Van's Air Force
The definitive Van's Aircraft support community! Buying, building or flying an RV? Join our exclusive family of mentors and enthusiasts!
Anyone planning on bucking rivets for the RV-15?
- Thread starter Gandor
- Start date
. I absolutely loved the ease of building my RV-12 (Legacy) with the pull rivets. I built 90 % of the plane in my garage, so I'm pretty sure my neighbors & family appreciated my choice as well, even if they didn't know it.I’m set up for solid rivet, so why not. Flush rivets would look nicer in my humble opinion! 
I agree solid flush riveting is going to look nicer, not sure if it's 3-500hr of time nicer hahaI’m set up for solid rivet, so why not. Flush rivets would look nicer in my humble opinion!
If you are looking to go fast, the -15 is the wrong choice.
PilotjohnS
Well Known Member
Yes, as many as i can i would like to dimple and use-3 for a slippery airframe, but i think that is not in the cards. I think - 4. 1/8” Flush would make for really strong airframe. Maybe the RV16 will use -3 flush or 3/32 pop rivets. Hint hint. But in reality, to use 1/8 driven will put a lot of stress through the skins, so i think it will be hard to keep the skins from having smileys.
Last edited:
If you don't want all of the universal head pop rivets, I suppose you could dimple and use countersunk 1/8" pop rivets, yeah? Granted, I have zero idea if they are as strong as the universal heads. For me, if I went with the RV15, I'd be gleefully pulling pop rivets and laughing to myself how quickly it all goes together!
If you look at a Bonanza wing, the leading edge has flush rivets. Past the spar are dome. Sooo, maybe a combo.
However, when it comes to building fuel tanks, to use closed in pull rivets, there would be no way I would want to buck those rivets when I could pull them.
However, when it comes to building fuel tanks, to use closed in pull rivets, there would be no way I would want to buck those rivets when I could pull them.
My career has included some structural testing of flush versus universal-head blind rivets, including the ones used by Van's. I found the flush ones to be just as strong.
I found one tiny difference, which ends up being pretty much inconsequential: In areas where they take a substantial load, flush blind rivets are slightly more prone to having their heads fall off after a while due to fatigue. (I mean fatigue in the rivet, not in the surrounding material, to be clear... because fatigue in rivets is a relatively rare thing). Note that I said "in areas where they take a substantial load". This is what makes the difference inconsequential: Flush rivets are almost always used to attach an external skin to ribs/bulkheads, and the loads there are typically quite small (with some exceptions). The RV-12 has some flush blind rivets at the inboard leading edge, and many RVs have them on control surfaces, and I don't remember having heard of their heads popping off after years of flying, probably because the loads at those locations are a small fraction of what those rivets could take.
You see that on many airplanes; Flush rivets where the boundary layer is laminar (i.e. near the front) in order to keep the boundary layer laminar if possible (to keep drag low), universal head where the boundary layer is unavoidably turbulent and thick (i.e. near the back). See, for example, the aforementioned RV-12 inboard leading edge. And even jetliners have dome-head rivets on the tail cone; The boundary layer back there is so thick that the difference in drag would not be worth the work to countersink the holes.
Last edited:
Back when Zenith started selling kits using mostly pulled rivets (and designed around that choice), a number of people thought it was aviation structural heresy. This was a widespread and hotly voiced opinion at the time! I remember being told that our 801 would fall from the sky because of all those “pop rivets. “
Some Zenith builders apparently decided to use bucked rivets despite the increased work, although I’ve never seen such a bird. Perhaps they were never finished. 
The ship has pretty much sailed on that viewpoint, I think, and the RV-12 was a big reason.
As I understand it, often aircraft that are designed for pulled rivet construction are designed with a “higher density” of rivets than would be necessary for bucked. So if you go with bucked on a -15, you may REALLY be making extra work for yourself.
reminds me of the story of glueing frozen split peas on the spitfire wing to determine which flush rivets could be replaced with universal heads without impacting the top speed.
Likely true, but can't blame people for wanting to go fast at altitude and still be able to land on a sand bar in the river. Just out of curiosity, how much airspeed at cruise would be sacrificed by pop rivets compared to bucked rivets? Ballpark guess...
I STILL don't understand why so many people relate solid rivets to "flush" and pulled rivets to "round-head". I've built several airplanes with flush pulled rivets. Including my current project.
I don't do flush rivets for speed. I use them because they look better, they're easier to paint, and easier to clean.
