Toobuilder
Well Known Member
One thing that has always bugged me about my Rocket is the fact that the builder used -30 length bolts in the center section instead of the correct -28 (grip length). The extra length was compensated for with 3 washers per bolt. Sloppy. Since I had a bunch of brand new -28 fasteners in hand, I thought it a good opportunity to dump all the washers and upgrade to lightweight nuts. I did not expect to find the obvious wear on a low time airframe (358 hours). Though the bolts were generally a tight fit and had to be driven out it seems that the bolt holes are not reamed to match the steel straps. As a result, the spar and the straps are "working" instead of being locked together.
See attached:
You can see the wear from the steel strap below the head in opposition to the wear from the spar laminations. The large area directly under the head is where the huge stack of washers was, so it shows no wear.
Bolts loaded in shear, especially in critical joints like this, need to be fitted to reamed, perfectly round holes. A twist drill will not accomplish this, no matter what. And if you can push the bolt into the hole by hand its not doing anything for the joint. Ideally they should be driven into place, with the bolt making contact with and displacing all the elements of the assembly.
I bring this up because this airframe was reportedly built by a "hired gun" who has done MANY airframes in the RV world. One of the bolts was well beyond a slip fit - it will rattle in the hole. This bolt might as well be left out because its only adding weight. If he let this out of his shop, then there more out there.
If you're flying an airplane that you built and let one of these slide, you might want to pull it out an look at it once in a while. As for me, I'm in for some oversize bolts and a regular inspection program from here on.
See attached:
You can see the wear from the steel strap below the head in opposition to the wear from the spar laminations. The large area directly under the head is where the huge stack of washers was, so it shows no wear.
Bolts loaded in shear, especially in critical joints like this, need to be fitted to reamed, perfectly round holes. A twist drill will not accomplish this, no matter what. And if you can push the bolt into the hole by hand its not doing anything for the joint. Ideally they should be driven into place, with the bolt making contact with and displacing all the elements of the assembly.
I bring this up because this airframe was reportedly built by a "hired gun" who has done MANY airframes in the RV world. One of the bolts was well beyond a slip fit - it will rattle in the hole. This bolt might as well be left out because its only adding weight. If he let this out of his shop, then there more out there.
If you're flying an airplane that you built and let one of these slide, you might want to pull it out an look at it once in a while. As for me, I'm in for some oversize bolts and a regular inspection program from here on.
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