Spar attach fittings, flox or microballons?

[southwind32]

Getting ready to install the spar attach fittings (doublers) and the strut attach fitting. The instructions say to use a little bit of micro balloons. Is flox ok to use in this case, that's what I've been using in other mixtures, I have that, but don't have any micro balloons.
Thanks
Brian

[efwd]

Should be micro balloons. It maintains dissimilar metal separation. You should have got a small jar of it in the kit. Mine is a white plastic jar.
Eddie

[southwind32]

Don't have any, so flox shouldn't be used? Where can I get micro balloons?

[bumsteer]

ACS,Wicks, Amazon, EBay, some hobby stores. Do a search and many sources should pop up with maybe something local. Just curious, sounds like you have used flox in other mixtures. Flox was called for in these correct and not microballoons?

Rick

[HighWing]

Brian,
I have often used Tap Plastics. The closest I see to you is in Stockton. I suspect, though,, you might find it in most stores selling fiberglass supplies.

[efwd]

As John McBean would certainly say. "we have that here at Kitfox".
It's a simple phone call.

[southwind32]

Is there different kinds of micro balloons? if so, what kind do I look for? Obviously, I know nothing about this stuff LOL.
Thanks
Brian

[ken nougaret]

As far as i know all microballoons are the same. I used the the stuff when i was building rc planes 30 yrs ago.

[southwind32]

Thanks for the reply. Talked to Debra at Kitfox today, need to use micro balloon for to protect the two different materials. Flox wouldn't do the job. So, I have some micro balloon being shipped to me. Bet not to many of you are getting micro balloons for Christmas :)
Brian

[efwd]

I'm getting an Interior!;)

[jiott]

I've heard they are filled with Helium for major weight reduction-use liberally:D

[southwind32]

having never used Micro balloons, and failing to ask Debra, how much of the micro balloons do you use? Are there instructions on the bottle?

[aviator79]

I'm getting an Interior!;)

I'm getting a whole plane! (Some assembly required.) :D

[t j]

having never used Micro balloons, and failing to ask Debra, how much of the micro balloons do you use? Are there instructions on the bottle?

I don't have my manual any more but it seems it was about a tea spoon or so was enough in the hysol mixture for one spar attach bracket.

On another note, they are tinny, light, and like micro ball bearings. Be very careful not to spill any. Also don't sneeze towards them. They will fly every where. It's difficult to gather them back up.

Don't get them near your nose or mouth. They are easily inhaled and quite harmful if inhaled.

[efwd]

The qty of the microballoons to hysol is not specified in the manual. You use only enough to provide for a layer of balloons to remain between the two dissimilar metals. It is very little. The previous stated qty would be sufficient. There is no information on the jar you will receive.
Eddie

[southwind32]

Ok, thanks for the info. I think when I get them, I'll take 1 micro balloon and mic it, then figure the area of the spar attach, and multiply it out to see how many micro balloons I need to count out to form a layer, and then maybe add 1 or 2 extra to be on the safe side............NOT !! :confused:
About a teaspoon sound better :D

Thanks again.
Brian

[efwd]

LOL, had me scared for a second.

[jrevens]

Things change over the years of course, but what I got in my kit was a small zip lock bag with a very small quantity of micro balloons - maybe a teaspoon. I happened to have a big half-gallon can of the stuff from my model airplane days, and so I used a little of that too. I've thought a bit about the whole theory of using them for separation between dissimilar metals as Kitfox suggests, and my personal analysis and opinion is that it is probably not really the best idea. Again, this is my opinion only. First of all, when they are added to the epoxy mix they decrease the strength of the bond... probably an insignificant amount considering the small quantity used, but there all the same. Next, in order to have corrosion you need moisture. If the fittings and spar, for instance, are clean and dry when assembled properly with the epoxy, you will have a very nice air & water tight coupling at the contact surfaces, and there will be a thin layer of epoxy between the majority of the surface areas with or without micro balloons anyway. Those surfaces are not a perfect fit and a thin layer of epoxy is necessary to form a strong bond anyway - you don't and can't squeeze it all out even if you wanted to (and you don't). So, what about the little places of point contact that will be there between the two surfaces? They will be there with or without micro balloons in the mix - the balloons slip & slide with the epoxy and move out of the way to a certain extent. Lastly, what about all the S.S. rivets going into the aluminum spar... do you think there will be a layer of micro balloons between the surfaces of the expanded rivets and the aluminum? I don't, and those holes and rivets are all over the fittings. Those rivets are really making very good metal to metal contact when they are expanded. So, even if you had this "perfect' layer of micro & epoxy between the faying surfaces, you still have these rivets which would really cause concentrated points where electro-chemical corrosion could occur. Check your spar attach fittings to spars with an ohmmeter and I think you'll see that there is all kinds of metal to metal contact. I could be very wrong, but that's how I see it now. Any structural guys out there with a good working knowledge of this issue? I'd like to hear if I'm off-base about this. BTW, I did use micro on my build, and I'm certainly not saying anyone shouldn't based on these thoughts, but I'm curious about the whole thing.