I don't do flush rivets for speed. I use them because they look better, they're easier to paint, and easier to clean.
rmartingt
Well Known Member
I'm not planning to build a -15 but pull vs. bucked rivets seems one of those things that won't make a big time difference in the end. Perhaps a week or two overall, and that's if you build slow like me? Deburring, wiring, priming/paint prep, fiberglass (
), p-clamps, and all the other fiddly bits seem to eat up more of the time. But then, way back when I'd started on a Sonex (before switching to an RV) I was planning to dimple and buck for drag reduction (which never hurts) and appearance.
Now if someone made self-locating auto-retrieving tools that I could just summon back to my hand by voice after setting them down 10 seconds ago and losing them, that would be a worthwhile investment
), p-clamps, and all the other fiddly bits seem to eat up more of the time. But then, way back when I'd started on a Sonex (before switching to an RV) I was planning to dimple and buck for drag reduction (which never hurts) and appearance.Now if someone made self-locating auto-retrieving tools that I could just summon back to my hand by voice after setting them down 10 seconds ago and losing them, that would be a worthwhile investment
How much is “that much longer”?
300 hours?
500 hours?
It is certainly an option but I’m curious as to the gain. Is it just for looks? It is likely that for an aircraft if this type, the performance gains would be marginal…especially flying around on 26”+ tires.
Why such small tires?
Who cares, building an airplane isn’t a race. At least is a real airplane that has a tailwheel
There is - but it does depend on the type of pulled rivet. The most commonly used pulled rivets in aircraft’s such as the Sonex or Zenith lines is a Cherry stainless (“N” type if I recall without looking it up). I recently did some calculations on these versus the usual AD solid review we use, and the Cherry’s gave about 10-20% more strength in both shear and tension. But as we all know, the solids are more than adequate for the job (or so say the designers)….so either one will be fine from a strength standpoint.
There are many other types of pulled rivets, so if you are considering substitutions, always do your own math!
Remember those will be drilled for 1/8” rivets. That’s a lot more banging, bucking and dimpling energy on thin parts that you used little 3/32” rivets for. Solid rivets sounds like a plan for lots more smiles and dents on pretty skins. On a -8 the most common rivet by far was an 3-3.5. If they use the same material thickness on the -15 The 4-3.5 length isn't available so you would be trimming every rivet or running a longer than optimum rivet in every hole which adds its own challenge.
Last edited:
According to Zenith, there is a difference (at least with the domed pulled Avex rivets they used back in the day) - the pulled ones are NOT as strong. Their aircraft kits are apparently designed with that strength difference in mind (read: more rivets, basically).
I suspect quality control (or perhaps “accommodation of lower skill sets”) is another advantage with pulled rivets. Easier to do a serviceable job with pulled rivets.
There are differences. The "LP4"/"CS4" pulled rivets used on the RV-12 skins (and elsewhere) have a certain strength... but the AD41H/AD42H/AK42H pop rivets used on the fuel tanks have a different (higher, I think) strength... and Cherry rivets have a different (even higher) strength. That's just for 1/8" blind rivets. You can look up online (or, worst case, calculate; multiplying the allowable stress of a solid/driven rivet by the cross-sectional area) the strength of each kind of rivet. You'll find that some are under 100 lbf and some are over 600 lbf, just among the kinds used in RVs. And usually those numbers conservatively disregard the "help" from the dimples, which add some strength i.e. relieve the rivet from having to carry the full shear load.
PilotjohnS
Well Known Member
PilotjohnS
Well Known Member
if it looks faster it must be. but i think i will trust Vans and not go to far off plans.
For the SPEED, man!Why such small tires?
Yeah, true but you needn’t start that BS thread again.
nilberg
Well Known Member
I like flush rivet because the surfaces are nested in each other. I would imagine that shear loads are somewhat absorbed in the dimples larger surfaces instead all going into the rivet shafts.
...and yet the engineers designed it with pulled rivets.
Jjackh10
Well Known Member
Flush pulled rivets or round head pulled rivets?
I would guess round head but as the final design isn’t available, it’s just speculation.
PilotjohnS
Well Known Member
Here is a thought, design it for 3/32” pulled rivets so we all could use pulled or flush as we wish. It will probably end up being a little over designed, but that isn't so bad for a bush plane.
The pull rivets in the 3-32 size have very limited length. The 1/8" size rivets have a wider range of length for the various depths of metal.
The 2 biggest advantages of solid rivets are cost and weight. Pulled rivets are expensive and heavy.
