Sikaflex debate continues.

Note from moderator. THis new thread created and moved from this thread.

David-aviator said:

Part of the issue with some of us is we get an idea or notion in our heads to do something and in the process do not consider all the evidence concerning the matter. In other words, we want something to be such and such and come to believe it will be so, no matter what.

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Very true David...we want to believe what we want to believe. And no topic highlights it better than the Sikaflex canopy issue.

There are many builders out there who are petrified to drill holes in their canopy for fear of causing a crack. They WANT to believe that there is a better solution.

And this is despite the fact that Vans recommends against using Sikaflex as a substitute for mechanical fasteners.....and despite the fact that Sika themselves recommend strongly against it....and despite the fact that there are no Sikaflex RVs with any substantial hours on them....and despite the fact that none of the early adopters have any experience in polymeric glazing systems....and despite the fact that virtually all posters with a background in mechanical engineering advise extreme caution.

Despite everything, builders who WANT to believe it works find comfort in the fact that there are a growing number of other builders (who also WANT to believe it works) opting for the Sikaflex route.

And what makes the whole phenomenon particularly frightening is that, in the absence of any engineering documentation (because no-one with with any real-world experience in polymeric glazing systems will put his name to it) virtually every Sikaflex canopy is fabricated slightly differently.

Additionally, it is my observation that those who desperatley WANT to believe in the merits of the Sikaflex solution are often quite hostile to any poster who puts forward any information or data that suggests there might be intrinsic problems.

As a result people with a scientific background have opted out of the debate and left the asylum to be run by the inmates.

When it comes to major (or even minor) structural modifications to Van's drawings, it stands to reason that builders need to take a very conservative approach to internet advice....because in a game where you have IT specialists, bookkeepers and firemen building aircraft there may not necessarily be any safety in numbers.

PS My apologies to any IT specialists, bookkeepers and firemen out there.

I say this tongue in cheek, but I guess I neglected to add "sikaflex haters" to my post above...I do think that it would be a good thread and would make a good section.

I don't want to hijack this one, but I think that the Sikaflex installations have actually proven more problem free in use than have the fasteners (speaking only in terms of canopy cracking) and have been used successfully all over the world for 6 or 7 years in a variety of tormenting field conditions around the world. That Sika says "don't do it" doesn't surprise me...they have corporate lawyers like my company does. If you ask us if our product is suitable for aviation use I guarantee I can give you the answer before it ever gets to the technical department. Actually Van's has not put anything in writing about using Sika as a canopy attachment method...if you ask 3 people there, you'll get three different answers. One of their engineers looked at my installation and liked it. I showed him the destructive testing I had done and the elongation data from the Sika tech sheets and he commented that maybe that's how all plexi should be attached. Just another data point. Are we "Sikaflexers" beta testers? Yep. Has there been one problem or even a hint of a problem in an actual install in 6 years? Not that I'm aware of. I don't have a definitive answer in terms of hours flown under a Sikaflex installation, I guess I would be more interested to know the calendar time and the use conditions. Again, I didn't mean to hijack the direction of the thread, only to elaborate that this is a perfect example of how there can be many views on a topic, and I do completely respect Bob Barrow's input on it. One of my friends, who's a respected A&P will tell you that he feels fuel injection systems are an accident waiting to happen. The Sikaflex canopy attachment method is something all of us should follow and I'd like to see all the posts related to it in their own basket, because I know there's a lot of them and a lot of people using the techniques, which are now fairly well documented and evolved.

Captain Avgas said:

....and despite the fact that there are no Sikaflex RVs with any substantial hours on them....

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I think Kahuna may argue with you on this one....

This Forums Peer Review

It's always about the source. I would snoop any forum for a good while looking at questions that I already know the answer to before using it as a possible source.
For building tips and tricks simple peer review works. Nothing like an open forum for that!
I have not seen any 'bad' information that has not been challenged by others in this forum. Sometimes that challenge goes beyond constructive, but in the end those who post erroneous information for any reason are normally challenged to support their statement.

Considering the number of pros on this site peer review is a misstatement in my case

*I always call Vans if I question the integrity of a modification or alternation of their plans.

Sanity Check

I didn't build my airplane. I pretty well understand mechanical things, to a degree, but have had little experience building or repairing anything mechanical.

Anyway, I've needed advice on some very basic things regarding my airplane and have found the advice given to be generally high quality, with pilots going out of their way to be helpful. Obviously on any given subject, some are more helpful than others.

I sanity check the advice before taking it. That is, I make sure it doesn't defy common sense or the laws of physics. Multiple posts with the same or similar advice helps if the subject is a little esoteric.

Bob Brown said:

That Sika says "don't do it" doesn't surprise me...they have corporate lawyers like my company does. If you ask us if our product is suitable for aviation use I guarantee I can give you the answer before it ever gets to the technical department.

Click to expand...

Of course it might also be possible that Sika do not recommend Sikaflex in this crucial structural application because they know that it is a relatively cheap single-pack polyurethane product formulated more for ease of application than long term performance and that over time its elasticity and its adhesion will deteriorate.

In actual fact polymethyl methacrylate (PMMA) or "acrylic" as it is commonly known is notoriously difficult to obtain a good bond to. Sikaflex itself will not bond to PMMA. An interlayer (or adhesion promoter) needs to be used. In the case of Sikaflex its 209 primer contains 25% MEK and 20% Ethyl Acetate. Both of these are solvents known to break down the cross links of the long chain molecules in PMMA. In the longer term that might very well lead to edge cracking (one case already reported).... the very thing builders were anxious to avoid.

In reality the early adopters of the RV Sikaflex process have their canopies fastened more with hope than good science.

But I do not intend to move Paul's excellent thread sideways by getting bogged down in the technicalities of the Sikaflex issue.

I will instead refer to a very good piece of financial advice that my father once gave me. He said, son, never put your hard earned money into an investment that you do not COMPLETELY understand....even if others are queuing up to do so.

I can't help but think that advice might loosely have some relevance to builders contemplating major mods to Vans aircraft....if you don't completely understand the technology then it might be best to exercise conservative restraint....regardless of what others may be proposing on the internet.

Captain Avgas said:

But I do not intend to move Paul's excellent thread sideways by getting bogged down in the technicalities of the Sikaflex issue.

Click to expand...

LOL...too late!

