Flush vs Protruding Rivets

[GlenNJ]

Chris,
If you go the solid rivet route with your build, please let us know how you rivet the skins on difficult to reach areas like the tail feathers. Because they have a frame, I don't know how the tail feathers can be solid riveted. The only thing I can figure is the C-channel rear spar must be left off as the top and bottom skins are riveted. Then the rear spar would be riveted on. It would still be hard to reach the leading edge rivets.
Another reason one might want to flush rivet the skins, would be if the airplane is polished or waxed on a regular basis. I have waxed a few airplanes, and removing wax around protruding rivets is a pain in the butt.
Glen

[rlweseman]

Excellent reply Chris! Very informative and helpful!

[PlaneDan]

Chris,

Thank you very much. That was very informative and a good read for any newbie, like me. I think I will stay with the flush pull for the tail and go from there. I want to learn how to dimple anyway and I have a lot of RV builder friends here at CUB who are anxious to see a Panther on the field and very willing to help.

[csjohnson65]

Hi Dan - I had this conversation with Dan and Paul when I made a visit to SPA headquarters. I think you have a choice of protruding vs flush, and with flush, pull vs solid, and even aluminum vs stainless steel!

Protruding/pull rivets are faster and easier to build with and have less risk of error. They are less aerodynamic (Paul estimated that they cost maybe 2mph at top speed), and some people don't like the look.

Flush rivets add the dimpling step, and solid rivets adds the need to use a rivet gun instead of a rivet puller. Each of those take a bit more time and increase the possibility for errors and therefore rework. In fact, Dan said that if you're a newbie and use solid rivets and a rivet gun, you're almost assured to damage a piece of skin along the way and have to order a replacement.

Protruding rivets, well, protrude above the surface of the skin like pimples. Flush rivets create a smooth surface, though solid rivets are even smoother than pull because pull have a pin in the center that gets cut off after being pulled through the rivet head, and sometimes that cut is pretty flat and smooth, while sometimes a little pointed and sharp. Personally, I just like the smooth look and feel (e.g. run your hand of the top of a line of rivets) of the flush, solid rivets, so I'll take the extra time and buy the additional tools.

IIRC, Dan estimated an additional 40 hours to do the dimpling, another 40 to use solid rivets, and overall 100 hours total to account for inspections and rework. If he reads this he can clarify or correct, but ultimately it sounded like an extra 1-3 weeks of build time, which isn't much to get your preferred result.

Dan and Paul also pointed out that on the prototype they used flush/pull rivets on the top of the wing for the sleeker look, and protruding rivets underneath where they're not immediately visible. Even more options!

Great to have so many choices! But as you'll hear experienced builders often say, build the plane you want and you'll have few if any future regrets.

Chris

[PlaneDan]

Yea, right. I needed a good laugh.

[Tony Spicer]

Dan,

Your build time would be increased by 3.72 percent, +/- 2 percent.

Tony

[PlaneDan]

So, how much time would I be signing up for

[psalter]

In most places flush is mainly for looks. Protruding head eliminates the need for dimpling, which is an extra step and takes a bit more time.

So, it is strictly a builders choice for taking longer and using flush, or make it easier and quicker by using protruding.

There are a few places were a flush rivet is required, due to other structure in that area.

[PlaneDan]

Given that this is an option, why would a person choose protruding rivets? Please explain as I have just ordered my kit with flush and then started wondering why anyone would choose protruding. It is not too late for me to change my mind on this as I am just now sending the check.