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M20J Cowling rebuild

jetdriven

By jetdriven
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jetdriven
jetdriven

So last weekend, we began to tackle the ratty old, worn out, 34 year-old M20J cowling. This is prep for a repaint this fall. The paint was cracking next to the hump and all the cowl fastener holes wer

CCAS
CCAS

Ever since I bought my '89 J model I've never been happy with the condition of my beat-up lower cowling so I recently decided to have it repaired to improve durability.  My goal was to strengthen the

jetdriven
jetdriven

Mooney sells a kit you install a pin on the upper forward part of the cabin door. It holds the door tightly when in flight.  Before painting I stripped the front half of the wing and applied a bu

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bradp Grand Master

bradp

Posted
Posted

Possibly troutdale.

Alternatively you could probably bring it to any boat shop and they could do the composite / body work prior to paint and / or redo the gelcoat on the fiber.  In fact a boat shop might do a better job than average A&P.

 

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N201MKTurbo Grand Master

N201MKTurbo

Posted
Posted
36 minutes ago, bradp said:

Possibly troutdale.

Alternatively you could probably bring it to any boat shop and they could do the composite / body work prior to paint and / or redo the gelcoat on the fiber.  In fact a boat shop might do a better job than average A&P.

 

Make sure they use the correct materials. Most boat shops would use polyester resin which would be a disaster.

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gsxrpilot Grand Master

gsxrpilot

Posted
Posted
17 minutes ago, xcrmckenna said:

I’m trying to get.@jetdriven to spend a month in Oregon but I don’t think that is going to happen.... The plane will be at Advanced in Troutdale next week to work on the gear. I’ll run it by Greg.


Sent from my iPhone using Tapatalk

Just bring your plane to Texas... :-)

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jetdriven Grand Master

jetdriven

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I live in DC now. 

 Also like I’ve written many times before used aircraft structural Epoxy.  if it doesn’t belong on a Long-EZ wing spar it doesn’t belong on a cowling either. A buddy of mine had a Bellanca Super Viking and he took it down to some local boat shop and they put literally 1/4” of boat resin and loose weave boat cloth on it.  Then a hot coat to make it look all deep and glossy. It was no stronger than it was before but it weighed 5lb more. 

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  • 3 weeks later...
testwest Experienced

testwest

Posted
Posted

Byron is correct. I have used MGS L285 epoxy (Aircraft Spruce)...it is the structural epoxy used to build certificated Cirrus and Diamond airplanes. Yep....it is $142 bucks for a gallon of resin and $35 for a quart of hardener. But worth it.

MGS L335 is a little cheaper, not as good on the physicals but perfect for fairing and smaller parts.

 

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  • 6 years later...
Bartman Mentor

Bartman

Posted
Posted

NecroTread resurrection alert.  

I followed this thread in 2013 and saved in my Mooney Repairs folder. Since then we have upgraded servers and the pictures are no longer available, but the information remains and is of high value.  I have one question. Thank you Byron for posting this. 
 

I’m pretty sure I can clean the cowl up and apply the carbon fiber in layers, but I don’t have the equipment for the vacuum bagging.  Is it critical to do vacuum bagging or can I achieve the desired results without bagging?

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A64Pilot Grand Master

A64Pilot

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Are we sure Mooney used Epoxy?

It’s honestly not real common in aircraft non structural areas like wingtips and cowls etc., just as a for instance we Used Polyester in Thrush aircraft and have done so since the 60’s. There is however a reduced flammability resin that’s required for aircraft, think like your interior fabrics. Both Epoxy, Vinylester and Polyester resins burn like the pertroleum products they are. Ever seen a fiberglass boat burn? Glass doesn’t burn, it’s the resin that does.

One reason besides expense Vinylester or Polyester is used because you can use Gelcoat, Gelcoat gives a nicer, smoother finish, you can’t Gelcoat Epoxy, it won’t stick. For that reason the very few Epoxy boats that are built have to be painted for instance.