We should really start a(nother) thread for this topic...but just to respond to what you wrote about Sikaflex. The following is from their website:
"Sikaflex® 295UV is a moisture curing polyurethane sealant/adhesive that exhibits outstanding UV resistance. This high strength elastic adhesive is specifically formulated for use with plastic windows. Sikaflex® 209 is a black primer that develops tenacious adhesion to acrylic and polycarbonate. Used as a system, Sikaflex® 295UV and SikaPrimer® 209 provides very durable adhesion to plastic windows."

Now, whether you need to add the 209 primer or not, who cares? I would think a problem would exist if you DIDN'T use the primer. Your logic is like saying that you shouldn't use paint because without primer, it wouldn't stick to metal. Do I COMPLETELY understand everything there is to know about primer and paint? No, but I'm going to paint my airplane anyway.

Thank goodness I was born with a aptitude for not listening to nay sayers. I would have left a lot of fun on the table.

Someone eventually has to try a real world application. Someone has to have the kahuna's to do it. Some may die trying for you and for the movement to progress. Someone has to report back how its going for something new.

My report is, canopy is hangin in after 600 hours. If it comes off, its likely not the end of the world. I got bigger things to worry about. But mostly I dont worry. I review, analyze, apply my collective experience, and then I usually just go for it. Sometimes on blind faith alone and hope for the best. Ive flown my plane down canyons I would never survive if the engine quit. Oh well. SO what. Im having fun, life is good. I put my faith and trust in my aptitude and press on. If I make a smokin hole, well that will suck. Mostly for my family. But they know me and they know Ill probably die trying. But someone has to do it.

Poor Van probably has a heart atttack everytime hee see my plane fly. Fat engine, over gross, full of complicated gadgets, so far over Vne it even makes me pucker, canopy glued on, cam locks instead of piano hinge, four coats of paint when 2 will do, flying those scarey formations..... Hes just gonna have to get over it. Someones got to do it! We have to progress, learn, share, and have fun doing it.

Thanks for leading the way Kahuna! As long as the rest of us stay about two steps back, we know we're in safe territory...

As for the canopy, I'll be joining you in about 18 months on that experiment. My wings ship next week...

lostpilot28 said:

The following is from their website:
"Sikaflex? 295UV is a moisture curing polyurethane sealant/adhesive that exhibits outstanding UV resistance. This high strength elastic adhesive is specifically formulated for use with plastic windows. Sikaflex? 209 is a black primer that develops tenacious adhesion to acrylic and polycarbonate. Used as a system, Sikaflex? 295UV and SikaPrimer? 209 provides very durable adhesion to plastic windows."

Click to expand...

Sonny, you beat me to it...took me a while to get to this point in the thread.

Sure hope mine stays on!!

Sikaflexing my canopy in just a few weeks...

My Sikaflex canopy install (a slider) is so far like new after three years of use. I'm aware of several others about the same age, also with no problems...everyone would do it again. If there is anyone out there who has had problems with a Sikaflex install (assuming you used proper surface preparation of all surfaces, proper adhesive thickness, correct primer, etc), I'd really like you to post the details of what problems you've had. Although Cpt. Avgas mentioned there have been problems with installs, I have not been made aware of one yet after 6 years of watching. I think the installs with the most amount of time are in South Africa, where they started using it 6 years ago. As far as I can tell (on my own installation), the only downside is a perhaps a little extra weight and a completely stained shirt.

I have had the misfortune of having to redo a canopy on my F1 that was bonded on with Sika.

I had to mechanically remove the canopy. In the process I destroyed the bubble. And in that same process I wanted to see how well Sika holds up.

I can say with 100% certainty there's no freakin way the canopy bonds will fail before the canopy and the frame fail. No way.

You guys gluing the canopies on need not lose any sleep.

3yrs, 210hrs, good as new sika slider. When I read the original sport aviation article I talked with Sika. The technical support guy said three things:

* Officially they can't recommend this - my plane will fall out of the sky
* Then he said, it sounded very cool and that unofficially he thought it was quite promising
* All of their trade advertising had never generated as much interest as they had heard from aircraft builders - unfortunately their lawyers would freak if they provided 'official' support but he's happy to answer questions on the boat or bullet train I'm making.

The test pieces I made (one of which has been sitting in my back yard since I built the plane) still seem very well bonded - but I'm not an aero engineer, I admit I was placing a bit of trust in the various folks I talked with about this.

hi all,

fortunately, there were people that led the way experimenting with sikaflex... thank you guys! admittedly at a slightly higher risk of having to possibly redo the canopy, run into long-term issues etc...

fact is, the joint (as new) won't fail before either the canopy breaks or the frame is damaged. we did a sample piece with intentionally adverse conditions, no scuffing, no cleaner, just primer and sikaflex and that plexi will break way before the bond will let go!

in the 30year plus timeframe there's all kinds of trouble you could run into, of which the canopy being one of the lesser problematic. it's highly unlikely that a bond would fail instantly & everywhere without previous signs during inspections. e.g. the front joint between the top skin and the canopy would appear much more prone to problems / "delamination", more UV exposure, thinner joint, sanded to a fairing, than the joints along the siderails and canopy frame. yet i'm sure that half of these joints are capable of holding the canopy in place.

my 20cts although not 100% scientific ;-)

bernie

I don't know anything about Sikaflex......but

Guys,
I'm with Kahuna on this one. For the record I don't know squat about Sikaflex and I haven't even gotten to that stage of my kit.

Rutan has a saying I love, "true innovative research is doing something half of the folks say can't be done and the other half say maybe it can be done." Now gluing on canopies isn't exactly like putting a plastic airplane into space with no heat shields, but the point remains that it take some courage to try new things. I think as a society we are getting alittle too safety sensititive-IMHO.

Good bless you sikaflex guys for doing your homework and having the guts to experiment. We will all benefit from your innovation, wether we glue on our canopies or not.

Now about this naysayers, I appreciate their input to, if it is backed up by some common sense and data. This allows fools to not rush in without knowing the potential effects. There is also the benefit of maybe discouraging someone from experimenting who may not have the patience or skills to do the job correctly.

What I don't like is guys saying you can't deviate from the plans or you'll die with nothing to back it up. I plan to just ignore those posts and focus on what I believe is relevant on either side of a particular debate.

Let the debates continue.....

