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Upper Cowling Damage

jrock836

Well Known Member
My upper cowling has cracks and paint damage, mostly around the Phillips head screws. While I work on my Annual next month, I’m thinking about sending my upper cowling to the paint shop for repair and repaint. Has anyone found a better washer/screw combo to use that will protect the paint and distribute the load better than the little plastic washers under the phillips screw head? Is there maybe some type of washer that has a collar that would fit into a counter sunk hole? There has to be something better than the existing setup. Although the existing screws do a good job of holding the cowling in place, it doesn’t really seem to be a well thought out solution.
 
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Look for Tinnerman washers. They are designed for countersunk applications and distribute the load over a much larger area than just the screw head. Here's what Spruce offers (note they come in different sizes):

https://www.aircraftspruce.com/catalog/hapages/nas549washers2.php

Thanks.. Those might work and will most likely hide much of the flaking paint around the screw heads, if I decide to wait on painting..

Has anyone else done anything differently on an already completed RV12 cowling?
 
I use countersunk washers everywhere...
-
 

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That is one location where I have not used the C'sink washers. My upper cowl is scheduled for cosmetic upgrade.
 
Hi Jim.. Did you use them on the front of your fiberglass cowling near the intakes?

I just performed an oil change so had to reinstall the cowl. Like others, I use conical washers on every flat-head screw on the exterior, including the landing light lenses. Just for the fun of it, I took one and turned it upside down on the forward cowl screws to which you’re referring. They actually didn’t look too bad. Something you might want to evaluate for yourself.
 
I just performed an oil change so had to reinstall the cowl. Like others, I use conical washers on every flat-head screw on the exterior, including the landing light lenses. Just for the fun of it, I took one and turned it upside down on the forward cowl screws to which you’re referring. They actually didn’t look too bad. Something you might want to evaluate for yourself.

Pictures please, I can't quite visualize this.
 
I thought to take a photo, but then thought, what for, nothing to see 😊. Guess I was wrong. Since the forward cowl screws aren’t counter sunk, I simply turned the washer over so the cone faced away from the cowl. Yes, the screw head sat high in the cone, but the washer distributed the load from the screw around the hole - what I believed the original posting was trying to accomplish.
 
Probably better way to accomplish this... why not just get Stainless Steel flat washer? Perhaps a thin shim washer would be ideal.
 
Thanks for the input guys.. I can now see there's not a widely used method used by most of you guys.. Guess I will just play around with it and see what I can come up with that does a better job of protecting the paint and hopefully looks decent..

Cheers!
 
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Hi Joe,
I looked for washers that would allow to withstand radial and axial loads without deforming the substrate (fiberglass), but without success. For the axial load the washer must compress the fiberglass and for the radial load the washer must enter the fiberglass with a cylindrical, not conical hole, to avoid deformations and fractures.
Finally I decided to make some special turned washers, and make a tool to prepare the hole in the fairing in correspondence with the fixing hole. The installed washers are glued (epoxy) and painted. So far (4 years) they hold very well and the fairings still adhere without deformation or fractures.
Here the link to the images.
https://www.dropbox.com/sh/49ialxn7q69v90x/AAAvXSdry6mpZ5JdQGuvddEca?dl=0
Claudio
 
My upper cowling has cracks and paint damage, mostly around the Phillips head screws....Has anyone found a better washer/screw combo to use that will protect the paint and distribute the load better than the little plastic washers under the phillips screw head?

Curiouser and curiouser.

I think the question here is why you're getting cracks and paint damage under nylon washers and AN526 screws. It's not the washer and screw choice, which are structurally superior to tinnermans. It more likely goes back to prep and paint choices.

Look at the back side of the panel. Do the cracks extend through the fiberglass? Now look close at the painted side. Are the cracks in the paint only?
 
