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Repairing ARF Cowl

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Old 10-02-2016, 06:42 PM
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acdii
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Default Repairing ARF Cowl

I bounced my P-47 off a roof via its wing tip on landing and munched the cowl. Since it is an ARF cowl it is gel coated(painted), and not like the glass cowls I have in kits. The gel coat flakes off where it cracked so I need to figure out how best to repair it with West Systems. It held its shape, so I can reinforce the interior with heavy cloth, but I need to also fill in the outer shell where the Gell coat sheared off.
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Old 10-03-2016, 08:39 AM
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Good question, I have some minor cracks on some of my ARF cowls that could use some repair. I could benefit from this information also.

Also, have you considered just purchasing a new replacement cowl? Assuming it is available. I have done that a couple of times for different ARFs to save myself a lot of work.
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Old 10-03-2016, 10:39 AM
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Not for this one, its at least 10 years old or more and hasn't been in production for at least 8 or more. I "might" find one that "might" fit from FGS, but since they have a no return, if it doesn't I would be stuck with it. If I can repair it back to it's original shape, I can make a mold off it. That way I can paint it to match better. Not sure what to do with the cowl once it is repaired due to the Gel on it.
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Old 10-03-2016, 11:11 AM
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1. Wash in sink with really soapy solution of dish soap.
2. Rinse and dry thoroughly.
3. Sand damaged area thoroughly inside and out with with 80 grit sand paper.
4. Remove sanding debris with clean shop air.
5. Cut 2 tailored plies of 4-6 ozs. plain weave fiberglass cloth.
6. Using medium CA or your favorite epoxy resin layup the interior of the cowling and allow to cure, I personally use the CA for my layups on small repairs like this.
7 Sweep the exterior in the flaking areas with a thin coat of bondo, allow to cure and re-sand with 80 grit.
8. Clean with shop air and utilizing medium CA, or your favorite epoxy resin along with1 ply of 3/4 oz. cloth, placed over the exterior reworked area.
9. Allow to cure and feather edge sand glass cloth edges with 180 grit sand paper, while scuff sanding the entire cowling as you go.
10. Prime fill and top coat.

Bob

Last edited by sensei; 10-03-2016 at 11:14 AM.
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Old 10-03-2016, 12:30 PM
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Hi Bob, I tried that exact technique on the Top Flite ARF cowl, and it didn't work as the gel coat came apart after the first flight. It is almost as though I needed to remove all the painted surfaces, which leaves just the cloth, and nothing solid to hold the form. That technique works fine for those cowls that are unfinished with the cloth laid in the wet resin, but these cowls appear to be laid up on top of cured, or semi cured gel, the cloth will pull away very easily once it cracks. None of the inner cloth is damaged, just the outer shell where it cracked and is peeling away, so was trying to figure out how to bond the shell back to the cloth without leaving pockets of air between them.

The ideal method would be to make a solid block for the cowl to slip over, apply resin to the outside and then place a bag over it and vacuum it tight until it cured, but I dont have anything that will work for that.

If I peel off the shell, I would lose all the detail in it, and possibly its shape as well. Now I wish I had actually made a mold off this one even with the crack it had.
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Old 10-03-2016, 05:55 PM
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Here is what it looks like.




You can see the back of the coat, smooth, no imprints of the fabric.



And the cloth shows very little resin.





Here is a cowl I made from the plastic cowl in the P-51 kit. Had a little too much air in the first batch, but it still came out pretty good for the first one.



Would be so easy to repair that big cowl if it were like this one, then I could do exactly what you listed to repair it, but the big one is a mess and if I try ti sand it I'm afraid it might come apart. So I need a way to stabilize it, and thats what I am looking for here.
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Old 10-04-2016, 03:23 AM
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Perfect, the pictures help allot, and I have repaired cowlings and wheel pants that were equally damaged in this way. That looks like gel coat with an epoxy layup to me. Bad idea if it is...