I for one am one of the Sikaflex guys. I sleep very well knowing that my canopy will hold togather. I am would be more worried about a eventual crack due to the pulled rivets than my canopy blowing off. I had the misfortune of cracking my first canopy during final installation. After that experience and replacing my canopy with a Todds canopy, I started looking for better alternatives. I have 0 holes in my canopy and 0 chances of cracks due to drilled holes. I know there are plenty of drilled canopies out there that have not cracked and may never crack. I just choose to go a different way. A better way for me which I believe to be safe. The bond is stronger then the canopy itself ever will be. Will I have the same opinion 10 years from now? I'll re-post in 2018. Some one please remind me.
Let me throw a plug in for Todds canopies. Hands down a better canopy or at least mine was.
Live Strong
Chad

Was going to say something earlier, but did not want to hijack the other topic. Now that it has moved I'll jump in.

The original article writer and pioneer Chalkie Stobbart in South Africa dumped a whole lot of information on the RVclubSA website.

Go Read it if you want, then test, then make up your own mind. You need to risk your own but in your plane, if you don't like it do it the traditional way. I always caution when I see any 'talk' in absolutes or extremes, or talk about "experience" but not walked the "expierence", but that is for that other thread again.

I Sika'ed mine, but only before I tested it myself, making samples, fastner and glue samples, from the canopy cut-offs and breaking it. Then I read the Sika Datasheets also myself. When I saw my real life test examples, with Datasheets in hand and others confirming what I saw first hand it was an easier decision for me to go the Sika route. It is one of the least things I worry about on my plane.

It is under the Articles/Technical section.
http://www.rvclubsa.com/

Regards
Rudi

Ughh. I usually try and avoid participating in these never ending debates, but for some reason I can't resist today.

I'm not trying to claim that I'm an authority here, but instead give some info on my background. I'm a mechanical engineer specializing in aero-structures. During school (after 10 years of building furniture for a living) I worked as an intern in an adhesives laboratory at one of your national labs.

I HAVE NOT DONE ANY FORMAL TESTING YET, SO EVERYTHING BELOW IS AN EDUCATED OPINION--NOT A FACT.

As an ME, I'm of the opinion that it is downright irresponsible to use mechanical fasteners directly between two surfaces that have a 10x difference in their coefficients of thermal expansion. http://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion. My 6' long acrylic canopy has a nearly 10x thermal expansion difference with its steel slider frame. In RV8's in particular, using mechanical fasteners with no way to allow for movement between the parts is asking for trouble. We can enlarge the rivet holes in the canopy, but not by enough, and now we're asking the rivets to do something they weren't designed to do. We can enlarge the holes even more, insert rubber bushings, use fender washers over rubber washers, and attach with screws, but now we've got screws sticking out all over the place. All of this completely ignores the fact that Acrylic is highly notch sensitive and we're adding huge stress risers by putting holes in it.

To me this sounds like a good place for the proper adhesive. We need something flexible. We need a thick bond line so that the adhesive can absorb the movement between the two pieces being bonded. A thin bond line or a stiff adhesive would take us back to square one. Acrylic is hard to bond to directly, so maybe someone makes a primer to promote adhesion--it may do that by breaking down SOME of the internal bonds in the Acrylic and inserting itself in there. Sounds like that oughta work, but I'll leave it to the chemists. Now if I could only find a product like that.....

People tend to fear adhesives. You can't see what's going on like you can with a good mechanical fastener. Adhesives do tend to have a finite life; I'm sure Sika does. I plan on doing some testing with Sikaflex because (in theory) it's a much better option than mechanical fasteners. If I like what I see I will use it on my canopy. I will do that knowing full well that I'm being a test pilot. I will inspect frequently and make sure I'm comfortable with the idea that some year down the road I might have to replace the canopy. If I do bond my canopy I will FOLLOW THE MANUFACTURER'S DIRECTIONS EXACTLY. With adhesives you really can't hope for the best, you have to work for the best. Many of the examples of canopy bonding tecniques I've seen out there are scary. This especially means that I will have a thick bond line and will make sure all of the adhesive is applied within specified time limits after priming. None of this tack the canopy with a few blobs and back fill later stuff for me.

G

On the thermal note. Its probably worth noting for my application that I tend to be harsh in terms of temperatures.

My canopy has sat outside in the harsh winter of NH below zero, take off with dual cabin heat a blazin, gone from the nuclear temperatures of the SW desert to altitudes in the 20's, and everywhere in between. Canada to Mexico in all temeratures and weather that I would not expect most RV to be in. Climb and descend speeds that I suspect only a small handful of actual RV's have ever done.

Given my total wreckless abuse, I just cant imagine how this canopy is ever gonna come off. All glue joints look as new. Further, given the limited loads placed on the canopy, Im even further stretched to imagine a failure of any kind. I think elmers glue would keep it on the frame. OK maybe not elmers. But geez, this stikaflex is way overkill IMHO.

Im not sure I mentioned that my skirts and canopy and windscreen are glued. Course the windscreen is glassed in too.

The one drawback of the glue is the weight. It must be 1000 times heavier than the rivets would have been. Maybe more. But its a lot.

Gluing It

We do periodic inspection of our planes in order to detect signs of impending failure, whether the inspection object be aluminum, steel, fiberglass, rubber, mystery substance electronics. Why should canopy glue seams be excluded?

Given the comprehensive process of the glue installation, I don't see how sudden failure can occur if the seams are routinely inspected. Seems to me documented periodic close inspections of the entire canopy attach system will most likely show signs of trouble in isolated areas, giving enough notice that corrective action is required.

Good enough for me - currently rearrangng the shop to start canopy installation.

Mine's glued too...

When both my son and I were considering Sikaflex, I had the opportunity to talk with one of the very early Sikaflex adopters, who happens to live nearby. He worked with both Sikaflex and Van when bonding his canopy, and a lot of testing was done. His agreement, up front, with Van was that if Van didn't approve, he would never publicly recommend Sikaflex.
Here's the bottom line: done PROPERLY, the Sikaflex bond is stronger than the plexi. The most critical item in doing things properly is to do the application according to the instructions (duh!), especially the timeframe for applying the primer and glue. The testing demonstrated that if you don't apply the Sikaflex within the proper timeframe after applying the primer, the bond joint is significantly degraded It was this dependency that made Van uncomfortable and therefore did not approve. He wants things to work even with a goodly amount of 'user error'. I don't blame him a bit.