Why would a -4 flush be pillowed? P-51 has a very clean wing and I haven’t observed many that were pillowed.
I agree. I built a Moni motor-glider back in the 80's with 1/8" flush solid rivets and there was no "pillowing".
Yes, I will!
A few thoughts not yet mentioned...
To at least some degree, traditional solid riveting of skins to aircraft structures requires some design consideration in order to assure access for bucking all rivets as an assembly goes together.
When a design decision is made to make blind rivet assembly the recommended and primary method (such as was done on the RV-12), it greatly frees up the design process because different structures can be designed with no internal access if there are other design benefits (simplified structure, lighter weight, lower cost, etc).
That is one of the great things about blind rivets from a design perspective, but it can make it challenging or even impossible to use conventional riveting methods for some portions of a riveted aircraft, if that method wasn't "designed in".
For the RV-15 engineering prototype the majority (possibly all) of the fuselage could have been solid riveted as designed. Probably the vertical tail as well.
The horizontal tail... not so much, but with the major redesigns that have taken place, that is now unknown to me. The wings, flaps and ailerons in particular would have required adding some access holes in skins and even then some portions may have been difficult.
We will have to see what the design configuration is of the kit when released, to see what is possible and what workarounds are needed, if any.
The idea that preping for flush riveting adds a huge amount of work time is false. I would estimate I spend somewhere between 50 - 100 hrs preping for flush rivets on a typical 2 seat RV (probably closer to the 50 than the100).
What does add a lot of additional time is installing solid rivets compared to the speed a structure can be skinned using blind rivets.
So for those wanting a flush riveted airplane but don't want to add a lot of additional build time, flush blind rivets would be the way to go.
To at least some degree, traditional solid riveting of skins to aircraft structures requires some design consideration in order to assure access for bucking all rivets as an assembly goes together.
When a design decision is made to make blind rivet assembly the recommended and primary method (such as was done on the RV-12), it greatly frees up the design process because different structures can be designed with no internal access if there are other design benefits (simplified structure, lighter weight, lower cost, etc).
That is one of the great things about blind rivets from a design perspective, but it can make it challenging or even impossible to use conventional riveting methods for some portions of a riveted aircraft, if that method wasn't "designed in".
For the RV-15 engineering prototype the majority (possibly all) of the fuselage could have been solid riveted as designed. Probably the vertical tail as well.
The horizontal tail... not so much, but with the major redesigns that have taken place, that is now unknown to me. The wings, flaps and ailerons in particular would have required adding some access holes in skins and even then some portions may have been difficult.
We will have to see what the design configuration is of the kit when released, to see what is possible and what workarounds are needed, if any.
The idea that preping for flush riveting adds a huge amount of work time is false. I would estimate I spend somewhere between 50 - 100 hrs preping for flush rivets on a typical 2 seat RV (probably closer to the 50 than the100).
What does add a lot of additional time is installing solid rivets compared to the speed a structure can be skinned using blind rivets.
So for those wanting a flush riveted airplane but don't want to add a lot of additional build time, flush blind rivets would be the way to go.
I think that the existence of factory built -15s with pulled universal head rivets would support resale value of kit built airplanes that match what the factory does. Flush/solid rivet airplanes will be oddballs, may raise questions about other deviations along the way. This thinking may extend to insurance as well, as it seems to do with current E-LSA builds. Just speculating, as this is kind of a new paradigm.
Its a function of rivet size and skin thickness. Larger rivets needing higher air pressure. On the RV-3B the plans call out -4's along the upper fuselage longeron at 2" spacing. Most "modern" -3B builders replace the -4's with -3's at tighter spacing due to the negative affect of pounding -4s into thin skins. After comparing my -3B with tiny rivets to other RV-3's with 1/8" rivets I was glad I made the decision to go with smaller rivets. Perhaps pillowing is the wrong word. The skin doesn't appear quite as flat to me.
Last edited:
The end result with the 1/8 rivets is more of a technique issue than it is rivet size in this instance. With the substantial substructure of the main longeron, the same level of finish quality is possible with either size rivet. In instances of a thin skin attaching to the flange of a light weight rib structure, there can be a difference.
PilotjohnS
Well Known Member
Ya but the p51 was built with well trained women assemblers who were light years above my abilities
We call those wives.
Deviate from the plans and build it out of .040
. Seriously, what’s the tail kit to finished ratio? Turning the pull rivets into solids may be making a mountain out of a molehill.
