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Front Windscreen Unbonded at top

Lynnb

Well Known Member
Well I'm looking for some suggestions, been happily flying along for 100 hours now when this morning I was cleaning the front window and noticed a section at the top that flexed a little. Well upon closer inspection I realized there is about a 10 inch section that has come unbonded. Here's a little video of it:
https://youtu.be/8QgYgjnWus4

I installed the windows with Lord Adhesive. I originally had an issue with some of the adhesive not curing on one of the rear side windows, I'm not sure if this is a similier issue or just what, but I'm looking for suggestions on re-bonding. On the fortunate side I'm not painted yet. I know someone will say I needed to glass in the windows, but was planning to let the paint shop do that work.

Any thoughts? This has been a deflating morning to say the least.

Lynn
 
You are quite fortunate to find this before paint. I would definitely pull it, as it is likely there are more areas of poor adhesion. With appropriate care taken, you should be able to get all of the adhesive off the acrylic and F/G. Just be sure to sand aggressively to be sure all of the old adhesive is gone. I would start with razor blades or exacto knife, then chemicals (starting with mineral spirits), then to sanding once all visible traces of adhesive are gone. The acrylic is a 1/4" thick, so you have a bit of margin to scrape off trace amounts.

You may want to consider sikaflex to re-bond it, as there is no mixing involved and therefore lower chances of a repeat failure, guessing that the issue was improper proportions of the two parts due to issues in the mixing nozzle or the twin pump gun. The downside to prepackaged two part tubes, is that manufacturing issues, such as a large air bubble, are difficult to notice by the untrained observer.

I would call Lord to see if heat may help with removal, as you are likely going to struggle to get blades into the joint when separating the windscreen. Some research should help you find unique shaped blades that will help.

Glassing in the bottom of the window is mostly a cosmetic exercise, as the epoxy has a very weak bond to acrylic and only marginally better bond to aluminum. I am certain that it helps hold the window rigidly in it's place, but suspect that 95% of what is keeping it from departing the aircraft is the adhesive bond to the F/G on the sides and top, as those adhesives DO have a strong bond to acrylic. Glassing in the sides and top is purely cosmetic.

Larry
 
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Glassing in the window is mostly a cosmetic exercise, as the epoxy has a very weak bond to acrylic and only marginally better bond to aluminum.

Larry

On the windshield of a -10, glassing in the windshield gives you a fiberglass lip that is bonded to the fiberglass top across the top and two sides of the windscreen. It *should* be a robust capture mechanism for the windscreen.
 
On the windshield of a -10, glassing in the windshield gives you a fiberglass lip that is bonded to the fiberglass top across the top and two sides of the windscreen. It *should* be a robust capture mechanism for the windscreen.

I wouldn't disagree with that. However it is a very small and thin piece of F/G extending over the acrylic and I highly doubt it would hold that acrylic in place if the adhesive let go. Not saying it may not help, but I still believe that the adhesive must be robust to keep the windshield in place. I don't think I would trust that little lip to hold my acrylic in place at 200 MPH. Just guessing here, as I am not a structural engineer.
 
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If you're taking the windscreen out, then it's not too late to consider the SilPruf method.

No fiberglassing over the acrylic is necessary or desirable with that route. Not aware of any failures to date, either.
 
Had this happen to me in a 6 I was ferrying. Scared the s—- out of me as it sounded like an air raid siren went off 3” from my ears as it vibrated in the airstream.
The fairing delaminated the whole length of the roll bar so I was able to flex it forward and locate the screw holes in the plexi, remove every second one, drill & countersink the fairing for longer screws that would go through the fairing/plexi/roll bar. A light film of PRC was applied between, than screwed down. Solved the Screaming Demon.

I’ve used a variation of this method on all my w/shield fairings since.

I just realized your delamination was on a 10. My comments above are more appropriate to 2 place sliders…
 
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I’m guessing it would be challenging to remove the glass without destroying it. If you can, then starting over would be the preferred approach. If not, then your fix it in place options are limited.