Hi Joe,
I looked for washers that would allow to withstand radial and axial loads without deforming the substrate (fiberglass), but without success. For the axial load the washer must compress the fiberglass and for the radial load the washer must enter the fiberglass with a cylindrical, not conical hole, to avoid deformations and fractures.
Finally I decided to make some special turned washers, and make a tool to prepare the hole in the fairing in correspondence with the fixing hole. The installed washers are glued (epoxy) and painted. So far (4 years) they hold very well and the fairings still adhere without deformation or fractures.
Here the link to the images.
https://www.dropbox.com/sh/49ialxn7q69v90x/AAAvXSdry6mpZ5JdQGuvddEca?dl=0
Claudio

I can’t believe I’m saying this, but those are some beautiful washers. Too bad no one produces them. Really spiffy.
 
Another option...

This may be an option for your cowling. I used these the secure my fuel tanks which were painted separately from the wings as I didn't want to be dealing with painted screws when removing the tanks. (Yes, tank removal is not uncommon!) They are called flush or finishing washers and can be purchased for all the screw sizes we typically use.




[url=https://flic.kr/p/2a5Wypq]
 
Hi Joe,
I looked for washers that would allow to withstand radial and axial loads without deforming the substrate (fiberglass), but without success. For the axial load the washer must compress the fiberglass and for the radial load the washer must enter the fiberglass with a cylindrical, not conical hole, to avoid deformations and fractures.
Finally I decided to make some special turned washers, and make a tool to prepare the hole in the fairing in correspondence with the fixing hole. The installed washers are glued (epoxy) and painted. So far (4 years) they hold very well and the fairings still adhere without deformation or fractures.
Here the link to the images.
https://www.dropbox.com/sh/49ialxn7q69v90x/AAAvXSdry6mpZ5JdQGuvddEca?dl=0
Claudio

Wow, those are beautiful!
 
Nickel Plated Flat Washer - Does that have 100 deg countersink to match aviation flat head screw?

Where to buy / PN?
 
The only countersunk screws on my cowling are for the upper cowling attachment pin retainer plate. Everything else uses #8 round head machine screws with flat washers. No cracks after 9 years and just shy of 1100 hours.
 
This may be an option for your cowling. I used these the secure my fuel tanks which were painted separately from the wings as I didn't want to be dealing with painted screws when removing the tanks. (Yes, tank removal is not uncommon!) They are called flush or finishing washers and can be purchased for all the screw sizes we typically use.

Hey, Ron, I have a box of these washers and never discovered the perfect use for them, but- just this week (first 'annual' since paint) got some paint turn-out with my screws (@#$%^&). Will these stick to the paint and prevent that post paint?
 
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Hey, Ron, I have a box of these washers and never discovered the perfect use for them, but- just this week (first 'annual' since paint) got some paint turn-out with my screws (@#$%^&). Will these stick to the paint and prevent that post paint?

They may not stick to the paint but they will keep your screws from messing up the paint.
 
I finally remembered to take some photos of my issues.. The photo where the spinner is visible shows the fine crack in the cowling..
 

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Looks like a paint problem rather than a fastener problem.

I agree.

The paint is being extruded out from under the screws. Once the paint is moving on the cowl surface, the bond to the substrate is compromised and damage will continue.

One common cause is an excessively thick layer of paint that takes a long time to fully cure.

Add to that, reassembly only a few days after the paint was applied and this is often what happens.


BTW, the screws being used at the front of the cowl are not what is recommended. The plans call for washer head screws because they have some smooth / unthreaded shank where they pass through the cowl.
Using common truss head screws results in the threads baring on the edge of the screw holes which will accelerate elongation / wear in the holes.
 
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I agree.

The paint is being extruded out from under the screws. Once the paint is moving on the cowl surface, the bond to the substrate is compromised and damage will continue.

One common cause is an excessively thick layer of paint that takes a long time to fully cure.

Add to that, reassembly only a few days after the paint was applied and this is often what happens.


BTW, the screws being used at the front of the cowl are not what is recommended. The plans call for washer head screws because they have some smooth / unthreaded shank where they pass through the cowl.
Using common truss head screws results in the threads baring on the edge of the screw holes which will accelerate elongation / wear in the holes.


Have a part number handy? I’ll add some to my next Van’s order.. Looking at KAI 38.07, I’m seeing a truss head screw listed, AN526C832R8. Not positive, but I believe that’s what I currently have..