Last summer, at one of our Chapter's Young Eagle events, I happened to talk to one of the dad's who asked me if I knew of any homebuilts that had glued their canopies on with Sikaflex. I told him that both my son and I had done so. It turns out he is one of the tech reps for Sikafles, and had spoken to a number of builders (of 'boats' and 'off road vehicles' of course ), but had never seen a glued canopy. At that time my plane was still home in the garage. Hopefully he comes back this year and I can show him and even give him a ride.

Sika debate alive and well...

As the author of the, prehaps infamous, article in the Sport Aviation I am pleased to see that the Sika debate is alive and well. No system is perfect; Van will tell you that aviation is a series of compromises, Sika is just one of these. I am busy building an RV-9 and this will have a Sika glued slider, holes in Plexi seems so archaic. Even Van now calls for the Plexi in the RV-10 to be glued in, but not with Sika.

My RV-6 now has (only) 400 hours which included a flight to OSH in 2003. This flight had me flying through ice, rain and desert conditions; the canopy is still attached. Kahuna seems to fly through similar weather regularly; he need not worry about the Sika joint as there are thousands of Acrylic windows glued with Sika into yachts all around the world and I am sure these vessels are parked out in the weather all their lives.

My RV would have more hours by now, had I not sold my FWF to another RV builder and set my heart on the DeltaHawk engine; two years wasted, waiting patiently but now I am back in the air with a new XP-IO-360 and the MT prop that was ordered for the DH engine.

One person who researched the Sika option in the USA reported the following discussion with a Sika agent... "Sorry, we do not support your application", right after that, "now that I have said that, how can I really help you............ We talked for a while, Steve mentioned that his phone has been ringing off the hook ever since the Sport Aviation article came out. He kinda jokingly grumbled that he has had more response to an article Sika did not write, for a use Sika does not support in a magazine Sika did not know about, than what his total advertisement budget generated last year."

Makes you think....... Doesn't it?

Hi Chalkie!

Glad you chimed in! After a few emails to you, I glued my -8 canopy, about three years ago now! Even glued the skirts! It's still hanging in there! Since then, I have been involved, in one way or another, with about three other canopies being glued. If I remember correctly, you, like another person who responsed, destroyed a canopy trying to get it loose. Comments on that?
I don't know how long it'll take, or how many flight hours will have to be logged, before the Sika method will prove itself. Seems with all the canopies that have been glued since your article, there's got to be quite a few collective hours. Might make an interesting survey Doug!

rvpilot said:

Seems with all the canopies that have been glued since your article, there's got to be quite a few collective hours. Might make an interesting survey

Click to expand...

O.K., I will set up a poll for this.

How it all started...

As I wrote in the Sport Aviation article all those years ago; the seed was planted when I assisted an RV-6A builder to remove his windscreen after he had managed to do a nose-over. He had applied a Sika automotive windscreen adhesive to the base of his rivited windscreen, to seal it, to prevent air/water ingress. He had used no primer at all on either the Plexi or the top fuselage skin. The only contact area of the Sika and Plexi, was the smoothed/rounded lower edge of the windscreen.

We were not able to pull the broken bits of windscreen off the aircraft without seriously damaging the fuselage skin; we had to cut the adhesive to free the windscreen pieces.

This had me thinking; this has to be a real good adhesive and the rest is history, as the saying goes...

And thanks for that Chalkie. I read your early writings...and read Jim Cone's article about canopy fitting and read all the product info...and proceeded. Since then, a number of people have used it on canopies...from RV4's to RV9's (and all those numbers in between). One of my neighbors did such a slick job of using Sika on his RV7 slider install, he didn't even use a fiberglass layup strip on the aft edge of his windscreen...the windscreen and canopy edges meet up with a uniform gap and the sika itself is the seal between the roll bar and the canopy...absolutely no airleak (and it's "Oregon waterproof"). Hmmm, that sounds like a topic for another Sport Aviation article...hint hint Scott! Like many other builder techniques, this one has and will continue to evolve. I am still not aware of one single problem with degradation or adhesion when all the installation instructions have been followed. If and when those signs DO show up, I am quite sure there will be evidence visible at the edges of adhesive beads. Right now (three years after the install), you'll rip your fingernails before you can get under the edges of the beads on mine.

Hey Mike-

Any way the poll can collect hours on planes with the SikaFlex??

Bill, this is the first poll I have done------------I dont know if I can make it dance to that tune, but I will give it a try.

Well, I couldnt add a second poll, so I started a new thread dedicated to the issue.

http://www.vansairforce.com/community/showthread.php?t=29869

An early convert

My original RV 6 windshield acquired a large crack from the roll bar down in front of my vision while at 10 000 ft and the thought of it possibly departing our company was high on the agenda. The decision to replace it was easy but the method was at the time a subject for debate. This was Jan 2004 and Chalkie had just convinced another local RV builder to consider the Sika method.

George Morphis, (PhD Mech Eng), prefers to do his own gathering of technical data and, with a response from Sika much like that reported on this forum, decided to go ahead. When my repair came up I had both George and Chalkie bending my ear. The facts that were available were laid out for me but both downplayed the lack of long proven success. The removal of the old windshield did however demonstrate a known weakness in the fact that it literally fell out after removing the roll bar screws.

The Sika recommendations were followed with considerable care and the job went easily and amazingly fast. Now there were three of us and to date I believe I have a structure that is is better than it ever was and so do the others.

I can see reason for Van's caution but if done properly it is a superior method. My RV 9 under construction will be done this way with the only hole being the one for the handle.

I am qualified to assess the threat of solvents in the pimer and these should have been chosen to give it a bite without creating a long term threat. Sika has a long history of success on acrylic windows in boats so I would credit them with having done their homework.

Noel Drew
Durban
South Africa

ZU- APF (first flying RV in South Africa)

Glasairs, Lancairs, Various other plastic fantastic aeroplanes glue their canopies on with Sikaflex or similar.

I will follow their lead, hopefully with some expert guidance from a Dutchman or two

I had a Grumman Traveler (Sliding canopy certified 4 seater). I had to replace the front windscreen, and it was glued on to the window frame. I don't remember the type of glue, but that was the certified repair.

Captain Avgas said:

Note from moderator. THis new thread created and moved from this thread.


