Flush vs standard rivets?

[EdW]

I'm about to start skinning my tail surfaces, and have been spending (too much?) time watching you-tube and other build logs. See some airplanes with countersunk rivets, but most with standards. Is there a really, really good reason to flush rivet an airplane like a Onex? The dimpling alone adds a lot of construction time.

Since I'm an old poot I have no desire for aerobatics and such, just getting my fat posterior airborne is my goal. I'm starting to rethink my flush rivet decision.

Common sense prevails.

Ed

[gammaxy]

If you're rethinking it, I'd say just go with the standard ones to save construction time. The official word from the factory is the drag difference is negligible and I believe them. Your plane will loop and roll just fine either way. I don't think anyone does it for a reason other than looks.

[Bryan Cotton]

Flush riveting is a metal illness. I flush riveted my scratch built Hummelbird. I'd say if you have any inkling to get well bail out now. The main reason to flush rivet airplanes in our class is if it brings enough joy to your heart to make the time worth it.

[keithrhode]

I completed my Sonex in 2010 using the standard rivets. I recently completed a Panther using flush rivets, needs DAR inspection. The added time to flush rivet is minimal once set up with a C frame fixture and supporting table. If I were to build another Sonex, I would flush rivet. Looks better and easier to clean and polish if desired.

[peter anson]

I'll agree with Keith on this one. Buy a good quality dimple die set - the Cleaveland Tools DIENQ. The dimple die fits a 3/32" or #40 pilot hole and the dimpling process enlarges the hole to damn near final size. A friend used them with a C frame and the results are superb. I just wish I had done the same. If you paint the finished aircraft you can rub back between coats if you need to. It might not make much difference to performance but it sure won't do any harm and looks great.

Peter

[lpaaruule]

I flush riveted my Sonex and would probably not do it again. In addition to the dimpling, you must countersink every hole in thicker metal that the skins come in contact with. So all the longerons, and vertical angles. Finding you've missed one of these after you've started permenantly installing the skin isn't fun.

In addition, I probably made it even harder because I noticed that even using a C-Frame to dimple the skins, the holes didn't always line up perfectly, making inserting the rivet, and getting a good fit more difficult. My solution to this was to dimple at #40, reassemble, then updrill to #30. That way the holes would line up, there would be no stress cracks on the hole edges from the dimpling, and the rivets would go in easily. This was an additional step vs dimpling at #32 or #33 and calling it good because the skins had to be removed again for deburring.

Flush riveting has also compelled me to put extra effort into making other things like antennas more aerodynamic as well. It all takes time.

[Sonerai13]

You will greatly increase your workload during building and thus increase the time it takes, and you will get ZERO performance increase. So you really, really need to have a burning desire for the look of flush rivets in order to make it worth the work. If your primary goal is to complete and fly the airplane in the least amount of time, don't even think about flush riveting (other than the leading edges of the wing, as per plans).

[NWade]

As my Sonex with flush (pulled) rivets nears completion, I am happy to chime in on this:

I'm a glider pilot first and foremost, so the idea of a smooth-skinned Sonex appealed to me. The factory said it was possible and the cost was minimal, so I went for it. And while I'm very happy with the results, I have to concur with Joe that you really shouldn't do it unless you have a very compelling reason! (And even a 5mph difference is not a compelling reason IMHO).

The Sonex line of aircraft are capable of handling flush rivets; but they weren't designed for flush rivets from day 1. This is not a criticism of the design, just a fact. And the upshot of that fact is that some places on the airframe are very fiddly or time-consuming to dimple and prepare for flush rivets. You also have to countersink some structural members for flush-head screws in some areas, if you want a truly flat skin on the fuselage. And once you do that, you're looking at fasteners of different lengths than are specified in the plans - so you have to buy more hardware and do some trial-and-error fitting. All in all, these efforts add up to a notable time difference. And again, as someone who's in the home stretch of getting to first flight, I am now in the position to realize that building the basic airframe is the fast/"easy" part of the build! Things really feel like they bog down when you get to your electrical system, canopy, FWF, and other finishing bits. The sooner you can get to that "fiddly bits" stage, the less likely you'll be to suffer burnout and fail to finish the airplane.

Good luck on your project!

--Noel

[EdW]

OK, you've convinced me. My plans and packing sheet both show the countersunk rivets. Can anyone give me the correct part number for the standard rivets needed? Looks like two different lengths.

I really want to thank you all for your thoughts and assistance. We silver-haired foxes need all the help we can get.

Ed

[WaiexN143NM]

Hi ed,
Good luck with the build. Understand you already have your kit and countersunk rivets. The best thing you could do is go on the website and order a complete reg. rivet kit for whatever model your'e building, legacy or B, or onex.
While your at it order the WB hardware package for your plane.

WaiexN143NM
Michael