Emp fairings

[Auburntsts]

Folks,
I've started working on my emp fairings and have noticed that some builders have bonded in aluminum backing strips on the internal side of the fiberglass fairing flanges in order to give the blind rivets something more to bite into than the raw fiberglass. Nothing from Van's calls for doing that (the plans, Chapter 5, etc). Am I asking for trouble later on if I stick to the plans and rivet the fairings on as is without the backing strips?

[rvbuilder2002]

Originally Posted by Auburntsts

Folks,
Am I asking for trouble later on if I stick to the plans and rivet the fairings on as is without the backing strips?

It works fine with no doubler strips added (many RV's are flying this way), but many builders feel better if they add them.

[Bugsy]

I used a strip of 1" kevlar that I expoxied in place as a backing for the rivets and also provide strength. Whatever you do or dont do for backing, I think the key is to proseal the the tip on and then poprivet. Once on the thing is solid. So if you proseal and one of the poprivets didnt seat well your still golden having the proseal hold the thing tight for the life of the plane.

Good luck

[Andy Hill]

An easy solution is just to make some AL 'washers', say ~0.25" x ~0.25" square. Just use this instead of a whole strip - easier and lighter, but giving the same benefit. I am not talking of "precise" fabrication, just some AL sheet offcuts cut into rough shape and drilled... and maybe epoxied in...

[Brantel]

Even easier is to pic up a couple packs of "Rivet Washers" at Lowes or Home Depot. They only cost a few cents a pack. They have a perfect 1/8" ID and work great. They are usually sold right next to the pop rivet guns and rivets.

I used E6000 to tack them in place with a cleco for a few hours. Then riveted them on...

Originally Posted by Andy Hill

An easy solution is just to make some AL 'washers', say ~0.25" x ~0.25" square. Just use this instead of a whole strip - easier and lighter, but giving the same benefit. I am not talking of "precise" fabrication, just some AL sheet offcuts cut into rough shape and drilled... and maybe epoxied in...

[roee]

Either Al backing strips or the "rivet washers" technique should help protect the fiberglass from being crushed by the pop rivet as it's being pulled. It'll also help minimize damage to the fiberglass at the rivet line if later the tip takes an impact in the direction of pulling the fiberglass tip apart from the empennage putting the rivet in tension.

The advantage of a continuous Al backing strip bonded into the tip will also strengthen the structure in the shear direction, i.e. if the the tip later takes an impact pulling it away from the empennage putting the rivets in shear.

Bonding the tips to the tail surfaces using proseal, flox, whatever, should also strengthen it in shear.

All of these techniques do strengthen the installation. But the question is how strong is strong enough. I'm confident that no RV has ever crashed because its emp tips didn't have backing strips. But some probably have been damaged too easily on the ground with "casual" impacts to the emp tips. Personally, I chose to add Al backing strips and bond the tips in place because it's easy, adds only negligible weight, and adds a lot of robustness.