Very true David...we want to believe what we want to believe. And no topic highlights it better than the Sikaflex canopy issue.

There are many builders out there who are petrified to drill holes in their canopy for fear of causing a crack. They WANT to believe that there is a better solution.

And this is despite the fact that Vans recommends against using Sikaflex as a substitute for mechanical fasteners.....and despite the fact that Sika themselves recommend strongly against it....and despite the fact that there are no Sikaflex RVs with any substantial hours on them....and despite the fact that none of the early adopters have any experience in polymeric glazing systems....and despite the fact that virtually all posters with a background in mechanical engineering advise extreme caution.

Despite everything, builders who WANT to believe it works find comfort in the fact that there are a growing number of other builders (who also WANT to believe it works) opting for the Sikaflex route.

And what makes the whole phenomenon particularly frightening is that, in the absence of any engineering documentation (because no-one with with any real-world experience in polymeric glazing systems will put his name to it) virtually every Sikaflex canopy is fabricated slightly differently.

Additionally, it is my observation that those who desperatley WANT to believe in the merits of the Sikaflex solution are often quite hostile to any poster who puts forward any information or data that suggests there might be intrinsic problems.

As a result people with a scientific background have opted out of the debate and left the asylum to be run by the inmates.

When it comes to major (or even minor) structural modifications to Van's drawings, it stands to reason that builders need to take a very conservative approach to internet advice....because in a game where you have IT specialists, bookkeepers and firemen building aircraft there may not necessarily be any safety in numbers.

PS My apologies to any IT specialists, bookkeepers and firemen out there.

Click to expand...

Well, what the "believers get hostile about is when someone names off a whole list of "facts" that are not facts. Sika supplier says "they don't support it" which is very different from saying they strongly recommend against it. There are several with many hours on them, and there is real data: several have done coupon tests that show that the sikaflex is stronger than the plex.

Maybe wait 'till the guinea pigs have more hours.

My advice to those contemplating Sikaflex is to wait until those who are currently the guinea pigs have considerably more hours on their RVs. Waiting for longer term results would seem to be a conservative and prudent thing to do given the ramifications of a canopy failure.

Builders may ask themselves if using sealant as a sole means of restraint on polymeric windows is such a great idea why didn't some-one think of it earlier and use it in on a certificated plane.....well they have...but without long term success.

The last certificated plane that I am aware of to use sealant as a sole means restraint for a polymeric window was the PAC 750XL, a NON PRESSURISED 10 seat turbo prop with a MTOW of 7500lbs designed and built in New Zealand by Pacific Aerospace.

Selected Service Difficulty ref # 510004120 issued by the Civil Aviation Safety Authority of Australia issued January-February 2007 indicates that a co-pilot's door window of a PAC 750XL seperated in flight. The departing window struck the tail-plane. Investigations found that the window was only secured using sealant. No other mechanical device was used.

It is relevant that the plane's total time in service was 1171 hours. It is further relevant that Pacific Aerospace tried a couple of different brands of sealant without long term success.

According to Brian Emery, Chief Operating Officer for Pacific Aerospace, the company has now reverted to "picture frame" mechanical restraints on all polymeric windows to effectively design the problem out.

Sikaflex 295 is a cheap one-pack polyurethane sealant. It is known to gradually degrade and lose elasticity over time when exposed to UV. Probably of more importance is that the Sikaflex 209 black primer is even more prone to UV degradation than the sealant.

Typically RVs are not particularly waterproof so most owners keep them hangared. When away from the hangar most owners also use canopy covers. This tends to limit the amount of UV exposure that the typical RV canopy receives. In other words problems with UV degradation of the Sikaflex may not present itself for many flying hours on a typical RV. Reports from a few pilots with a few hundred hours would not comfort me. The PAC 750XL expererience might indicate that, depending on whether the plane is hangared or not, 1000+ hours might be more revealing.

I state these facts only to bring some balance to the discussion because I perceive that there is a lot of frenzied enthusiasm out there among RV builders for Sikaflexed canopies .... but not much technical expertise or long term experience.

I'm not saying that all the RV Sikaflex canopies will eventually fail. I'm just saying that until there are a LOT more hours flown one might consider that the jury is still out.

/rant/

When someone tries to make their point by subtly changing key words or facts, they (not just their argument) lose credibility. For example, the word "Sealant" was repeatedly used rather than Adhesive. Obviously two different meanings, and it's implied that those "Guinnea Pigs" aren't using a product intended for this purpose.

The PAC 750XL aircraft that used "Sealant" to hold it's windows in place is neither here nor there. Do we know what product was used on the PAC 750XL? Do we know how it was used and in what conditions? Were the bonding surfaces similar to our application? Without that application being virtually identical to our application this data point is pretty much useless.

Regarding Sikaflex having the tendency to degrade in UV. Maybe that's true, but again, we don't know under what conditions. I, for one, plan to cover the center brace of my slider canopy - the only part that would be exposed to UV since everything else is covered by an aluminum skirt and/or paint. I guess all those folks flying composite aircraft shouldn't fly them in daylight since composites are "known" to degrade gradually in UV, as well.

OK, so I'll get off my soapbox and say that my point is this - everything has a finite lifespan. I'm willing to bet that Sikaflex will last far longer than a lot of other critical parts of my airplane. I'm not going to wait for "more hours" to accumulate with the "Guinnea Pigs" so I feel absolutely sure that it will never fail. I'd be waiting a very long time. This is just my opinion, and it may be wrong...take it for what it's worth. But, it is my choice to deviate from the plans and I do so at my own risk with full knowledge of the consequences. That said, I think Sikaflex will work just fine for this application.

All I have to say is -- at least those P-Mags did have failures.. so the discussion had some merit.. but all this Sika FUD is just waste of time.

Can it fail -- sure.. will it? probably not..

In the end, there are those who do it and those who sit there and keep saying how it can't be done...


Bob.. buy one tube for testing.. test it out.. if you are able to break it after proper application... don't use it on your canopy

1000+ Hours on Sikaflex Bonded Canopy

It appears that I am the high hours test article for bonding the canopy with Sika. My RV-9A now has 1060 hours over nearly three years. No signs of any problems with the bond as yet.

We commute daily in the RV and it is hangared at night and sits on the ramp with a canopy cover during the day. It has seen temperature extremes, 115+ degrees in Vegas and single digit temperatures in flight.

