Fuselage skinning question

I am ready to place the skins on the frame and start drilling. I have read about two methods, one is to mark out the spacing and drill the holes in the frame, them place the skin on the frame and drill from the underside through the "pilot" hole".

The other option I have seen is the place the skins on the frame, strap it down, the drill pilot holes throughout the underside of the frame, though the skin, then move to the outside to final drill the holes.

Is there a consensus, or another option I am missing?, thanks in advance.

Either method will work but wanted to give you another option (less difficult in my opinion).

My -6 manual had me strapping the skin to the frame and marking registration points for realignment. I then marked the stringers and bulkheads onto the skin. Remove skin. Mark center lines on all affected stringers and bulkheads. Layout rivet spacing per plans. Drill skins undersized and use the holes to locate the center lines of bulkheads and stringers for final drilling. Cleco's as you go. Worked great for me. YMMV

After trying a few different methods, I perfered to mark and drill the structure and then back-drill through the skin once it was in place. But both methods do the job.

Edit:

Keep in mind that is is really easy to flex the bulheads when strapping down the skin. No matter what method you use, you will not be able to have the skin fully strapped in place when you start drilling without flexing the bulkheads. It takes to much force to hold the skin 100% conformed. (this applies to the curved top skin, not the bottom or sides.

Skinning

I prefer to drill all of my holes in the bulkheads and ribs first. This way all of your spacing works out and your are not "guessing" in some of the areas like lap joints or edges. You have to get creative in some spots around the baggage bulkhead and the tail cone. I strap my skins on with ratchet straps and wood stringers and back drill them with someone holding a piece of wood in the area I am drilling to keep things tight. I have clecoes inside as I am drilling to hold the area where I hit the wood stringers. My assistant clecoes any open areas outside. The tail cone I do all of the skins as far back as I can until I cannot back drill anymore. Then I remove one side skin and back drill from the outside with a long 12" drill bit. Back drill all holes with 3/32 bits and 1/8. When you get all the holes drilled, then put the skins back and chase each hole with #30 and #40 drill bits. Don't drill with the numbered bits first or you will have enlarged holes when you go to buck the rivets.
In places I could not back drill I used a small bent scribe to mark the hole through the bulkhead or rib and then when I pulled the skins off, I drilled the hole on the bench. This is my 4th RV and the method works well.
Also, back rivet everything you can, squeeze every rivet you can and only buck rivets the old fashion way when you have to. You will have a much smoother surface when finished.

Mevans said:

I am ready to place the skins on the frame and start drilling. I have read about two methods, one is to mark out the spacing and drill the holes in the frame, them place the skin on the frame and drill from the underside through the "pilot" hole".

The other option I have seen is the place the skins on the frame, strap it down, the drill pilot holes throughout the underside of the frame, though the skin, then move to the outside to final drill the holes.

Is there a consensus, or another option I am missing?, thanks in advance.

Click to expand...

I went with the first option, but made the initial 'pilot hole' in the frame a true pilot hole with a 1/6 drill.

This way the drill out to #41 from the inside can't screw up the initial hole. Using 6 inch and 12 inch long #41 bits from the inside helps you work around the internal structure.

The j-stringers are somewhat flexible so this method ensures that edge distances can be kept. Stiffen the bullheads with plywood to ensure they stay straight during this process.

Thank you all. I have marked out the frame with a sharpie and plan on drilling a pilot hole there first. I will then put the skins and go larger from the inside like mentioned above. Thank you also for the confirmation of backriveting all I can, I was leaning that way.