Ultralight aluminum tube structure bolt and hole clearances.

I have a typical sail cloth over aluminum tube structure ultralight that has quite a bit of "slop" in all the bolted members. AC43.13 stipulates much closer fit than this structure exhibits. But I've been told several conflicting things about bolt clearances on part 103 or similar structure LSA. i have no prior experience with this type of aircraft structure. All my previous Plane projects have been in wood with 4130 bolt on fittings etc. or helping others with their all aluminum monocoque structures. Any one that can give me the scoop on proper safe bolt hole clearances in such structures, I would be very appreciative.

Steve

I cant help with the clearance legalities but can you drill the holes out to allow bushing's cut to lenght to fit the tube and have the ID of the bushing's sized to slip fit your bolt's? sorry could'nt help much

I would say it depends on the particular part. A spar held rigid with tension cables might allow some clearance and easy assembly.
A sloppy elevator torsion spar connection would not be good.
Check if the size is from wear or just normal manufacture tolerance. An oval shape indicates wear.

AC43.13 really doesn't apply to this sort of structure. Your best bet, if possible, is to contact the manufacturer. If it's worn, it's usually possible to drill the holes out for the next size larger bolt. Another solution for a worn hole is to rivet a sleeve inside or outside the tube and redrill through the sleeve.

Thanks for response. yes, I have purchased some small tubes for possible use as bushings. An added benefit would be mitigation of the tube "crush" issue that does not allow a very tight bolt clamp force through tube wall. Just a bit concerned with dissimilar metals in a water bird. Figure Aluminum tube will be fine, but how about brass?

Thanks. Yes, agreed, some joints not critical load, flutter considerations etc.. There are some holes clearly elongated, those parts I will replace. Most are just drilled oversize, and where they must be press, or zero play fit, At this point, after checking for cracks, corrosion, I'll ream to be a press fit over a bushing the length of OD diameter of tube.

Thank you very much. Was beginning to think I had a collection of worthless aluminum tubing as every hole was quite loose around the bolts. I do recall decades ago hang gliding with a friend, erecting his Rogallo wing. I grabbed a plastic headed mallet to help insert bolts and he asked "what is that for". This is a foreign world to me.

I have contacted the company that supports these older Buccaneers, but response has been poor. But then, they have had a huge loss recently and will likely require time to sort out moving forward.

Bushings across the tube are one solution-- I've seen it done with small tubes flared out on the outside of the main tube to hold them in place-- but I was speaking of a short section of tube slipping into or over the original tube, then redrilling it for the original size bolt. Some people even did this on brand new ultralights to prevent wear. You can sleeve it on the outside with a tube 1/8" larger OD and .058" wall. On the inside you can go 1/8" smaller if the original tube is .058 wall, or you can slit a piece of tubing the same OD as the original and compress it to push it in... or go inside and outside. A couple of pop rivets to hold the bushing in place before redrilling it, it'll be stronger than the original.

I wouldn't recommend brass, use aluminum. Another approach (which I wouldn't recommend on a seaplane, though) is a close fitting hardwood plug epoxied into the tube.

Thanks, there are some tubes were the sleeve idea would work well. Nixing all brass, just Aluminum.

If you're going to drill out the elongated hole use a piece of tubing as a bushing, make it a few thousands shorter than the diameter of the tube you're putting it in. The very slight amount of compression helps stabilize the tube walls in a high stress area. I got this advice from a stressman at Pilatus and it makes sense to me.

sounds like good advice, thanks.