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The RV15 High wing bush plane

Graham wrote:

The riveting process is not the major risk to parts, in my view.

Not if you know how to do it. It also depends on where you set the standard for yourself. There is nothing a “good and thick” spackle/paint job cannot hide If there is something even worse “bad taste” than bulbed solid rivets on skins, it’s a thick paint job. But again, we are talking about taste/appearance. They all seem to fly just fine regardless.

As the Vans CEO said in that video (or perhaps another one) was that it’s up to the builder what he wants to do on the RV-15. If the builder wants solid rivets, he can use solid rivets. If he don’t want to bother with solid rivets, he can use pulled rivets. IMO it won’t make any measurable change in the structural integrity of the airplane throughout it’s lifetime. One major difference though. With pulled rivets, one man can do everything. With bucked rivets, two persons are needed lots of places.

The elephant is the circulation
ENVA ENOP ENMO, Norway

LeSving wrote:

This is why people start with the horizontal tail, and builds two of them

I have made a few mistakes and had to order a few replacement parts, but I do not intend to make such a mess of it as to build two horizontal stabilisers! The riveting process is not the major risk to parts, in my view.

EGLM & EGTN

Peter wrote:

Surely nobody would use pulled rivets (also called “pop rivets”) except to save labour costs

Then you should take a look at the fasteners Boeing uses in various structures. On the skin they don’t use rivets at all, but something called slugs. Essentially an aluminium rod that is squized in place using special tooling. To get them flush, they are shaved using a special shaver.

The thing is, there are a whole specter of various “pop rivets”. Some are structural, some are not. Some requires special tools like for instance the Cherry Max (I got my set used). Some only requires a pop rivet tool you can purchase at the grocery store. The only thing they have in common really is they are all much more expensive than solid rivets.

In an industry environment it is not clear to me how pop rivets would save cost. It’s actually faster with solid rivets, but it requires more planning and more skilled personnel. For the places you just cannot do with bucked rivet, you simply use Cherry Max (it’s a drop in replacement) or whatever else fits. In a homebuilding environment a pulled rivet has the advantage because it doesn’t require any skills. It becomes faster and the result is more consistent. One single wrong blow with the rivet gun or a misplaced/wrong bucking bar may ruin the whole skin (at least you can forget about that perfect polished aluminium surface). It takes practice. This is why people start with the horizontal tail, and builds two of them

In the end it’s just looks IMO. We are talking about recreational aircraft, not industry tools like a Boeing.

The elephant is the circulation
ENVA ENOP ENMO, Norway

High quality blind structural rivets are an expensive to buy, high engineered solution that after installation performs almost as well as the very inexpensive to buy solution. The highly engineered and intolerant aspect also extends to the holes, driven rivets are conversely more tolerant of hole misalignment, fill the holes completely without any real doubt, and thereby provide a very reliable shear loaded joint. They’re also better at sealing fluids, if that’s a consideration.

None of the above or the issues mentioned by others takes away from the value of high quality blind structural rivets or e.g. CNC skins that provide great pre-drilled hole alignment. That’s all great stuff in its place, as is saving installation labor, but when the part is built and finished I prefer to own and use the simpler, better rivet solution in most areas of an aircraft structure.

On my aircraft I recently had to replace some worn fittings that had been the subject of a long ago A.D. in which their attachment had been reengineered and reinforced. Blind rivets were used to reattach the fittings at that time, to make the job easier. To do the recent job some tooling and considerable effort was involved and I did much of it, but asked my A&P to remove and replace the fittings and rivets themselves. Removing blind rivets takes some skill that he has and I don’t and if we damaged the holes we’d be screwed – this is a highly loaded joint that mounts the horizontal tail. He did well and also replaced them with solid rivets despite having to make a clever bucking bar to make that possible. That made me happy.

Re flush rivets, people working based on facts determined long ago that they provide no useful aero. benefit once you get past the main spar on a wing, and similarly elsewhere on the aft skins of a light plane. It is not any more ‘proper’ in engineering to use flush rivets where they do no good, and that’s why you see them used sparingly by light aircraft designers.

