Riveting: Which Side Does the Factory Head Go On?

[aeropunk]

I'm getting to the point in the -8 empennage kit where I'll be riveting the HS-609 reinforcement bars to the HS-603 rear spar, and I can't tell from the plans which side of the assembly the factory heads of the rivets should be on. Various online builders' logs show it done both ways.

Am I missing something in the plans, or is there a "standard practice" I should be following, as with e.g., threaded fasteners? I know I've seen the answer "it doesn't matter" in several other threads here, but I was just curious what the thought process is. Thanks.

[chaskuss]

Brian,
Standard practice is to install the factory head onto the thinner piece [spar web in this case]. Sometimes you must ignore this rule, if following it will make it difficult or impossible to get the rivet gun/set onto the factory head. That caveat does not apply to your parts, so install the factory head to the spar web.
Charlie Kuss

[bruceh]

So I'm a new builder also and in my several months of experience I have determined several considerations.

Esthetics - do the factory heads look better on one side or another?
Ease of installation - can you get a good shot at installing the rivet better from one side or the other?
Ease of replacement - if I screw up setting this rivet, can I get the drill on the factory head to drill it out?

Other than those, try to keep the factory head on the thinner material. I riveted my wing ribs to the rear spar and went for the esthetics (the rest of the rivets on the rear spar doubler were showing the factory heads). Unfortunately, the rib is the thinner material and when squeezing the rivet it tended to pull up the rib flange around the shop head.

[flion]

Generally speaking, rivets are like bolts. The head goes up or forward. But that's just a guideline, and not nearly as important as with bolts. A more important consideration can be the thickness of material; the head should go next to the thinner material and the bucking bar next to the thicker material. There can be other considerations, too. If there are clearance issues, it's often easier to plan around the manufactured head (I'm thinking of the aft deck on my -6A, where the horizontal stab has a spacer to clear the deck rivets; driven the other way, if that were possible, an underdriven rivet might interfere). And that brings us to what is probably the most important consideration: which orientation can you drive the rivet in. In the above example, it is simply not practical to have someone crawl into the tail and drive rivets in that tight space while you buck outside. In the area you are working, it doesn't make a lot of difference either way so you can fall back on the final consideration: what looks better to you? Generally, if an unusual orientation is critical, the plans will note it.

[gpiney]

I've noticed that the plans 'point' to where the factory head goes. The callout on the drawing points to the side for the factory head.