Cracked side window - what's the fix?

[Slick Nick]

My plane is always stored in a heated hangar. Up at altitude, I was showing about -37*C OAT today when I Heard a "pop" randomly, figured it was just one of my water bottles expanding. Took me awhile to notice it, a crack in my side window from the storm window hole down to the bottom. 

What's the fix for this? My plane has relatively new paint, so replacing the whole window is somewhat out of the question. Is there an approved procedure to grind and epoxy this? It whistles slightly over about 150 knots now. 

Doesnt have to look perfect, its very well out of my field of view. 

[Bartman]

Sorry, this is the first thing that came to my mind, and I could not resist.

[EricJ]

Yes, there are some approved repair methods in AC 43.13, Chapter 3 Section 3.   There are several alternative methods to doing repairs for cracks like that.

Changing the side windows falls under Preventive Maintenance in the US, so it's something that an owner can do here.   I don't know what the rules are in Canada.    You should be able to do it without bothering the paint if you're careful.    I think there's a procedure in the SMM for changing out the side windows, but generally they're not too complicated.

 

[Fly Boomer]

1 hour ago, Slick Nick said:

Doesnt have to look perfect, its very well out of my field of view. 

I have seen cracks laced up with safety wire.  Series of holes drilled on each side of crack, and lace it up like your trainers.

[MikeOH]

Would some kind of low viscosity solvent wick into the crack and 'weld' the plastic?

[Slick Nick]

1 hour ago, EricJ said:

Yes, there are some approved repair methods in AC 43.13, Chapter 3 Section 3.   There are several alternative methods to doing repairs for cracks like that.

Changing the side windows falls under Preventive Maintenance in the US, so it's something that an owner can do here.   I don't know what the rules are in Canada.    You should be able to do it without bothering the paint if you're careful.    I think there's a procedure in the SMM for changing out the side windows, but generally they're not too complicated.

 

Aren’t the side windows riveted / bolted in? Or is it a threaded stud / nut arrangement?

[Pinecone]

1 hour ago, MikeOH said:

Would some kind of low viscosity solvent wick into the crack and 'weld' the plastic?

If they are basic acrylic sheet, simple MEK will wick in and "weld" the plastic.

[A64Pilot]

As the crack has run it’s course, I’d leave it alone, I believe anything you do other than replacement is going to make it look worse.

I assume thin CA (super glue) would seal it, I’ve never tried, MEK is so thin I’d want a syringe or something as an applicator, even one drop is going to run I think.

I’d practice on scrap first though.

In the mean time maybe a strip of clear tape to stop the whistle?

[A64Pilot]

10 hours ago, Slick Nick said:

Aren’t the side windows riveted / bolted in? Or is it a threaded stud / nut arrangement?

I haven’t even looked, but often there is a retainer strip that is riveted and sometimes they are replaced with screws, but I have no idea on a Mooney. My old C-140 it’s all screws, just a few minutes work, so it apparently differs from one make to the other.

Edited February 12 by A64Pilot

[AJ88V]

Stop drilling is the standard method to minimize  crack growth in your plexiglass window.  Basically you drill a small hole directly in front of the crack (but not actually on the crack).  Then, when the crack continues to grow, it will reach the hole which has a smooth, round surface to relieve the tension that produced the crack in the first place and the crack will not propagate beyond the hole.

In @Slick Nick's case, the crack has essentially reached the stop hole by reaching the pilot's window cutout (as @A64Pilot pointed out :)).  The crack likely started at one of the screws holding the window in at its bottom edge.  Since the window is also bonded in place with sealant around the edges at the airframe, there is no risk of the "broken" piece of plexi coming loose.

You can put a dab of clear silicone in the small stop gap hole.  Have never heard of using anything to weld the crack back up.  The risk is that you won't make the crack go away but instead make it into a smudgy mess.  If I were to try anything, it would be cyanoacrylate (Crazy Glue) applied with the tiniest syringe needle available.  Cyanoacrylate is essentially liquid acrylic that polymerizes when exposed to water in the air (or your skin, as we've all experienced).

[Slick Nick]

Thanks everyone! I think what I'll do is put a thin strip of 3M clear PPF on each side of the window and leave it alone. I suspect that trying to use any sort of adhesive or epoxy will just make a huge mess. I want to keep the water out of there, as it would have a good chance of freezing at altitude and potentially cracking the window more.