My canopy is a slider so it has quite a bit of secondary connection as part of the installation. The windscreen has fiberglass at the leading edge. The slider is trapped under the fiberglass lip to the windscreen, also trapped between two riveted strips along the side and I added one more mechanical connection at the top rear around the slider frame as "suspenders". I do not believe that if the bond fails that it will be catastrophic.

I did not need the aluminum strip along the top from near the handle toward the aft end of the canopy. I did have the strip painted on the canopy to provide UV protection for the adhesive.

As others have mentioned, it is CRITICAL to any bond that the preparation be correct.

I will continue to inspect the bonds and report back if I find any issues.

Thanks to all who have provided information for us to make our own "informed" decision.

Don't light the candles yet.

lostpilot28 said:

When someone tries to make their point by subtly changing key words or facts, they (not just their argument) lose credibility. For example, the word "Sealant" was repeatedly used rather than Adhesive. Obviously two different meanings, and it's implied that those "Guinnea Pigs" aren't using a product intended for this purpose.

Click to expand...

Ok Sonny, you explain to us all what the technical difference is between an adhesive and a sealant. And perhaps you can also describe where cured silicon (which has reasonably similar elastomeric physical properties to cured Sikaflex) falls in your semantic spectrum ie. is it an adhesive or a sealant (and I'll give you a clue....it's BOTH !!!)

Incidentally, Sika themselves describe Sikaflex as a "bonding and sealing" compound.

In reality Sikaflex is primarily a sealant because it has the ability to form an elastomeric bead of low tensile modulus and can therefore accomodate differential movement between mating surfaces by flexing.

The problem for many people who are attempting Sikaflex canopies is that they lack the technical knowledge to ensure long term success (note that I said MANY people not ALL people). Many are bogged down in the notion that some-how the success of the system depends purely on the adhesive grip of the Sikaflex to the acrylic. In their simplistic vision they think they are "glueing" on the canopy. That is why Sonny above is so infatuated with the importance of Sikaflex being an "adhesive" and being critical of me for calling it a "sealant".

But in reality the key to success depends more on creating the optimum joint geometry to ensure that the sealant bead can flex laterally. This ensures that high stresses do not build up at the sealant bond surface as a result of the vastly different coefficients of linear thermal expansion of acrylic and steel. The actual tensile stresses on the sealant under loads normal to the bonded surface will be quite minimal. However the shear stresses in the sealant due to lateral loads from differential expansion will become massive as the sealant bead height approaches zero.

If you don't understand what this all means then I would respectfully suggest that you are not a good candidate for attempting the exercise.

In reality there are many different Vans canopies on the different models and with some it is impossible to create an optimum Sikaflex joint geometry AT ALL LOCATIONS without serious modifications to the canopy design. For instance on the RV7 slider it is impossible to maintain the minimum sealant bead depth fully around the front bow without major changes to the existing side skirt. My perception is that builders using Sikaflex on the RV7 slider do not make any mods to the skirt....they simply taper off the depth of the bead to zero over the steel tube as it approaches the side skirt. This means that there is no depth of bead to flex at the very point on the perimeter of the canopy (the corners) where the differential movement is the greatest.

Do I have long term reservations about this practice from a technical viewpoint...you betcha. It's just bad science. As the sealant progressively loses it's elasticity and its adhesion with age and exposure these will be the areas where the sealant will start to delaminate.

Truly, some of the things I see some people doing with Sikaflex (and advocating others should do) scares the bejeebers out of me. For instance take a look at posting #6 on this recent VansAirforce Sikaflex thread.
http://www.vansairforce.com/community/showthread.php?t=25727&highlight=sikaflex
Read it. This chap is advocating that there is no need whatsoever for any spacers between the steel tube and the acrylic when forming the sealant bead (ie zero sealant bead height between the acrylic and the steel tube at its highest point of curvature).

And what is scary is not that the suggestion was made....what is truly scary is that NOT ONE PERSON in that thread subsequently commented on this quite dangerous proposal.

I have an engineering background and for a number of years was actively involved in the design and construction of large scale commercial polymeric glazing systems. I have a reasonably good grip on the problems involved.

I looked at Sikaflex VERY carefully before I decided not to go that way. In the end I chose to design a floating canopy with oversized holes, silicon bushings, and specially machined fasteners. Would I advocate this approach to others. No....not until I have well over 1000 hours up. The one thing I have really learned about polymeric glazing systems is that despite all the theory the only thing that truly proves the product is time in the field.

And that's equally true for the Sikaflex canopy.

Jim Bray's comments and report on his RV9A are encouraging. But I wouldn't be lighting the candles on the celebration cake just yet. It's still early days in terms of the big picture.

Wow Bob, all them smarts and you completely missed my point. Here's a clue, it wasn't about the technical aspects of Sikaflex.

I'm not going to argue with you...but I'll make you a deal - if I'm wrong and Sikaflex doesn't do an adequate job of being a canopy attaching adhesive for any RV'er who's properly applied it, then I'll give you a public apology and concede that you may be right. If it does, then you give me one. How long should we give this to pan out, really?

I guess that's a little of an unfair advantage for me, because it seems that no RV builder who's used it has ever had a problem, but I can't see any other way to satisfy this disagreement. Unless you were to take Radomir's suggestion and actually do some testing yourself, that is.

Wow !!!!

This is an awesome thread. The guy with the Engineering background is right about many things. I am a Contractor and Waterproofer. Sika Flex is not classified as an adhesive. It does have adhesive quality's to it but it's ASTM testing procedures do not qualify it as an adhesive.

It is not a structural component. Therefore in construction practices by definition it can not replace a structural component such as a bolt or screw. In every structural application I have ever used Sika Flex to waterproof and seal a bond to metal,steel,plastic,lead concrete, and a host of other materials we have always used a mechanical fasteners of some kind.

Thermal shock is the type of testing that is going on here. Hot to cold then back to hot. This is laboratory stuff here. It may not be obvious to all that there is no ASTM tests to prove or disprove it's success or failure. This means some RV builders may have success and others may not. It's all about time Aye?

These things I know to be true. It does have a shelf life(a date stamped on it), application life, and elongation functional life spans. It can be to thick or tooled incorrectly to function properly. Some shapes will cause breakdown sooner than others.

