Oversize holes in fuse/spar centre section

kens_cockpit · #1 07-21-2013, 07:20 PM

I am building a QB -8.

I have installed the bolts to convert the -8 from the -8A in the centre section as shown on the plan.

The bolts were tight to get in the ? holes, particularly the bottom ones. I therefore got a right angle ?? drill and ran it through two of the bottom holes in the centre section on the bottom right hand side. Of course they are now oversize and the bolts can wiggle in them. Once they are torqued they don?t move of course but almost until they are fully torqued there is a little play.

What I did was silly. It was the result of wanting to get back into things after some time away from building. A little patience would have been better combined with a little amount of sandpaper around some dowel just to free up the hole perhaps. Anyway it?s done now. What should I do?
a. Leave it as is and torque the bolts correctly
b. Drill out the holes to the next size bolt and install that size bolt and torque correctly. It will probably be difficult but not impossible to drill the hole nice and perpendicular to the spar when I do that (Why that didn?t stop me using the right angle drill the first time I do not know)
c. Sell the kit to someone who won?t keep making stupid mistakes



I've got an email into Vans support to ask them also. I'll post the response from them but just thought I'ld get the wisdom of the forum too.

Thanks for your help.

BillL · #2 07-21-2013, 09:15 PM

I really don't have an answer for you, but fasteners on aircraft typically are mostly loaded in shear, so the bolt shaft and the hole should be relatively tight. (not in the engine) This also means that a drill is not the proper tool to yield the correct size. The reamer, a solid reamer is best for this and you can get them from good aircraft tool suppliers. If it turns out that you do need to go up in size, be sure to use a reamer. I like the piloted reamers that have a pilot to align them before cutting to size. They are much easier to use and yield a good, round, straight hole, even if operated freehand.

Vans will get the engineering staff to answer since the spar is a highly stressed part and may wish you to ream the hole just to remove any scratches resulting from the drill. They may just say check the bolt torque more often. Regardless, they know the design and stresses best.

Good luck with your build.

Pmerems · #3 07-22-2013, 07:46 AM

I am not familiar with the 8A but I have a 7A. If these holes mount the gear weldments then you might be OK. If the bolts aren't close tolerance bolts, just AN4-? then based on the manufacturing tolerances of the bolts you could have play in the hole. Additionally if these are for the weldments the weldment might also have a 1/4+ diameter hole for tolerance stack up reasons.

How much play do you think you have in the holes? If you know a machine shop with gage pins you can borrow them and get the "true" size of the hole but it might not be perfectly round.

I am sure you're not the first person who had this problem.

You can send me a private message and I will give you my phone number if you want to talk through this further.

Andrew M · #4 07-22-2013, 02:13 PM

NAS6604-**X or -**Y are 1/64 and 1/32 oversize.
http://www.gen-aircraft-hardware.com/store.asp
I understand the holes in the spar are opened up?
PM sent with phone number. Call me, I deal with a similar issue professionally.

scsmith · #5 07-22-2013, 07:28 PM

Those bolts hold the landing gear weldment onto the center section on the -8A.

On the -8, they are just fillers. There are so many fasteners holding the center section together, The shear load from the fuselage into the spar is carried mostly on the outboard bolts and the wing spar attach bolts. Other than just clamping everything together so nothing moves around, the bolts you are asking about don't do much at all.

Torque them to spec and then don't give them a second thought.

kens_cockpit · #6 07-23-2013, 05:42 PM

After talking to the engineering department they are not worried about these two holes having been final reamed as long as you are not talking about the actual wing attach bolts.

I take this to mean they do not require the bolt holes (which are not the wing attach bolts) to be final reamed and the fact that they have been drilled to slightly oversize does not worry them. That seems to be consistent with what Steve has said above.

Thank you all for your thoughts and particularly Andrew who has pointed me to some useful resources for correct bolt fitting.