For me I’d add a couple of bids of carbon fiber over the glass, top and sides. Steps needed:
- Do whatever you can to clean out the existing gap between the glass and the cabin top.
- Figure out how to get the glass to lay flat on the cabin lip. I’m guessing injection of some adhesive then some weights while it sets.
- Tape off the glass so that you only have the cabin top lip showing through the glass along the edges.
- Sand the glass lip, and a couple of inches aft on the cabin top with 80 grit or so paper.
- Fill the gap between the gap with micro, let it set then sand flush.
- Lay up two bids of carbon over the area, keep it just shy of the tape on the glass. Add peal-ply over the layup and let it set.
- Apply a skim coat of micro over the layup and onto the cabin top. Let it set and then sand to feather in the overlay with the cabin top.

The follow up will be to see if you have the same problem on the door or side glass. If so, fix it before paint.

I did this approach on my first RV-10 as almost every RV-10 I saw that followed the instructions (like it seems you did) had “window framing” - a perfect crack all around the window where the gap was just filled in with micro before paint. The plane has been flying now for 10 years and has not suffered the same fate.

For the current RV-10 build I’m still debating between this tried and true approach or the Silpruf methods that seems to be popular.

Carl
 
Thanks for all the comments, keep them coming. I sent to same question to Van's, right now I'm just trying to build up the motivation to start working on this. Guess it's true the building and maintence never end. ;)

Lynn
 
Using the cabin top/windscreen as a mold, I laid up what I subsequently called an eyebrow panel. This was bonded to the top area of the canopy bow (I used West G Flex) and then the panel, windscreen edge, and windscreen flange were match drilled. Small bolts/washers/locknuts completed the belt and suspenders attachment. The holes were slightly larger than the bolt shank to allow some slight movement.

Pic3.JPG

Pic9a.JPG

Pic9.JPG

==dave==
N102FM
 
Well I heard back from Van's and they suggested injecting some adhesive underneath it to stabalize that area, then layer glass on top. So I think I'll start with that approach for now and see where it gets me. I need to get a pin behind the windscreen and see if the adhesive in that area is still goey, that's what I had on the back window when it never cured.

Thanks for all comments,
Lynn
 
I would now suspect the doors and the rear windows. Carl has a very good suggestion a good description. I would definitely layup at least 2 layers bid and fill in the gap with micro. If you don’t, you will have cracking around all the windows within 100 hours
 
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It looks like the bond between the adhesive and the fiberglass is what failed. I would has thought that the adhesive to plexi bond would be the weak point.

You could remove some of the fiberglass from the cabin top to give better access to the joint between the plexi and fiberglass lip. Use a thin flexible blade to remove some of the failed adhesive. Then inject adhesive per vans suggestion. What adhesive you choose will be a tough one. You will want to make sure it is at a minimum compatible with the Lord adhesive.

Take special care to protect the inside of the window. You don't want to add scratches to it or leaked adhesive onto it.
 
I would start with razor blades or exacto knife, then chemicals (starting with mineral spirits), then to sanding once all visible traces of adhesive are gone.
Larry

I wouldn't be putting any "mineral spirits" anywhere near that windscreen. That would be a really good way to end up with multiple stress cracks and a total loss of the windscreen.
 
Well I heard back from Van's and they suggested injecting some adhesive underneath it to stabalize that area, then layer glass on top. So I think I'll start with that approach for now and see where it gets me. I need to get a pin behind the windscreen and see if the adhesive in that area is still goey, that's what I had on the back window when it never cured.

Thanks for all comments,
Lynn

I would exercise caution on that approach. The issue is that the current adhesive in that open joint is likely uncured, based upon your previous experience/findings. If that is the case, injecting new adhesive into that joint will not help as it cannot adhere to the gooey, uncured material that itself is not adhered or only lightly adhered to the acrylic or the F/G. IMHO, the entire glass installation should be considered suspect and appropriate steps taken. You just don't know if or how many other areas have uncured or partially cured adhesive.

Sure, laying a thick glass layer over the windshield should/may keep it from departing the aircraft, but what if more adhesive lets go? Your windshield will start rattling around inside the gap.

Larry
 
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I wouldn't be putting any "mineral spirits" anywhere near that windscreen. That would be a really good way to end up with multiple stress cracks and a total loss of the windscreen.

Mineral spirits is one of the approved solvents for cleaning the acrylic according to the manufacturer. It is even recommended in the RV6 builders manual.
 