[efwd]

Good point John. You brought up a point that I have been pondering myself. What about those Stainless rivets in aluminum structures?
Eddie

[jiott]

Interesting points to ponder John. Based on what I have read in the marine industry, epoxy and microballoon mixtures are commonly recommended for a bedding in attaching fittings to somewhat uneven surfaces. They claim it thickens the epoxy so it is less likely to be squeezed out, and also some sources claim it actually strengthens the bond. Based on this, I believe the benefit it provides on our spar fittings is more of a good solid gap filling bed that also provides dissimilar metal separation due to squeeze-out resistance, rather than a separation of only a microballoon diameter. Will cotton flox do the same thing we wonder? I don't know, except I do know that the marine industry definitely specifies microballoons rather than flox. Flox seems to be specified mostly for sag resistance rather than separation in my research.

Regarding SS rivets in aluminum and steel, none of these materials are too far separated on the galvanic corrosion chart, meaning the corrosion activity is not too active, and as you say, without an electrolyte (moisture) the activity potential is much reduced.

[jrevens]

Hi Jim & Eddie,

Stainless steel rivets and aluminum have been used successfully for many decades in experimental aircraft designs that I know of. However, stainless steel can actually be quite far from aluminum on the galvanic corrosion chart... it depends on if it is "active" or "passive". But as has been said, it is critical to seal the contact area from moisture and/or prime the metal, traditionally with something like zinc chromate - an excellent protective coating for aluminum in contact with dissimilar metals - now considered a health hazard and difficult to get anymore. I have been in the habit of dipping stainless steel rivets in zinc chromate primer before inserting and pulling them on other airplane projects that I've done. Not only for corrosion protection, but to make them a little easier to drill out if it becomes necessary, without spinning in the hole.

I think that perhaps the marine industry uses a lot of micro balloons because of weight and especially ease of sanding or shaping. You're talking about applications where large quantities, percentage wise, of micro balloons are used. Flox filled epoxy can be quite tough and hard to sand. As far as electrically insulating two metal surfaces, the flox is also non-conductive (as is epoxy of course).

I don't think that the tiny amount of micro balloons specified in this application does much to make the epoxy a "good solid gap filling bed" any more than straight epoxy.

[HighWing]

My thinking is much like Johns. I have used “tons” of micro-balloons over the years. Typically used in surface smoothing over fiberglass layups. I was first introduced to it when a neighbor was building a Verieze. Thus was long before my Kitfox days – late 70s. You could always walk down a row of hangars and recognize the ones occupied by the plastic airplane guys. White dust covering the apron out front. They would roll them out front for the sanding, then back in to apply more “micro” in the low spots. In my minds eye, micro-balloons were like miniature glass Christmas tree ornaments – very fragile, thin walled, microscopic glass spheres. This is where the light weight and low structural strength (very easy to sand) comes in. In my mind’s eye, they would easily crush to very fine glass powder under the compressive forces of riveting. I have often thought that something like the milled glass fibers available as a thickening and strengthening agent might work a bit better for the purpose. All this said, however, 4000 plus kits out there and never a whisper of an issue with the recommended technique.