In mechanical engineering outside of aircraft structures many people have no idea that rivets of many kinds are a stronger, better and more reliable way to join thin materials. I recently went through a somewhat hilarious episode where I proposed using Cherrymax blind rivets to fasten a shear loaded joint securely on a piece of machinery. I then had to convince some people involved in manufacturing (of all things) that they would be ‘at least as good’ as loose tolerance screws in sloppy holes. I think it took four meetings going over the same ground but I did get it done in the end.

Last Edited by Silvaire at 16 Aug 17:20

Surely nobody would use pulled rivets (also called “pop rivets”) except to save labour costs. They look crap, are hard to drill out, cause drag, are a pain to respray …

The problem with solid rivets is that to do them properly (flush) you have to either use a thicker skin, or dimple the skin and then you need a thicker material under it with a countersink in it (or some such) which is labour intensive.

Administrator
Shoreham EGKA, United Kingdom

Graham wrote:

I think the problem most people have with pulled rivets is the appearance

I think so too. Flushed solid rivets looks nice (bulbed heads not so much). Pulled rivets looks cheap. The reality is that pulled rivets are much more expensive than solid rivets. The Sonex aircraft use pulled stainless steel rivets. For the same dimension they are exactly as strong as solid aluminium rivets. Pulled rivets are normally hallow, as the ones used on Sonexes. There are more expensive pulled aluminium rivets like the Cherry Max where a solid steel stem makes up for most of the strength.

Another thing is corrosion. Solid rivets are best in this respect. Solid flush rivets is the best (strength, weight, corrosion and appearance). But I think for a small GA aircraft the strength, weight and corrosion issues are so minor it doesn’t matter (you just add a few or subtract a few rivets and you get the same overall strength). It’s really only appearance left.

The elephant is the circulation
ENVA ENOP ENMO, Norway

LeSving wrote:

From a QA point pulled rivets is preferable to achieve consistent quality of the riveted joints when the job is done by amateurs. Besides, as the saying goes, Vans have doubled the number of rivets needed to make up for errors done by the average builder (have no clue if that is true or not).

I think the problem most people have with pulled rivets is the appearance. I certainly find the look unattractive.

There are a two aspects to the solid rivet issue. Firstly there is the generally-accepted idea that Vans aircraft are over-riveted – opinions vary on by how much. Secondly, in their build information they quote research which suggests that the difference in strength between perfectly-set rivets and some really quite ‘ugly’ ones is basically so small as to be immeasurable, so long as you don’t violate a few basic rules. They say this in the context of advising you not to drill out less-than-perfect rivets, suggesting you’ll weaken it more by enlarging the hole even if your second attempt is absolutely perfect.

EGLM & EGTN

That’s a cool picture

The weight of rivets is a fraction of the weight of paint some people put on these planes. Just saying

From a QA point pulled rivets is preferable to achieve consistent quality of the riveted joints when the job is done by amateurs. Besides, as the saying goes, Vans have doubled the number of rivets needed to make up for errors done by the average builder (have no clue if that is true or not).

Pulled or not, they have really hit the nail with this design IMO. The only thing is the engine. If a 390 with 220 hp is required to get decent performance, this means (AFAIK) that leaded fuel is required. Maybe the aircraft is very heavy?

The elephant is the circulation
ENVA ENOP ENMO, Norway

my favourite take of the -15
(Photo courtesy Van’s Aircraft, Inc.)

Dan
ain't the Destination, but the Journey
LSZF, Switzerland

I did take a look at Oshkosh, where it was surrounded by people non-stop. What was attractive to me in person was design features (e.g. Fowler flaps and big stabilator) that promise a comfortable, wide speed range. That apparently includes a decent cruise speed using a four cylinder Lycoming and fixed gear.

I spent $90 on Avgas yesterday just dinking around after reassembling my plane, and that was enough. 180 HP is a good number.

What I didn’t like is seeing the engineering prototype covered mostly in pulled rivets, but I understand the idea is that you could build it with solid rivets if wanted. That would be my choice for the strongest, lightest structure but I can also understand the appeal of pulled rivets for a solo builder.

Last Edited by Silvaire at 07 Aug 16:49
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