I have purchased and used more of this sealant and others of the same chemical make up than most people can conceive (truck loads in 55 gallon drums). We remove and replace tilt up building caulk joint connections filled with Sika Flex every ten years do to elongation shear(That is a fancy construction term to say it's separating from it's self. Oh, By the way I know more than one Sika Chemist and Rep and I would want them on my job to tell me what to do. They don't have a clue what most of their products do or how to use the properly ).

It alone as a structural member is not for me. It does not make the clear definition. If you want to be a canopy test pilot for all of us excellent . Just make sure everyone flying with you understands they are the definition of an experimental canopy test pilot too Good luck to you all on your quest to Sika test piloting history. And If I'm still alive when they put it in as the preferred method of canopy attachment my hat will be off to you all!!! I'm so glad I found this place to kill time and learn stuff!
Alan

Not a contest

lostpilot28 said:

I'm not going to argue with you...but I'll make you a deal - if I'm wrong and Sikaflex doesn't do an adequate job of being a canopy attaching adhesive for any RV'er who's properly applied it, then I'll give you a public apology and concede that you may be right. If it does, then you give me one. How long should we give this to pan out, really?

Click to expand...

This is not a contest. My comments are simply an attempt to raise the Sikaflex topic to a higher technical level....to take it beyond the self congratulatory back slapping and examine some of the limitations of the technology. Hopefully that might enable prospective users to make a better assessement of the technology.....or at least make more informed design decisions in the event that they opt to proceed.

For my trouble, people who have no technical understanding of the technology (but who endorse it and promote it without reservation) accuse me of trying to trick people with semantic sleight of hand. Others call me a "nay-sayer". It's all so horrible...a public stoning of the pagan by the religious zealots.

In the end I doubt the success or failure of the Sikaflex canopy will ever be a black and white affair. I expect some canopies might survive for a decade or more...MAYBE even permanently if they are really well designed and largely protected from UV exposure and extreme climates. Others I expect will fail within a few years because they have poorly designed joint geometries and/or were installed using dubious quality control procedures. As I noted earlier, there's not much knowledge or consistency of correct application techniques out there. There are so many laymen doing their own thing in an area which is notoriously difficult, even for expert designers, to master.

The nature of the impending failures of those canopies that are inadequately designed/constructed will also be difficult to determine. My best guess is that delamination will initially be local in nature and if picked up early through regular vigilant sealant inspection a major catastophic loss of a canopy with no mechanical fasteners could be avoided. But who really knows.

Incidentally the PAC 750 XL turbo prop that lost it's window in flight had an acrylic window sealed to an epoxy composite frame. That's a MUCH more favourable combination in respect of differential thermal movement than the Vans canopy which is acrylic on steel. The coefficient of linear thermal expansion (CLTE) of steel is approx 12 and of acrylic 80. Thats a massive expansion/contraction difference and it largely explains why acrylic bonded to steel is such a difficult task to pull off successfully.

Builders who refer to glass windscreens on cars being succesfully bonded need to understand that the CLTE of glass at 8 is virtually the same as steel at 12....so the differential movement is negligible and thus there is negligible shear stress placed on the sealant.

Anyway, be careful out there. I'm going back to working on my plane now.

Cap'n

I, for one, do appreciate the info. My canopy was rivetted on a long time ago and I have no intention of messing with it, but if I were building again I would certainly find the Sika method attractive from an aesthetic standpoint. However, just because it looks like an elegant solution doesn't make it so. The thermal expansion differences and the UV issue are enough to make me doubt the long term reliability, but I'm afraid most of the "engineering" going on in homebuilt aircraft is of the "try it and see if it seems to work" variety.

A case in point is the internal rudder stop that several RV's are using. It has been expressed very clearly on this site that this design, while looking very nice, places much greater stress on the rudder hinge assembly than that imposed by the Van's design. The response was essentially that lots of folks use em and have never seen a problem.

It seems to me that sooner or later a glued canopy will encounter a "perfect storm" of old age, inadequate gap, excessive UV exposure, and extreme temp change, and that'll be that. At that time we'll have our first real bit of test data and hopefully machine and man are not banged up too bad in the process.

RV-9, 380 hours, 18 months, hangared, sits on the ramp occasionally with a lightweight cover. Windscreen, slider canopy, side skirts, fiberglass aft fairing, all bonded with Sikaflex. Apart from the sideskirts which also have the pop rivets per the plans, there are no other mechanical fasteners.

Just another datapoint.

I'm aware of the potential for trouble so I do inspect the bonds regularly and in detail. So far no signs of trouble at all. (Wish I could say the same for some of the pop-rivets that hold on some of the other fiberglass fairings, etc.)

If I were to do it again I think I'd be 50/50 (maybe 60/40 in favor) on the Sikalfex route, primarily because there is some complexity to the process - particularly the time limits on each step of the prep, application, curing, etc. I think that's particularly challenging if its the first time you've done it. With mechanical fasteners I assume you can work at your own speed. Not so with Sika - you HAVE to work within its proscribed time limits.

Having said that - what made me chose Sikaflex in the first place was that I didn't feel confident in the plans method, given the different rates of expansion of plexi and steel. Not to mention the potential problems of putting holes in plexi. One thing to note there is that those "potential problems" have become real problems for a good number of installations, whereas I'm not aware of any problems on RVs with Sika ... yet.

One chooses one's poison I guess.

Cheers for Capt'n Avgas

Whether you want to admit it or not, Bob is raising the safety level for all of you about to use Sikaflex, by continuing to provide legitimate engineering concerns regarding canopy attach methods. Just because you have huevos doesn't mean you are wise. There is a lot of wisdom in Bob's comments that should seriously be considered to ensure the most sound use of the material.

I left the debate a long time ago for just the reason that Bob pointed out. There is a lot of enthusiasm for the product, but little engineering going into the solution. I read a lot of "I don't know about ...., but...." Makes one wonder why they are posting in the first place - talk about the need for a lawyer!

Four other issues to consider when designing your joints with adhesives:

Make sure ALL surfaces are properly prepared for bonding. This includes the steel and the powder coating on the frame. I have seen the powder coating bubble off my parts due to poor surface prep. Hopefully everyone is stripping the paint off their frames where they are bonding so that they are not relying on the unknown paint to steel adhesion.

The material has poor tear resistance. Once a tear starts, it will readily grow, especially if the material has been squeezed to a thin bond line by the installation.