[jiott]

I am wondering if maybe we should be using quite a bit more "micro" in our epoxy mixtures to actually get the thickening squeeze-out resistance. I don't remember the build manual actually saying much about how much to use. We all assume very little is needed, but maybe more is better. I had quite a bit of microballoons left over when my project was done. This is all academic talk because as Lowell said, 4000 kits and not a whisper of any issues. It hasn't been mentioned, but I think the powder coating on the spar fittings has as much to do with dissimilar metal separation and the lack of corrosion issues as anything. When you rough up a powder coated surface for bonding I think it is important NOT to get down to bare metal in any spots.

[David47]

?...Any structural guys out there with a good working knowledge of this issue? I'd like to hear if I'm off-base about this. BTW, I did use micro on my build, and I'm certainly not saying anyone shouldn't based on these thoughts, but I'm curious about the whole thing.

Yes John, I'll put my hand up as an aircraft structures design guy with 40+ years as one ... and you're right. The use of micro balloons has not a lot to do with corrosion protection. It's a bulking and filling measure. As Lowell suggests, If you want some strength, add chopped fibre. If you want more strength, use epoxy and directional tapes or fabric. S/S fasteners contacting the sides of the hole when the rivet expands will most likely have a very thin layer of adhesive between fastener and hole sides anyway, which is a good thing.

Using S/S rivets in aluminium has been the practice in home built aircraft for many years. As Jim said, the two materials are reasonably close on the galvanic corrosion chart, but having said that, I've wet installed all my rivets using an epoxy primer. Just a personal preference. For corrosion to start, you need as a minimum, moisture and a potential difference between the two metals to start pushing ions around. In this case, the adhesive acts as the barrier between the two, similar to the use of a fibreglass ply between a carbon skin and an aluminium alloy rib, spar, frame or longeron. So I'm not surprised that there haven't been corrosion issues in the steel spar doublers to aluminium tube joints. But as a further precaution for my build, I've also heavily coated this area with primer just to make sure I don't get moisture ingress. Again, a personal preference. .....;)

[Mikerv9a]

Getting ready to install the spar attach fittings (doublers) and the strut attach fitting. The instructions say to use a little bit of micro balloons. Is flox ok to use in this case, that's what I've been using in other mixtures, I have that, but don't have any micro balloons.
Thanks
Brian

As a builder of a Long-EZ, I can tell you that microballoons is ONLY used for fill and joining pieces of foam together. It has no structural/tear strength and is subject to cracking . Flox is flocked cotton and is only used to create rigid structural joints. It cures as hard as solid epoxy. I don’t buy that flox is not “compatible” with dissimilar metals, it’s just epoxy that is saturated with the flox to keep it from flowing out of the space where it’s used.
If this is a structural bond you’re making, I would NOT use microballons.

[jrevens]

As a builder of a Long-EZ, I can tell you that microballoons is ONLY used for fill and joining pieces of foam together. It has no structural/tear strength and is subject to cracking . Flox is flocked cotton and is only used to create rigid structural joints. It cures as hard as solid epoxy. I don’t buy that flox is not “compatible” with dissimilar metals, it’s just epoxy that is saturated with the flox to keep it from flowing out of the space where it’s used.
If this is a structural bond you’re making, I would NOT use microballons.

Thanks for confirming what I wrote and thought, Mike. The fittings in question are attached with a lot of rivets, and the epoxy should add additional strength to the joint, so why not make the joint as strong as possible and not decrease the strength with micro, while still sealing the contact area between the dissimilar metals from air and moisture? My original comments were just voicing what have been my thoughts from the beginning of my Kitfox project. The original idea to use micro-balloons might have been advanced by someone with incorrect or incomplete knowledge of the structural issues involved. Obviously, history has shown those joints, assembled that way, have been safe and strong enough. I don't mean to insult or disparage anyone's intelligence, but IF there is a better way to do something, I think we all would like to know about it.

[Guy Buchanan]

Adding microballoons to epoxy weakens it. However, sometimes tiny glass beads are added to epoxy for bond line thickness control. If your perfect assembly squeezes out all the epoxy, you have no adhesive bond, and therefore no strength. The glass beads maintain a .005" thickness minimum bond thickness thereby enabling epoxy adhesion. If your epoxy is being used to simply keep out water and thereby inhibit corrosion then adding microballoons will lighten things a little and maybe help keep the epoxy in place by thickening it a little. Strength is irrelevant.