Anyway nothing wrong with using epoxy, you can use Epoxy on Polyester, but you can’t put Polyester on Epoxy, or shouldn’t anyway as it may dis-bond.

https://support.jamestowndistributors.com/hc/en-us/articles/4405692701339-Can-polyester-resin-be-applied-over-a-2-part-epoxy-based-primer#:~:text=Polyester resin does not achieve,or for fiber reinforcement applications.

Anyway 99% of people that work on boats or Corvettes will do a good job, A&P’s are getting better and better with composites now because it’s getting more and more common.

If you’re unsure, go with Epoxy, you can Epoxy any other kind of resin, for repairs the additional cost isn’t significant in my opinion.

Vacuum bagging for repairs is overrated, the old school way of Squeegeeing resin can get your fabric to resin ration down as low as vacuum bagging. Vacuum bagging is primarily used in manufacturing because it can be used to draw a thinned resin through the lay up, it’s quicker and easier and less messy than wet lay up, and I think requires less skill.

In my opinion Carbon fiber in non structural composites is more of a sales gimmick than anything else, and Carbon Fiber brings with it the possibility of serious galvanic corrosion if it contacts aluminum, so make sure it can’t come into contact with aluminum.

https://www.corrosionpedia.com/galvanic-corrosion-of-metals-connected-to-carbon-fiber-reinforced-polymers/2/1556

The strength of course comes from the glass, not the resin, resin only adds weight, so you want as little resin as you can get away with. There is a lot of Engineering that goes into fiberglass layup, in general unidirectional glass with different layers laid in different directions is much stronger than glass fabric that looks like regular woven fabric, but for repairs woven glass is fine, an ounce or two of weight isn’t going to hurt, and Cowlings and wing tips aren’t structural like a wing spar.

Cheap boats used to be built with chopper guns that sprayed a resin wetted chopped strand that quickly built up bulk and weight but wasn’t very strong. That’s not used as much as it used to be because resin is a petroleum product and got expensive in 1973 I think it was. Chopped strand mat is still common where bulk is desired.

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N201MKTurbo Grand Master

N201MKTurbo

Posted
Posted
6 hours ago, A64Pilot said:

Are we sure Mooney used Epoxy?

It’s honestly not real common in aircraft non structural areas like wingtips and cowls etc., just as a for instance we Used Polyester in Thrush aircraft and have done so since the 60’s. There is however a reduced flammability resin that’s required for aircraft, think like your interior fabrics. Both Epoxy, Vinylester and Polyester resins burn like the pertroleum products they are. Ever seen a fiberglass boat burn? Glass doesn’t burn, it’s the resin that does.

One reason besides expense Vinylester or Polyester is used because you can use Gelcoat, Gelcoat gives a nicer, smoother finish, you can’t Gelcoat Epoxy, it won’t stick. For that reason the very few Epoxy boats that are built have to be painted for instance.

Anyway nothing wrong with using epoxy, you can use Epoxy on Polyester, but you can’t put Polyester on Epoxy, or shouldn’t anyway as it may dis-bond.

https://support.jamestowndistributors.com/hc/en-us/articles/4405692701339-Can-polyester-resin-be-applied-over-a-2-part-epoxy-based-primer#:~:text=Polyester resin does not achieve,or for fiber reinforcement applications.

Anyway 99% of people that work on boats or Corvettes will do a good job, A&P’s are getting better and better with composites now because it’s getting more and more common.

If you’re unsure, go with Epoxy, you can Epoxy any other kind of resin, for repairs the additional cost isn’t significant in my opinion.

Vacuum bagging for repairs is overrated, the old school way of Squeegeeing resin can get your fabric to resin ration down as low as vacuum bagging. Vacuum bagging is primarily used in manufacturing because it can be used to draw a thinned resin through the lay up, it’s quicker and easier and less messy than wet lay up, and I think requires less skill.