The paint is what it is at this point. Looking to hide existing damage and reduce future damage until I can get the cowling re-painted.
 
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I’m with you Joe.
My 12, s/n120401, used truss screws all over the place to include the cowl, spinner, and was according to plans. But I noticed with the 12iS I’m helping with the cowl fasteners identified washer head screws. I immediately thought the plans were wrong and reverted to the truss screws.
Tomorrow when I go back to the 12iS build I will review the hardware call outs and replace the screws with what the plans call out. It will be an easy swap out since we are a long way from startup or paint.
 
Have a part number handy? I’ll add some to my next Van’s order.. Looking at KAI 38.07, I’m seeing a truss head screw listed, AN526C832R8. Not positive, but I believe that’s what I currently have..

It looks like the correction hasn't made its way through on the Legacy ULS plans yet, but the 12iS KAI DWG 37iS/U-12 shows AN525-832R8.

They are cad. plated instead of stainless, so don't look as pretty, but they will help minimize wear in the screw holes of time.
 
AN525-832R8__5ef2579491658.jpg
 
Screws for cowling, etc.

Very interesting - I'm wondering if I should replace the 'old' screws on my vintage build with these - places life anywhere that the canopy plastic parts of the canopy are secured with the older stainless screws??? That would be approximately 100 replacement screws. And now I'm wondering about if it would be good to replace the screws in the gas inlet and spinner???
 
Very interesting - I'm wondering if I should replace the 'old' screws on my vintage build with these - places life anywhere that the canopy plastic parts of the canopy are secured with the older stainless screws??? That would be approximately 100 replacement screws. And now I'm wondering about if it would be good to replace the screws in the gas inlet and spinner???

The locations specified on the cowl are because of experience with those locations. The other locations you mentioned haven’t been a problem so the other screw type is used.
 
Washer?

Stupid question: I purchased the new screws. Do I also use a nylon washer with them or just the screw?
 
I finally remembered to take some photos of my issues.. The photo where the spinner is visible shows the fine crack in the cowling..

That's a paint problem. Do you know the brand and product line of the primer and/or primer surfacer under that red paint?

FWIW, I've run AN526's and nylon washers over 1000 hours now, and this -8 cowl is loaded a lot higher than a 12. All the screw areas still look like new.
.
 

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That's a paint problem. Do you know the brand and product line of the primer and/or primer surfacer under that red paint?

FWIW, I've run AN526's and nylon washers over 1000 hours now, and this -8 cowl is loaded a lot higher than a 12. All the screw areas still look like new.
.

Dan how is your spinner attached? I don't see any screws. Camera tricks?
 
Screwless Spinner

Dan how is your spinner attached? I don't see any screws. Camera tricks?

Im not sure if it can be searched with the new format forum, but it has been posted with great detail in photos and text.

Dr Glass Innovation did a nice job again.
 
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FWIW, I've run AN526's and nylon washers over 1000 hours now, and this -8 cowl is loaded a lot higher than a 12. All the screw areas still look like new.
.

Not a direct comparison though….
The RV’s-12 cowl is made from wet layup glass / epoxy, and it is also much thinner.
 
screw spec per KAI

I posted this a couple days ago in another thread. Just trying to get the facts clear in my head. The current KAI for RV-12 posted on Van's website, p. 38-07, still says AN526C for the front six screws on the upper cowling. The comparable RV-12iS KAI, p. 37iS/U-12, says AN525. The factory notification process has never sent me any recommendation to change the screws on the RV-12. AN525 makes sense, and I will switch them next time I have the cowling off.
 
I posted this a couple days ago in another thread. Just trying to get the facts clear in my head. The current KAI for RV-12 posted on Van's website, p. 38-07, still says AN526C for the front six screws on the upper cowling. The comparable RV-12iS KAI, p. 37iS/U-12, says AN525. The factory notification process has never sent me any recommendation to change the screws on the RV-12. AN525 makes sense, and I will switch them next time I have the cowling off.

I saw you post, and posted an answer in that thread.
 
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