Rivets

[rfidler]

Flush vs Std Rivets?
Advantages of both types?
Any advice to offer to a novice builder?
All I know is flush can pop easily if not done correctly and even so if they are installed correctly.
Thanks

[Bryan Cotton]

Hi and welcome to the forums!

If you feel like you really have to have flush rivets, then go for it. There are additional costs, partly for rivets and you may want fancier tools if you are doing a lot. If you are on the fence then I would skip the flush rivets. I used to have a flush rivet bias. When I saw Tim Stearn's polished Waiex with non-flush pops I really thought it looked great.

Flush rivets have more shear strength, because the metal is dimpled together. You don't actually need the extra shear strength as the airplane is designed around universal head rivets. I don't think any airframer would design using the additional shear strength of flush rivets. I have worked for two. Flush should be easier when it is time to paint or polish. It will add time to your build. Every hole you have to pilot drill, final drill, and deburr. Take all that and add dimpling or countersinking to every sheet you go through. It adds time.

Novice vs expert - no factor. Always play with some scrap before you try any new skill, or if an old skill is rusty.

[mike20sm]

I struggled with this decision too even to the point that I initially ordered the kit with the flush rivets and then shortly after doing more research had them exchange them for the standard rivets. For me it was less about looks and all about performance, but at the speeds the sonex flies I found any benefits to be negligible and not worth the extra effort for my needs. At the workshop I attended, I think I remember John Monnett's take on Flush vs. Standard as a bit comical. He joked how glider pilots have smooth airplanes and then intentionally make them unsmooth by adding turbulators. So if you go with the standard rivet just think of them as turbulators :)
Remember that there are flush rivets on the front section of the wing which is standard for all the planes, which is were it's more critical to the airflow.

[dhogue]

Am building with flush rivets.

Sonex Tech Support answers to my countersink and flush rivet dimple questions:
When you countersink you do so after the hole has been drilled to the final size (#30 for a 1/8” rivet).
When you DIMPLE it is best to drill undersize (#31 or #32 drill) and then dimple, as dimpling stretches the hole.

A pneumatic rivet puller/dimpler is a good idea in terms of speeding up the build time and much easier than using the hand tools.

[marsolgp]

When I flush riveted my Waiex (all except bottom of fuselage) I drilled holes to #40, dimpled, then reamed all holes to #30…. just another option. I did find, through experimenting with scrap metal, that dimpling AFTER drilling to #30, the hole was a little big. Of course the type and method of dimpling has an effect on finished hole also.

See Cleaveland tool P/N 'DIENQ' for dimple dies and explanation of process that I used.

[NWade]

When I flush riveted my Waiex (all except bottom of fuselage) I drilled holes to #40, dimpled, then reamed all holes to #30…

G - While that method can work, multiple builders (myself included) find it very hard to debur the hole (since you're drilling after dimpling). It certainly produces the "best" hole this way, assuming you can fully debur both sides of the hole properly.

Like many others, I found it simpler to drill with a #32, then debur, then dimple as the final step. YMMV!

NOTE: I am one of those afore-mentioned glider pilots. ;-) ...And while I'll point out that turbulators on gliders are placed in a very precise location only in specific spots (usually on the underside of the wing back near trailing edge / control surfaces), its not worth a lengthy debate - you're not aiming for the same level of precision on a Sonex and you aren't concerned with maximizing L/D like we do on sailplanes (i.e. wing surface waviness less than 0.004").

A Sonex with all-flush-rivets (such as the one I'm building) will see a slight performance increase; but at most it'll be just a few mph. In my experience (wings and empennage complete), the flush rivets add ~10% - 15% to your total build-time. This is because of both the dimpling process, and some extra fiddly-ness with some parts because they weren't designed with flush riveting in mind. If I did it all over again, I would probably just go with standard rivets - even though its hard for my brain to accept a non-smooth skin. At the end of the day, anything that's a barrier to finishing and flying the airplane is a BadThing(tm).

--Noel
Sonex #1339 - Wings & Empennage Complete, Fuselage starting soon
Center-stick, TD, Turbo-Aerovee, Flush-Rivets, Aerobatic-Ailerons

[Rynoth]

Has anyone polished a flush-rivet Sonex? Seems to me that the dimpling might cause a more distorted reflection if going for polish. However flush rivets would leave a great surface for painting I'd think.

[13brv3]

I'm certainly following this discussion with interest. I'll likely be building a Onex very soon, and I've already been debating this as I look at the kit order forms. After building 3 RVs, standard blind rivets just seem so wrong, but it's also one of the reasons the project appeals to me. Believe it or not, I'm pretty tired of dimpling ;)

Cheers,
Rusty (trying to resist flush rivets)

PS- Ryan, your time lapsed build video is spectacular!!!

[Bryan Cotton]

Rusty,
I built an RV4 tail and most of a hummelbird with solid flush rivets. I restored most of a 1946 C140 with all solid rivets. I used to work at Sikorsky and Schweizer where rivets were generally solid. I am a solid rivet guy. On the other hand, the SS pops are strong and very easy. When I see my 14 year old plugging through them I know I made the right choice. It is fun and productive when it is rivet time. Come on over to the dark side, you can always go back on your next project.

[LarryEWaiex121]

Rusty,

Here is a completely different take on the rivet matter. First off I don't profess to have any knowledge of the mechanical characteristics of the flush vs. pop. I simply ended up going the pop route do to the fact I knew upfront that I was going to be doing 95% of the work on this plane unassisted. That was a big decider for me.
In regard to the "looks" aspect of the pop rivets vs. flush, I have some perspective on both. My leading edges on my Waiex are both standard flush, but also filled, primed and painted. Its not unusual at fly-ins for people to ask me about my leading edge and what I used to bond it on? Well its not bonded, but filled. I took a chance on the filler aspect of things.
I can also say that with the passing of 4 yrs, almost 450hrs of active flying and many heating and cooling cycles out in the sun, there has been some limited movement beginning to show in the paint. It's beginning to show slight rings around some rivets.
The balance of the plane is stock pop rivets. Most of fuselage polished, tail polished, tips painted and accent paint lines on the fuselage.
Entire wings, cowl and bottom of fuselage painted. Easier to clean and maintain.
I get a lot of compliments on the overall visual balance of the plane. Some question the N number size and background? Oh well. I just tell them it was my choice and that's how it came out and I'm not Picaso.
Good luck with whatever you choose, but for my two cents I wouldn't go the flush route. I never felt I was getting the security on the finished job as well as the standard headed pops. Additionally, I also get compliments on the polished finish with the rivets doing their shinny job also. I think the rivets add interest to the whole picture. So I have a bit off all of the above and like that standard rivets the best.

Larry
Waiex, 121YX, Jabiru 3300 solid, 449 hrs