In my opinion Carbon fiber in non structural composites is more of a sales gimmick than anything else, and Carbon Fiber brings with it the possibility of serious galvanic corrosion if it contacts aluminum, so make sure it can’t come into contact with aluminum.

https://www.corrosionpedia.com/galvanic-corrosion-of-metals-connected-to-carbon-fiber-reinforced-polymers/2/1556

The strength of course comes from the glass, not the resin, resin only adds weight, so you want as little resin as you can get away with. There is a lot of Engineering that goes into fiberglass layup, in general unidirectional glass with different layers laid in different directions is much stronger than glass fabric that looks like regular woven fabric, but for repairs woven glass is fine, an ounce or two of weight isn’t going to hurt, and Cowlings and wing tips aren’t structural like a wing spar.

Cheap boats used to be built with chopper guns that sprayed a resin wetted chopped strand that quickly built up bulk and weight but wasn’t very strong. That’s not used as much as it used to be because resin is a petroleum product and got expensive in 1973 I think it was. Chopped strand mat is still common where bulk is desired.

It is epoxy. It is in the manual. And you are supposed to add antimony trioxide powder to it.

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Bartman Mentor

Bartman

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Posted

I did some reading and watched a couple of YouTube videos.  I don’t have a vacuum pump but I think I could rig up the bags you use for clothing and use a shop vac, and then rely on the integrated valve to maintain the vacuum.  It may require some cutting and modifications, but it’s a possibility.

I’m in no rush as this project as we will be flying a lot thru November for college football games.  I’ll start this in December when she goes in for annual inspection.  In the meantime I may locate a loaner from an aircraft buddy or partner with a local car body shop. I will acquire the supplies and do some testing and create a learning project. 

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N201MKTurbo Grand Master

N201MKTurbo

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26 minutes ago, Bartman said:

I did some reading and watched a couple of YouTube videos.  I don’t have a vacuum pump but I think I could rig up the bags you use for clothing and use a shop vac, and then rely on the integrated valve to maintain the vacuum.  It may require some cutting and modifications, but it’s a possibility.

I’m in no rush as this project as we will be flying a lot thru November for college football games.  I’ll start this in December when she goes in for annual inspection.  In the meantime I may locate a loaner from an aircraft buddy or partner with a local car body shop. I will acquire the supplies and do some testing and create a learning project. 

You should use real vacuum bag material. The stuff you are suggesting will probably bond to the resin. Then you would need to sand the plastic off the carbon fiber. It will take forever and look like hell.

You can get all the proper vacuum bag supplies on Amazon for reasonable money.

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CCAS Apprentice

CCAS

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Posted

Ever since I bought my '89 J model I've never been happy with the condition of my beat-up lower cowling so I recently decided to have it repaired to improve durability.  My goal was to strengthen the damaged or weak areas with new fiberglass in order to give it more integrity for the next couple years as I save for a complete re-paint of the plane. I didn't take great before-and-after photos but I'm happy with how it turned out....the after photos were taken before the cowl flaps and landing light lens went back in.        

Old cowl.jpg

Repaired cowl1.jpg

Repaired cowl2.jpg

Repaired cowl3.jpg

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CCAS Apprentice

CCAS

Posted
Posted
On 9/5/2024 at 5:34 PM, EricJ said:

Looks nice!   The cowl flap hinges are a potential problem area. 

 

My maintenance log tells me your're not wrong.  Cowl flap hinges have been addressed more than once. Last repair a couple Annuals ago was by Arapahoe Aero in Centennial, CO and the hinges have been doing well since.  

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Elijah Contributor

Elijah

Posted
Posted (edited)
On 9/1/2024 at 7:17 PM, Bartman said:

NecroTread resurrection alert.  

I followed this thread in 2013 and saved in my Mooney Repairs folder. Since then we have upgraded servers and the pictures are no longer available, but the information remains and is of high value.  I have one question. Thank you Byron for posting this. 
 

I’m pretty sure I can clean the cowl up and apply the carbon fiber in layers, but I don’t have the equipment for the vacuum bagging.  Is it critical to do vacuum bagging or can I achieve the desired results without bagging?

