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Vertical stabilizer attach

Dorfie

Well Known Member
Did anyone install nutplates where the vert stab rear spar attaches to the F-1012A and B fuselage bulkheads? Plans call for AN3 nuts and bolts and washers and there is not easy access to especially the bottom ones.
Thanks.
Johan
 
I don't think nut plates count as structural hardware, and it is the spar attach you're talking about here. I'd at least run it by Vans' engineering.

And those nuts aren't really that hard to get to, compared to some others.
 
Those nuts are easy to get to. Nutplates don't count as structural hardware, I would use the hardware called out in the plans.
 
Nutplates not structural?

I asked that same question with Van's several months ago. This in regards to the 4 bolts that hold the forward stabilizer to the fuselage on my RV8. They assured me that this was an acceptable substitution. I will admit that this is a different aircraft, with different stresses and design features.
Any stress that would strip 4 nutplates off those bolts would probably tear something else off first.
 
I strongly recommend caution when thinking about substituting a nut plate for a regular nut. Not because a regular nut is necessarily stronger than a nutplate, but because the bolt likely needs to be sized differently (at the very least installed with a lot more care).

Except for a few cases, bolts are loaded primarily in shear in an RV structure. The best shear strength is attained by having the fastened structure bare its shear load against the full diam. of the bolt shank.

If you look closely at an AN bolt, the shank has has a slightly radiused area as it transitions from the load baring shank into the threaded portion. When we select bolt lengths on highly (shear) loaded fasteners, it is standard practice to to use a bolt length that will have this radiused area protrude beyond the structure so that the structure shear load is baring only on teh full diam. portion of the bolt, and then use washers as needed so that the nut doesn't shank out (run out of threads) when it is fully torqued. This is part of the reason for the "at least one but no more than three threads showing" rule of thumb. Following that rule of thumb will help assure that you are not using a bolt that is too short (has full shank penetration) or too long (risk of shanking out).

If a nut plate is used instead of a regular nut, the bolt sizing task gets more difficult. Nutplates have some un-threaded relief to allow a bolt shank to slightly protrude out of the material being fastened, but it is much more difficult to adjust the bolt length to work properly. The only way is to use washers under the bolt head. If the bolt is overly long the nutplate might shankout and seem to have reached full torque before the full tension load of the bolt is applied to the parts. If the bolt is too short, the parts may not be entirely baring on the full shank diam of the bolt.

So, I am not saying it should not be done. In fact there are some places on RV's it is specified (z brackets for the fuel tanks is one that comes to mind). But that you need to use a lot more care when installing the fasteners. When done in situations that the material being fastened is thick, it is a lot less critical because there is a lot of baring area on the bolt.

I personally wouldn't recommend using nutplates in either of the locations mentioned in this thread. If nothing else, because there is little benefit. Both locations are not difficult to access.... I have done it many many times with no helper. In most instances, these bolts will be a one time installation at final assembly and will probably never be removed.
 
I won't assume that your goal is to build the airplane in a reasonable amount of time, but if it is, you should think long and hard about deviating from the plans for something as trivial as this. There are many more places in your future with more difficult to attach hardware--this one is no big deal.

-Rob
 
Apart from anything else, I would have thought it would be just as difficult to get to the bottom holes with a bucking bar to fi the nutplates!

Honestly, those nuts are not hard to fit.
 
Thank you all

Thanks for all the answers and excellent explanations. Very educational. Much appreciated. And no, I do not deviate from the plans on my own without the blessing from VANS.

On this same line of work, when you do final installation of the surfaces (after having them on and off a few times with the nuts and bolts tightened and removed a few times), do you use NEW nuts and bolts? That is what I am planning to do unless instructed otherwise.
Johan
 
As far as I know, there is no advantage in fitting new bolts unless you have over-torqued them.

I have a big pot of used nuts which I use for test fitting and then I put new ones on for final. In fact, I NEVER re-use a lock-nut. We are talking cents on a $175,000 aeroplane, so it doesn't make any sense to me. I guess if you were away from base and had to fix something it would be OK but even then I think I will carry some spares in my flyaway tool kit.
 
Re use hardware

I don't ever reuse nyloc nuts either. Bolts I reuse unless the cad surface is messed up, then I replace those too. Like the previous post said cents on a 175K airplane...
 
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