1. Wash with really soapy dish soap, rinse and dry thoroughly.
2. Chip away everything that comes off easily.
3. Thin CA everything else, all edges and micro cracks on the exterior side.
4. Abrade interior with 80 sand paper, clean and place 2 plies of 4-6 oz. plain weave cloth and your favorite epoxy resin on the interior area that is effected and allow to cure.
5. Abrade exterior with 80 grit sandpaper, preferably using a DA sander with 80 grit sanding pads
6. Sweep lightly with bondo, sand, and repeat as needed.
7. place one ply of 3/4 oz. on the exterior and your favorite epoxy resin.
8. After full cure, feather edge glass while sanding entire cowling, clean, prime and sand as needed, and topcoat.

Bob
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Old 10-04-2016, 05:06 AM
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OK, I will give that a try. The CA wont interfere with the epoxy in the cloth? That was one of my concerns.
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Old 10-04-2016, 05:34 AM
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No, not at all, it may run through the interior from some of the porosity I see in the glass, but after cure just scuff with the 80 grit and continue on.

Bob
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Old 10-04-2016, 06:58 AM
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Thanks, I will do that, hopefully I can restore the panel lines too and if it comes out OK, I will make a mold off it and build a better cowl.
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Old 10-04-2016, 08:28 AM
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Refresh my aging memory what brand of ARF was it? I wonder if Fiberglass Specialties would have something in the correct diameter and correct length or longer to replace it. It would leave you with making your rivets if any but it would make replacing it a lot simpler.

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Old 10-04-2016, 12:25 PM
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Its a Hanger 9 P-47 Razorback 150 from ~ 2005. They don't have a cowl for this one.
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Old 10-04-2016, 12:52 PM
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Bummer!
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Old 10-04-2016, 02:46 PM
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Originally Posted by acdii View Post
Its a Hanger 9 P-47 Razorback 150 from ~ 2005. They don't have a cowl for this one.
Typical ARF deal. They get cancelled and not long after that, no more spares.
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Old 10-04-2016, 05:30 PM
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Yep. Need a wing tube for it, but thankfully they used a normal sized one. It is a shame they stopped making it, it is a very tough plane.
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Old 10-05-2016, 05:26 AM
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I think they see ARF buyer as being like cell phone buyers always looking for the newest and latest model on the market. Some ARF buyers seem to have an insatiable desire for something new, buy it, crash, it, drop in the trash bin on the way to the car, and buy the next one. Meanwhile all the builders race to the bin to salvage the crash and end up flying their "new" airplane a few weeks later. The ARF flier is never the wiser! ;-)

acdii is not an ARF buyer, he is a builder who dabbles in ARFs.hence he is repairing an ARF.

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Old 10-05-2016, 06:58 AM
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Yep. I kinda feel dirty flying an ARF, then I pull out my SIG Cub and fly my colors and all is right with the world. Only reason my Somethin Extra is an ARF is because I didn't have time, or a place to build the kit version. But I have crashed it, er, landed, yes thats it, landed it wrong a few times so it has had multiple repairs. So far none of my planes have reached the bin stage yet.
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Old 10-05-2016, 07:24 AM
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In my view builders generally alter the ARF's construction to fix the problem areas, etc and personalize their airplane. That makes it a hybrid and not a true ARF. You shouldn't feel dirty flying it.
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Old 10-05-2016, 07:44 AM
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Well, the P-47 I didn't do a thing to except assemble it, until now. Oh I take that back, I built a hatch in the top hatch to access the switches and fuel dot so they are not visible. Now when I repair the cowl, it will be better and stronger, so I guess you could say I made it my own. I know of guys who busted up the fuse and have no clue how to repair it, and it is actually pretty simple to repair, getting it all to fit the way it did originally is the challenge.
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Old 10-05-2016, 01:33 PM
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Originally Posted by acdii View Post
. I know of guys who busted up the fuse and have no clue how to repair it, and it is actually pretty simple to repair, getting it all to fit the way it did originally is the challenge.
You hit the nail on the head with that comment.
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Old 10-23-2016, 04:46 PM
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Well first step completed. Cleaned it, buffed it and applied a couple layers of cloth inside with West Systems. On the outside I spread the left over epoxy into the cloth to help bridge the gaps between the gel and the glass. Going to take some sanding and filling on the outside, but the strength of the cowl is so much better now, and it adds a little needed weight.




I will get more of the outside after sanding the applied epoxy on the outside, I didn't get any of it after applying it. While I was at it I used what I had left to repair the cowl for my Mustang. It may not look pretty, but it is functional and thats all that matters in the end.
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