I recently did some fiberglass repairs to my top cowl. I added several layers of fiberglass cloth to strengthen the area around the "bump" on top the cowl which always cracks. Mine had a lot of cracks and the fiberglass was "flexible" aka broken in spots. I went with fiberglass for 2 reasons; 1 I had it on hand, and 2 I figure the rest of the cowl is fiberglass and has held up for nearly 50 years, so why reinvent the wheel. They just made it a little bit too thin on top, which a couple extra layers will fix. 

I have done fiberglass repairs before and my experience is over a large area with curves (like a cowl) it's hard to get the cloth to both lay flat AND get all the excess epoxy out. (can usually do one or the other but not both). As others have said, more is not better when it comes to the amount of epoxy in the fabric. So for those reasons I chose to buy the stuff to vacuum bag it - it was not expensive but I had some of the stuff on hand. I'll give you a quick list in case you want to do the same:

BTW the sealant tape is key, I doubt another type of tape would work so if you skimp on anything, don't skimp on that. Or the peel ply. :D I used the other half of the AC gauge manifold to bleed vacuum off as needed to pull about 15" of vacuum. 

I paint on the epoxy (I used aeropoxy), lay on a layer of cloth, get it all wetted out, then paint more epoxy, next layer of cloth, etc. Then the peel ply. Then the breather material. Then put the sealant tape down around the area (clean a strip with alcohol right before putting down the tape) and put the inside half of the vacuum port somewhere you have a flat spot. Finally the plastic film, push it down tightly all around onto the sealant, hook up the port and then start pulling vacuum. As it tightens up you'll hear any leaks and I was able to seal them up by just squeezing the tape down more. It's thick and rubbery and tries to "suck" into the cracks sealing leaks as the vacuum pulls down.

Anyway, I was very happy with the results. It looks as good as the factory glass. Definitely worth the extra effort. 

 

 

Edited by Elijah
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LANCECASPER Grand Master

LANCECASPER

Posted
Posted
39 minutes ago, Elijah said:

I recently did some fiberglass repairs to my top cowl. I added several layers of fiberglass cloth to strengthen the area around the "bump" on top the cowl which always cracks. Mine had a lot of cracks and the fiberglass was "flexible" aka broken in spots. I went with fiberglass for 2 reasons; 1 I had it on hand, and 2 I figure the rest of the cowl is fiberglass and has held up for nearly 50 years, so why reinvent the wheel. They just made it a little bit too thin on top, which a couple extra layers will fix. 

I have done fiberglass repairs before and my experience is over a large area with curves (like a cowl) it's hard to get the cloth to both lay flat AND get all the excess epoxy out. (can usually do one or the other but not both). As others have said, more is not better when it comes to the amount of epoxy in the fabric. So for those reasons I chose to buy the stuff to vacuum bag it - it was not expensive but I had some of the stuff on hand. I'll give you a quick list in case you want to do the same:

BTW the sealant tape is key, I doubt another type of tape would work so if you skimp on anything, don't skimp on that. Or the peel ply. :D I used the other half of the AC gauge manifold to bleed vacuum off as needed to pull about 15" of vacuum. 

I paint on the epoxy (I used aeropoxy), lay on a layer of cloth, get it all wetted out, then paint more epoxy, next layer of cloth, etc. Then the peel ply. Then the breather material. Then put the sealant tape down around the area (clean a strip with alcohol right before putting down the tape) and put the inside half of the vacuum port somewhere you have a flat spot. Finally the plastic film, push it down tightly all around onto the sealant, hook up the port and then start pulling vacuum. As it tightens up you'll hear any leaks and I was able to seal them up by just squeezing the tape down more. It's thick and rubbery and tries to "suck" into the cracks sealing leaks as the vacuum pulls down.

Anyway, I was very happy with the results. It looks as good as the factory glass. Definitely worth the extra effort. 

 

 

How is that J coming @Elijah ?

 

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Elijah Contributor

Elijah

Posted
Posted
3 hours ago, LANCECASPER said:

How is that J coming @Elijah ?

 

It's pretty much done, we're working on paperwork and I'm doing misc cosmetic stuff, like the upper cowl. I mean I don't know if an old airplane is ever "done" but it's ready to fly, let's put it that way! I should update my thread :)

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