Regarding corrosion. Most anyone who has worked on ocean racing yachts can attest that aluminum hates stainless and will, over time, turn to powder under the affects of galvanic corrosion. However it's a fair amount of time and requires much more salt water than I hope most of our wings are seeing. Anyone buying an aircraft that's spent a major part of its life on floats on salt water would be well advised to boroscope the wings though, to make sure there's no evidence of corrosion.

[jrevens]

Adding microballoons to epoxy weakens it. However, sometimes tiny glass beads are added to epoxy for bond line thickness control. If your perfect assembly squeezes out all the epoxy, you have no adhesive bond, and therefore no strength. The glass beads maintain a .005" thickness minimum bond thickness thereby enabling epoxy adhesion. If your epoxy is being used to simply keep out water and thereby inhibit corrosion then adding microballoons will lighten things a little and maybe help keep the epoxy in place by thickening it a little. Strength is irrelevant...

Good comments, Guy. My parting thoughts are these... based on several things, including the tiny quantity of micro I got in my kit and the lack of any real accurate guidance as far as mixing ratio with the epoxy, I think that the probability is slim that anything really beneficial, including maintaining separation, weight reduction, or thickening the epoxy, is being accomplished in this instance, and therefore it may be a waste of time and possibly a strength reducing one at that. If the joint has been designed for adequate strength with rivets alone, then strength of the epoxy is irrelevant.

[jrevens]

Yes John, I'll put my hand up as an aircraft structures design guy with 40+ years as one ... and you're right. The use of micro balloons has not a lot to do with corrosion protection. It's a bulking and filling measure. As Lowell suggests, If you want some strength, add chopped fibre. If you want more strength, use epoxy and directional tapes or fabric. S/S fasteners contacting the sides of the hole when the rivet expands will most likely have a very thin layer of adhesive between fastener and hole sides anyway, which is a good thing. ...

...

Good comments... thank you, David!

[ken nougaret]

John, you mentioned "IF" the design was strong enough for rivets alone .... Does anyone know if tests have been done based on only rivets only?

[bumsteer]

Perhaps John McB or a Kitfox structural engineer could offer some insight on this subject.

Rick

[rosslr]

Hey Rick,

I suggest you rad Dave's post below. He has a few qualifications and a bit of experience in this area.

cheers

r

[bumsteer]

Read it. I have a degree in aeronautical engineering and have no problem with what he says, still would like to hear what the factory says.

[efwd]

You wouldn't expect them to contradict the fact that they asked us to include the micro-balloons would you?
As with all professions, I bet you would find differing opinions on the matter of using micro-balloons in this application.
Eddie

[Av8r3400]

Read it. I have a degree in aeronautical engineering and have no problem with what he says, still would like to hear what the factory says.

It says to use micro-baboons in the builders manual. What purpose does it serve to have a "factory rep" repeat it here?

There have been literally thousands of these planes built this way. There has never been an inflight failure of this airframe design.

If you have a better way, it's experimental, go for it. Invent a better mouse trap.

[jrevens]

It says to use micro-baboons in the builders manual. ...

Are micro-baboons bigger and stronger than micro-chimps? :confused:

You made me laugh, Larry... very good points, though.

[Av8r3400]

Who ever invented spell check should burn in h@ll...

That'll teach me to try and make a serious point, I wind up looking like a micro-baboon.

[efwd]

You can thank John for pointing that out. I read right over it as if correct.

[ken nougaret]

Heck, i read Johns post twice, didnt see it and wondered what he was laughing about.

[PapuaPilot]

That is hilarious, I got my laugh of the day. :D

I'm right in the middle of my condition inspection. Maybe I need to verify whether it has micro-baboons or micro-balloons because I didn't build the wings.

What do you get if you mix micro-baboons with Gorilla glue?

[Av8r3400]

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTlko2-xidz2AdRs-0UBZmir5iH355XJ65fXc5t0k4RbvLFCVrV7A

[southwind32]

That is hilarious, I got my laugh of the day. :D

I'm right in the middle of my condition inspection. Maybe I need to verify whether it has micro-baboons or micro-balloons because I didn't build the wings.

What do you get if you mix micro-baboons with Gorilla glue?