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Mineral spirits is one of the approved solvents for cleaning the acrylic according to the manufacturer. It is even recommended in the RV6 builders manual.

The problem with "mineral spirits" is that it is a generic name encompassing a wide range of chemical solvents, some of which are more dangerous than others. Here's an extract from Wikipedia.

White spirit (UK & Ireland)[note 1] or mineral spirits (US, Canada), also known as mineral turpentine (AU/NZ), turpentine substitute, and petroleum spirits, is a petroleum-derived clear liquid used as a common organic solvent in painting.[1] There are also terms for specific kinds of mineral spirits, including Stoddard solvent and solvent naphtha (petroleum). Mineral spirits are often used as a paint thinner, or as a component thereof, though paint thinner is a broader category of solvent. Odorless mineral spirits (OMS) have been refined to remove the more toxic aromatic compounds, and are recommended for applications such as oil painting.

Acrylic (PMMA) has very limited chemical resistance and a lot of RV canopies have ended up with cracks in them because builders used the wrong chemicals on them. In reality there are very few solvents that are safe to use on heat formed acrylic.

Personally I would not use anything other than isopropyl alcohol (properly identified) or kerosene. Even then I'd use those sparingly, particularly at cut edges and holes where there is a high probability of existing microscopic cracking.
 
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The problem with "mineral spirits" is that it is a generic name encompassing a wide range of chemical solvents, some of which are more dangerous than others. Here's an extract from Wikipedia.

White spirit (UK & Ireland)[note 1] or mineral spirits (US, Canada), also known as mineral turpentine (AU/NZ), turpentine substitute, and petroleum spirits, is a petroleum-derived clear liquid used as a common organic solvent in painting.[1] There are also terms for specific kinds of mineral spirits, including Stoddard solvent and solvent naphtha (petroleum). Mineral spirits are often used as a paint thinner, or as a component thereof, though paint thinner is a broader category of solvent. Odorless mineral spirits (OMS) have been refined to remove the more toxic aromatic compounds, and are recommended for applications such as oil painting.

Acrylic (PMMA) has very limited chemical resistance and a lot of RV canopies have ended up with cracks in them because builders used the wrong chemicals on them. In reality there are very few solvents that are safe to use on heat formed acrylic.

Personally I would not use anything other than isopropyl alcohol (properly identified) or kerosene. Even then I'd use those sparingly, particularly at cut edges and holes where there is a high probability of existing microscopic cracking.


WHen I looked at our canopies manufacturer's documentation, both kerosene and mineral spirits were approved and Iso alcohol was not. Given that this mfg was in the US, I assumed they meant the MS that we are offered in the US, though I suppose that could be argued. Naptha, in hte US, is a different product line and sits next to MS on the shelf. It is a more refined solvent than MS.

I would agree that kerosene is probably a safer choice than MS, as it is less refined.
 
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In your opinion, why are those solvents a better choice than Mineral Spirits?

This is a web page from Industrial Specialties Manufacturing. Click on the link and then download their complete Acrylic Chemical Compatibility Chart.

https://www.industrialspec.com/resources/acrylic-aka-pmma-chemical-compatiblity-chart

It rates both isopropyl alcohol and kerosene as class A (excellent, no effects) and mineral spirits as class B (good, minor effects).

However as I have stated earlier the bigger danger with using “mineral spirits” is that a range of products may be marketed as “mineral spirits”, some of which maybe more insidious than others. If the product is marketed as isopropyl alcohol or kerosene then you can have a high degree of confidence in what you are buying.

It is interesting to note that the ratings above are only for ambient temperatures (20 degrees C). All of the above products are very dangerous on acrylic at nominally elevated temperatures (50 degrees C). That’s not very hot. For that reason I wouldn’t be applying any solvents whatsoever to a canopy that was outside in the sun.

Acrylic is very susceptible to a really extensive range of chemicals. You just can’t be too careful with it. And Vans canopies in particular are problematic. Firstly they are heavily thermoformed and therefore contain considerable locked-in thermal stresses. Secondly builders don’t tend to take the steps required to eliminate microscopic cracking created during the cutting of edges and the drilling of holes. And thirdly Vans canopies are an absolute nightmare to replace if they crack.
 
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