[Pinecone]

It would depend on if there is any gap.  No gap, thin CA would work.  If there is any gap, they make medium and thick CA.  My favorite brand from model airplane days is Mercury Adhesives.  I think Amazon carries them.

This one doesn't need it, but you could also glue a piece of thin acrylic over the crack. That would look better than stitching with safety wire.

[Slick Nick]

1 minute ago, Pinecone said:

It would depend on if there is any gap.  No gap, thin CA would work.  If there is any gap, they make medium and thick CA.  My favorite brand from model airplane days is Mercury Adhesives.  I think Amazon carries them.

This one doesn't need it, but you could also glue a piece of thin acrylic over the crack. That would look better than stitching with safety wire.

There's no gap really. If I were to do anything more involved, I'd probably grind out a bit of the crack on the inside and use a clear acrylic epoxy. But I'll try the clear PPF strips for now and see how it holds up.

[pirate]

When I use to be in the aircraft window polishing business I used thin CA for customers with minor cracks like this, had good results. 

[Brian2034]

Looks like it’s ran its course (from the vent window to the outer edge of the window)

We’ve always had luck with CA glue on cracked windows, it’s thin and should wick into the crack. If you’re worried about a mess you can tape along the sides of the crack, that would keep the glue contained. I’m guessing the crack relieved a stress in the window. You can also scrape any excess residue glue off the window with a razor blade. Also sometimes if your lucky the glue will wick in nicely and the crack almost disappears.

[Slick Nick]

Alright, you guys have convinced me. I'm going to try with some thin CA glue instead. I'll mask both sides and make sure to use a needle tip. With the storm window open, there is just enough "give" if i were to push from the inside and apply glue from the outside, that the edge of the crack opens up ever so slightly. Opening it, applying a drop or two of glue, and then letting go might give just enough time for the glue to wick into the crack and help its appearance. The thin glue I have lists a working time of 3-5 seconds so I'll need to be quick.

Edited February 12 by Slick Nick

[EricJ]

29 minutes ago, Slick Nick said:

With the storm window open, there is just enough "give" if i were to push from the inside and apply glue from the outside, that the edge of the crack opens up ever so slightly. 

I think that's an indication that it needs to be properly repaired.   There's actually a fair amount of stress on the window during cruise, which is why there's a limit on opening the storm window (it'll slam shut and take the window out if it's open and you close it at too high of a speed).    Having the window fail in flight would not be a good thing.

[PT20J]

You also want to make sure it doesn't leak water. The storm window area can leak water down behind the trim panel and there is a bracket there that attaches the window that is pop riveted with steel rivets to a structural tube and if water collects there it can rust out the rivets and leak down inside the tube and migrate to the bottom tube where it rusts the tube out. By '91 I think Mooney was covering the rivet heads with Proseal, but earlier models just had bare rivets.

[Yetti]

I think it's pretty standard crack to have on a Mooney.    I have seen several with them.   Mine is in the middle of the storm window.

[Bartman]

On 2/12/2025 at 6:46 PM, PT20J said:

You also want to make sure it doesn't leak water. The storm window area can leak water down behind the trim panel and there is a bracket there that attaches the window that is pop riveted with steel rivets to a structural tube and if water collects there it can rust out the rivets and leak down inside the tube and migrate to the bottom tube where it rusts the tube out. By '91 I think Mooney was covering the rivet heads with Proseal, but earlier models just had bare rivets.

This is by far the most important post on this thread.  

[Utah20Gflyer]

My plane has that crack and so far it has been a non issue, maybe I’ll look into the CA glue because I can’t help but try to improve things.  I personally wouldn’t consider replacing a window over that defect.  But to each their own.  

[A64Pilot]

On 2/12/2025 at 12:41 PM, pirate said:

When I use to be in the aircraft window polishing business I used thin CA for customers with minor cracks like this, had good results. 

@pirate

Is the RV-7 your building an A model, nose gear?

If so do you have the new engine mount that has the gear leg that uses Mooney shock biscuits?

[pirate]

On 2/15/2025 at 7:08 PM, A64Pilot said:

@pirate

Is the RV-7 your building an A model, nose gear?

If so do you have the new engine mount that has the gear leg that uses Mooney shock biscuits?

I’m building the -7       Tailwheel / Slider. 

Just moved it to my new place so I can proceed with the fire wall forward.