Micro Go Booms :D

[David47]

.... The fittings in question are attached with a lot of rivets, and the epoxy should add additional strength to the joint, so why not make the joint as strong as possible and not decrease the strength with micro, while still sealing the contact area between the dissimilar metals from air and moisture? My original comments were just voicing what have been my thoughts from the beginning of my Kitfox project.

Just a comment on yours John. Joints like this that are bonded and riveted gain most of the strength from the adhesive, provided the adhesive has sufficient shear strength, which Hysol has. The rivets provide clamp up and squeeze out of the adhesive, and also provide residual strength in the event the adhesive degrades. Case in point is the Aloha Airlines 737 that suffered major structural failure when the fuselage lap joints unzipped the fuselage section above the cabin floor. The primary cause was degradation of the adhesive bondline of bonded and riveted skin lap joints, which then caused high loading on the rivets over time, which eventually lead to multiple fatigue cracks between rivet holes and then bingo, the joint(s) let go. There's a lot more to this story than that but it serves to demonstrate the idea.

With respect to Kitfox, the wing joints are a proven design with many years of safe operation, all having been built to the manual requirements so that speaks for itself. In my particular case, however, I didn't use micro-balloons (or micro-baboons per Larry's redefinition ..!!) for the very reason you said. Maximum joint adhesive strength. But that's a personal choice and something I can do because my aeroplane is Experimental. ;)

[cposer]

Anyone thought about using cherrymax instead of SS rivets for the spar attach fittings?

[efwd]

If I recall, they are really expensive.

[jrevens]

Anyone thought about using cherrymax instead of SS rivets for the spar attach fittings?

Another question - why would you want to do that? There is nothing wrong with using the rivets furnished in the kit. I think they have been well-proven to be adequate and safe for this application. In my opinion only, you could certainly use the stainless steel CherryMax rivets for the spar attach fittings if you wanted, or the slightly oversized version if you had an oversized hole within the tolerances of that oversized version of the rivet, but as Eddie said, they are very expensive.

[Flybyjim]

Being an experimental aircraft you can do as you please, that is part of the fun building however for me if the suppling company, aka Kitfox, has a proven history of saftey with their design I will stay with their plans and listed parts to complete the build.

[David47]

I bought Cherrymax for precisely this use. But didn't use them (duh). As I said earlier, the adhesive does the work. The limiting strength, should the adhesive fail, is the bearing strength of the tube, making the type of rivet used irrelevant. An opinion ... I'd just use the ss rivets with the kit.

[jiott]

Spend your extra money where it matters, like some nice options you will enjoy.

[Guy Buchanan]

The other problem with the Cherry-Max rivets (I have them) is that they're big and ugly on the leading edge. I minor consideration, to be sure, but worth mentioning for all you Oshkosh aspirants. ;)

[cposer]

Another question about the spar fittings. They seem to be very tight when I slide them on a trial piece of 2 1/2" aluminum tubing and leave scratches when I take them off. How do you get them on without damaging the spar? Any suggestions would be appreciated.

[aviator79]

They are indeed tight. The Hysol that you'll smear on them will lubricate them a little as you install them. Just go slowly and carefully. They will scratch the spar a bit, but it shouldn't be so severe as to create a concern with fatigue crack initiation or stress concentration. As an extra margin, the area will be reinforced with a steel doubler (the bracket), and a liberal quantity of structural adhesive to fill any scratches.

[Esser]

They are indeed tight. The Hysol that you'll smear on them will lubricate them a little as you install them. Just go slowly and carefully. They will scratch the spar a bit, but it shouldn't be so severe as to create a concern with fatigue crack initiation or stress concentration. As an extra margin, the area will be reinforced with a steel doubler (the bracket), and a liberal quantity of structural adhesive to fill any scratches.

And really make sure they are deburred throughly with nothing that will caus a stress riser.

[jiott]

Maybe I'm a little paranoid about this most highly stressed, extremely important structural area, but I personally would not trust the Hysol to protect against scratches. A scratch caused by sliding on the bracket is transverse to the spar, the worst possible direction for a stress riser on the spar. My brackets were also too tight to get on without danger of scratches, so I put them in a vise (padded jaws) and spread them just a little until they slipped on nicely. Very easy to do.

[efwd]

That is what I did as well.
Eddie