Wing Center Section Bolts

[Toobuilder]

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.

[vfrazier]

Mike,

Let us know where you get the oversize bolts. I'm sure that others will need them too. Might as well post the part numbers you choose.

[Walt]

Sorry to hear of your problems, some folks think the "hired guns" that have built multiple aircraft must be "experts", when I hear that's who built an airplane I start looking for the shortcuts taken when a person is strictly building airplanes to make money.

Without a quality control system "production" generally takes precedence over quality.

[Toobuilder]

Originally Posted by vfrazier

Mike,

Let us know where you get the oversize bolts. I'm sure that others will need them too. Might as well post the part numbers you choose.

I'm looking at titanium Hi-Lok pins now (HL10V12-28) They are available in one and two oversizes so I should be able to clean up ALL my holes and shed a few pounds in the process. I'm considering replacing the steel straps with Ti as well, but trying to match drill and ream this mess on the ship is going to be tough enough as it is... Might just call the steel "good enough".

That said, any "newly developed" Rocket kit (ahem) could incorporate these changes easily. There is a lot of weight in all that steel, and targeting this area will pay weight dividends quickly.

[JonJay]

Michaael - have you measured the wear? I doubt you can measure it. I believe Cad plating thickness to be less than .001 and more like .0001. Are you sure the wear is the bolt working? Similar wear in the second picture will occur as you drive the bolt in,especially if it was driven in for trial fit, then out, then back in.
I am not saying your observations are not correct, but you won?t be able to get an oversized bolt into your existing holes without reaming. Reaming to tolerances better than .001 will require precision tooling and processes. I doubt you will be able to do it by hand. You could easily make things worse, no disrespect.
I would encourage you to speak with Wayne at Phlogiston.
If anyone knows RV4 spars it is Wayne.

Prompted by your post I will be removing some bolts at my next CI. I expect to find displaced Cad plating. I don?t believe you can drive them in, through the steel strap and the stack up of aluminum bar stock without some plating ?damage?. If the bolt was driven in, and allowed to turn while being torqued down, you might see damaged plating.

This early Spar design is the most robust of all. This was purposeful as build variances where expected. I would make sure your observations are indeed a working bolt. If it is, you should find particulate in the hole and/or on the bolt. You may be able to pick this up with a magnet and examine under a magnifier. It may just be an oily smear, but still will be magnetic. I don?t see that on your bolts.

Anyway, unless you have assembled and disassembled enough RV spars to know, I wouldn?t assume, based on what I see in the pics, that the bolts are working without further examination. I don?t care who built it.

[Toobuilder]

Originally Posted by Walt

Sorry to hear of your problems, some folks think the "hired guns" that have built multiple aircraft must be "experts", when I hear that's who built an airplane I start looking for the shortcuts taken when a person is strictly building airplanes to make money.

Without a quality control system "production" generally takes precedence over quality.

Yep. "Trust, but verify" is a familiar saying... Should have done a lot more of the later before buying this one. The good thing is that I have not found anything "unfixable" yet.

[Toobuilder]

Originally Posted by JonJay

Michaael - have you measured the wear? I doubt you can measure it. I believe Cad plating thickness to be less than .001 and more like .0001. Are you sure the wear is the bolt working? Similar wear in the second picture will occur as you drive the bolt in,especially if it was driven in for trial fit, then out, then back in.

I have not mic'd the bolt, but I can feel the discontinuity with a fingernail. This is more than through the cad... Its into the base metal. I'd expect if this was damage from installation, it would show drag marks down the shank, rather than wear on one half of the circumference at the strap locations, then similar wear 180 degrees apart at the spar lamination. The second picture is the same bolt, but only showing the lamination area... Flip it over and you would see perfect cad plating in the middle (lamination), and obvious wear at the strap locations above and below. This is wear from two opposing members in shear.

...I am not saying your observations are not correct, but you won?t be able to get an oversized bolt into your existing holes without reaming. Reaming to tolerances better than .001 will require precision tooling and processes. I doubt you will be able to do it by hand. You could easily make things worse, no disrespect.
I would encourage you to speak with Wayne at Phlogiston.
If anyone knows RV4 spars it is Wayne...

I will talk to Wayne as well as my structures people at work before I start anything. I do understand what it takes to produce perfect, close tolerance fastener holes in an aircraft primary structure, so I'm not taking the process lightly, believe me.

I appreciate the comments.

[JonJay]

Thanks for posting this and keep us up to speed with what you find.

[Toobuilder]

An update, though no resolution yet.

Spoke to a very helpful Wayne at Phlogiston and it does look like my center section will need some attention. He does have the +1 and +2 oversize bolts required as well as a reaming jig if I need it (I'll certainly need a jig, but I may machine one of my own). Apparently, this is a pretty common issue and he says the jig has been "all around the world".

So I have an "out" through Wayne, but since I'm not in a particular rush I'll start scouring the globe for the "ultimate" fix - the Ti Hi-Lok fasteners and fabrication of new Ti straps. I dont know how much I'm going to have to pay for the Hi-Loks, but even the oversize bolts are $30 each, so I'm in for a big bill regardless.

[wilddog]

Would tapered pins work in place of bolts?