Bond quality inspection cannot be done visually, or with other non-destructive means for that matter. Looking at the bond will not mean you can tell if it is good.

Build in damage growth arresting features. Something is needed to prevent any disbond from growing catastrophically.

Making engineering decisions without considering engineering issues is not bravery to tackle the unknown, it is foolishness.

The most productive use of this thread perhaps is to accept engineering reality and design the lowest risk joint using the material of interest, keeping an open mind that once they analysis is done, the material may not be that interesting after all.

The weakest link

BJohnson said:

Make sure ALL surfaces are properly prepared for bonding. This includes the steel and the powder coating on the frame. I have seen the powder coating bubble off my parts due to poor surface prep. Hopefully everyone is stripping the paint off their frames where they are bonding so that they are not relying on the unknown paint to steel adhesion.

Click to expand...

Brice Johnson makes several very astute and important observations in his post, none of them more important than the one above. It is a point that I specifically raised on a previous thread. I know that there are a number of builders going the Sikaflex route that have stripped back Van's powdercoating and re-coated (the more technically tuned-in ones).....but I also know that many have not.

It is not an easy or cheap option to strip and re-coat a canopy frame. For complete stripping it requires either blasting or chemical stripping (I chose the latter on mine and recommend it).

The other consideration (and it's a serious consideration) is that the frame can easily be deformed or otherwise physically damaged by subcontractors during re-coating. If it's damaged it's a large and expensive object to replace and freight and you may have weeks of work invested in it.

When I first considered using Sikaflex I started at the start. And the start is the quality of the adhesion of the powdercoat to the steel. It doesn't matter how careful or confident you are of the bond of the Sikaflex to the powdercoat if the powdercoat is not well bonded to the steel. The system will fail at the weakest link.

So I contacted Vans and asked them to supply me with their written specification for pretreatment and powdercoating as issued to their coating subcontractor. I was absolutely amazed when they came back and advised me that they DID NOT HAVE a written specification....and furthermore they were sourcing their powdercoating through a number of different subcontractors.

What this means is that Van's powdercoating is price driven and of very dubious commercial quality. This was reinforced to me when I decided to strip Van's powdercoating off my own canopy frame and recoat it. This gave me the opportunity to try some destructive testing on Vans original powdercoat. I discovered that the steel had not been properly degreased or pre-treated (not even a cheap iron phosphate pretreatment...pretty disgraceful actually). In some areas the powdercoat adhesion was virtually nil. In other words in some areas it was encapsulating the steel but was not properly bonded to it.

In the final analysis Vans powdercoating cannot be relied upon for a Sikaflex canopy. A Sikaflex canopy MUST be a 100% quality control program through-out. If Vans do not have a quality control program for their coating system then YOU have to strip off his powdercoating and develop your own.

Of course that raises other problems for the layman. If he doesn't understand coatings technology and doesn't know what to specify then he may get a second coating job that is no better quality than the first.

It's amazing we're all still alive.

Sika is in Last Place!

Warning Long Post!

OK, Obviously being the new guy(member one week with 1/2 dozen posts) who's has never flown an RV, has yet to order one rivet, has sat only in one RV8, and just reviewing his preview plans who's going to listen. I just can't understand one thing about this debate(not knowing the long history and where it started). There is not one shred of Sika ASTM test procedure data that even supports anything close to this type of application. But who am I to question the Home Builder Gods of Wisdom.

Sika is in last place! It's ASTM testing results puts it on the bottom of the list compared to other industrial caulk. It sounds like people have been listening to Sika about how GREAT they think they are

I'm going to stop looking at this thread even though there has been some good discussion on practical application procedures for a change in design structure(boy that was a mouth full). There has also been some killer macho stud comments.

Just because some one reads the tech sheet on a product and sees the words "adhesive qualities" and "approved material for adhesion and application" or "UV stable"they think this stuff is KING! And they say to themselves "I can't wait to use this stuff to replace my safety belt". Well sorry to inform you that ASTM testing shows it to be at the bottom compared to GE and Sonoborne for it's approved applications.

So this great debate can continue about the "best way" or "how too"or "the proper way" or "should you". I wonder how many builders would use the weakest rivet when building their airplane. Hey let's take a poll on that.

If your going to use a caulk sealant that is not tested as a structural adhesive and has no structural value rating by ASTM chose the best one. Sonneborn has the best ASTM non structural adhesive canopy test pilot caulking material on the market. Which one you ask? I'm not going to tell because it doesn't have any structural value either!!!

I have seen all Sika caulking products fail internally on building structures after 10 years. Doing what is designed and tested for. The caulking materials I use to replace Sika last up to thirty years. The outside test data exceeds thirty years of 400% elongation longevity and I have projects over 25 years old were the caulk does not need to be replaced.

To think who ever started this idea of mounting a canopy with a caulking sealant (probably book read Engineer with more experience than me building an airplane). RV Sam while taking a break from attaching his canopy was caulking his shop door and thought to himself, "Hmm, boy this stuff is sticky, Hmm I wonder". Then he found the manufactures tech sheet and said "it really is that sticky".

Like I said before good luck on your Sika test piloting. Sorry to bring bad news about Sika to you guys that have already done this. Most likely you don't care. Your "Rebels with out a Fastener" in your canopy. Thanks for all you do and be careful out there. Thanks to you all, I'm learning that this is what "experimental" is all about!

Alan

Courage

Bob Brown said:

It's amazing we're all still alive.

Click to expand...

Bob, I take it from your one-liner that you are one of the builders who applied the Sikaflex directly to Van's suspect powdercoating. Very brave of you.

Show us!!

N23J said:

Warning!

Sika is in last place! It's ASTM testing results puts it on the bottom of the list compared to other industrial caulk.
ASTM testing shows it to be at the bottom compared to GE and Sonoborne for it's approved applications.

If your going to use a caulk sealant that is not tested as a structural adhesive and has no structural value rating by ASTM chose the best one. Sonneborn has the best ASTM non structural adhesive canopy test pilot caulking material on the market.

I have seen all Sika caulking products fail internally on building structures after 10 years.

Thanks to you all, I'm learning that this is what "experimental" is all about!

Alan

Click to expand...

Show us the SIKA product that you are talking about..............

Bob,

What sort of prep and coating did you use to replace the powder coat?

Paige
RV-8A