skin on first. It does tie things together well but instrument wiring was a pain. Mike, I was wondering if your advice would change somewhat if the instrument panel was made so that it hinged or was easily removable? I didn't do that either so that several changes and additions I have made to the instruments since have been rotten jobs and my wiring has been getting progressively messier. One Australian builder, Brian Ham, has even made a removable access panel in the floor. He did it so he could service the hydraulics for his toe brakes, but it would obviously be useful for panel access.

Peter
Sonex 894

[ScottM-Sonex1629]

This is a great idea to leave off the skin if you have a taildragger!

If building a tri-gear model, that skin needs to be on to mark and cut the openings for the two main gear legs...and if you left the skin off, and placed the airplane on its landing gear during assembly, the entire main gear legs, axles, etc would need to be removed to install the skin later.

[mike.smith]

I did it all the wrong way and riveted the bottom skin on first. It does tie things together well but instrument wiring was a pain. Mike, I was wondering if your advice would change somewhat if the instrument panel was made so that it hinged or was easily removable? I didn't do that either so that several changes and additions I have made to the instruments since have been rotten jobs and my wiring has been getting progressively messier. One Australian builder, Brian Ham, has even made a removable access panel in the floor. He did it so he could service the hydraulics for his toe brakes, but it would obviously be useful for panel access.

Peter
Sonex 894

I have a removable panel, but still had the bottom skin off. There is just so much stuff that has to get done down there, including installing and rigging the wings. If I needed the bottom skin on for anything, I just put it in place temporarily with a couple dozen clecos. From other comments here I can see why the nose dragger would be problematic. I don't know how much trouble it is to remove the gear etc, but at least for the tail dragger I counted my blessings every day up to my DAR inspection, that I had left the bottom skin off. For a tail dragger there was no downside whatsoever to leaving off the bottom skin.