Emp fairing and csinkng longerons

Page 12-6

Attaching the dimpled emp gap cover requires csinking the longerons for #6 screw, which would be #27 bit. BUT, the longerons will be tapped with #36 drill. I don't see how I can use a countersink without a larger pilot hole - how have folks done this? Do you countersink without a pilot hole? Recipe for disaster in my hands!

Drill to 40 and use #40 CS until you get to dimple size. Then drill/tap for screw.

But 40 countersink won't get me to point of being able to use #6 countersink?? I don't follow

You don't need (or want) a #6 countersink for this job. You can set the depth of the cage with a #40 piloted countersink for any size dimple or screw that has a head diameter up to the outside diameter of the countersink bit (3/8" for all that I have). In your case, drill a #40 hole in a piece of 0.125 scrap and increase the depth of the countersink until you can fit a #6 dimple in another piece of scrap the same thickness as the gap cover in it. Hopefully there will be enough thickness left after drilling to #36 to tap for the screw.

Not much...

Just did this step and used the #40 pilot countersink. Worked fine. Then drilled to #36 and tapped the hole. Only enough material to get about 2 threads. I suppose it would be ok as long as you don't run those screws in with a screw gun...

I believe that I am going to use Click Bond nut plates, instead. I used them for the winghtips and there were enough left over to do the fairing so I will be drilling the tapped holes out and bonding the nut plates to the longerons...

I'm still a ways out from this step on my -7, but would there be a problem riveting a regular K1000-06 nutplates on the interior face of the longeron? Limited access at that point in the build, maybe?

You can be a touch shallow on the countersink and it will look fine outside. That will leave maybe 3 whole threads.

longranger said:

I'm still a ways out from this step on my -7, but would there be a problem riveting a regular K1000-06 nutplates on the interior face of the longeron? Limited access at that point in the build, maybe?

Click to expand...

That's what we did on our -10. There just didn't seem to be enough "meat" for the threads to grab, not to mention the longerons are soft aluminum.

Jason

I did not CS, not enough threads left IMHO. I just used very flat pan head SS screws AN526C-632R6. It looks just fine and there is adequate thread engagement. If you have already dimpled the cover, I would not use a standard nutplate, but a clickbond nutplate would be an alternative.

Haven't reached this step yet but I'm not particularly worried. I know that some people with other RV models have riveted the lower empennage fairing in place but mine were installed as directed and they've been fine. I was worried less about the number of threads as the fact that there was no locking action, but I didn't apply threadlock until after the 40 hour Phase I. No screws lost. By comparison, I've seen more than one production aircraft with missing fairing and panel screws on walk-around. One C-182 I know regularly loses a screw in the tail fairing (the same one; all the others don't move). That's one of the things a pre-flight is for.